JPH09284989A - Protective relay, and method and protective relay system for estimating timing to zero residual magnetic flux - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent malfunction by breaking a main transformer so that the residual magnetic flux of the iron core of the main transformer may be settled within a given zero range, when a protective relay outputs a trip signal and breaks the main transformer from a power system. SOLUTION: A protective relay has a system input means 1 which measures the primary voltage V1 and current 11 and the secondary voltage V2 and current 12 of a main transformer 1, and outputs output signals 11-14. This has a protective relay operating circuit 2 which detects the accident of a power system or inside a transformer with the data 11-14 of the system input means 1, and outputs trip signals 21. A forecasting circuit 5 forecasts the timing to zero the residual magnetic fluxes of the iron core of the main transformer with the data 11-14 of the system input means 1. A logical circuit 3 takes the AND of the trip signal 21 of the protective relay operating circuit 2 and a magnetic flux forecast signal 55 of the forecasting circuit 5, and outputs a trip signal 31. Therefore, the residual magnetic flux of the iron core of the main transformer is settled within the specified zero range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective relay for protecting a transformer, a method for predicting the timing of zero residual flux, and a protective relay system.

[0002]

2. Description of the Related Art A protective relay that protects a main transformer of a power system outputs a trip command when an accident in the power system or the inside of the transformer is detected, and is installed at an input / output stage of the main transformer. Break the fault current with the breaker. FIG. 5 is a configuration diagram of a main part of a protective relay system for protecting a main transformer of a power system used in the related art and the present invention. In FIG. 5, the three-winding transformer (main transformer) TR in which the primary winding w1 and the secondary winding w2 are Y-connected and the tertiary winding w3 is Δ-connected is cut off to the power system, respectively. It is connected via devices S1 and S2. Then, the voltage and current on the primary side and the secondary side of the three-winding transformer TR are input to the protective relay RY via the voltage transformers PT1 and PT2 and the current transformers CT1 and CT2. When the protective relay RY detects an internal fault in the power system or the main transformer TR, it outputs a trip command 21 and the breaker S1, S2 installed at the input / output stage of the main transformer TR detects the fault current. Cut off.

However, when the accident current is interrupted at random timing, the inside of the iron core of the transformer is generally demagnetized and residual magnetic flux remains, so that the circuit breaker must be re-operated to recover the power system after the accident recovery. When turned on, a large exciting inrush current flows through the main transformer TR. This magnetizing inrush current is detected as an abnormal current by the protective relay RY, and there is a possibility that the trip command 21 is output and the reclosing failure occurs.

As a countermeasure against such an inrush current, in the protection relay RY of the prior art, the malfunction of the protective relay RY is prevented by utilizing the fact that the excitation inrush current has a large second harmonic component. FIG. 6 shows an example of such a malfunction prevention measure. In FIG. 6, the protective relay RY is a ratio differential relay 87 that detects an internal fault in the power system or the main transformer TR, an exciting inrush current detection element 86, and a ratio differential relay.
And an output of 87 and the negative output of the output of the exciting inrush current detection element 86.

With this configuration, the protective relay RY sends the trip command 21 from the ratio differential relay 87 to the exciting inrush current of the exciting inrush current detecting element 86 by the exciting inrush current flowing when the circuit breakers S1 and S2 are closed again. By denying the above, the protection relay RY is prevented from outputting the trip command 21GA, and the malfunction of shutting off the power system again is prevented.

[0006]

However, in the protective relay of the prior art, the exciting inrush current detecting element is caused by the difference in the capacity of each main transformer, the amount of iron core, or the normal magnetic flux density level with respect to the saturated magnetic flux density of the iron core. The detection sensitivity must be adjusted, and various inrush current levels of the excitation inrush current detection element must be examined.

The present invention has been made in view of the above points, and an object thereof is to solve the above-mentioned problems and to set the magnitude of the exciting inrush current when the main transformer is reconnected within a predetermined range. Provided are a protection relay that keeps the detection sensitivity of the inrush current detection element constant and prevents malfunction and malfunction as a protection relay system, a method of predicting the timing of zero residual flux, and a protection relay system. It is in.

