CN101170252A - Judgement procedure for digital transformer differential protection to prevent TA secondary circuit failure from leading to mistaken operation - Google Patents

Abstract

The invention discloses a method for preventing differential protection misoperation of a digital transformer caused by such errors as short circuit, open circuit and etc. on the secondary circuit of a current transformer. Criterions for the errors in the TA secondary circuit are as follows: when a digital transformer protection device is running normally (a primary system accessed by the transformer does not go out of order), if the TA secondary circuit error is determined as that one- or two-phase current drops by 30 percent or higher, and difference current exists, then, the TA secondary circuit is determined as being out of order. On the premise of sudden current change: the current after the sudden change drops rather than increases, and the primary system has errors, or at least one-phase current will increase; therefore, one- or two-phase current of three-phase current drops by 30 percent or higher at the side; meanwhile, the three-phase current at other sides does not vary. If the conditions are met, the TA secondary circuit is determined as being out of order; after the TA secondary circuit goes out of order, an alarm signal is launched, and a latched or an unlatched difference protection outlet can be selected.

Description

The digital transformer differential protection to prevent TA secondary circuit failure from leading to mistaken operation discriminating program

Technical field

The present invention relates to field of power, relate more specifically to the method for relaying protection.

Background technology

Current transformer (TA) secondary circuit failure comprises secondary circuit open circuit and short circuit two big classes:

TA secondary circuit open circuit comprises: have a phase, two-phase or three-phase all to open a way in A, B, the C three-phase and open a way mutually with N.

The TA secondary loop short circuit comprises: AN, BN, CN, AB, BC, CA, ABC, ABCN short circuit.

At digital transformer protector, under the normal operation, differentiating the TA broken string and be by checking has one mutually or two-phase no current and have spill current in all separate electric currents, promptly be judged to the TA broken string.When current break was arranged, criterion was as follows:

The after-current of undergoing mutation reduces (rather than increase);

One phase or two-phase no current arranged in this side three-phase current, and offside three-phase current no change.

Be judged to TA secondary circuit broken string when satisfying above-mentioned condition, behind the TA secondary circuit broken string, send alarm signal, and can select locking or the outlet of non-Blocking Differential Protection.

This shows that the harmfulness of secondary circuit open circuit draws attention, and has taked to prevent the measure of differential protection protective device misoperation.

The secondary loop of mutual inductor short circuit is to the influence of transformer differential protection:

For simplicity, for transformer and the current transformer wiring schematic diagram of analyzing usefulness, as shown in Figure 1:

Suppose that transformer is 2 winding transformers, voltage ratio is 1: 1, Δ 11 ⁰/ Δ 11 ⁰Wiring;

The P1 terminal of a transformer primary side current instrument transformer 1TA and a winding of secondary side current instrument transformer 2TA is installed in bus bar side (the P2 terminal is installed in transformer side);

1TA, 2TA secondary circuit all adopt star-star connection, and all the S2 terminal are connected into the N phase;

According to above-mentioned wiring principle, normally there is following relation under operation and the external fault condition between 2TA secondary loop current and the 1TA secondary loop current:

${\stackrel{.}{I}}_{2A}=-\stackrel{.}{I_{1A}}$ ${\stackrel{.}{I}}_{2B}=-\stackrel{.}{I_{1B}}$ ${\stackrel{.}{I}}_{2C}=-\stackrel{.}{I_{1C}}$

2TA secondary loop current under normal operation and the external fault condition can be represented with the 1TA secondary loop current.The 2TA secondary loop current represents with the 1TA secondary loop current,

Under normal operation and the external fault condition, the 2TA secondary loop current represents with the 2TA secondary loop current, equivalent circuit as shown in Figure 2:

Conventional transformer differential protection TA secondary circuit adopts the circulation principle wiring, and under the normal operation, the CURRENT DISTRIBUTION schematic diagram was as shown in Figure 3 when CN, the short circuit of AB phase took place in the secondary circuit:

Among Fig. 3: A, B, C are three-phase spill current relay.

By Fig. 3 b as seen, owing to adopt the circulation principle wiring, when the short circuit of CN phase took place in the secondary circuit, the electric current that flows into short dot m was I _1C, the electric current that flows out short dot m remains I _1C, with identical before the short circuit (no current flows through among the short-circuit conductors mn), so differential protection can not malfunction.But during the short circuit of CN phase C is differed current relay C short circuit, if short dot long-term existence transformer differential protection might tripping.

Consequence is same as described above when in like manner, single-line to ground faults such as AN, BN taking place in the secondary circuit.

