CN105518958B - DC power network currents differential protecting method and its system - Google Patents

Abstract

The invention discloses a kind of DC power network currents differential protecting method and systems.Method includes the following steps：Sampled value obtains step：Obtain the pole tension sampled value and electrode current sampled value in the local terminal and remote terminal of DC circuits；Fault component extraction step：Fault component pole tension value is calculated according to the pole tension sampled value of local terminal and remote terminal respectively；And fault component electrode current value is calculated according to the electrode current sampled value of local terminal and remote terminal respectively；Bei Jielong models calculate step：By calculating the local terminal calculated in fault component extraction step and the fault component pole tension value of remote terminal and fault component electrode current value based on Bei Jielong models, the fault component electrode current value at the Chosen Point on the DC circuits between local terminal and remote terminal is obtained；Current differential protection determination step：If Bei Jielong models, which calculate the fault component electrode current value at the Chosen Point of local terminal and remote terminal obtained in step, meets predetermined current differential protection criterion, internal fault is judged.The present invention is removed the interference of the charging current of distribution without long time lengthening, is then greatly improved the calculating speed of the present invention using Bei Jielong models.

Description

DC power network currents differential protecting method and its system

Technical field

This application involves DC power network currents differential protecting method and its systems.

Background technology

In existing HVDC systems, it is typically based on the protection before the traveling wave of local measurements and is used as main protection, classical electricity It flows differential protection and is used as stand-by protection.However their the shortcomings that, is：Main protection, and can to the poor sensitivity of high resistance failure It can the malfunction in LCC DC power grids；And stand-by protection has very slow movement speed.

In existing two terminals HVDC systems, the speed of the variation before the traveling wave of direction is based primarily upon for the main protection of power transmission line Rate and amplitude.This kind of protection has clear advantage, is exactly that it only uses local measurements and has very to metallic fault Fast movement speed.

But a shortcoming of this kind of protection is its (poor) very low to the sensitivity of high resistance failure.Usual ＞ 200Ohm Fault resstance may result in baulk because the amplitude of wavefront is largely dependent upon fault resstance.Therefore, high electricity Resistance failure has to be removed by the standby current differential protection of its movement speed very slow (such as ＞ 0.5s).This does not significantly conform to Reason.

In addition, physical features of the protection based on the smoothing reactor in HVDC systems, smoothing reactor can slow down electricity Rheology.In some type of DC network systems (for example, some type of series connection MTDC systems), row caused by external fault Wave will not flow through smoothing reactor, and the above-mentioned HVDC protections based on traveling wave will not act or malfunction.In the worst situation Under, if outside DC failures are happened on the circuit with higher voltage level, then even larger than by interior before its traveling wave Before traveling wave caused by portion's failure.This can be to the existing HVDC protection bands based on traveling wave come burden.

Fig. 1 is the chart shown before the traveling wave of the inside and outside DC failures in LCC DC power grids.

As shown in Figure 1, the rate of change of the wavefront from internal fault and external fault is absolutely identical when starting. Meanwhile it is even more much bigger than before the traveling wave of internal fault before the traveling wave of external fault, because the voltage level of outside line is higher.

In traditional traveling-wave protection device, as shown in Fig. 2, three different measured values will start to determine whether that the wave exists There is enough amplitudes in specified time.First measured value is calculated just before wavefront and just in 10 samplings Wave between after (0.2ms) is poor.Second calculates with third measured value just before wavefront and just at 25 times and 35 Wave between after secondary sampling (0.5ms and 0.7ms) is poor.If three measured values are both greater than threshold value, line fault is detected.

In view of the wavefront of the external fault in Fig. 1 is even greater than the wavefront of internal fault, and external and internal fault two The rate of change of person has identical rate, therefore existing HVDC main protections will the malfunction in LCCDC power grids in this case. In other words, existing HVDC traveling-wave protections cannot be directly used in LCC DC power grids.

In existing HVDC systems, the stand-by protection commonly used in power transmission line is Line Current Differential Protection.Classical electricity Stream differential relaying algorithm is used in this kind of protection.This kind of protection (such as high electricity when main protection (traveling-wave protection) cannot work Hinder failure) action.

The typical criterion of current differential protection has been illustrated below,

|I_DL-I_{DL_FOS}| ＞ max (120A, 0.1 × | I_DL+I_{DL_FOS}|/2)

Wherein I_DLIt is the electric current of local side, I_{DL_FOS}It is the electric current of remote side.

Another typical criterion of current differential protection has been illustrated below,

||I_DL|-|I_{DL_FOS}| | ＞ 90A

In general, the sensitivity of current differential protection can be fairly good if setting is appropriate.But its movement speed is too slow. Its actuation time is usually hundreds of milliseconds or even several seconds.Main reason is that failure transient and charging current will greatly shadows Ring the protection algorism.Therefore, long delay is necessary to ensure reliability.

Main protection and stand-by protection may all be influenced by high impedance fault.

1) to the influence of traveling-wave protection

Existing traveling wave criterion is：

|W_COMM|=| Z_COMI_COM-U_COM| ＞ 350kV

|W_POLE|=| Z_DIFI_DIF-U_DIF| ＞ 210kV

Wherein, Z_COMIt is common mode wave impedance, Z_DIFIt is differential mode wave impedance, W_POLEIt is pole wave, W_COMMIt is earthwave.

I_COMIt is common mode current, U_COMIt is common-mode voltage, I_DIFIt is differential-mode current, U_DIFIt is differential mode voltage.

The protection detects wave head using the rate of change of earthwave.

|dW_COMM/ dt | ＞ 396kV/ms

When circuit accesses the earth by big impedance, D/C voltage is declined with small rate of change, is caused existing based on row The malfunction of the protection of wave.

If traveling-wave protection malfunctions, control and protection system will postpone to eliminate failure.

2) to the influence of voltage changing rate and low-voltage variation

The criterion of voltage changing rate is：

D_UT=dU_dl/ dt ＜ -396kV/ms＆U_dl＜ 200kV, wherein U_dlIt is line voltage distribution, D_UTIt is corresponding variation speed Rate.

When circuit accesses the earth by big impedance, general who has surrendered leads to voltage changing rate false protection under small D/C voltage Make.

3) to the influence of current differential protection

The typical criterion of current differential protection has been illustrated below：

|I_DL-I_{DL_FOS}| ＞ max (I_SET, k × | I_DL+I_{DL_FOS}|/2)

Wherein I_SETIt is fixed current setting value, is normally set to 120A, k is the coefficient of ratio, is normally set to 0.1.

In order to ensure the action under conditions of big impedance fault, setting value I_SETA small value is normally set to k.Therefore Delay time must be set to long enough to avoid the malfunction as caused by capacitance charging current.

If quickly protection (traveling-wave protection) malfunction, back-up protection will postpone work.And delay time it is too long without It can guarantee the stable operation of electric system.

Invention content

Therefore, an aspect of of the present present invention provides a kind of DC power network currents differential protecting method, includes the following steps：

Sampled value obtains step：It obtains the local terminal of DC circuits and the pole tension sampled value and electrode current of remote terminal is adopted Sample value；

Fault component extraction step：Fault component is calculated according to the pole tension sampled value of local terminal and remote terminal respectively Pole tension value；And fault component electrode current value is calculated according to the electrode current sampled value of local terminal and remote terminal respectively；

Bei Jielong models calculate step：Pass through the sheet calculated in fault component extraction step based on the calculating of Bei Jielong models Ground terminal and the fault component pole tension value of remote terminal and fault component electrode current value, obtain local terminal and remote terminal it Between DC circuits on Chosen Point at fault component electrode current value；

Current differential protection determination step：If calculate the local terminal obtained in step and long-range end in Bei Jielong models Fault component electrode current value at the Chosen Point at end meets predetermined current differential protection criterion, then judges internal fault.

Preferably, DC power grids are bipolar, and DC circuits include anode DC circuits and cathode DC circuits, local terminal packet Anode local terminal and cathode local terminal are included, remote terminal includes anode remote terminal and cathode remote terminal, anode DC lines Road is electrically connected anode local terminal and anode remote terminal, and cathode DC circuits electrical connection cathode local terminal and cathode are long-range Terminal, it is identical with from Chosen Point to the distance of cathode local terminal to the distance of anode local terminal from Chosen Point, and from choosing The distance for pinpointing anode remote terminal is identical with from Chosen Point to the distance of cathode remote terminal；It further includes：

Pole modular transformation step：By remotely whole to anode local terminal, anode remote terminal, cathode local terminal and cathode Each fault component pole tension value in end carries out pole modular transformation, obtains each modulus of local terminal and remote terminal Fault component mode voltage value；And by long-range to anode local terminal, anode remote terminal, cathode local terminal and cathode Each fault component electrode current value in terminal carries out pole modular transformation, obtains each mould of local terminal and remote terminal The fault component mould current value of amount；

Bei Jielong models calculate step and further include：

Fault component mode voltage value by each modulus that local terminal and remote terminal are calculated based on Bei Jielong models With fault component mould current value, the fault component line wave voltage of each modulus of local terminal and remote terminal is obtained respectively Value；

The fault component line wave voltage value of local terminal and remote terminal is converted into local terminal and long-range end respectively The fault component line wave current value at end；

The Chosen Point on DC circuits is determined according to the fault component line wave current value of local terminal and remote terminal respectively The local terminal at place and the fault component mould current value of remote terminal；

Mould pole-change is carried out by the fault component mould current value of each modulus to the local terminal at Chosen Point, is obtained Each fault component electrode current value in the anode local terminal and cathode local terminal at the Chosen Point on DC circuits is obtained, And mould pole-change is carried out by the fault component mould current value of each modulus to the remote terminal at Chosen Point, it obtains The fault component electrode current value of anode remote terminal and cathode remote terminal at Chosen Point.