[0008]

In order to achieve the above object, in the present invention, a main transformer and one of the main transformers are provided.
When a fault is detected in the power system or the transformer, a trip command is issued to the circuit breaker that is connected to the power system and is connected to the secondary side and the secondary side. In the protective relay that outputs, a system input means that measures the voltage and current on the primary and secondary sides of the main transformer, and a trip signal that detects an accident in the power system or the transformer based on the data from this system input means. Protective relay calculation circuit that outputs the output, a prediction circuit that predicts the timing to zero the residual magnetic flux of the iron core of the main transformer from the data from the system input means, a trip signal of the protection relay calculation circuit, and a prediction of the magnetic flux zero of the prediction circuit. And a logic circuit that performs a logical product with a signal.

Further, the prediction circuit calculates the induced voltages E1, E2 on the primary side and the secondary side of the main transformer based on the data from the system input means and the transformer data, and the induced voltages E1, E2 are calculated.
When the ratio of 2 is equal to the ratio of the number of primary windings and the number of secondary windings of the main transformer within the predetermined tolerance, the voltage and current on the primary and secondary sides of the main transformer are Healthy voltage,
Considered as current, when the ratio of induced voltage E1, E2 is outside the allowable error range of the ratio of primary and secondary windings, the voltage and current on the primary and secondary sides of the main transformer are When the protective relay outputs a trip command, the voltage and current on the primary side or the secondary side of the main transformer are regarded as voltage and current, and the voltage and current on the primary phase are
When the current is a current, the timing time series at which the residual magnetic flux of the iron core is zero is the time series at which the residual magnetic flux is zero, with the time series delayed by 90 electrical degrees from the timing at which the induced voltages E1 and E2 become zero. If there is a sound phase in the other phase, the timing time series for zero residual flux is only the electrical angle at which each phase of the main transformer is structurally determined from the timing time series of zero residual flux obtained from the above healthy phase. The timing time series is shifted, and this timing time series is corrected with the voltage and current at the time of accident to make a timing time series with zero residual magnetic flux, and when all phases are in the accident phase, obtained from the healthy voltage and current immediately before the accident occurs. Output the trip command by correcting the timing time series obtained from the power system frequency with the timing time when the residual magnetic flux is zero when the sound condition is correct as the timing time series with zero residual magnetic flux by correcting the voltage and current values at the time of the accident. The magnetic flux zero prediction signal to be output is output in advance of the delay time from the timing time series of these residual magnetic flux zero until the circuit breaker receives the trip command and opens the circuit, by a deviation time from the cycle of the power system frequency.

With this configuration, when the protective relay outputs the trip command and shuts off the main transformer from the power system, it is possible to shut off the residual magnetic flux of the iron core of the main transformer so that the residual magnetic flux falls within a predetermined zero range. it can. Further, the main transformer, the first and second breakers arranged on the primary side and the secondary side of the main transformer for connecting to the power system, and the primary side and the secondary side of the main transformer. In the protective relay system of the electric power system, which includes the protective relay that inputs the voltage and current of, and outputs the trip command to the circuit breaker when an accident in the electric power system or the transformer is detected, the protective relay system is It is equipped with a third circuit breaker that is turned on by a trip command and a low-frequency power source that is applied to the main transformer through this third circuit breaker, and the protective relay outputs a trip command and the main transformer from the power system. When shutting off the transformer, the trip command shuts off the main transformer from the power system by at least the first breaker,
The circuit breaker shall apply a low-frequency power source to the main transformer and shut off the residual magnetic flux of the iron core of the main transformer so that it remains within a predetermined zero range.

With this configuration, the residual magnetic flux of the iron core of the main transformer is cut off so that the residual magnetic flux falls within a predetermined zero range. Therefore, the circuit breaker is reclosed and the magnetic field is rushed when the main transformer is closed. It is possible to suppress the magnitude of the current within a predetermined range and prevent malfunction and malfunction of the protective relay system.

[0012]

1 is a block diagram of a protective relay as one embodiment of the present invention, FIG. 2 is a block diagram for explaining a method of predicting the timing of zero residual flux in one embodiment, and FIG. Is an equivalent circuit diagram of a main transformer, and FIG. 4 is a block diagram illustrating a protective relay system as another embodiment according to the present invention.