By Fig. 3 c as seen, owing to adopt the circulation principle wiring, when the short circuit of AB phase took place in the secondary circuit, the electric current that flows into short dot m was I _1A, the electric current that flows out short dot m remains I _1A, the electric current that flows into short dot n is I _1B, the electric current that flows out short dot n remains I _1B, with identical before the short circuit (no current flows through among the short-circuit conductors mn), so differential protection can not malfunction.But during the short circuit of AB phase A, B are differed current relay A, B short circuit, if short dot long-term existence transformer differential protection might tripping.

Consequence is same as described above when in like manner, two-phase phase faults such as BC, CA taking place in the secondary circuit.

Adopt when in the TA secondary circuit TA broken string taking place under the circulation principle wiring normal operation, can flow through load current in the spill current relay; Because the definite value of conventional transformer differential protection is to adjust according to 10% (TA10% error) greater than passing through property of maximum fault current, the spill current definite value is much larger than maximum load current; Therefore the conventional transformer differential protection can misoperation when TA break, is provided with alarm of TA broken string and locked loop in the protective device, sending broken string alarm while Blocking Differential Protection when the TA broken string takes place.

Adopt when permanent short trouble takes place in the TA secondary circuit of circulation principle wiring, might cause tripping, because the short circuit electric parameters does not change, being difficult to sow searches out the alarm criterion, and this is the obvious weakness of circulation principle wiring.

The independent respectively protective device of introducing of digital transformer differential protection device TA secondary side current not according to the circulation principle wiring, utilizes the data volume of each side TA secondary current to calculate spill current in the secondary circuit.

Wherein one group of TA secondary circuit breaks down, and to the not influence of other TA electric current, still can influence the calculated value of spill current.

In the digital transformer differential protection, the TA secondary loop short circuit may cause that the transformer differential protection misoperation is the distinctive problem of digital transformer differential protection, does not exist at the conventional transformer differential protection.

But; in digital transformer differential protection; may cause the transformer differential protection misoperation at the TA secondary loop short circuit; still there is not reliable locking measure at present; though; digital transformer differential protection has been taked measure to the secondary loop of mutual inductor broken string: " phase or a two-phase no current arranged in this side three-phase current " is as TA broken string criterion, but criterion is unreasonable.

Summary of the invention

In digital transformer differential protection, the TA secondary circuit failure may cause that the transformer differential protection misoperation is the distinctive problem of digital transformer differential protection, does not exist at the conventional transformer differential protection.The present invention proposes a kind of digital transformer differential protection that prevents and cause the method for differential protection malfunction because of the TA secondary circuit failure:

A kind of digital transformer differential protection prevents that the secondary loop of mutual inductor fault from causing the method for differential protection misoperation; in the digital transformer differential protection device; with the independent respectively protective device of introducing of each side current transformer TA secondary side current of transformer; utilize the data volume of each side TA secondary current to calculate spill current, it is characterized in that:

In normal operation is under primary system that transformer the inserts situation about not breaking down, check have in the three-phase current one mutually or biphase current descend 30% or more than, and have spill current, then be judged as this side current transformer TA secondary circuit failure;

Having under the prerequisite of current break, when the after-current of undergoing mutation reduces, have in this side three-phase current one mutually or biphase current descend 30% or more than, and other side three-phase current no change then is judged as this side current transformer TA secondary circuit failure;

Under the prerequisite of current break,, then be judged as the primary system fault when the after-current of undergoing mutation increases;

According to above-mentioned determination methods, after judging current transformer TA secondary circuit failure, send alarm signal, and select whether Blocking Differential Protection exports.

Said method can be differentiated current transformer TA effectively and whether have short circuit or open circuit fault, sends alarm signal, selects whether Blocking Differential Protection exports, for preventing that digital transformer differential protection is because of the current mulual inductor malfunction malfunction.

Description of drawings

Accompanying drawing 1 is transformer and current transformer wiring schematic diagram for analysis usefulness.

Accompanying drawing 2 is the equivalent circuit figure of Fig. 1 under normal operation and the external fault condition.

Accompanying drawing 3 is a CURRENT DISTRIBUTION schematic diagram before and after circulation principle wiring CN, the short circuit of AB phase.

CN, AB phase short circuit front and back CURRENT DISTRIBUTION schematic diagram for taking place in accompanying drawing 4 in the digital transformer differential protection 1TA secondary circuit.

CN, AB phase short circuit front and back current vector figure for taking place in accompanying drawing 5 in the digital transformer differential protection 1TA secondary circuit.

Accompanying drawing 6 is decision logic figure.

Embodiment

The CURRENT DISTRIBUTION schematic diagram was as shown in Figure 4 when CN, the short circuit of AB phase took place in the digital transformer differential protection 1TA secondary circuit:

Among Fig. 4: A ₁, B ₁, C ₁Be 1TA three-phase current transformer in the protective device, A ₂, B ₂, C ₂Be 2TA three-phase current transformer in the protective device.

