CN105425112A - Fault wire selection method and apparatus of undercurrent grounding system - Google Patents

Abstract

The invention provides a fault wire selection method and apparatus of an undercurrent grounding system, and the fault wire selection method comprises the steps of adjusting an arc extinguishing coil and making it work in an undercompensation state; calculating a zero sequence admittance value of each wire when the arc extinguishing coil after time-delay; adjusting the arc extinguishing coil symmetrically and making it work in an overcompensation state; calculating a zero sequence admittance value of each wire when the arc extinguishing coil works in an overcompensation state after time-delay; comparing a variance of the zero sequence admittance value of each wire when the arc extinguishing coil works in an undercompensation state and an overcompensation state; and selecting the wire that has a maximum zero sequence admittance value variance as the fault wire. By taking the zero sequence admittance variance as wire selection criteria, a good anti-transition resistance capability is provided; even if the zero sequence admittance variance of a non-fault wire is not equal to zero lead by measurement error by a mutual inductor, the variance is far less than the variance of a fault wire. Therefore, a high wire selection accuracy and reliability are provided.

Description

A kind of fault-line selecting method of small current neutral grounding system and device

Technical field

The present invention relates to technical field of power systems, particularly relate to a kind of fault-line selecting method and device of small current neutral grounding system.

Background technology

Small current neutral grounding mode most widely used in electric system is neutral by arc extinction coil grounding.During neutral by arc extinction coil grounding system generation single-phase earthing; due to the compensating action of arc suppression coil; fault current will become very little; simultaneously due under arc suppression coil works in " over-compensation " state; the phase place of faulty line zero-sequence current will become identical with non-fault line, and this becomes very difficult with regard to making the selection of protective device to faulty line.

The current failure line selection problem for small current neutral grounding system has the fault-line selecting method of multiple different principle, and these methods can be divided into the failure line selection technology based on steady-state quantity and the large class of the failure line selection technology two based on transient according to the source of fault-signal.

Fault-line selecting method anti-interference based on transient is poor; meanwhile, the transient state component in fault current can change, when fault occurs in line voltage zero passage along with the difference of electrical network phase angle during fault; transient state component is almost nil, therefore in principle, there is protection's dead-zone.

Based on most widely used in the failure line selection technology of steady-state quantity be remnant current increment method.But practical operating experiences shows, remnant current increment method route selection accuracy rate when metallic earthing and low-impedance earthed system is higher, but along with the increase of transition resistance, route selection accuracy rate obviously declines.Zero sequence admittance method has good anti-transition resistance ability in theory, but is also seldom employed because actual route selection accuracy rate is not high.

Summary of the invention

Technical matters to be solved by this invention is, provides one to have good anti-transition resistance ability, the fault-line selecting method of route selection accuracy rate and the higher small current neutral grounding system of reliability and device

In order to solve the problems of the technologies described above, the invention provides a kind of fault-line selecting method of small current neutral grounding system, comprising:

Step S1, regulates arc suppression coil, makes it work in under-compensation state;

Step S2, calculates the zero sequence admittance value of each outlet when arc suppression coil works in under-compensation state after time delay;

Step S3, symmetrical adjustment arc suppression coil, makes it work in over-compensation state;

Step S4, calculates the zero sequence admittance value of each outlet when arc suppression coil works in over-compensation state after time delay;

Step S5, the variable quantity of more each outlet zero sequence admittance value when arc suppression coil works in under-compensation state and over-compensation state respectively, the outlet selecting zero sequence admittance value variable quantity maximum is fault outlet.

Wherein, described arc suppression coil is post-set arc suppression coils, there is high short-circuit impedance, and two ends reflection two thyristors in parallel, regulate arc suppression coil specifically to refer in described step S1 and step S3 and Trigger Angle by changing described thyristor make the reactance of described arc suppression coil change to obtain different compensativities.

Wherein, in described step S2 or step S4, the mode calculating zero sequence admittance value be by the zero sequence current measurement value of acquisition compared with residual voltage measured value.

Wherein, the obtain manner of described residual voltage measured value is:

For the bus-bar potential transformer being configured with open-triangular winding, described residual voltage measured value obtains by measuring at the open-triangular winding two ends of voltage transformer (VT);

For the bus-bar potential transformer not configuring open-triangular winding, the three-phase voltage value summation that described residual voltage measured value is recorded by three-phase windings is averaged acquisition again.