The protective relay system illustrated in FIG.
Main transformer TR, circuit breakers S1 and S2 arranged on the primary side and secondary side of this main transformer TR to connect to the power system, and shut off when an accident in the power system or transformer TR is detected. vessel
It consists of a protective relay RY that outputs a trip command to S1 and S2. When this protective relay RY outputs a trip command and shuts off the main transformer TR from the power system, the main transformer
By shutting off so that the residual magnetic flux of the TR core falls within a predetermined zero range, for example, within a few percent of the saturation magnetic flux density of the iron core, the circuit breakers S1 and S2 are reclosed and the main transformer TR is turned on. When connected, it is possible to prevent the magnetic flux density for exciting the iron core from reaching the saturation magnetic flux density level regardless of the polarity of the power supply voltage applied to the main transformer TR. As a result, when the main transformer TR is reconnected, the magnitude of the exciting inrush current can be suppressed within a predetermined range, and malfunctions and malfunctions of the protective relay system can be prevented.

Now, assuming that the main transformer TR is composed of, for example, a three-phase transformer (hereinafter, shown by suffixes a, b, and c when distinguishing each phase of three phases), a protective relay. Primary side voltage V1a, V1b, V1c, primary side currents I1a, I1b, I1c, secondary side voltage V2a, V2b, V2c, secondary side current I2a, input to RY The magnetic fluxes φa, φb, φc of the iron core may be predicted from I2b, I2cy, and the three phases may be individually cut off at the timings when the magnetic fluxes φa, φb, φc are close to zero.

[0015]

【Example】

(Embodiment 1) In FIG. 1, a protective relay RY is a main transformer.
System input means 1 that measures the voltage V1, current I1 and voltage V2, current I2 on the primary side of TR and outputs output signals (data) 11, 12, 13, 14 and this system input means Data 11, 12, 13 from the protective relay arithmetic circuit 2 which detects an accident in the power system or the transformer TR from the data 11, 12, 13 and 14 and outputs a trip signal 21 ,14
Prediction circuit 5 that predicts the timing of zeroing the residual magnetic flux of the iron core of main transformer TR, trip signal 21 of protection relay arithmetic circuit 2 and magnetic flux zero prediction signal 55 of prediction circuit 5, and the trip command is obtained. And a logic circuit 3 for outputting 31.

As described in the prior art, the protective relay arithmetic circuit 2 has the function of the ratio differential relay 87 for detecting an internal fault in the power system or the main transformer TR, and the exciting inrush current detecting element.
And a logic element AND for performing a logical product of the function output of the ratio differential relay 87 and the negative output of the function output of the exciting inrush current detection element 86. Here, the purpose expressed by the function is the data obtained from the system input means 1 regarding the characteristics of the ratio differential relay 87 and the excitation inrush current detection element 86.
Sampling processing is performed at high speed by 11,12,13,14,
This is a representation including a circuit obtained by digital arithmetic processing.

Further, in the illustrated example, in the predicting circuit 5, the time delay until the protection relay RY outputs the trip command 31 and the breaker cuts off the main transformer TR from the power system is set as the breaker delay time parameter 51. It is configured so that it can be set.
With this configuration, when the protective relay arithmetic circuit 2 outputs the trip command 21 and shuts off the main transformer TR from the power system, the trip command 31 is output at the timing of the magnetic flux zero prediction signal 55 calculated by the prediction circuit 5. By the main transformer TR
The residual magnetic flux of the iron core can be cut off at a timing when the residual magnetic flux falls within a predetermined zero range.

The protective relay RY will be described below with reference to FIGS.
A method of predicting the timing of making the residual magnetic flux of the iron core of the main transformer TR zero by the predicting circuit 5 of FIG. In FIG.
The prediction circuit 5 includes a voltage V1, a current I1 and a voltage V2, a current I2 on the primary side of the main transformer TR measured by the system input means 1.
Based on the data 11,12,13,14 of the main transformer and the transformer data 52 (r1, x1, r2, x2, g0, b0) shown in FIG.
Calculate the induced voltages E1 and E2 on the secondary and secondary sides.