Easily, pole tension sampled value includes：u_LP(t), i.e. the voltage sample value of anode local terminal；u_LN(t), i.e., it is negative The voltage sample value of pole local terminal；u_RP(t), i.e. the voltage sample value of anode remote terminal；u_RN(t), i.e. cathode remote terminal Voltage sample value；Wherein t refers to the time；

Electrode current sampled value includes：i_LP(t), i.e. the current sampling data of anode local terminal；i_LN(t), i.e., cathode is local eventually The current sampling data at end；i_RP(t), i.e. the current sampling data of anode remote terminal；i_RN(t), i.e. the electric current of cathode remote terminal is adopted Sample value；

Fault component pole tension value includes：Δu_LP(t), i.e., and u_LP(t) fault component of corresponding anode local terminal Voltage value；Δu_LN(t), i.e., and u_LN(t) the fault component voltage value of corresponding cathode local terminal；Δu_RP(t), i.e., and u_RP (t) the fault component voltage value of corresponding anode remote terminal；Δu_RN(t), i.e., and u_RN(t) corresponding cathode is remotely whole The fault component voltage value at end；

Fault component electrode current value includes：Δi_LP(t), i.e., and i_LP(t) fault component of corresponding anode local terminal Current value；Δi_LN(t), i.e., and i_LN(t) the fault component current value of corresponding cathode local terminal；Δi_RP(t), i.e., and i_RP (t) the fault component current value of corresponding anode remote terminal；Δi_RN(t), i.e., and i_RN(t) corresponding cathode is remotely whole The fault component current value at end；

Fault component mode voltage value includes：Δu_L0(t), i.e. the fault component common-mode voltage value of local terminal；Δu_L1(t), That is the fault component differential mode voltage value of local terminal；Δu_R0(t), i.e. the fault component common-mode voltage value of remote terminal；Δu_R1 (t), i.e. the fault component differential mode voltage value of remote terminal；

Fault component mould current value includes：Δi_L0(t), i.e. the fault component common-mode current value of local terminal；Δi_L1(t), That is the fault component differential-mode current value of local terminal；Δi_R0(t), i.e. the fault component common-mode current value of remote terminal；Δi_R1 (t), i.e. the fault component differential-mode current value of remote terminal；

Fault component traveling wave voltage value includes：Δu_L0+(t), i.e. the fault component common mode direct wave voltage of local terminal Value；Δu_L0-(t), i.e. the fault component common mode backward-travelling wave voltage value of local terminal；Δu_L1+(t), i.e. the failure of local terminal Component differential mode direct wave voltage value；ΔΔu_L0-(t), i.e. the fault component differential mode backward-travelling wave voltage value of local terminal；Δ u_R0+(t), i.e. the fault component common mode direct wave voltage value of remote terminal；Δu_R0-(t), i.e. the fault component of remote terminal is total to Mould backward-travelling wave voltage value；Δu_R1+(t), the fault component differential mode direct wave voltage value of remote terminal；Δu_R1-(t), remotely The fault component differential mode backward-travelling wave voltage value of terminal；

Fault component travelling wave current value includes：Δi_L0+(t), i.e. the fault component common mode direct wave electric current of local terminal Value；Δi_L0-(t), i.e. the fault component common mode backward-travelling wave current value of local terminal；Δi_L1+(t), i.e. the failure of local terminal Component differential mode direct wave current value；Δi_L1-(t), i.e. the fault component differential mode backward-travelling wave current value of local terminal；Δi_R0+ (t), i.e. the fault component common mode direct wave current value of remote terminal；Δi_R0-(t), i.e. the fault component common mode of remote terminal Backward-travelling wave current value；Δi_R1+(t), i.e. the fault component differential mode direct wave current value of remote terminal；Δi_R1-(t), i.e., far The fault component differential mode backward-travelling wave current value of journey terminal；

Fault component mould current value at Chosen Point includes：Δi_L0Failure at the Chosen Point of (x, t), i.e. local terminal Component common-mode current value；Δi_L1Fault component differential-mode current value at the Chosen Point of (x, t), i.e. local terminal；Δi_R0(x, t), Fault component common-mode current value i.e. at the Chosen Point of remote terminal；Δi_R1Failure at the Chosen Point of (x, t), i.e. remote terminal Component differential-mode current value, wherein x are Chosen Points；

Fault component electrode current value at Chosen Point includes：Δi_LPAt (x, t), the i.e. Chosen Point of anode local terminal Fault component electrode current value；Δi_LNFault component electrode current value at (x, t), the i.e. Chosen Point of cathode local terminal；Δi_RP Fault component electrode current value at (x, t), the i.e. Chosen Point of anode remote terminal；Δi_RNThe choosing of (x, t), i.e. cathode remote terminal Fault component electrode current value at fixed point.

Easily, in fault component extraction step, fault component pole tension value and failure point are calculated in the following ways Measure pole tension value：

Wherein T represents predetermined time delay；

In pole modular transformation step, fault component mode voltage value and fault component mould current value are calculated in the following ways：

Step is calculated in Bei Jielong models to include：

Fault component line wave voltage value is calculated in the following ways：

Wherein Z_C0It is common mode wave impedance；Z_C1It is differential mode wave impedance；

Fault component line wave current value is calculated in the following ways：

The fault component mould current value at Chosen Point is calculated in the following ways：

Wherein, v₀It is the gait of march of fault component common mode traveling wave, v₁It is the gait of march of fault component differential mode traveling wave；

The fault component electrode current value at Chosen Point is calculated in the following ways：

Easily, current differential protection determination step includes：

If meet | Δ i_LP(x, t)+Δ i_RP(x, t) | ＞ I_res, then state is judged for anode internal fault, if met |Δi_LN(x, t)+Δ i_RN(x, t) | ＞ I_res, then judge state for cathode internal fault, wherein I_resIt is predetermined threshold value；

Otherwise, differential protection will not be activated.

Preferably, DC power grids are monopoles：

Bei Jielong models calculate step and further include：

By being based on Bei Jielong models, the fault component pole tension value and fault component of local terminal and remote terminal are calculated Mould current value obtains the fault component pole traveling wave voltage value of local terminal and remote terminal respectively；

The fault component pole traveling wave voltage value of local terminal and remote terminal is converted into local terminal and long-range end respectively The fault component line wave current value at end；

According to local terminal and the fault component pole travelling wave current value of remote terminal, determine at the Chosen Point on DC circuits Local terminal and the fault component electrode current value of remote terminal.

Easily, in fault component extraction step, fault component pole tension value and failure point are calculated in the following ways Measure pole tension value：

Wherein, T represents predetermined time delay, Δ i_L(t) be local terminal fault component electrode current value, Δ i_R(t) it is remote The fault component electrode current value of journey terminal, Δ u_L(t) be local terminal fault component pole tension value, Δ u_R(t) it is remote terminal Fault component pole tension value, i_L(t) be local terminal current sampling data, i_R(t) be remote terminal current sampling data, u_L (t) be local terminal voltage sample value, u_R(t) be remote terminal voltage sample value, t refers to the time；

Step is calculated in Bei Jielong models to include：

Fault component pole traveling wave voltage value is calculated in the following ways：

Wherein Z_CIt is wave impedance, Δ u_L+(t) be local terminal fault component pole direct wave voltage value；Δu_L-(t) it is The fault component pole backward-travelling wave voltage value of local terminal；Δu_R+(t) be remote terminal fault component pole direct wave voltage Value；Δu_R-(t) be remote terminal fault component pole backward-travelling wave voltage value；

Fault component pole travelling wave current value is calculated in the following ways：

Wherein, Δ i_L+(t) be local terminal fault component pole direct wave current value；Δi_L-(t) it is local terminal Fault component pole backward-travelling wave current value；Δi_R+(t) be remote terminal fault component pole direct wave current value；Δi_R-(t) It is the fault component pole backward-travelling wave current value of remote terminal；

The fault component electrode current value at selected location is calculated in the following ways：

Wherein Δ i_L(x, t) is the fault component electrode current value at the Chosen Point of local terminal；Δi_R(x, t) is long-range end Fault component electrode current value at the Chosen Point at end, v are the gait of march of fault component traveling wave.

Easily, include in current differential protection determination step：

If meet | Δ i_L(x, t)+Δ i_R(x, t) | ＞ I_res, then state is judged for internal fault, wherein I_resIt is default Threshold value.

Easily, current differential protection determination step further includes：

If state is determined into internal fault, error protection order is sent to activate differential protection；Otherwise, will not swash Differential protection living.

It is above-mentioned including being suitable for performing when running on computers another aspect provides a kind of computer program The computer program code of all steps of either side.

It is yet another aspect of the present invention to provide the computer programs according to above-mentioned record in computer-readable medium.

It is yet another aspect of the present invention to provide a kind of DC power network currents differential protective system, including with lower module：

Sampled value obtains module：Obtain the pole tension sampled value and electrode current in the local terminal and remote terminal of DC circuits Sampled value；

Fault component extraction module：Fault component is calculated according to the pole tension sampled value of local terminal and remote terminal respectively Pole tension value；And fault component electrode current value is calculated according to the electrode current value of local terminal and remote terminal respectively；

Bei Jielong model computation modules：By being based on Bei Jielong models, calculate and calculated in fault component extraction step Local terminal and the fault component pole tension value of remote terminal and fault component electrode current value, obtain local terminal and it is long-range eventually The fault component electrode current value at the Chosen Point on DC circuits between end；

Current differential protection determination module：If the local terminal obtained in Bei Jielong model computation modules and long-range end Fault component electrode current value at the Chosen Point at end meets predetermined current differential protection criterion, then judges internal fault.

Preferably, DC power grids are bipolar and DC circuits include anode DC circuits and cathode DC circuits, local terminal packet Anode local terminal and cathode local terminal are included, remote terminal includes anode remote terminal and cathode remote terminal, anode DC lines Road is electrically connected anode local terminal and anode remote terminal, and cathode DC circuits electrical connection cathode local terminal and cathode are remotely whole End, it is identical with from Chosen Point to the distance of cathode local terminal to the distance of anode local terminal from Chosen Point, from Chosen Point to The distance of anode remote terminal is identical with from Chosen Point to the distance of cathode remote terminal, further includes：

Pole modular transformation module：By remotely whole to anode local terminal, anode remote terminal, cathode local terminal and cathode Each fault component pole tension value in end carries out pole modular transformation, obtains each mould in local terminal and remote terminal The fault component mode voltage value of amount；And by remote to anode local terminal, anode remote terminal, cathode local terminal and cathode Each fault component electrode current value in journey terminal carries out pole modular transformation, obtains each of local terminal and remote terminal The fault component mould current value of modulus；

Bei Jielong model computation modules further include：

By being based on Bei Jielong models, the fault component mode voltage value of each modulus of local terminal and remote terminal is calculated With fault component mould current value, the fault component line wave voltage of each modulus of local terminal and remote terminal is obtained respectively Value；

The fault component line wave voltage value of local terminal and remote terminal is converted into local terminal and long-range end respectively The fault component line wave current value at end；

The Chosen Point on DC circuits is determined according to the fault component line wave current value of local terminal and remote terminal respectively The local terminal at place and the fault component mould current value of remote terminal；

Mould pole-change is carried out by the fault component mould current value of each modulus to the local terminal at Chosen Point, is obtained Each fault component electrode current value in the anode local terminal and cathode local terminal at the Chosen Point on DC circuits is obtained, And mould pole-change is carried out by the fault component mould current value of each modulus to the remote terminal at Chosen Point, it obtains The fault component electrode current value of anode remote terminal and cathode remote terminal at Chosen Point.