Wherein, the obtain manner of described zero sequence current measurement value is:

For the circuit having configure dedicated zero sequence current mutual inductor, described zero sequence current measurement value is measured by zero sequence current mutual inductor and is obtained;

Be configured with the circuit of threephase current transformer for non-configure dedicated zero sequence current mutual inductor, described zero sequence current measurement value to be averaged acquisition by current value summation that threephase current transformer records again.

Wherein, also comprise before described step S1:

Step S0, drops into arc suppression coil and compensates when system zero sequence voltage exceedes phase voltage 15%.

Wherein, in described step S1, described arc suppression coil works in under-compensation state, specifically refers to that system off resonance degree is 5% ~ 10%.

Wherein, in described step S3, described arc suppression coil works in over-compensation state, specifically refers to that system off resonance degree is-10% ~-5%.

Wherein, in described step S2 or step S4, described time delay is 3 ~ 10 cycles.

The present invention also provides a kind of fault line selection device of small current neutral grounding system, comprising:

Arc suppression coil, makes it work in under-compensation state or over-compensation state by changing its compensativity;

Tuned cell, for changing the compensativity of described arc suppression coil, thus makes it be operated in under-compensation or over-compensation state;

Measuring unit, for the zero-sequence current of measuring system residual voltage and each outlet;

Route selection unit, for calculating the variable quantity of the zero sequence admittance value of each outlet more each outlet zero sequence admittance value when arc suppression coil works in under-compensation state and over-compensation state respectively, and selects the maximum outlet of zero sequence admittance value variable quantity to be fault outlet.

Wherein, described arc suppression coil is post-set arc suppression coils, has high short-circuit impedance, and two ends reflection two thyristors in parallel.

Wherein, described route selection unit calculate the mode of zero sequence admittance value be by the zero sequence current measurement value of acquisition compared with residual voltage measured value.

Wherein, described measuring unit comprises:

Residual voltage measured value acquiring unit, obtains residual voltage measured value for measuring at the open-triangular winding two ends of voltage transformer (VT), or to be averaged residual voltage measured value by the three-phase voltage value summation that three-phase windings records again.

Zero sequence current measurement value acquiring unit, obtains zero sequence current measurement value for being measured by zero sequence current mutual inductor, or is averaged by the current value summation that threephase current transformer records again and obtain zero sequence current measurement value.

Wherein, the fault line selection device of described small current neutral grounding system also comprises:

Delay unit, during for working in under-compensation state or over-compensation state at arc suppression coil, 3 ~ 10 cycles of time delay;

Described route selection unit starts at described delay unit time delay 3 ~ 10 all after dates the zero sequence admittance value calculating each outlet.

The present invention has following beneficial effect: by adopting zero sequence admittance variable quantity as route selection criterion, even if the change of transition resistance causes the zero-sequence current of each circuit to change, but change because residual voltage is also corresponding, zero sequence admittance value does not change substantially, has good anti-transition resistance ability; In addition, when arc suppression coil works under under-compensation and over-compensation two states, the zero sequence admittance of faulty line will change between third quadrant and the second quadrant; Even if non-fault line causes its zero sequence admittance variable quantity to be not equal to zero due to measurement error of transformer, but also much smaller than the variable quantity of faulty line, therefore has higher reliability.

Accompanying drawing explanation

In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

Fig. 1 is the schematic flow sheet of the fault-line selecting method of the embodiment of the present invention one one kinds of small current neutral grounding systems.

Fig. 2 a is in the embodiment of the present invention, neutral by arc extinction coil grounding system single-phase earthing system schematic.

Fig. 2 b is in the embodiment of the present invention, neutral by arc extinction coil grounding system single-phase earthing zero-sequence network schematic diagram.

Fig. 3 is in the embodiment of the present invention, and the zero sequence admittance of each outlet during fault measures vector plot.

Fig. 4 is in the embodiment of the present invention, and before and after arc suppression coil regulates, the zero sequence admittance of each outlet measures vector plot.

Fig. 5 is the structured flowchart of the fault line selection device of the embodiment of the present invention 21 kinds of small current neutral grounding systems.

Embodiment

Below with reference to the accompanying drawings the preferred embodiments of the present invention are described.