The ratio E1 / E2 of the induced voltages E1 and E2 is the ratio (w1 / w1) of the number of turns of the primary winding w1 and the secondary winding w2 of the main transformer TR within a predetermined allowable error range. When w2 is equal to the winding ratio a), the voltages V1, V2, currents I1, I2 on the primary and secondary sides of the main transformer TR are checked from the viewpoint of whether there is an internal fault in the main transformer TR.
Is the healthy voltage 11,12 and the healthy current 13,14. Induced voltage
E1 / E2 ratio E1 / E2 is the ratio of primary and secondary winding numbers (w1 / w2)
When it is out of the allowable error range of, it is assumed that an accident has occurred inside the main transformer TR, and the voltages V1, V2 and currents I1, I2 on the primary and secondary sides of the main transformer at this time are Voltage at accident 4
1,42, current at accident 43,44.

3A shows an equivalent circuit diagram of one phase of the main transformer TR, and FIG. 3B shows a vector diagram of one phase of the main transformer TR. In (A) of Fig. 3, if the primary side voltage of the main transformer TR is V1, the primary side current is I1, and the primary side impedance is (r1 + jx1) as transformer data, the primary side induced voltage E1
There is a vector operation relation of (1) between and.

[0021]

[Equation 1] E1 = V1− (r1 + jx1) × I1 (1) Also, the secondary side voltage of the main transformer TR is V2, the secondary side current is I2, and the secondary side impedance is transformer data. To (r2 + jx
2), there is a relation of the vector operation of the equation (2) with the secondary induced voltage E2.

[0022]

[Equation 2] E2 = V2 + (r2 + jx2) × I2 (2) Then, the admittance of the excitation circuit of the iron core is Y (= g0 + jb
0) and the excitation current is Im, there is a relation of the vector operation of the equation (3) with the primary side induced voltage E1.

[0023]

[Equation 3] E1 = Im / (g0 + jb0) (3) V1, I1, V2, and I2 in Eqs. (1) and (2) are voltage and current data 11 measured by the system input means 1. , 12,13,14 and (r
1 + jx1), (r2 + jx2) is the data given in advance as the transformer data 52 (r1, x1, r2, x2), so the primary side induction is performed by performing vector operation based on these data. The voltage E1 and the secondary side induced voltage E2 can be obtained.

FIG. 3B illustrates the vector operation of the above equations (1) to (3). In FIG. 3B, when the magnetic flux φ is shown by a vector perpendicular to the origin O,
1 in the direction 90 degrees ahead of the magnetic flux φ, that is, in the horizontal direction
Next, the secondary induced voltages E1 and E2 and the magnetizing current Ic flow. In the illustrated example, when the load is a resistive load, the secondary side voltage V2 and the current I2 are on the same vector line, and the secondary side impedance (r2 + jx2) and the secondary side current I2 are derived from the vector of this voltage V2.
The secondary induced voltage E2 is at the point where the vector product of is added. Further, the primary side voltage V1 is at a point where the vector product of the primary side impedance (r1 + jx1) and the primary side current I1 is added from the vector of the primary side induced voltage E1.

Next, the case where the protective relay RY outputs the trip command 31 will be described. The method of predicting the timing time series to make the residual magnetic flux of the iron core zero is the voltage of the healthy phase 11, 12,
There are the following three prediction methods depending on the presence / absence of currents 13 and 14.
That is, (1) voltage V1, V2, current on the primary or secondary side of the main transformer TR
When I1, I2 are voltage 11,12 and current 13,14 of sound phase, the timing time series t1, t2, ...
The time series delayed by 90 ° in electrical angle from the timings t1 ′, t2 ′, ... At which the induced voltages E1, E2 calculated by the prediction circuit 5 become zero become the timing time series t1, t2 ,.

(2) The timing time series t1b, t2b, ... When the residual magnetic flux of the accident phase (for example, the b phase) is set to zero, if there is a sound phase (for example, the a phase) in the other phase, the above (1) Main transformer from timing time series t1a, t2a, ...
The timing time series is shifted by an electrical angle (for example, 120 ° or 240 ° in the case of a three-phase transformer) in which each phase (a, b, c phase) of TR is structurally determined, and voltage 41, 42, current 43 , 44, the timing time series t1b, t2b, ... Are corrected to obtain the residual magnetic flux zero timing time series t1b ′, t2b ′ ,.