Easily, pole tension sampled value includes：u_LP(t), i.e. the voltage sample value of anode local terminal；u_LN(t), i.e., it is negative The voltage sample value of pole local terminal；u_RP(t), i.e. the voltage sample value of anode remote terminal；u_RN(t), i.e. cathode remote terminal Voltage sample value；Wherein t refers to the time；

Electrode current sampled value includes：i_LP(t), i.e. the current sampling data of anode local terminal；i_LN(t), i.e., cathode is local eventually The current sampling data at end；i_RP(t), i.e. the current sampling data of anode remote terminal；i_RN(t), i.e. the electric current of cathode remote terminal is adopted Sample value；

Fault component pole tension value includes：Δu_LP(t), i.e., and u_LP(t) fault component of corresponding anode local terminal Voltage value；Δu_LN(t), i.e., and u_LN(t) the fault component voltage value of corresponding cathode local terminal；Δu_RP(t), i.e., and u_RP (t) the fault component voltage value of corresponding anode remote terminal；Δu_RN(t), i.e., and u_RN(t) corresponding cathode is remotely whole The fault component voltage value at end；

Fault component electrode current value includes：Δi_LP(t), i.e., and i_LP(t) fault component of corresponding anode local terminal Current value；Δi_LN(t), i.e., and i_LN(t) the fault component current value of corresponding cathode local terminal；Δi_RP(t), i.e., and i_RP (t) the fault component current value of corresponding anode remote terminal；Δi_RN(t), i.e., and i_RN(t) corresponding cathode is remotely whole The fault component current value at end；

Fault component mode voltage value includes：Δu_L0(t), i.e. the fault component common-mode voltage value of local terminal；Δu_L1(t), That is the fault component differential mode voltage value of local terminal；Δu_R0(t), i.e. the fault component common-mode voltage value of remote terminal；Δu_R1 (t), i.e. the fault component differential mode voltage value of remote terminal；

Fault component mould current value includes：Δi_L0(t), i.e. the fault component common-mode current value of local terminal；Δi_L1(t), That is the fault component differential-mode current value of local terminal；Δi_R0(t), i.e. the fault component common-mode current value of remote terminal；Δi_R1 (t), i.e. the fault component differential-mode current value of remote terminal；

Fault component traveling wave voltage value includes：Δu_L0+(t), i.e. the fault component common mode direct wave voltage of local terminal Value；Δu_L0-(t), i.e. the fault component common mode backward-travelling wave voltage value of local terminal；Δu_L1+(t), i.e. the failure of local terminal Component differential mode direct wave voltage value；Δu_L0-(t), i.e. the fault component differential mode backward-travelling wave voltage value of local terminal；Δu_R0+ (t), i.e. the fault component common mode direct wave voltage value of remote terminal；Δu_R0-(t), i.e. the fault component common mode of remote terminal Backward-travelling wave voltage value；Δu_R1+(t), i.e. the fault component differential mode direct wave voltage value of remote terminal；Δu_R1-(t), i.e., far The fault component differential mode backward-travelling wave voltage value of journey terminal；

Fault component travelling wave current value includes：Δi_L0+(t), i.e. the fault component common mode direct wave electric current of local terminal Value；Δi_L0-(t), i.e. the fault component common mode backward-travelling wave current value of local terminal；Δi_L1+(t), i.e. the failure of local terminal Component differential mode direct wave current value；Δi_L1-(t), i.e. the fault component differential mode backward-travelling wave current value of local terminal；Δi_R0+ (t), i.e. the fault component common mode direct wave current value of remote terminal；Δi_R0-(t), i.e. the fault component common mode of remote terminal Backward-travelling wave current value；Δi_R1+(t), i.e. the fault component differential mode direct wave current value of remote terminal；Δi_R1-(t), i.e., far The fault component differential mode backward-travelling wave current value of journey terminal；

Fault component mould current value at Chosen Point includes：Δi_L0Failure at the Chosen Point of (x, t), i.e. local terminal Component common-mode current value；Δi_L1Fault component differential-mode current value at the Chosen Point of (x, t), i.e. local terminal；Δi_R0(x, t), Fault component common-mode current value i.e. at the Chosen Point of remote terminal；Δi_R1Failure at the Chosen Point of (x, t), i.e. remote terminal Component differential-mode current value, wherein x are Chosen Points；

Fault component electrode current value at Chosen Point includes：Δi_LPEvent at (x, t), the i.e. Chosen Point of anode local terminal Hinder component electrode current value；Δi_LNFault component electrode current value at (x, t), the i.e. Chosen Point of cathode local terminal；Δi_RP(x, T), i.e., the fault component electrode current value at the Chosen Point of anode remote terminal；Δi_RN(x's, t), i.e. cathode remote terminal is selected Fault component electrode current value at point.

Easily, in fault component extraction module, fault component pole tension value and failure point are calculated in the following ways Measure pole tension value：

Wherein, T represents predetermined time delay；

In pole modular transformation module, fault component mode voltage value and fault component mould current value are calculated in the following ways：

Include in Bei Jielong model computation modules：

Fault component line wave voltage value is calculated in the following ways：

Wherein Z_C0It is common mode wave impedance；Z_C1It is differential mode wave impedance；

Fault component line wave current value is calculated in the following ways：

The fault component mould current value at Chosen Point is calculated in the following ways：

Wherein, v₀It is the gait of march of fault component common mode traveling wave, v₁It is the gait of march of fault component differential mode traveling wave；

The fault component electrode current value at Chosen Point is calculated in the following ways：

Easily, current differential protection determination module includes：

If meet | Δ i_LP(x, t)+Δ i_RP(x, t) | ＞ I_res, then state is judged for anode internal fault, if met |Δi_LN(x, t)+Δ i_RN(x, t) | ＞ I_res, then state is judged for cathode internal fault, wherein, I_resRepresent predetermined threshold value；

Otherwise, differential protection will not be activated.

Preferably, DC power grids are monopoles：

Bei Jielong model computation modules further include：

By being based on Bei Jielong models, the fault component pole tension value and fault component of local terminal and remote terminal are calculated Mould current value obtains the fault component pole traveling wave voltage value of local terminal and remote terminal respectively；

The fault component pole traveling wave voltage value of local terminal and remote terminal is converted into local terminal and long-range end respectively The fault component line wave current value at end；

It is determined at the Chosen Point on DC circuits according to the fault component pole travelling wave current value of local terminal and remote terminal Local terminal and the fault component electrode current value of remote terminal.

Easily, in fault component extraction module, fault component pole tension value and failure point are calculated in the following ways Measure pole tension value：

Wherein T represents predetermined time delay, Δ i_L(t) be local terminal fault component electrode current value, Δ i_R(t) it is remote The fault component electrode current value of journey terminal, Δ u_L(t) be local terminal fault component pole tension value, Δ u_R(t) it is remote terminal Fault component pole tension value, i_L(t) be local terminal current sampling data, i_R(t) be remote terminal current sampling data, u_L (t) be local terminal voltage sample value, u_R(t) be remote terminal voltage sample value, and t refers to the time；

Include in Bei Jielong model computation modules：

Fault component pole traveling wave voltage value is calculated in the following ways：

Wherein, Z_CIt is wave impedance, Δ u_L+(t) be local terminal fault component pole direct wave voltage value；Δu_L-(t) it is The fault component pole backward-travelling wave voltage value of local terminal；Δu_R+(t) be remote terminal fault component pole direct wave voltage Value；Δu_R-(t) be remote terminal fault component pole backward-travelling wave voltage value；

Fault component pole travelling wave current value is calculated in the following ways：

Wherein, Δ i_L+(t) be local terminal fault component pole direct wave current value；Δi_L-(t) it is local terminal Fault component pole backward-travelling wave current value；Δi_R+(t) be remote terminal fault component pole direct wave current value；Δi_R-(t) It is the fault component pole backward-travelling wave current value of remote terminal；

The fault component electrode current value at selected location is calculated in the following ways：

Wherein Δ i_L(x, t) is the fault component electrode current value at the Chosen Point of local terminal；Δi_R(x, t) is long-range end Fault component electrode current value at the Chosen Point at end, v are the gait of march of fault component traveling wave.

Easily, include in current differential protection determination module：

If meet | Δ i_L(x, t)+Δ i_R(x, t) | ＞ I_res, then state is judged for internal fault, wherein I_resIt is default Threshold value.

Easily, current differential protection determination module further includes：

If state is determined into internal fault, error protection order is sent to activate differential protection, otherwise will not be swashed Differential protection living.

Bei Jielong models are based on distributed constant and telegraph equation (wave equation).Therefore, the present invention uses Bei Jielong models, Therefore long time lengthening is not needed to eliminate the interference of the charging current of distribution, so as to substantially increase the calculating of present invention speed Degree.

Meanwhile the present invention removes influence of the load current to differential protection using fault component, it is sensitive so as to improve Degree.

Description of the drawings

Fig. 1 shows the chart before the traveling wave of the inside and outside DC failures in LCC DC power grids；

Fig. 2 shows the instrumentation plans of traditional traveling-wave protection device；

Fig. 3 shows the flow chart for illustrating DC power network currents differential protecting method according to the present invention；

Fig. 4 schematically shows fault components to be distributed power grid；

Fig. 5 shows the state when generation internal fault in circuit；

Fig. 6 shows the state when generation external fault in circuit；

Fig. 7 shows simulation model；

Fig. 8 shows analog result；

Fig. 9 shows the structure mould block diagram of DC power network current differential protective systems；

Figure 10 shows monopolar HVDC system.

Specific embodiment

Hereinafter, with reference to attached drawing, pass through the specific embodiment more detailed description present invention.