Please refer to shown in Fig. 1, the embodiment of the present invention one provides a kind of fault-line selecting method of small current neutral grounding system, comprising:

Step S1, regulates arc suppression coil, makes it work in under-compensation state;

Step S2, calculates the zero sequence admittance value of each outlet when arc suppression coil works in under-compensation state after time delay;

Step S3, symmetrical adjustment arc suppression coil, makes it work in over-compensation state;

Step S4, calculates the zero sequence admittance value of each outlet when arc suppression coil works in over-compensation state after time delay;

Step S5, the variable quantity of more each outlet zero sequence admittance value when arc suppression coil works in under-compensation state and over-compensation state respectively, the outlet selecting zero sequence admittance value variable quantity maximum is fault outlet.

Below in conjunction with Fig. 2 a, Fig. 2 b, the principle of the fault-line selecting method of the present embodiment is described.

Neutral by arc extinction coil grounding system single-phase earthing schematic diagram as shown in Fig. 2 a, Fig. 2 b, C in figure ₁~ C _nbe respectively the ground capacitance of n bar outlet in system, L is arc suppression coil inductance value, for the A phase voltage of system power supply, R _ffor the transition resistance of trouble spot, Z ₁and Z ₂be respectively positive sequence impedance and the negative sequence impedance of system.If the zero sequence current measurement value of each outlet in system is respectively the zero sequence current measurement value flowing through arc suppression coil is

From Fig. 2 b, ignore line impedance in zero-sequence network after, for non-fault line i (i=2 ..., n), its zero sequence admittance value is the ratio of zero sequence current measurement value and the residual voltage measured value recorded:

$Y_{i0}=\frac{{\stackrel{\·}{I}}_{i0}}{{\stackrel{\·}{U}}_0}={\mathrm{j\ωC}}_i---\left(1\right)$

From above formula, for non-fault line, its zero sequence admittance value is the actual zero sequence admittance value of circuit.

Assumed fault circuit is circuit 1, then for faulty line 1, its zero sequence admittance value is:

$Y_{10}=\frac{{\stackrel{\·}{I}}_{10}}{{\stackrel{\·}{U}}_0}---\left(2\right)$

In formula (2) meet:

${\stackrel{\·}{I}}_{10}=-(\underset{i=2}{\overset{n}{\Σ}}{\stackrel{\·}{I}}_{i0}+{\stackrel{\·}{I}}_{L0})---\left(3\right)$

Namely the zero sequence current measurement value of faulty line 1 be all non-fault lines and arc suppression coil zero sequence current measurement value superimposed after negative value.

Formula (3) is substituted into formula (2) can obtain

$Y_{10}=\frac{-(\underset{i=2}{\overset{n}{\Σ}}{\stackrel{\·}{I}}_{i0}+{\stackrel{\·}{I}}_{L0})}{{\stackrel{\·}{U}}_0}=-(\underset{i=2}{\overset{n}{\Σ}}{Y}_{i0}+Y_{L0})---\left(4\right)$

From formula (4), for faulty line 1, its zero sequence admittance value is not the actual zero sequence admittance value of circuit, but in system all non-fault lines and arc suppression coil zero sequence admittance value superimposed after negative value.

As shown in Figure 3, if consider the resistance value of circuit, then the zero sequence of non-fault line measures the first quartile that admittance should be positioned at admittance complex plane; And for faulty line, when arc suppression coil work in respectively under-compensation, complete compensate and over-compensation state time, zero sequence admittance measured value lays respectively at third quadrant (vector 1), transverse axis bears semiaxis (vector 2) and the second quadrant (vectorial 3).

Because arc suppression coil general work is in " over-compensation " state, therefore after system earth, the zero sequence admittance measurement vector of faulty line is generally positioned at the second quadrant.For post-set arc suppression coils, after there is ground connection in system, device carries out in the process of route selection, the reactance value of adjustable arc suppression coil, make it work in " under-compensation " and " over-compensation " two states respectively, corresponding faulty line zero sequence admittance value should lay respectively at third quadrant (vectorial Y in Fig. 4 ₁₀) and the second quadrant (vectorial Y in Fig. 4 ₁₀'), its variable quantity △ Y ₁₀be the zero sequence admittance value variable quantity that arc suppression coil reactance value regulates front and back, namely

△Y ₁₀＝Y ₁₀'-Y ₁₀＝△Y _L0(5)