(3) When all phases are accident phases, a timing time series t0 (for example, three-phase) in which the sound residual magnetic flux obtained from the sound voltage 11 and current 12 and current 13 and 14 immediately before the accident is zero In the case of the power supply system, the timing time series obtained by shifting the time by the period based on the power system frequency f from t0a, t0b, t0c) is corrected by the fault voltage and current and the residual magnetic flux is zero. t1 ", t2", ...

Magnetic flux zero prediction signal for outputting trip command 31
55 is a timing time series of these residual magnetic flux zeros (t1, t2, ..., (2), t1b ', t2b', ..., (3), t1 ", t2",
...), the delay time Δt until the circuit breakers S1 and S2 receive the trip command 31 to open the circuit is output in advance by the time difference from the cycle based on the power system frequency f, so that the core of the main transformer TR is output. Can be cut off so that the residual magnetic flux of is within a predetermined zero range.

In the above description, taking the case of (1) as an example, the timing time series of zero residual flux is the timing t at which the induced voltages E1 and E2 calculated by the prediction circuit 5 become zero.
The time series delayed by 90 ° in electrical angle from 1 ', t2', ... is the time series t1, t2, ... with zero residual flux, but the induced voltage
The timing time series t1, t2, ... Which is the peak value of E1, E2 is obtained, and this timing is used as the timing time series t for zero residual flux.
It may be 1, t2, ...

(Second Embodiment) Next, a protective relay system as another embodiment will be described with reference to FIG. In the second embodiment, unlike the first embodiment, when the main transformer is cut off from the power system, the residual magnetic flux zero of the iron core of the main transformer is cut off without prediction, and a low-frequency power source is applied after the cutoff. ,
The residual magnetic flux of the iron core falls within a predetermined zero range.

In FIG. 4, the protective relay system of the present invention comprises a main transformer TR, a primary side of the main transformer TR and a secondary transformer.
Voltages on the primary and secondary sides of the main transformer TR and the first and second circuit breakers S1 and S2 that are provided on the secondary side and connected to the power system.
When V1, V2 and currents I1 and I2 are input and an accident in the power system or transformer is detected, a trip command to breakers S1 and S2 is issued.
It includes a protective relay RY that outputs 21, a third circuit breaker S3 that is turned on by a trip command, and a low-frequency power supply V3 that is applied to the main transformer TR via the third circuit breaker S3. Composed.

In such a configuration, when the protective relay RY outputs the trip command 21 and shuts off the main transformer TR from the power system, the trip command 21 causes at least the first circuit breaker S1 to disconnect the main transformer TR from the power system. The TR is cut off, the low frequency power supply V3 is applied to the main transformer TR by the third breaker S3, and the main transformer TR
The residual magnetic flux of the iron core is cut off so that the residual magnetic flux falls within a predetermined zero range.

As a result, when the main transformer TR is cut off, the residual magnetic flux of the iron core can be made close to zero.
The magnitude of the exciting inrush current when S1 is turned on again and the main transformer TR is turned on can be kept within a predetermined range, and malfunctions and malfunctions of the protection relay system can be prevented.

[0034]

As described above, according to the present invention, in the prior art, the detection sensitivity of the exciting inrush current detection element was examined for each main transformer. However, when the main transformer is cut off, the residual iron core remains. By making the magnetic flux near zero, the magnitude of the exciting inrush current when the circuit breaker is turned on again and the main transformer is reconnected is kept within a predetermined range, and the detection sensitivity of the exciting inrush current detection element is kept constant. It is possible to provide a protective relay that prevents malfunctions and malfunctions as a protective relay system, a method for predicting the timing of zero residual magnetic flux, and a protective relay system.

[Brief description of drawings]

FIG. 1 is a block diagram of a protective relay as an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a method of predicting a timing at which a residual magnetic flux becomes zero according to an embodiment.

[Fig. 3] Equivalent circuit diagram of main transformer

FIG. 4 is a block diagram illustrating a protection relay system as another embodiment according to the present invention.