Fig. 3 shows the flow chart for illustrating DC power network currents differential protecting method according to the present invention, and method includes following Step：

Step S301：Obtain the pole tension sampled value in the local terminal and remote terminal of DC circuits and electrode current sampling Value；

Step S302：Fault component pole tension is calculated according to the pole tension sampled value of local terminal and remote terminal respectively Value；And fault component electrode current value is calculated according to the electrode current sampled value of local terminal and remote terminal respectively；

Step S303：By being based on Bei Jielong models (Bergeron model), the local calculated in step S302 is calculated Terminal and the fault component pole tension value of remote terminal and fault component electrode current value are obtained between local terminal and remote terminal DC circuits on Chosen Point fault component electrode current value；

Step S304：If the fault component pole at the local terminal obtained in step S303 and the Chosen Point of remote terminal Current value meets predetermined current differential protection criterion, then judges internal fault.

Bei Jielong models are based on distributed constant and telegraph equation (wave equation).Therefore theoretically this method needs inherently And accurately account for the charging current being distributed during failure transient.

Therefore, the present invention is using Bei Jielong models, and so there is no need to long time lengthenings to eliminate the charging of distribution electricity The interference of stream, so as to greatly improve the calculating speed in the present invention.

Meanwhile in step s 302, pole tension sampled value is converted into fault component pole tension value, electrode current sampled value quilt It is converted into fault component electrode current value.Therefore, in this step, fault component pole tension value is divided from pole tension sampled value From fault component electrode current value is detached from electrode current sampled value.In this case, when breaking down in power grid, power grid Fault-free network and fault component network may be divided into, such fault component pole tension value and fault component electrode current value are Pole tension/current value in fault component network.In subsequent step S303 and S304, to fault component pole tension value and event Hinder component electrode current value and carry out pole modular transformation and applied to Bei Jielong models.That is, the present invention provides based on failure point The current differential protection of amount.Therefore, the present invention removes influence of the load current to differential protection using fault component, so as to carry It is highly sensitive.

In a preferred embodiment of the present invention, particularly, DC power grids are bipolar, and DC circuits include anode DC lines Road and cathode DC circuits, local terminal include anode local terminal and cathode local terminal, and remote terminal includes anode remotely eventually End and cathode remote terminal, anode DC circuits electrical connection anode local terminal and anode remote terminal, and cathode DC circuits are electrically connected Cathode local terminal and cathode remote terminal are connect, it is local to the distance of anode local terminal and from Chosen Point to cathode from Chosen Point The distance of terminal is identical, from Chosen Point to the distance of anode remote terminal and from Chosen Point to the distance phase of cathode remote terminal Together, it further includes：

Pole modular transformation step：By remotely whole to anode local terminal, anode remote terminal, cathode local terminal and cathode Each fault component pole tension value in end carries out pole modular transformation, obtains each mould in local terminal and remote terminal The fault component mode voltage value of amount and by remote to anode local terminal, anode remote terminal, cathode local terminal and cathode Each fault component electrode current value in journey terminal carries out pole modular transformation, obtains each of local terminal and remote terminal The fault component mould current value of modulus；

Step S303 is further included：

By being based on Bei Jielong models, the fault component mode voltage value of each modulus of local terminal and remote terminal is calculated With fault component mould current value, the fault component line wave voltage of each modulus of local terminal and remote terminal is obtained respectively Value；

The fault component line wave voltage value of local terminal and remote terminal is converted into local terminal and long-range end respectively The fault component line wave current value at end；

The Chosen Point on DC circuits is determined according to the fault component line wave current value of local terminal and remote terminal respectively The local terminal at place and the fault component mould current value of remote terminal；

Mould pole-change is carried out by the fault component mould current value of each modulus to the local terminal at Chosen Point, is obtained Each fault component electrode current value in anode local terminal and cathode local terminal at Chosen Point on DC circuits, passes through Mould pole-change is carried out to the fault component mould current value of each modulus of the remote terminal at Chosen Point, is obtained at Chosen Point just The fault component electrode current value of pole remote terminal and cathode remote terminal.

The fault component mode voltage for carrying out mould pole-change and fault component mould electric current are applied to Bei Jielong by this embodiment Model, so as to achieve particularly the Bei Jielong models of the fault component based on bipolar DC power grids.

In one embodiment：

Pole tension sampled value includes：u_LP(t), i.e. the voltage sample value of anode local terminal；u_LN(t), i.e., cathode is local eventually The voltage sample value at end；u_RP(t), i.e. the voltage sample value of anode remote terminal；u_RN(t), i.e. the voltage of cathode remote terminal is adopted Sample value；Wherein t refers to the time；

Electrode current sampled value includes：i_LP(t), i.e. the current sampling data of anode local terminal；i_LN(t), i.e., cathode is local eventually The current sampling data at end；i_RP(t), i.e. the current sampling data of anode remote terminal；i_RN(t), i.e. the electric current of cathode remote terminal is adopted Sample value；

Fault component pole tension value includes：Δu_LP(t), i.e., and u_LP(t) the fault component electricity of corresponding anode local terminal Pressure value；Δu_LN(t), i.e., and u_LN(t) the fault component voltage value of corresponding cathode local terminal；Δu_RP(t), i.e., and u_RP(t) it is right The fault component voltage value for the anode remote terminal answered；Δu_RN(t), i.e., and u_RN(t) failure of corresponding cathode remote terminal point Measure voltage value；

Fault component electrode current value includes：Δi_LP(t), i.e., and i_LP(t) the fault component electricity of corresponding anode local terminal Flow valuve；Δi_LN(t), i.e., and i_LN(t) the fault component current value of corresponding cathode local terminal；Δi_RP(t), i.e., and i_RP(t) it is right The fault component current value for the anode remote terminal answered；Δi_RN(t), i.e., and i_RN(t) failure of corresponding cathode remote terminal point Measure current value；

Fault component mode voltage value includes：Δu_L0(t), i.e. the fault component common-mode voltage value of local terminal；Δu_L1(t), That is the fault component differential mode voltage value of local terminal；Δu_R0(t), i.e. the fault component common-mode voltage value of remote terminal；Δu_R1 (t), i.e. the fault component differential mode voltage value of remote terminal；

Fault component mould current value includes：Δi_L0(t), i.e. the fault component common-mode current value of local terminal；Δi_L1(t), That is the fault component differential-mode current value of local terminal；Δi_R0(t), i.e. the fault component common-mode current value of remote terminal；Δi_R1 (t), i.e. the fault component differential-mode current value of remote terminal；

Fault component traveling wave voltage value includes：Δu_L0+(t), i.e. the fault component common mode direct wave voltage of local terminal Value；Δu_L0-(t), i.e. the fault component common mode backward-travelling wave voltage value of local terminal；Δu_L1+(t), i.e. the failure of local terminal Component differential mode direct wave voltage value；Δu_L0-(t), i.e. the fault component differential mode backward-travelling wave voltage value of local terminal；Δu_R0+ (t), i.e. the fault component common mode direct wave voltage value of remote terminal；Δu_R0-(t), i.e. the fault component common mode of remote terminal Backward-travelling wave voltage value；Δu_R1+(t), i.e. the fault component differential mode direct wave voltage value of remote terminal；Δu_R1-(t), i.e., far The fault component differential mode backward-travelling wave voltage value of journey terminal；

Fault component travelling wave current value includes：Δi_L0+(t), i.e. the fault component common mode direct wave electric current of local terminal Value；Δi_L0-(t), i.e. the fault component common mode backward-travelling wave current value of local terminal；Δi_L1+(t), i.e. the failure of local terminal Component differential mode direct wave current value；Δi_L1-(t), i.e. the fault component differential mode backward-travelling wave current value of local terminal；Δi_R0+ (t), i.e. the fault component common mode direct wave current value of remote terminal；Δi_R0-(t), i.e. the fault component common mode of remote terminal Backward-travelling wave current value；Δi_R1+(t), i.e. the fault component differential mode direct wave current value of remote terminal；Δi_R1-(t), i.e., far The fault component differential mode backward-travelling wave current value of journey terminal；

Fault component mould current value at Chosen Point includes：Δi_L0Failure point at the Chosen Point of (x, t), i.e. local terminal Measure common-mode current value；Δi_L1Fault component differential-mode current value at the Chosen Point of (x, t), i.e. local terminal；Δi_R0(x, t), i.e., Fault component common-mode current value at the Chosen Point of remote terminal；Δi_R1Failure point at the Chosen Point of (x, t), i.e. remote terminal Measure differential-mode current value；

Fault component electrode current value at Chosen Point includes：Δi_LPEvent at (x, t), the i.e. Chosen Point of anode local terminal Hinder component electrode current value；Δi_LNFault component electrode current value at (x, t), the i.e. Chosen Point of cathode local terminal；Δi_RP(x, T), i.e., the fault component electrode current value at the Chosen Point of anode remote terminal；Δi_RN(x's, t), i.e. cathode remote terminal is selected Fault component electrode current value at point.

This embodiment calculates respectively for anode and cathode, it is achieved thereby that respectively for the differential protection of two pole.

In one embodiment：

In step s 302, fault component pole tension value and fault component pole tension value are calculated in the following ways：

Wherein, T represents time delay；

In pole modular transformation step, fault component mode voltage value and fault component mould current value are calculated in the following ways：

Include in step S303：

Fault component line wave voltage value is calculated in the following ways：

Wherein, Z_C0It is common mode wave impedance；Z_C1It is differential mode wave impedance；

Fault component line wave current value is calculated in the following ways：

The fault component mould current value at Chosen Point is calculated in the following ways：

Wherein, v₀It is the gait of march of fault component common mode traveling wave, v₁It is the gait of march of fault component differential mode traveling wave；

The fault component electrode current value at Chosen Point is calculated in the following ways：

In one embodiment：

Include in step s 304：

If meet | Δ i_LP(x, t)+Δ i_RP(x, t) | ＞ I_res, then judge state for anode internal fault；If meet |Δi_LN(x, t)+Δ i_RN(x, t) | ＞ I_res, then judge state for cathode internal fault, wherein I_resRepresent predetermined threshold value；

Otherwise, differential protection will not be activated.

In one embodiment, DC power grids are monopoles：

Step S303 is further included：

By being based on Bei Jielong models, the fault component pole tension value and fault component of local terminal and remote terminal are calculated Mould current value obtains the fault component pole traveling wave voltage value of local terminal and remote terminal respectively；

The fault component pole traveling wave voltage value of local terminal and remote terminal is converted into local terminal and long-range end respectively The fault component line wave current value at end；

According to local terminal and the fault component pole travelling wave current value of remote terminal, determine at the Chosen Point on DC circuits Local terminal and remote terminal fault component electrode current value.