And for non-fault line i, before and after arc suppression coil regulates, its zero sequence admittance value is the actual zero sequence admittance value of circuit, variable quantity is zero in theory, considering may because the measuring error of mutual inductance value causes regulating front and back zero sequence admittance measured value to occur small difference, if its zero sequence admittance measured value is respectively Y _i0and Y _i0', as shown in Figure 4, then its variable quantity △ Y _i0meet

△Y _i0＝Y _i0'-Y _i0≈0(6)

If compared each outlet zero sequence admittance variable quantity, then what change quantitative change was large is faulty line, the optional circuit that is out of order accordingly, that is:

|△Y ₁₀|＝max(|△Y ₁₀|,|△Y ₂₀|,...,|△Y _n0|)(7)

The present embodiment utilizes post-set arc suppression coils reactance to regulate the zero sequence admittance value variable quantity of each outlet in front and back as route selection criterion, compared with existing remnant current increment route selection method and zero sequence admittance route selection method, all has obvious advantage:

1, anti-transition resistance ability is better than remnant current increment method

Existing remnant current increment method route selection accuracy rate when metallic earthing and low-impedance earthed system is higher, but along with the increase of transition resistance, route selection accuracy rate obviously declines, its reason is that the method adopts zero-sequence current variable quantity as criterion, and along with transition resistance increase, zero-sequence current variable quantity will sharply reduce, and faulty line and the difference of non-fault line on zero-sequence current variable quantity also will reduce.

And the present embodiment adopts zero sequence admittance variable quantity as route selection criterion based on the failure line selection technology of zero sequence admittance value variable quantity, though the change of transition resistance can cause the zero-sequence current of each circuit to change, but now the residual voltage of system is also corresponding changes, due to the ratio that zero sequence admittance is zero-sequence current and residual voltage, therefore zero sequence admittance does not change substantially, has good anti-transition resistance ability.

2, reliability is higher than zero sequence admittance method

Arc suppression coil is not regulated in zero sequence admittance method route selection process, only measure each outlet zero sequence admittance value and using its phase angle as route selection criterion.Because the capacitance to earth of transmission line of electricity is generally much larger than line impedance, though therefore the zero sequence admittance phase angle of non-fault line is positioned at first quartile and closely 90 degree; And arc suppression coil general work is in slight over-compensation state, now the zero sequence admittance phase angle of faulty line is positioned at the second quadrant and equally very close to 90 degree.Now once mutual inductor measurement exists error, namely route selection failure may be caused because of the phase angle misjudgment to zero sequence admittance.

And the present embodiment adopts zero sequence admittance variable quantity as route selection criterion based on the failure line selection technology of zero sequence admittance value variable quantity, when arc suppression coil works under under-compensation and over-compensation two states, the zero sequence admittance of faulty line will change between third quadrant and the second quadrant; Even if non-fault line causes its zero sequence admittance variable quantity to be not equal to zero due to measurement error of transformer, but also much smaller than the variable quantity of faulty line, therefore has higher route selection accuracy and reliability.

Below each step of the fault-line selecting method of the present embodiment is described in detail.

Before step S1, also comprise the step compensated by the residual voltage input arc suppression coil of system, particularly, step S0, drops into arc suppression coil and compensates when system zero sequence voltage exceedes phase voltage 15%.

In the present embodiment, arc suppression coil is post-set arc suppression coils, have at high short-circuit impedance, arc suppression coil two ends reflection two thyristors in parallel, by the Trigger Angle changing thyristor, the reactance of arc suppression coil is changed, thus obtain different compensativities, make arc suppression coil work in under-compensation state or over-compensation state.

In step S1, regulate arc suppression coil, make it work in under-compensation state, specifically refer to that system off resonance degree is 5% ~ 10%.

Time delay in step S2 is generally 3 ~ 10 cycles.Due to the ratio that zero sequence admittance value is zero sequence current measurement value and the residual voltage measured value recorded, therefore calculate the zero sequence admittance value of now each outlet, first will obtain zero sequence current measurement value and the residual voltage measured value of each outlet.