Current vector figure was as shown in Figure 5 when CN, the short circuit of AB phase took place in the digital transformer differential protection 1TA secondary circuit:

By Fig. 4 c as seen, CN phase metallic short circuit takes place in the 1TA secondary circuit, short-circuit impedance is during much smaller than the transformer impedance loop, C phase current I _CFlow back to TA by short dot m, n via N phase cable, the I of the electric current in the C phase current transformer before by short circuit _C(normal duty electric current) drops to zero; By Fig. 5 b as seen, calculate gained C and differ electric current I _CCL, on the numerical value when not being short-circuited C phase load electric current equate.

Because the current transformer impedance loop is extremely low in the protective device, C phase current I _CCan form part shunting in by short circuit current transformer point, Practical Calculation gained C differs electric current I _CCL, be slightly less than C phase load electric current.

When if short circuit takes place, load current is greater than differential protection action threshold value too, and transformer differential protection just has the possibility of misoperation.

By Fig. 4 d as seen, when the short circuit of AB phase takes place in the 1TA secondary circuit, A phase current I _1AWith A phase current I _1BMerge into an electric current-I by short dot m, n _1C,

As current transformer A ₁, B ₁When impedance loop equates between short dot ,-I _1CWill be at transformer A ₁, B ₁In respectively flow half.

By Fig. 5 C as seen, as current transformer A ₁, B ₁When impedance loop equates between short dot, calculate gained A and differ electric current I _ACL, B differs electric current I _BCLIt on the numerical value 0.866 times of load current when not being short-circuited.When if short circuit takes place, load current is greater than 1.15 times of differential protection action threshold value, and transformer differential protection just has the possibility of misoperation.

As current transformer A ₁, B ₁Unequal to impedance loop between the short dot, transformer A ₁, B ₁In must have one greater than 1/2nd-I _1C, must have one to calculate mutually on the gained spill current numerical value greater than 0.866 times of load current, cause misoperation easilier.

Obviously, when one phase, two-phase broken string take place the TA secondary circuit, calculate the gained spill current and equate with load current.

The characteristics of digital transformer differential protection TA secondary circuit failure:

The TA secondary loop short circuit may cause that the transformer differential protection misoperation is the distinctive problem of digital transformer differential protection, does not exist at the conventional transformer differential protection.

Compare with the normal running load electric current, the TA secondary circuit failure, the fault phase current only may descend, and can not rise.

TA secondary circuit failure, fault phase current may not drop to zero, the reasons are as follows:

From numerical value, the electric current in the fault phase current transformer drops to about 50% of load current during TA secondary circuit generation line to line fault, can not drop to zero.

From numerical value, owing to there is shunting in the fault phase current transformer, electric current can not drop to zero fully yet during TA secondary circuit single phase ground fault.

Under the half-open line state of TA secondary circuit that is caused by the loose contact of electric current connection sheet, the fault phase current may descend, but can not drop to zero fully.

Therefore, it is irrational will " phase or a two-phase no current being arranged " in this side three-phase current as one of TA broken string criterion.

Fig. 6 shows the correct criterion of TA fault proposed by the invention:

Digital transformer protector; normal operation (transformer insert primary system in do not break down) under the situation; differentiate the TA secondary circuit failure and be by check have in all separate electric currents one mutually or biphase current descend 30% or more than; and there is spill current, promptly is judged to the TA secondary circuit failure.Having under the prerequisite of current break:

The after-current of undergoing mutation reduces rather than increases, and primary system has fault to have at least a phase current to increase;

Have in this side three-phase current one mutually or biphase current descend 30% or more than, and other side three-phase current no change.

Be judged to the TA secondary circuit failure when satisfying above-mentioned condition, behind the TA secondary circuit failure, send alarm signal, and can select locking or the outlet of non-Blocking Differential Protection.

Claims (1)

1. a digital transformer differential protection prevents that the secondary loop of mutual inductor fault from causing the method for differential protection misoperation; in the digital transformer differential protection device; with the independent respectively protective device of introducing of each side current transformer TA secondary side current of transformer; utilize the data volume of each side TA secondary current to calculate spill current, it is characterized in that:

In normal operation is under primary system that transformer the inserts situation about not breaking down, and checks three-phase current, as one mutually or biphase current descend 30% or more than, and have spill current, then be judged as this side current transformer TA secondary circuit failure;

Having under the prerequisite of current break, when the after-current of undergoing mutation reduces, have in this side three-phase current one mutually or biphase current descend 30% or more than, and other side three-phase current no change then is judged as this side current transformer TA secondary circuit failure;

Under the prerequisite of current break,, then be judged as the primary system fault when the after-current of undergoing mutation increases;

According to above-mentioned determination methods, after judging current transformer TA secondary circuit failure, send alarm signal, and select whether Blocking Differential Protection exports.

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