[Fig. 5] Main part configuration diagram of a protective relay system that protects a main transformer of an electric power system

[Fig.6] Circuit diagram for preventing malfunction of protective relay RY due to inrush current of excitation

[Explanation of symbols]

 1 system input means 11,12,13,14,41,42,43,44 data 2 protection relay arithmetic circuit 21,31 trip signal 3 logic circuit 5 prediction circuit 51 parameter setting value 52, r1, r2, x1, x2, g0, b0 Transformer data 55 Flux zero prediction signal 86 Excitation inrush current detection element 87 Ratio differential relay V1, V2 Transformer voltage I1, I2 Transformer current E1, E2 Induced voltage Im Excitation current φ Magnetic flux S1, S2, S3 Break Transformer TR Main transformer V3 Low frequency power supply RY Protective relay PT1, PT2 Voltage transformer CT1, CT2 Current transformer

Claims (3)

[Claims] Claim: What is claimed is: 1. A main transformer and a circuit breaker, which is arranged on the primary side and the secondary side of the main transformer and is connected to the electric power system, together with a main system protective relay system. In a protective relay that outputs a trip command to the circuit breaker when an accident inside the transformer is detected, a system input means for measuring the voltage and current on the primary and secondary sides of the main transformer, and from this system input means Protection relay arithmetic circuit that detects an accident in the power system or transformer based on the data of the power transformer and outputs a trip signal, and a prediction circuit that predicts the timing to zero the residual magnetic flux of the iron core of the main transformer from the data from the system input means And a logic circuit that takes the logical product of the trip signal of the protective relay calculation circuit and the magnetic flux zero prediction signal of the prediction circuit.The protection relay outputs the trip command and the main transformer from the power system. When blocking, the main residual magnetic flux of the transformer core is cut off as fall within zero a predetermined range, protection relay, characterized in that. 2. A method for predicting the timing when the predicting circuit of the protective relay according to claim 1 sets the residual magnetic flux of the iron core of the main transformer to zero, in which the predicting circuit comprises data from the grid input means and the transformer. Based on the data and, the induced voltage E1, E2 of the primary side and the secondary side of the main transformer is calculated, and the ratio of the induced voltage E1, E2 is within the predetermined allowable error range. When the ratio of the number of primary windings and the number of secondary windings is equal, the voltage on the primary side and secondary side of the main transformer,
The current is regarded as a healthy voltage and current, and when the ratio of the induced voltage E1 and E2 is outside the allowable error range of the ratio of the primary and secondary winding numbers, the primary and secondary sides of the main transformer Voltage and current are regarded as fault voltage and current, and when the protective relay outputs a trip command, the voltage or current on the primary or secondary side of the main transformer is the voltage or current on a healthy phase. , The time sequence for making the residual magnetic flux of the iron core zero is the time sequence of 90 ° electrical angle delayed from the time when the induced voltages E1 and E2 become zero, as the timing sequence of zero residual magnetic flux, and the residual magnetic flux of the accident phase If there is a sound phase in other phases, the timing time series with zero is the timing time series with the electrical angle at which each phase of the main transformer is structurally determined from the timing time series of zero residual flux obtained from the sound phase. The voltage at the time of the accident,
This timing time series is corrected by the current value to make a timing time series with zero residual magnetic flux, and when all phases are in the accident phase, the sound voltage immediately before the accident occurs,
The timing command sequence obtained from the power system frequency with the timing time when the residual magnetic flux in a sound state is zero obtained from the current is used as the starting point, is corrected with the voltage and current at the time of an accident to be the timing sequence sequence with zero residual flux, and the trip command is issued. The flux zero prediction signal to be output shall be output in advance of the delay time from the timing time series of these residual flux zero to the time when the circuit breaker receives the trip command and opens the circuit, by the deviation time from the cycle of the power system frequency. A method for predicting the characteristic residual magnetic flux zero. 3. A main transformer, first and second breakers arranged on the primary side and the secondary side of the main transformer for connection with a power system, and a primary side of the main transformer and In the protection relay system of the power system, which comprises the protection relay that inputs the voltage and current of the secondary side and outputs the trip command to the circuit breaker when an accident in the power system or the transformer is detected, the system is , A third circuit breaker that is turned on by a trip command, and a low-frequency power source that is applied to the main transformer via this third circuit breaker, and the protection relay outputs a trip command and the mains from the power system. When shutting off the transformer, at least
The first circuit breaker disconnects the main transformer from the power system, the third circuit breaker applies a low-frequency power source to the main transformer, and the residual magnetic flux of the iron core of the main transformer falls within a predetermined zero range. A protective relay system that is characterized by: