CN108872769A - A kind of double earthfault test method - Google Patents

Abstract

A two-phase ground fault test method, the short-circuit sequence network of the circuit short-circuit is comprehensive zero-sequence impedance Z0, comprehensive negative-sequence impedance Z2, comprehensive positive-sequence impedance Z1, and the comprehensive zero-sequence impedance Z0 and comprehensive negative-sequence impedance Z2 are connected in parallel with the comprehensive The positive sequence impedance Z1 is connected in series to both ends of the system potential E, and the zero sequence current I0 flows through the integrated zero sequence impedance Z0, the negative sequence current I2 flows through the integrated negative sequence impedance Z2, and the positive sequence current flows through the integrated positive sequence impedance Z1 as Ⅰ1. A two-phase-to-ground fault test method that can use data to simulate, thereby reducing the short-circuit probability of two-phase-to-ground faults in the power system.

Description

A two-phase ground fault test method

technical field

The invention relates to a two-phase ground fault test method, in particular to a two-phase ground fault test method which can be accurately simulated in advance.

Background technique

Two-phase-to-ground short circuit is a type of fault with a high probability of occurrence in power systems. Since the fault mechanism is between two-phase short circuit and single-phase Scholars are confused. The relay protection equipment installed in the large-current grounding system must be able to reflect various faults (including two-phase ground faults) within the protected range, and be reliably cut off in the shortest possible time. In order to ensure that the installed relay protection equipment can play a protective role, acceptance inspection before commissioning and regular inspection during operation are mandatory items. However, none of the microcomputer relay testers used in the field has a fixed module for verifying the two-phase-to-ground fault, and it is difficult to re-deduce the state quantities of the two-phase-to-ground fault. The integrity of the test cannot be guaranteed, while increasing the risk of failure.

Contents of the invention

In order to solve the above technical problems, the present invention proposes a two-phase ground fault test method, which can use data to simulate a two-phase ground fault test method, thereby reducing the short-circuit probability of two-phase ground faults in the power system.

In order to achieve the above-mentioned technical features, the object of the present invention is achieved in this way: a two-phase ground fault test method, the short-circuit sequence network is integrated zero-sequence impedance Z0, integrated negative-sequence impedance Z2, integrated positive-sequence impedance Z1, integrated The zero-sequence impedance Z0 and the integrated negative-sequence impedance Z2 are connected in parallel and then connected in series with the integrated positive-sequence impedance Z1, connected to both ends of the system potential E, in which the zero-sequence current I0 flows through the integrated zero-sequence impedance Z0, and the negative sequence flows through the integrated negative-sequence impedance Z2 The current I2, the positive sequence current flowing in the comprehensive positive sequence impedance Z1 is I1; the zero sequence compensation coefficient K,

usually Z1=Z2 in static components;

Thus Z0=(1+3K)Z1

Assuming that the BC two-phase ground fault is taken as an example, the symmetrical component method is used to obtain:

Non-fault phase current: I _A ＝I _A1 +I _A2 +I _A0 ＝0

Among them, I _A1 is the positive sequence component of the A-phase current, I _A2 is the negative sequence component of the A-phase current, and I _A0 is the zero-sequence component of the A-phase current.

The fault leading phase current is: I _B ＝I _B1 +I _B2 +I _B0 ＝α ² I _A1 +αI _A2 +I _A0

The fault lagging phase current is: I _C ＝I _C1 +I _C2 +I _C0 ＝αI _A1 +α ² I _A2 +I _A0

where α is a unit vector operator, namely The above two formulas are based on the components of the non-fault phase

Calculated by vector operator.

The corresponding phasors are defined as follows: OH=I _B , OE=I _B1 , MH=I _B0 , EM=I _B2 ,

And △EMG is an equilateral triangle whose side length is the modulus of I ₂ , so:

And HF⊥EG at point F

Obtained from the phasor diagram:

Considering the setting of the positive sequence impedance angle Φ1, the fixed current method is used to simulate the fault, so as to obtain the general fault current calculation formula:

Leading phase current:

lag phase current

in is the leading phase angle of two phase-to-ground faults, is the phase angle of the lag phase, and φ is the calculated deflection angle.

Further speaking, the formula for finding the fault phase voltage is: the neutral current flowing into the relay element

Adjust the impedance according to the phase-to-phase short circuit of the line: Z _kn calculates the line voltage as follows:

U _φφ = mI _φφ Z _kn

Where I _ΦΦ is the line current, U _φΦ is the line voltage

In the formula, m is 0.7, 0.95 and 1.05 respectively;

Corresponding phase voltage The angle does not change.

The advantage of the present invention is that, using intuitive phasor analysis, the action equation for two-phase grounding faults is deduced, and the specific impedance value is substituted into the equation to accurately calculate the amplitude and phase angle of each electrical quantity, and then in various tests By setting these quantities in the instrument and applying them to the protection element, the action behavior of the protection in the event of a two-phase ground fault can be quickly simulated.

Description of drawings

The present invention will be further described below in conjunction with drawings and embodiments.

Figure 1 is the equivalent sequence network model of two-phase ground fault.

Figure 2 is a three-phase current phasor diagram assuming that the BC phase is grounded and short-circuited as an example.

Figure 3 is a test wiring diagram.

Figure 4. When the tester simulates the grounding short circuit of the BC phase, the power setting diagram of the tester corresponds to 0.95 times the set impedance.

Detailed ways

Embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

A two-phase ground fault test method, the short-circuit sequence network (as shown in Figure 1) is composed of integrated zero-sequence impedance Z0, integrated negative-sequence impedance Z2, integrated positive-sequence impedance Z1, integrated zero-sequence impedance Z0, and integrated negative-sequence impedance Z2 in parallel After that, it is connected in series with the comprehensive positive sequence impedance Z1, and connected to both ends of the system potential E, in which the zero sequence current I0 flows through the comprehensive zero sequence impedance Z0, the negative sequence current I2 flows through the comprehensive negative sequence impedance Z2, and the positive sequence current I2 flows through the comprehensive positive sequence impedance Z1. The sequence current is Ⅰ1; the zero-sequence compensation coefficient K,

usually Z1=Z2 in static components;

Thus Z0=(1+3K)Z1

Assuming BC two-phase ground fault, using the symmetrical component method (as shown in Figure 2):

Non-fault phase current: I _A ＝I _A1 +I _A2 +I _A0 ＝0

Among them, I _A1 is the positive sequence component of the A-phase current, I _A2 is the negative sequence component of the A-phase current, and I _A0 is the zero-sequence component of the A-phase current.

The fault leading phase current is: I _B ＝I _B1 +I _B2 +I _B0 ＝α ² I _A1 +αI _A2 +I _A0

The fault lagging phase current is: I _C ＝I _C1 +I _C2 +I _C0 ＝αI _A1 +α ² I _A2 +I _A0

where α is a unit vector operator, namely The above two formulas are based on the components of the non-fault phase

Calculated by vector operator.

The corresponding phasors are defined as follows: OH=I _B , OE=I _B1 , MH=I _B0 , EM=I _B2 ,

And △EMG is an equilateral triangle whose side length is the modulus of I ₂ , so:

And HF⊥EG at point F

Obtained from the phasor diagram:

Considering the setting of the positive sequence impedance angle Φ1, the fixed current method is used to simulate the fault, so as to obtain the general fault current calculation formula:

Leading phase current:

lag phase current

in is the leading phase angle of two phase-to-ground faults, is the phase angle of the lag phase, and φ is the calculated deflection angle.

As shown in Figure 3, take safety measures for the line protection device to be tested in accordance with the on-site safety work regulations, connect the test line of the tester with three voltages and three currents according to the wiring diagram of the line protection device, and turn on the power of the tester , enter the tester "current, voltage test" menu or "state sequence" menu, according to the parameters in the protection device setting list: the grounding distance impedance setting value Z _Kn to be tested, positive sequence impedance setting angle Φ1, zero sequence compensation coefficient K, using the fixed current method (that is, the short-circuit current is a fixed value), the current flowing into the protection device is calculated according to the following formula:

Leading phase current:

lag phase current

The simulated corresponding phase fault voltage is: U _Kφ ＝m(I _K +K3I ₀ )Z _kn ＝m(1+K)I _K Z _kn

Among them, m is 0.7, 0.95 and 1.05 respectively, and the corresponding phase fault voltage angle is simulated unchanged.