Particularly this embodiment realizes the Bei Jielong models of the fault component based on monopole DC power grids.

In one embodiment, in step s 302, fault component pole tension value and failure point are calculated in the following ways Measure electrode current value：

Wherein, T represents time delay, Δ i_L(t) be local terminal fault component electrode current value, Δ i_R(t) it is long-range end The fault component electrode current value at end, Δ u_L(t) be local terminal fault component pole tension value, Δ u_R(t) it is remote terminal event Hinder component pole tension value, i_L(t) be local terminal current sampling data, i_R(t) be remote terminal current sampling data, u_L(t) it is The voltage sample value of local terminal, u_R(t) be remote terminal voltage sample value, and t refers to the time；

Step S303 includes：

Fault component pole traveling wave voltage value is calculated in the following ways：

Wherein, Z_CIt is wave impedance, Δ u_L+(t) be local terminal fault component pole direct wave voltage value；Δu_L-(t) it is The fault component pole backward-travelling wave voltage value of local terminal；Δu_R+(t) be remote terminal fault component pole direct wave voltage Value；Δu_R-(t) be remote terminal fault component pole backward-travelling wave voltage value；

Fault component pole travelling wave current value is calculated in the following ways：

Wherein, Δ i_L+(t) be local terminal fault component pole direct wave current value；Δi_L-(t) it is local terminal Fault component pole backward-travelling wave current value；Δi_R+(t) be remote terminal fault component pole direct wave current value；Δi_R-(t) It is the fault component pole backward-travelling wave current value of remote terminal；

The fault component electrode current value at selected location is calculated in the following ways：

Wherein Δ i_L(x, t) is the fault component electrode current value at the Chosen Point of local terminal；Δi_R(x, t) is remote Fault component electrode current value at the Chosen Point of journey terminal, v are the gait of march of fault component traveling wave.

In one embodiment, step S304 includes：

If meet | Δ i_L(x, t)+Δ i_R(x, t) | ＞ I_res, then judge state for internal fault.

In one embodiment, step S304 is further included：

If state is determined into internal fault, error protection order is sent to activate differential protection, otherwise will not be swashed Differential protection living.

Bipolar DC power grids

In a preferred embodiment of the present invention, the fault component illustrated schematically that distribution power grid as shown in Figure 4, this hair Bright current differential protection method tries to calculate the Δ i in specific t moment at Chosen Point_LP(x, t) and Δ i_RP(x, t), with The judgement of positive electrode fault is made, and at the same time calculating the Δ i in specific t moment at Chosen Point x_LN(x, t) and Δ i_RN(x, T), to make the judgement of cathode failure.Local side 41 and remote side 42 can be communicated by communication line, and side 41 local in this way can Obtain whole parameter informations of local side 41 and remote side 42.Particularly, in the following manner can be used and calculate Δ i_LP(x, t), Δ i_RP (x, t), Δ i_LN(x, t) and Δ i_RN(x, t)：

Fault component electric current and voltage calculate

Fault component is calculated by the following formula (1)：

Wherein, T is time delay, and according to demand, T can be set to such as 10ms or 100ms.

Pole mode conversion

Fault component current value and voltage value Δ i are being obtained by formula (1)_LP(t), Δ i_LN(t), Δ u_LP(t), Δ u_LN (t), Δ i_RP(t), Δ i_RN(t), Δ u_RP(t) and Δ u_RN(t) it is to do pole modular transformation in next step so that maximum dose is converted into modulus after. The pole modular transformation matrix for voltage and current is given in formula (2).

Difference current based on Bei Jielong models calculates

In this step, Bei Jielong models (traveling wave propagation equation) will be based on, use the survey respectively from two terminals Magnitude calculates fault component traveling wave common mode and differential-mode current value at the Chosen Point x on protected circuit.

(1) fault component pattern traveling wave voltage value is calculated

Formula 3 can be used for calculating the common mode forward voltage traveling wave Δ u of local side fault component_L0+With backward voltage traveling wave Δu_L0-, the differential mode forward voltage traveling wave Δ u of local side fault component_L1+With backward voltage traveling wave Δ u_L1-, remote side fault component Common mode forward voltage traveling wave Δ u_R0+With backward voltage traveling wave Δ u_R0-And the differential mode forward voltage row of remote side fault component Wave Δ u_R1+With backward voltage traveling wave Δ u_R1-。

Wherein Z_C0It is common mode wave impedance, Z_C1It is differential mode wave impedance.

(2) fault component line wave current value is calculated

Formula 4 can be used for calculating the common mode forward current traveling wave Δ i of local side fault component_L0+With reverse current traveling wave Δi_L0-, the differential mode forward current traveling wave Δ i of local side fault component_L1+With reverse current traveling wave Δ i_L1-, remote side fault component Common mode forward current traveling wave Δ i_R0+With reverse current traveling wave Δ i_R0-And the differential mode forward current row of remote side fault component Wave Δ i_R1+With reverse current traveling wave Δ i_R1-。

(3) the fault component mould current value at selected location

Based on traveling wave principle, local terminal at Chosen Point x and remote terminal can be calculated using following formula 5 Fault component differential mode and common mode current, wherein the measured value by local terminal calculates the failure of the local terminal at Chosen Point x Component differential mode and common mode current calculate the fault component differential mode of the remote terminal at Chosen Point x by the measured value of remote terminal And common mode current：

(4) mould pole-change

In this step, for local and remote terminal the anode electricity at Chosen Point is calculated using mould pole-change Stream and cathodal current.Transformation matrix is shown in following formula 6：

For the criterion of activated current differential protection：

If meet following formula 7：

|Δi_LP(x, t)+Δ i_RP(L-x, t) | ＞ I_res (7)

Then state is determined into " anode internal fault ", so as to send error protection order, and activates the control of differential protection System.

If meet the following formula (8)：

|Δi_LN(x, t)+Δ i_RN(L-x, t) | ＞ I_res (8)

Then state is determined into " cathode internal fault ", so as to send error protection order, and activates the control of differential protection System.

Monopole DC power grids：

In a preferred embodiment of the present invention, as shown in Figure 10, wherein, Δ u_L(t) and Δ i_L(t) it is local terminal Fault component voltage and current, Δ u_R(t) and Δ i_R(t) be remote terminal fault component voltage and current,

Δi_L(x, t) is the electric current at point x calculated using local measurements,

Δi_R(x, t) is the electric current at point x calculated using long-range measured value,

As shown above, Bei Jielong models (telegraph equation, traveling-wave equation) will be based on, using the measured value point of two terminals The fault component electric current at Chosen Point " x " is not calculated.

For the current component calculated using local measurements, x be along circuit arbitrarily selected point and it is local eventually The distance between end.For example, if Chosen Point is remote terminal, then distance x is the length L of circuit；

For the current component calculated using long-range measured value, x be along circuit arbitrarily selected point and it is long-range eventually The distance between end.For example, if Chosen Point is remote terminal, then distance x is zero.

In following chapters and sections, calculating step will be described in detail.

Fault component electric current and voltage calculate

Calculate fault component method be：

In formula 9, u (t) and i (t) are the pole tensions and current sampling data measured.Δ u (t) and Δ i (t) is corresponding Fault component voltage and current value.T is time delay, and such as 10ms or 100ms can be set as needed into.According to we The fault component voltage value and current value at method, the two poles of the earth and both ends can be calculated such as formula 10.

Difference current based on Bei Jielong models calculates

In this step, Bei Jielong models (traveling wave propagation equation) will be based on, using the measured value from two terminals The travelling wave current at the Chosen Point x on protected circuit is calculated respectively.

Traveling wave component of voltage calculates

Formula 11 can be used to calculate forward voltage traveling wave Δ u_L+With backward voltage traveling wave Δ u_L-。

Travelling wave current component calculates

Then, formula 12 can be used to calculate forward current traveling wave Δ i_L+With reverse current traveling wave Δ i_L-。

Travelling wave current component at Chosen Point calculates

Based on traveling wave principle, the electric current at Chosen Point x can be calculated using formula 13.

Wherein, v is the gait of march of traveling wave；

T is the time；

X is any point along circuit, it can be intermediate point, endpoint, starting point or any other point；

Δi_L(x, t) is the fault component electric current at the Chosen Point x calculated using the measured value of local terminal；

Δi_R(x, t) is the fault component electric current at the Chosen Point x calculated using the measured value of remote terminal；

Difference current calculates

As shown in formula 14, difference current, and and threshold value comparison are calculated by electrode current.Inhibit if difference current is more than Electric current then means internal fault.Otherwise external fault is meaned.The criterion for detecting internal fault has been illustrated below.

|Δi_L(x, t)+Δ i_R(x, t) | ＞ I_res (14)

Performance evaluation

Classical differential protection in HVDC circuits

The criterion of typical classical differential protection has been illustrated below：

|I_Local+I_Remote| ＞ I_Set (9)

Wherein, I_LocalIt is local terminal electric current, I_RemoteIt is remote terminal electric current.

Fig. 5 shows the state when generation internal fault in circuit.For internal fault, have

|I_Local+I_Remote|=I_F+I_C (10)

Wherein, I_FIt is the fault current as shown in Figure 5 by fault branch, I_CIt is to flow through the capacitance being distributed along circuit Electric current, usually it is much higher than zero, especially for length grow transmission line of electricity.It compares with formula (9), we can be observed Protection philosophy can correctly work.

However, for external fault, condenser current will cause problem.Fig. 6 is shown when external fault occurs in circuit When state.For external fault, have

|I_Local+I_Remote|=I_C (11)

From formula (11) it is understood that in order to avoid the malfunction under external fault, setting value I_SetIt necessarily is greater than I_C.By In I_CIt is only temporarily present after a failure, the another method for avoiding malfunction is to make I_SetWhen remaining standard value, but using long Between delay come wait for until transient process disappear.

Usually in practical applications, it in order to not damage the sensitivity of Protection criteria under high impedance fault, uses second Method, i.e. long time delay (0.5s-1.5s).But then, response speed slows down.

The present invention

The present invention is based on the traveling-wave component that Bei Jielong models is used to calculate, circuit is made in consideration in wherein Bei Jielong models Distribution capacity.