Residual voltage measured value obtains by two kinds of modes: (1), for the bus-bar potential transformer being configured with open-triangular winding, can be measured at the open-triangular winding two ends of voltage transformer (VT) and obtain residual voltage measured value; (2) for the bus-bar potential transformer not configuring open-triangular winding, the summation of the three-phase voltage value that records by three-phase windings is averaged acquisition again, and circular is as follows:

${\stackrel{\·}{U}}_0=\frac{1}{3}({\stackrel{\·}{U}}_a+{\stackrel{\·}{U}}_b+{\stackrel{\·}{U}}_c)---\left(8\right)$

Zero sequence current measurement value also obtains by two kinds of modes: (1), for the circuit having configure dedicated zero sequence current mutual inductor, is measured by zero sequence current mutual inductor and obtained zero sequence current measurement value; (2) for non-configure dedicated zero sequence current mutual inductor but the circuit of configuration threephase current transformer, the current value recorded by threephase current transformer summation is averaged acquisition again, and circular is as follows:

${\stackrel{\·}{I}}_0=\frac{1}{3}({\stackrel{\·}{I}}_a+{\stackrel{\·}{I}}_b+{\stackrel{\·}{I}}_c)---\left(9\right)$

In step S3, the symmetrical arc suppression coil that regulates works in over-compensation state, specifically refers to that system off resonance degree is-10% ~-5%.

Time delay in step S4 is similarly 3 ~ 10 cycles.By the zero sequence current measurement value of each outlet of acquisition and residual voltage measured value after time delay, calculate the zero sequence admittance value of now each outlet.The zero sequence current measurement value obtaining each outlet is identical with step S2 with the mode of residual voltage measured value, repeats no more herein.

After obtaining the zero sequence admittance value of each outlet under arc suppression coil two kinds of duties, the zero sequence admittance variable quantity of trying to achieve each circuit is calculated further by formula (5) or formula (6), then the zero sequence admittance value variable quantity of more each circuit, is chosen as faulty line by formula (7) by outlet maximum for zero sequence admittance value variable quantity.

Shown in Fig. 5, corresponding to the fault-line selecting method of the small current neutral grounding system of the embodiment of the present invention one, the embodiment of the present invention two provides a kind of fault line selection device of small current neutral grounding system, comprising:

Arc suppression coil, makes it work in under-compensation state or over-compensation state by changing its compensativity;

Tuned cell, for changing the compensativity of described arc suppression coil, thus makes it be operated in under-compensation or over-compensation state;

Measuring unit, for the zero-sequence current of measuring system residual voltage and each outlet;

Route selection unit, for calculating the variable quantity of the zero sequence admittance value of each outlet more each outlet zero sequence admittance value when arc suppression coil works in under-compensation state and over-compensation state respectively, and selects the maximum outlet of zero sequence admittance value variable quantity to be fault outlet.

In the present embodiment, arc suppression coil is post-set arc suppression coils, there is high short-circuit impedance, and two ends reflection two thyristors in parallel, by the Trigger Angle changing thyristor, the reactance of arc suppression coil is changed, thus obtain different compensativities, make arc suppression coil work in under-compensation state or over-compensation state.

Wherein, route selection unit calculate the mode of zero sequence admittance value be by the zero sequence current measurement value of acquisition compared with residual voltage measured value.

Thus, the measuring unit of the present embodiment low current neutral grounding system fault route selecting device comprises:

Residual voltage measured value acquiring unit, obtains residual voltage measured value for measuring at the open-triangular winding two ends of voltage transformer (VT), or to be averaged residual voltage measured value by the three-phase voltage value summation that three-phase windings records again;

Zero sequence current measurement value acquiring unit, obtains zero sequence current measurement value for being measured by zero sequence current mutual inductor, or is averaged by the current value summation that threephase current transformer records again and obtain zero sequence current measurement value.

The present embodiment also comprises delay unit, during for working in under-compensation state or over-compensation state at arc suppression coil, and 3 ~ 10 cycles of time delay.Route selection unit starts at delay unit time delay 3 ~ 10 all after dates the zero sequence admittance value calculating each outlet.

Principle of work and the corresponding technique effect of the fault line selection device of the present embodiment small current neutral grounding system are similar to the embodiment of the present invention one, please refer to the explanation of the embodiment of the present invention one, repeat no more herein.

Above disclosedly be only present pre-ferred embodiments, certainly can not limit the interest field of the present invention with this, therefore according to the equivalent variations that the claims in the present invention are done, still belong to the scope that the present invention is contained.