According to the above method, assuming that the impedance Z _k2 = 1Ω, the positive sequence impedance angle When zero-sequence compensation K=0.48, simulate BC phase-to-ground fault, and use the derivation formula to calculate:

I _B ＝5∠-120°+13.58°-82°＝5∠171.58°

I _C ＝5∠120°-13.58°-82°＝5∠24.42°

Find the phase voltage corresponding to the set impedance at fault:

When m is 0.95, the fault voltage is 5.265V, and the protection operates reliably;

When m is 1.05, the fault voltage is 5.82V, and the protection is reliable and does not operate;

When m is 0.7, the fault voltage is 3.879V, and the protection action time is tested.

The tester is set up using the current, voltage or state sequence method as follows (Figure 4):

Apply electricity to keep the corresponding action impedance action time plus a certain margin time, and the impedance element will act.

The above-mentioned embodiments are only preferred technical solutions of the present invention, and should not be regarded as limitations on the present invention. The protection scope of the present invention should be the technical solution described in the claims, including the equivalent of technical features in the technical solutions described in the claims. The alternative is the scope of protection. That is, equivalent replacement and improvement within this range are also within the protection scope of the present invention.

Claims (3)

1. A two-phase ground fault test method, characterized in that: the short-circuit sequence network is composed of comprehensive zero-sequence impedance Z0, comprehensive negative-sequence impedance Z2, comprehensive positive-sequence impedance Z1, comprehensive zero-sequence impedance Z0, and comprehensive negative-sequence impedance Z2 in parallel After that, it is connected in series with the comprehensive positive sequence impedance Z1 and connected to both ends of the system potential E, in which the zero sequence current I0 flows through the comprehensive zero sequence impedance Z0, the negative sequence current I2 flows through the comprehensive negative sequence impedance Z2, and the positive sequence current I2 flows through the comprehensive positive sequence impedance Z1. The sequence current is I1, and the zero-sequence compensation coefficient is K; usually Z1=Z2 in static components; Thus Z0=(1+3K)Z1 Assuming that the BC two-phase ground fault is taken as an example, the symmetrical component method is used to obtain: Non-fault phase current: I _A ＝I _A1 +I _A2 +I _A0 ＝0 Among them, I _A1 is the positive sequence component of the A-phase current, I _A2 is the negative sequence component of the A-phase current, and I _A0 is the zero-sequence component of the A-phase current. The fault leading phase current is: I _B ＝I _B1 +I _B2 +I _B0 ＝α ² I _A1 +αI _A2 +I _A0 The fault lagging phase current is: I _C ＝I _C1 +I _C2 +I _C0 ＝αI _A1 +α ² I _A2 +I _A0 where α is a unit vector operator, namely The above two formulas are obtained by converting each component of the non-fault phase based on the vector operator; The corresponding phasors are defined as follows: OH=I _B , OE=I _B1 , MH=I _B0 , EM=I _B2 , And △EMG is an equilateral triangle whose side length is the modulus of I ₂ , so: And HF⊥EG at point F Obtained from the phasor diagram: Considering the setting of the positive sequence impedance angle Φ1, the fixed current method is used to simulate the fault, so as to obtain the general fault current calculation formula: Leading phase current: lag phase current in is the leading phase angle of two phase-to-ground faults, is the phase angle of the lag phase, and φ is the calculated deflection angle. 2. A kind of two-phase ground fault test method according to claim 1 is characterized in that: the formula for finding the fault phase voltage is: U _φ ＝(I _φ +K3I ₀ )Z ₁ , where U _φ is fault phase-to-phase voltage, I _φ is two-phase ground fault phase current, and I ₀ is zero-sequence current. 3. A kind of two-phase ground fault test method according to claim 1 is characterized in that: the formula for finding the fault phase voltage is: Into the neutral current of the relay element Adjust the impedance according to the phase-to-phase short circuit of the line: Z _kn calculates the line voltage as follows: U _φφ = mI _φφ Z _kn Where I _ΦΦ is the line current, U _φΦ is the line voltage where m is 0.7, 0.95 and 1.05 respectively, Corresponding phase voltage The angle does not change.