Thereby, it is possible to calculate accurate difference current, accurate difference current eliminates the charging current of discrete capacitor：

When internal fault occurs, the difference current of calculating is to flow through the fault current I of fault branch_F, for example, | Δ i_LP (x, t)+Δ i_RP(x, t) |=I_F；

When external fault occurs, the difference current that the present invention calculates is zero, such as | Δ i_LP(x, t)+Δ i_RP(x, t) | =0.

This allows the present invention not influenced by along the capacitance that circuit is distributed, so that it is guaranteed that movement speed.

Quick acting speed

Movement speed is extremely important for protection；It is a most important requirement to protection.When failure occurs When, system stability and personnel safety are on the hazard, and it is very useful to quickly isolate for system stability and personnel safety. Important stability and sensitivity are required to include to protection other two.Good protection philosophy must realize these three advantages：Soon Fast movement speed, stability and sensitivity.

Due to capacitance current, classical differential protection is unable to quick acting, and is waited for before transient phases are in the past, therefore limit Its speed is made.Different with classical differential protection, the present invention is not influenced by along the capacitance that circuit is distributed, therefore it can be with Realize faster movement speed.And be also due to it is not influenced by capacitance current, therefore it can use lower electric current Threshold value and realize higher sensitivity.

In view of depend on circuit length and communication lines by call duration time, action in most cases of the invention speed Degree is less than 15ms, and the actuation time of classical differential protection is 0.5s-1.5s.The algorithm of the present invention can be used as above-mentioned The main protection of LCC DC power grids, and can be used as the stand-by protection of other types of DC power grids, and can obtain higher than warp The movement speed of allusion quotation differential protection；And it can also be used as the main protection for short-term road, and the call duration time of wherein short-term road is short In other types of DC network systems or point-to-point HVDC systems.

Good sensitivity to high resistance failure

The sensitivity that the present invention has had high resistance failure because it is based on fault component, eliminates load current to difference The influence of dynamic protection, and load current reduces the sensitivity of classical differential protection.

Extensive adaptability

In this section, adaptability will be analyzed in terms of two：Operation principle and movement speed.

Operation principle relative adaptability

From the above analysis, Differential Protection Theory of the invention is only related to line parameter circuit value, it uses line parameter circuit value The electric current at point " x " is calculated, it does not require the topological structure of DC systems and control particularly.

Movement speed relative adaptability

Thus we understand movement speed in most cases of the invention less than 15ms.

Therefore, we can according to the requirement of the movement speed to different DC systems come select by the present invention relaying configuration into Main protection or stand-by protection.

For example, for the point-to-point DC circuits based on LCC technologies or DC power grids and with VSC technologies point-to-point DC Circuit, the present invention can either can serve as stand-by protection again as main protection.

For the DC power grids based on VSC technologies, the present invention can be used as stand-by protection, because of the requirement phase to movement speed Work as height, usually in 5ms.If the length of transmission line of electricity is short, time delay caused by communication can be reduced, so as to the present invention Main protection can be used as.

It should be pointed out that when being configured to stand-by protection, performance ratio of the invention is existing based on difference current Stand-by protection is much better, and the actuation time of the stand-by protection based on difference current is typically longer than hundreds of milliseconds.

Resonance influences

In the presence of along circuit distribution lines capacitance, because HVDC circuits are very long, line capacitance is big.When failure occurs When, there is big voltage and current concussion (" resonance "), some traditional protection philosophies, such as traditional electric current will be seriously affected Differential protection, low-voltage variation etc..

And the directional element of the present invention is based on Bei Jielong models, this model inherently considers " resonance ", without by " altogether Shake " it influences.

Simulation

Simulation model

Fig. 7 shows simulation model, and the 4 ends series connection MTDC of ± 800kV is inverse by Liang Ge converting plants (R1 and R2) and two Become station (I1 and I2) composition.The total length of transmission line of electricity is 2000km, including two branched lines (each 500km) and one Backbone (1000km).Each Inverter Station has configuration of the band there are one 12 pulse valve groups.Each rectifier converters will have across The nominal DC voltage of 400kV, each inversion converter is by with the nominal DC voltage across 373kV, and the ground connection electricity of HV DC lines Pressure is about 400kV (for R1 and I1) or about 800kV (for R2 and I2).

Present invention protection, relay 71,72 are located at two terminals of the power transmission line of upper+800kV shown in figure.It is and interior Portion's failure is in the end of+800kV circuits, and external fault is on+400kV circuits.And in this case extremely to pole wave impedance Z_CFor 264 Ω.

Fig. 8 shows analog result, and internal fault occurs in 2s, and external fault occurs in 4s.In Fig. 8,

The actual current of fault branch is flowed through when " IF "；

" Idif Bei Jielong " is the difference current calculated by the protection philosophy based on Bei Jielong models；

" Idif is classical " is the difference current calculated by classical differential protection.

Internal fault analysis

As shown in figure 8, internal fault occurs in 2s, fault resstance is 3000 ohm.

It should be noted that when internal fault occurs, " Idif Bei Jielong " and " IF " are not exactly the same, and reason is to be based on The principle of Bei Jielong models calculates difference current using fault component, and the fault component in this simulation only exists 50ms, because This two electric current after failure starts 50ms is different.But the time since failure (2s) to during 2.05s, according to based on shellfish The close enough physical fault electric current " IF " of difference current that the principle of outstanding dragon model calculates.

Difference current that classical protection calculates can be also obtained from Fig. 8 also close to physical fault electric current " IF ", but waveform Greatly.

External fault is analyzed

As shown in figure 8, external fault is happened at 4s.

When external fault occurs, fault current should theoretically be not present.However calculated according to classical differential protection Difference current (" Idif classical ") is quite big, when internal fault when 2s occurs even higher than difference current.Therefore we can Observe that classical differential current protection cannot distinguish between external fault and internal fault in transient process, before transient process disappearance It has to wait for.

" Idif Bei Jielong " shows the difference current that the present invention calculates.External fault can be observed from Fig. 8, it occurs The difference current calculated afterwards is very small, the difference current far smaller than calculated under internal fault.That is, it can be effectively regional Divide external fault and internal fault.

In short, analog result is shown compares with classical differential protection, the differential protection based on Bei Jielong models Smaller is influenced by line distribution capacitance.

Fig. 9 shows the structural model figure of DC power network current differential protective systems, including with lower module：

Sampled value obtain module 901, for obtain the pole tension sampled value of the local terminal of DC power grids and remote terminal and Electrode current sampled value；

Fault component extraction module 902, for being calculated respectively according to the pole tension sampled value of local terminal and remote terminal Fault component pole tension value；And according to the electrode current sampled value of local terminal and remote terminal to calculate fault component respectively extremely electric Flow valuve；

Pole modular transformation module, for by being carried out to the fault component pole tension value in local terminal and remote terminal Pole modular transformation obtains fault component mode voltage value and respectively by the fault component in local terminal and remote terminal Electrode current voltage value carries out pole modular transformation and obtains fault component mould current value respectively；

Bei Jielong model computation modules 903, for by being based on Bei Jielong models, calculating in local terminal and remote terminal Fault component mode voltage value and fault component mould current value, obtained respectively at Chosen Point in local terminal and remote terminal Fault component electrode current value；

Current differential protection determination module 904, if including the event in the local terminal and remote terminal at Chosen Point Barrier component electrode current value meet predetermined current differential protection criterion, then judge internal fault, then send error protection order with Differential protection is activated, otherwise will not activate differential protection.

Above-described embodiment is only used for describing several examples of the present invention, although these embodiments are described in detail, It should not be construed as limiting protection scope of the present invention.It will be noted that in the case of without departing from the technical concept of the present invention, Those skilled in the art can make several modifications and/or improvement, these wholes both fall within protection scope of the present invention.Therefore, originally The protection domain of invention depends on appended claims.

Claims (19)

1. a kind of DC power network currents differential protecting method, includes the following steps：

Sampled value obtains step：Obtain the pole tension sampled value in the local terminal and remote terminal of DC circuits and electrode current sampling Value；

Fault component extraction step：Fault component is calculated according to the pole tension sampled value of local terminal and remote terminal respectively Pole tension value；And fault component electrode current is calculated according to the electrode current sampled value of local terminal and remote terminal respectively Value；

Bei Jielong models calculate step：By calculating the local calculated in the fault component extraction step based on Bei Jielong models Terminal and the fault component pole tension value of remote terminal and fault component electrode current value are obtained between local terminal and remote terminal DC circuits on Chosen Point at fault component electrode current value；

Current differential protection determination step：If what is obtained in the Bei Jielong models calculating step is in local terminal and remotely whole Fault component electrode current value at the Chosen Point at end meets predetermined current differential protection criterion, then judges internal fault.

2. according to the method described in claim 1, wherein DC power grids are bipolar, and the DC circuits include anode DC circuits With cathode DC circuits, the local terminal includes anode local terminal and cathode local terminal, and the remote terminal includes anode Remote terminal and cathode remote terminal, the anode DC circuits are electrically connected the anode local terminal and the anode remotely eventually End, and the cathode DC circuits are electrically connected the cathode local terminal and the cathode remote terminal, from the Chosen Point to The distance of the anode local terminal is identical with from the Chosen Point to the distance of the cathode local terminal, and from the choosing The distance for pinpointing the anode remote terminal is identical with from the Chosen Point to the distance of the cathode remote terminal, also wraps It includes：

Pole modular transformation step：By to the anode local terminal, the anode remote terminal, the cathode local terminal and institute The each fault component pole tension value stated in cathode remote terminal carries out pole modular transformation, obtain local terminal and it is long-range eventually The fault component mode voltage value of each modulus in end；And by the anode local terminal, the anode remote terminal, Each fault component electrode current value in the cathode local terminal and the cathode remote terminal carries out pole modular transformation, Obtain the fault component mould current value of local terminal and each modulus in remote terminal；

The Bei Jielong models calculate step and further include：

Pass through the fault component mode voltage value based on Bei Jielong models calculating local terminal and each modulus of remote terminal and event Hinder component mould current value, obtain the fault component line wave voltage value of each modulus of local terminal and remote terminal respectively；

The fault component line wave voltage value of local terminal and remote terminal is converted into local terminal and long-range end respectively The fault component line wave current value at end；

Respectively according to local terminal and the fault component line wave current value of remote terminal, the choosing on the DC circuits is determined The fault component mould current value of local terminal and remote terminal at fixed point；

Mould pole-change is carried out by the fault component mould current value of each modulus to the local terminal at Chosen Point, is obtained Each fault component electrode current value in the anode local terminal and cathode local terminal at Chosen Point on the DC circuits, And mould pole-change is carried out by the fault component mould current value of each modulus to the remote terminal at Chosen Point, it obtains The fault component electrode current value of anode remote terminal and cathode remote terminal at Chosen Point.