Claims (15)

1. a fault-line selecting method for small current neutral grounding system, comprising:

Step S1, regulates arc suppression coil, makes it work in under-compensation state;

Step S2, calculates the zero sequence admittance value of each outlet when arc suppression coil works in under-compensation state after time delay;

Step S3, symmetrical adjustment arc suppression coil, makes it work in over-compensation state;

Step S4, calculates the zero sequence admittance value of each outlet when arc suppression coil works in over-compensation state after time delay;

Step S5, the variable quantity of more each outlet zero sequence admittance value when arc suppression coil works in under-compensation state and over-compensation state respectively, the outlet selecting zero sequence admittance value variable quantity maximum is fault outlet.

2. method according to claim 1, it is characterized in that, described arc suppression coil is post-set arc suppression coils, there is high short-circuit impedance, and two ends reflection two thyristors in parallel, regulate arc suppression coil specifically to refer in described step S1 and step S3 and Trigger Angle by changing described thyristor make the reactance of described arc suppression coil change to obtain different compensativities.

3. method according to claim 1, is characterized in that, in described step S2 or step S4, the mode calculating zero sequence admittance value be by the zero sequence current measurement value of acquisition compared with residual voltage measured value.

4. method according to claim 3, is characterized in that, the obtain manner of described residual voltage measured value is:

For the bus-bar potential transformer being configured with open-triangular winding, described residual voltage measured value obtains by measuring at the open-triangular winding two ends of voltage transformer (VT);

For the bus-bar potential transformer not configuring open-triangular winding, the three-phase voltage value summation that described residual voltage measured value is recorded by three-phase windings is averaged acquisition again.

5. method according to claim 3, is characterized in that, the obtain manner of described zero sequence current measurement value is:

For the circuit having configure dedicated zero sequence current mutual inductor, described zero sequence current measurement value is measured by zero sequence current mutual inductor and is obtained;

Be configured with the circuit of threephase current transformer for non-configure dedicated zero sequence current mutual inductor, described zero sequence current measurement value to be averaged acquisition by current value summation that threephase current transformer records again.

6. method according to claim 1, is characterized in that, also comprises before described step S1:

Step S0, drops into arc suppression coil and compensates when system zero sequence voltage exceedes phase voltage 15%.

7. the method according to any one of claim 1-6, is characterized in that, in described step S1, described arc suppression coil works in under-compensation state, specifically refers to that system off resonance degree is 5% ~ 10%.

8. the method according to any one of claim 1-6, is characterized in that, in described step S3, described arc suppression coil works in over-compensation state, specifically refers to that system off resonance degree is-10% ~-5%.

9. the method according to any one of claim 1-6, is characterized in that, in described step S2 or step S4, described time delay is 3 ~ 10 cycles.

10. a fault line selection device for small current neutral grounding system, is characterized in that, comprising:

Arc suppression coil, makes it work in under-compensation state or over-compensation state by changing its compensativity;

Tuned cell, for changing the compensativity of described arc suppression coil, thus makes it work in under-compensation or over-compensation state;

Measuring unit, for the zero-sequence current of measuring system residual voltage and each outlet;

Route selection unit, for calculating the variable quantity of the zero sequence admittance value of each outlet more each outlet zero sequence admittance value when arc suppression coil works in under-compensation state and over-compensation state respectively, and selects the maximum outlet of zero sequence admittance value variable quantity to be fault outlet.

11. devices according to claim 10, is characterized in that, described arc suppression coil is post-set arc suppression coils, have high short-circuit impedance, and two ends reflection two thyristors in parallel.

12. devices according to claim 11, is characterized in that, described tuned cell adopts the mode changing described turn on thyristors angle to change the compensativity of arc suppression coil.

13. devices according to claim 10, is characterized in that, the mode that described route selection unit calculates zero sequence admittance value is that the zero sequence current measurement value that obtained by measuring unit is compared with residual voltage measured value.

14. devices according to claim 13, described measuring unit comprises:

Residual voltage measured value acquiring unit, obtains residual voltage measured value for measuring at the open-triangular winding two ends of voltage transformer (VT), or to be averaged residual voltage measured value by the three-phase voltage value summation that three-phase windings records again;

Zero sequence current measurement value acquiring unit, obtains zero sequence current measurement value for being measured by zero sequence current mutual inductor, or is averaged by the current value summation that threephase current transformer records again and obtain zero sequence current measurement value.

15. devices according to claim 10, is characterized in that, also comprise:

Delay unit, during for working in under-compensation state or over-compensation state at arc suppression coil, 3 ~ 10 cycles of time delay;

Described route selection unit starts at described delay unit time delay 3 ~ 10 all after dates the zero sequence admittance value calculating each outlet.