3. according to the method described in claim 2, wherein described pole tension sampled value includes：u_LP(t), i.e. anode local terminal Voltage sample value；u_LN(t), i.e. the voltage sample value of cathode local terminal；u_RP(t), i.e. the voltage sample of anode remote terminal Value；u_RN(t), i.e. the voltage sample value of cathode remote terminal；Wherein t refers to the time；

The electrode current sampled value includes：i_LP(t), i.e. the current sampling data of anode local terminal；i_LN(t), i.e., cathode is local eventually The current sampling data at end；i_RP(t), i.e. the current sampling data of anode remote terminal；i_RN(t), i.e. the electric current of cathode remote terminal is adopted Sample value；

The fault component pole tension value includes：Δu_LP(t), i.e., and u_LP(t) fault component of corresponding anode local terminal Voltage value；Δu_LN(t), i.e., and u_LN(t) the fault component voltage value of corresponding cathode local terminal；Δu_RP(t), i.e., and u_RP (t) the fault component voltage value of corresponding anode remote terminal；Δu_RN(t), i.e., and u_RN(t) corresponding cathode is remotely whole The fault component voltage value at end；

The fault component electrode current value includes：Δi_LP(t), i.e., and i_LP(t) fault component of corresponding anode local terminal Current value；Δi_LN(t), i.e., and i_LN(t) the fault component current value of corresponding cathode local terminal；Δi_RP(t), i.e., and i_RP (t) the fault component current value of corresponding anode remote terminal；Δi_RN(t), i.e., and i_RN(t) corresponding cathode is remotely whole The fault component current value at end；

The fault component mode voltage value includes：Δu_L0(t), i.e. the fault component common-mode voltage value of local terminal；Δu_L1(t), That is the fault component differential mode voltage value of local terminal；Δu_R0(t), i.e. the fault component common-mode voltage value of remote terminal；Δu_R1 (t), i.e. the fault component differential mode voltage value of remote terminal；

The fault component mould current value includes：Δi_L0(t), i.e. the fault component common-mode current value of local terminal；Δi_L1(t), That is the fault component differential-mode current value of local terminal；Δi_R0(t), i.e. the fault component common-mode current value of remote terminal；Δi_R1 (t), i.e. the fault component differential-mode current value of remote terminal；

The fault component traveling wave voltage value includes：Δu_L0+(t), i.e. the fault component common mode direct wave voltage of local terminal Value；Δu_L0-(t), i.e. the fault component common mode backward-travelling wave voltage value of local terminal；Δu_L1+(t), i.e. the failure of local terminal Component differential mode direct wave voltage value；Δu_L0-(t), i.e. the fault component differential mode backward-travelling wave voltage value of local terminal；Δu_R0+ (t), i.e. the fault component common mode direct wave voltage value of remote terminal；Δu_R0-(t), i.e. the fault component common mode of remote terminal Backward-travelling wave voltage value；Δu_R1+(t), i.e. the fault component differential mode direct wave voltage value of remote terminal；Δu_R1-(t), i.e., far The fault component differential mode backward-travelling wave voltage value of journey terminal；

The fault component travelling wave current value includes：Δi_L0+(t), i.e. the fault component common mode direct wave electric current of local terminal Value；Δi_L0-(t), i.e. the fault component common mode backward-travelling wave current value of local terminal；Δi_L1+(t), i.e. the failure of remote terminal Component differential mode direct wave current value；Δi_L1-(t), i.e. the fault component differential mode backward-travelling wave current value of local terminal；Δi_R0+ (t), i.e. the fault component common mode direct wave current value of remote terminal；Δi_R0-(t), i.e. the fault component common mode of remote terminal Backward-travelling wave current value；Δi_R1+(t), i.e. the fault component differential mode direct wave current value of remote terminal；Δi_R1-(t), i.e., far The fault component differential mode backward-travelling wave current value of journey terminal；

The fault component mould current value in Chosen Point includes：Δi_L0Failure point at the Chosen Point of (x, t), i.e. local terminal Measure common-mode current value；Δi_L1Fault component differential-mode current value at the Chosen Point of (x, t), i.e. local terminal；Δi_R0(x, t), i.e., Fault component common-mode current value at the Chosen Point of remote terminal；Δi_R1Failure point at the Chosen Point of (x, t), i.e. remote terminal Differential-mode current value is measured, wherein x is Chosen Point；

Fault component electrode current value at the Chosen Point includes：Δi_LP(x, t), i.e., at the Chosen Point of anode local terminal Fault component electrode current value；Δi_LN(x, t), i.e., the fault component electrode current value at the Chosen Point of cathode local terminal；Δi_RP (x, t), i.e., the fault component electrode current value at the Chosen Point of anode remote terminal；Δi_RN(x, t), i.e., in cathode remote terminal Chosen Point at fault component electrode current value.

4. it according to the method described in claim 3, wherein, in the fault component extraction step, calculates in the following ways The fault component pole tension value and the fault component pole tension value：

Wherein, T is predetermined time delay；

In the pole modular transformation step, the fault component mode voltage value and the fault component mould are calculated in the following ways Current value：

Step is calculated in the Bei Jielong models to include：

The fault component line wave voltage value is calculated in the following ways：

Wherein, Z_C0It is common mode wave impedance；Z_C1It is differential mode wave impedance；

The fault component line wave current value is calculated in the following ways：

The fault component mould current value at Chosen Point is calculated in the following ways：

Wherein, v₀It is the gait of march of fault component common mode traveling wave, v₁It is the gait of march of fault component differential mode traveling wave；

The fault component electrode current value at Chosen Point is calculated in the following ways：

5. according to the method described in claim 3, wherein, the current differential protection determination step includes：

If meet | Δ i_LP(x, t)+Δ i_RP(x, t) |>I_res, then judge state for anode internal fault；If meet | Δ i_LN (x, t)+Δ i_RN(x, t) |>I_res, then state is judged for cathode internal fault, wherein, I_resRepresent predetermined threshold value；

Otherwise, differential protection will not be activated.

6. according to the method described in claim 1, wherein described DC power grids are monopoles：

The Bei Jielong models calculate step and further include：

By being based on Bei Jielong models, the fault component pole tension value and the failure of local terminal and remote terminal are calculated Component mould current value obtains the fault component pole traveling wave voltage value of local terminal and remote terminal respectively；

The fault component pole traveling wave voltage value of local terminal and remote terminal is converted into local terminal and long-range end respectively The fault component line wave current value at end；

According to local terminal and the fault component pole travelling wave current value of remote terminal, the Chosen Point on the DC circuits is determined The local terminal at place and the fault component electrode current value of remote terminal.

7. according to the method described in claim 6, institute is wherein calculated in the following ways in the fault component extraction step State fault component pole tension value and fault component pole tension value：

Wherein T represents predetermined time delay, Δ i_L(t) be local terminal fault component electrode current value, Δ i_R(t) it is long-range end The fault component electrode current value at end, Δ u_L(t) be local terminal fault component pole tension value, Δ u_R(t) it is remote terminal event Hinder component pole tension value, i_L(t) be local terminal current sampling data, i_R(t) be remote terminal current sampling data, u_L(t) it is The voltage sample value of local terminal, u_R(t) be remote terminal voltage sample value, and t refers to the time；

Step is calculated in the Bei Jielong models to include：

Fault component pole traveling wave voltage value is calculated in the following ways：

Wherein, Z_CIt is wave impedance, Δ u_L+(t) be local terminal fault component pole direct wave voltage value；Δu_L-(t) it is local The fault component pole backward-travelling wave voltage value of terminal；Δu_R+(t) be remote terminal fault component pole direct wave voltage value；Δ u_R-(t) be remote terminal fault component pole backward-travelling wave voltage value；

The fault component pole travelling wave current value is calculated in the following ways：

Wherein, Δ i_L+(t) be local terminal fault component pole direct wave current value；Δi_L-(t) be local terminal failure Component pole backward-travelling wave current value；Δi_R+(t) be remote terminal fault component pole direct wave current value；Δi_R-(t) it is remote The fault component pole backward-travelling wave current value of journey terminal；

The fault component electrode current value at selected location is calculated in the following ways：

Wherein Δ i_L(x, t) is the fault component electrode current value at the Chosen Point of local terminal；Δi_R(x, t) is remote terminal Fault component electrode current value at Chosen Point, v are the gait of march of fault component traveling wave.

8. according to the method described in claim 7, wherein, include in the current differential protection determination step：

If meet | Δ i_L(x, t)+Δ i_R(x, t) | ＞ I_res, then state is judged for internal fault, wherein I_resIt is predetermined threshold value.

9. the method described in any one in claim 1-8, wherein the current differential protection determination step also wraps It includes：

If state is determined into internal fault, error protection order is sent to activate differential protection, otherwise will not activate difference Dynamic protection.

10. a kind of computer including suitable for performing method as described in one of claim 1 to 8 when running on computers The computer-readable medium of program code.

11. a kind of DC power network currents differential protective system, including with lower module：

Sampled value obtains module：Obtain the local terminal of DC circuits and pole tension sampled value and the electrode current sampling of remote terminal Value；

Fault component extraction module：Fault component is calculated according to the pole tension sampled value of local terminal and remote terminal respectively Pole tension value；And fault component electrode current value is calculated according to the electrode current value of local terminal and remote terminal respectively；

Bei Jielong model computation modules：Based on Bei Jielong models, calculated in the fault component extraction module by calculating Local terminal and remote terminal the fault component pole tension value and the fault component electrode current value, obtain local terminal The fault component electrode current value at the Chosen Point on DC circuits between remote terminal；

Current differential protection determination module：If the local terminal that is obtained in Bei Jielong model computation modules and remote terminal The fault component electrode current value at Chosen Point meets predetermined current differential protection criterion, then judges internal fault.

12. system according to claim 11, wherein, the DC power grids are that bipolar and described DC circuits include anode DC circuits and cathode DC circuits, the local terminal include anode local terminal and cathode local terminal, the remote terminal packet Anode remote terminal and cathode remote terminal are included, the anode DC circuits are electrically connected the anode local terminal and the anode is remote Journey terminal, and the cathode DC circuits are electrically connected the cathode local terminal and the cathode remote terminal, are selected from described The distance of point to the anode local terminal is identical with from the Chosen Point to the distance of the cathode local terminal, from the choosing The distance for pinpointing the anode remote terminal is identical with from the Chosen Point to the distance of the cathode remote terminal, also wraps It includes：

Pole modular transformation module：By to the anode local terminal, the anode remote terminal, the cathode local terminal and institute The each fault component pole tension value stated in cathode remote terminal carries out pole modular transformation, obtain local terminal and it is long-range eventually The fault component mode voltage value of each modulus in end and by the anode local terminal, the anode remote terminal, Each fault component electrode current value in the cathode local terminal and the cathode remote terminal carries out pole modular transformation, Obtain the fault component mould current value of each modulus of local terminal and remote terminal；

The Bei Jielong model computation modules further include：

By being based on Bei Jielong models, the fault component mode voltage value of each modulus of local terminal and remote terminal is calculated With the fault component mould current value, the fault component line wave to each modulus of local terminal and remote terminal is obtained respectively Voltage value；

The fault component line wave voltage value of local terminal and remote terminal is converted into local terminal and long-range end respectively The fault component line wave current value at end；

Respectively according to local terminal and the fault component line wave current value of remote terminal, the Chosen Point on DC circuits is determined The local terminal at place and the fault component mould current value of remote terminal；

Mould pole-change is carried out by the fault component mould current value of each modulus to the local terminal at Chosen Point, is obtained Each fault component electrode current value in anode local terminal and cathode local terminal at Chosen Point on DC circuits and Mould pole-change is carried out by the fault component mould current value of each modulus to the remote terminal at Chosen Point, is obtained selected The fault component electrode current value of anode remote terminal and cathode remote terminal at point.

13. system according to claim 12, wherein, the pole tension sampled value includes：u_LP(t), i.e., anode is local eventually The voltage sample value at end；u_LN(t), i.e. the voltage sample value of cathode local terminal；u_RP(t), i.e. the voltage of anode remote terminal is adopted Sample value；u_RN(t), i.e. the voltage sample value of cathode remote terminal；Wherein t refers to the time；

The electrode current sampled value includes：i_LP(t), i.e. the current sampling data of anode local terminal；i_LN(t), i.e., cathode is local eventually The current sampling data at end；i_RP(t), i.e. the current sampling data of anode remote terminal；i_RN(t), i.e. the electric current of cathode remote terminal is adopted Sample value；

The fault component pole tension value includes：Δu_LP(t), i.e., and u_LP(t) fault component of corresponding anode local terminal Voltage value；Δu_LN(t), i.e., and u_LN(t) the fault component voltage value of corresponding cathode local terminal；Δu_RP(t), i.e., and u_RP (t) the fault component voltage value of corresponding anode remote terminal；Δu_RN(t), i.e., and u_RN(t) corresponding cathode is remotely whole The fault component voltage value at end；

The fault component electrode current value includes：Δi_LP(t), i.e., and i_LP(t) fault component of corresponding anode local terminal Current value；Δi_LN(t), i.e., and i_LN(t) the fault component current value of corresponding cathode local terminal；Δi_RP(t), i.e., and i_RP (t) the fault component current value of corresponding anode remote terminal；Δi_RN(t), i.e., and i_RN(t) corresponding cathode is remotely whole The fault component current value at end；

The fault component mode voltage value includes：Δu_L0(t), i.e. the fault component common-mode voltage value of local terminal；Δu_L1(t), That is the fault component differential mode voltage value of local terminal；Δu_R0(t), i.e. the fault component common-mode voltage value of remote terminal；Δu_R1 (t), i.e. the fault component differential mode voltage value of remote terminal；

The fault component mould current value includes：Δi_L0(t), i.e. the fault component common-mode current value of local terminal；Δi_L1(t), That is the fault component differential-mode current value of local terminal；Δi_R0(t), i.e. the fault component common-mode current value of remote terminal；Δi_R1 (t), i.e. the fault component differential-mode current value of remote terminal；

The fault component traveling wave voltage value includes：Δu_L0+(t), i.e. the fault component common mode direct wave voltage of local terminal Value；Δu_L0-(t), i.e. the fault component common mode backward-travelling wave voltage value of local terminal；Δu_L1+(t), i.e. the failure of local terminal Component differential mode direct wave voltage value；Δu_L0-(t), i.e. the fault component differential mode backward-travelling wave voltage value of local terminal；Δu_R0+ (t), i.e. the fault component common mode direct wave voltage value of remote terminal；Δu_R0-(t), i.e. the fault component common mode of remote terminal Backward-travelling wave voltage value；Δu_R1+(t), i.e. the fault component differential mode direct wave voltage value of remote terminal；Δu_R1-(t), i.e., far The fault component differential mode backward-travelling wave voltage value of journey terminal；

The fault component travelling wave current value includes：Δi_L0+(t), i.e. the fault component common mode direct wave electric current of local terminal Value；Δi_L0-(t), i.e. the fault component common mode backward-travelling wave current value of local terminal；Δi_L1+(t), i.e. the failure of remote terminal Component differential mode direct wave current value；Δi_L1-(t), i.e. the fault component differential mode backward-travelling wave current value of local terminal；Δi_R0+ (t), i.e. the fault component common mode direct wave current value of remote terminal；Δi_R0-(t), i.e. the fault component common mode of remote terminal Backward-travelling wave current value；Δi_R1+(t), i.e. the fault component differential mode direct wave current value of remote terminal；Δi_R1-(t), i.e., far The fault component differential mode backward-travelling wave current value of journey terminal；

The fault component mould current value in Chosen Point includes：Δi_L0Failure point at the Chosen Point of (x, t), i.e. local terminal Measure common-mode current value；Δi_L1Fault component differential-mode current value at the Chosen Point of (x, t), i.e. local terminal；Δi_R0(x, t), i.e., Fault component common-mode current value at the Chosen Point of remote terminal；Δi_R1Failure point at the Chosen Point of (x, t), i.e. remote terminal Differential-mode current value is measured, wherein x is Chosen Point；

The fault component electrode current value at Chosen Point includes：Δi_LPAt (x, t), the i.e. Chosen Point of anode local terminal Fault component electrode current value；Δi_LNFault component electrode current value at (x, t), the i.e. Chosen Point of cathode local terminal；Δi_RP Fault component electrode current value at (x, t), the i.e. Chosen Point of anode remote terminal；Δi_RNThe choosing of (x, t), i.e. cathode remote terminal Fault component electrode current value at fixed point.

14. system according to claim 13 wherein in the fault component extraction module, calculates in the following ways The fault component pole tension value and the fault component pole tension value：

Wherein, T represents predetermined time delay；

In the pole modular transformation module, the fault component mode voltage value and the fault component mould are calculated in the following ways Current value：

Include in the Bei Jielong model computation modules：

The fault component line wave voltage value is calculated in the following ways：

Wherein Z_C0It is common mode wave impedance；Z_C1It is differential mode wave impedance；

The fault component line wave current value is calculated in the following ways：

The fault component mould current value at Chosen Point is calculated in the following ways：

Wherein, v₀It is the gait of march of fault component common mode traveling wave, v₁It is the gait of march of fault component differential mode traveling wave；

The fault component electrode current value at Chosen Point is calculated in the following ways：

15. system according to claim 13, wherein the current differential protection determination module includes：

If meet | Δ i_LP(x, t)+Δ i_RP(x, t) | ＞ I_res, then judge state for anode internal fault；If meet | Δ i_LN(x, t)+Δ i_RN(x, t) |>I_res, then state is judged for cathode internal fault, wherein, I_resRepresent predetermined threshold value；

Otherwise, differential protection will not be activated.

16. system according to claim 11, wherein, the DC power grids are monopoles：

The Bei Jielong model computation modules further include：

By being based on Bei Jielong models, the fault component pole tension value and the failure of local terminal and remote terminal are calculated Component mould current value obtains the fault component pole traveling wave voltage value of local terminal and remote terminal respectively；

The fault component pole traveling wave voltage value of local terminal and remote terminal is converted into local terminal and long-range end respectively The fault component line wave current value at end；

The Chosen Point on the DC circuits is determined according to the fault component pole travelling wave current value of local terminal and remote terminal The local terminal at place and the fault component electrode current value of remote terminal.

17. system according to claim 16, wherein, in the fault component extraction model, count in the following ways Calculate the fault component pole tension value and the fault component pole tension value：

Wherein T represents predetermined time delay, Δ i_L(t) be local terminal fault component electrode current value, Δ i_R(t) it is long-range end The fault component electrode current value at end, Δ u_L(t) be local terminal fault component pole tension value, Δ u_R(t) it is remote terminal event Hinder component pole tension value, i_L(t) be local terminal current sampling data, i_R(t) be remote terminal current sampling data, u_L(t) it is The voltage sample value of local terminal, u_R(t) be remote terminal voltage sample value, and t refers to the time；

Include in the Bei Jielong model computation modules：

The fault component pole traveling wave voltage value is calculated in the following ways：

Wherein, Z_CIt is wave impedance, Δ u_L+(t) be local terminal fault component pole direct wave voltage value；Δu_L-(t) it is local The fault component pole backward-travelling wave voltage value of terminal；Δu_R+(t) be remote terminal fault component pole direct wave voltage value；Δ u_R-(t) be remote terminal fault component pole backward-travelling wave voltage value；

The fault component pole travelling wave current value is calculated in the following ways：

Wherein, Δ i_L+(t) be local terminal fault component pole direct wave current value；Δi_L-(t) be local terminal failure Component pole backward-travelling wave current value；Δi_R+(t) be remote terminal fault component pole direct wave current value；Δi_R-(t) it is remote The fault component pole backward-travelling wave current value of journey terminal；

The fault component electrode current value at selected location is calculated in the following ways：

Wherein Δ i_L(x, t) is the fault component electrode current value at the Chosen Point of local terminal；Δi_R(x, t) is remote terminal Fault component electrode current value at Chosen Point, v are the gait of march of fault component traveling wave.

18. system according to claim 17, wherein, include in the current differential protection determination module：

If meet | Δ i_L(x, t)+Δ i_R(x, t) | ＞ I_res, then state is judged for internal fault, wherein I_resIt is predetermined threshold value.

19. according to the system described in any one in claim 11-18, wherein, the current differential protection determination module is also Including：

If state is determined into internal fault, error protection order is sent to activate differential protection, otherwise will not activate difference Dynamic protection.