CN105929217A - Method for discriminating tail current in ineffective protection based on DC component blocking - Google Patents

Abstract

The invention discloses a method for discriminating ineffective protection tail current based on DC component blocking. The method uses proportion of DC component in a phase current to determine an ineffective tail current. The method is easy to operate, has high efficiency, greatly reduces the time of a replay protection apparatus in discriminating the ineffective tail current, and effectively increases accuracy in discriminating the ineffective tail current. The method makes it possible that when a fault current occurs, the ineffective protection does not refuse initiation, and when a CT tail current occurs, the ineffective protection is not wrongfully initiated, and the method accelerates phase-splitting and ineffective protection, prevents enlargement of an accident, and provides better safeguard for safe and stable operation of a power grid.

Description

A Method for Discriminating Current Tailing of Failure Protection Based on DC Component Blocking

technical field

The invention relates to a method for judging the tailing of a failure protection current based on DC component blocking, and belongs to the field of relay protection of electric power systems.

Background technique

The relay protection device is an inseparable part of the power system, and it is the most basic, important and effective technical means to ensure the safety of power equipment and prevent and limit large-scale power outages in the power system. However, when a fault occurs in the system, the relay protection device issues a trip command, and the circuit breaker is disconnected to remove a fault, there is still an attenuating current on the secondary side of the electromagnetic current transformer, that is, CT (Current Transformer, current transformer) tailing Phenomenon. CT tailing current may cause the current criterion of circuit breaker failure protection to fail to return quickly, and the failure protection may malfunction after reaching the delay time, which will expand the fault range and cause serious consequences such as large-scale power outages. At present, there are not many methods for judging the current tailing of failure protection, and the criterion that the tailing current does not exceed zero is generally used. However, after the tailing current passes through the CT of the protection device, the phenomenon of current zero crossing may occur, and its applicability is not strong. .

Contents of the invention

In order to solve the above-mentioned technical problems, the present invention provides a method for judging the current tailing of a failure protection based on DC component blocking.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A method for judging the tailing of a fault protection current based on DC component blocking, comprising the following steps,

Step 1, define the maximum number of branches as M;

Step 2, define X=1;

Step 3, read the failure switch input of the Xth branch;

Step 4, calculating the failure current condition;

Step 5, calculating the effective value I of the phase current fundamental wave of the previous cycle of the X branch;

Step 6, if I<NI _n , then go to step 7, if I≥NI _n , then the failure trailing current discrimination starts, go to step 8;

Among them, In is the rated current, and _N is the multiple of the rated current that can be set;

Step 7, judge whether X is less than M, if yes, then X=X+1, go to step 3, if not, then go to step 2;

Step 8, calculating the DC component I _z in the phase current;

Step 9: Judging whether I _z /I≥K1 _set and I _z /I _rms ≥K2 _set are true, if true, it is judged as a failure trailing current, the corresponding phase failure protection is blocked, and the process ends; if not, the process ends;

Among them, K1 _set and K2 _set are threshold values, and I _rms is the true effective value of the phase current.

The same branch is judged according to the phase. If the A phase is satisfied, only the A phase failure protection will be blocked, and the B phase, C phase or three phase failure will not be blocked; multiple branches are independent of each other and are judged separately.

The beneficial effects achieved by the present invention: the present invention utilizes the proportion of the DC component in the phase current to judge the failure trailing current, which is simple and efficient, greatly reduces the time for the relay protection device to judge the failure trailing current, and effectively improves the failure trailing current. Tail current discrimination is accurate, failure protection does not refuse to operate when fault current occurs, failure protection does not malfunction when CT tail current occurs, and phase-separated locking failure protection is accelerated to prevent accident expansion and provide better protection for safe and stable operation of the power grid .

Description of drawings

Fig. 1 is a flowchart of the present invention.

Fig. 2 is the logic diagram of the starting criterion of the failure tail current.

Figure 3 is a logic diagram of the failure tail current criterion.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings. The following examples are only used to illustrate the technical solution of the present invention more clearly, but not to limit the protection scope of the present invention.

As shown in Figure 1, a current tailing discrimination method for failure protection based on DC component blocking includes the following steps:

Step 1, define the maximum number of branches as M.

Step 2, define X=1.

Step 3, read the failure switch input of the Xth branch.

Step 4, calculating the failure current condition;

Step 5, calculate the effective value I of the phase current fundamental wave of the previous cycle of the Xth branch.

Step 6, if I<NI _n , then go to step 7, if I≥NI _n , then the failure tailing current discrimination starts, go to step 8; where, In _is the rated current, N is the multiple of the rated current that can be set .

As shown in Figure 2, the start-up criteria for the tailing current of the failure include the failure switch input, the condition of the failure current and the size of the previous cycle current of the branch, where the conditions of the failure current include zero-sequence current, negative-sequence current and abrupt current. Phase A failure switch input = 1, Phase A failure current condition is satisfied and IA≥NIn phase "AND" constitutes the A phase failure trailing current starting criterion, B phase and C phase criteria are the same as A phase; three phase failure switch input = 1. Three-phase current conditions are met and I _a ≥ NI _n , I _b ≥ NI _n , I _c ≥ NI _n -phase "AND" constitutes the three-phase failure trailing current start-up criterion, I _a , I _b , and I _c are respectively A, B, C phase current fundamental RMS value; A phase or B phase or C phase failure tailing current start "or" three-phase failure tailing current start, then "failure tailing current criterion start = 1", enter Failure tailing current discrimination logic.

Step 7, judge whether X is smaller than M, if yes, then X=X+1, go to step 3, if not, go to step 2.

Step 8, calculating the DC component I _z in the phase current.

Step 9, judge whether I _z /I ≥ K1 _set and I _z /I _rms ≥ K2 _set are established, if established, it is judged as a failure trailing current, the corresponding phase failure protection is blocked, and the process ends; if not established, the process ends; , K1 _set and K2 _set are the threshold values, and I _rms is the true effective value of the phase current.

As shown in Figure 3, I _az in the figure is the DC component in the A-phase current, I _arms is the true effective value of the A-phase current, I _bz is the DC component in the B-phase current, I _brms is the true effective value of the B-phase current, and I _cz is the DC component of the C-phase current, and I _crms is the true RMS value of the C-phase current. After the failure trailing current discrimination is started, it enters the judgment logic of the failure tailing current to distinguish whether the current at this time is the failure tailing current or the fault current. "Failure trailing current start = 1", I _az /I _a ≥ K1 _set and I _az /I _arms ≥ K2 _set make "AND", if the three conditions are met at the same time, then the A-phase failure protection of this branch will be blocked; B-phase The criterion of phase C is the same as that of phase A; when the three conditions of phase A, B, and phase C are all satisfied at the same time, the three-phase failure protection will be blocked. The same branch is judged according to the phase. If the A phase is satisfied, only the A phase failure protection will be blocked, and the B phase, C phase or three phase failure will not be blocked; multiple branches are independent of each other and are judged separately.

The above method uses the proportion of the DC component in the phase current to judge the failure trailing current, which is simple and efficient, greatly reduces the time for the relay protection device to judge the failure tailing current, and effectively improves the discrimination accuracy of the failure tailing current. The failure protection does not refuse to operate when the current is flowing, and the failure protection does not malfunction when the CT tails the current, and accelerates the phase separation blocking failure protection, preventing the accident from expanding, and providing a better guarantee for the safe and stable operation of the power grid.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made. It should also be regarded as the protection scope of the present invention.

Claims (2)

1. a failure protection current tail method of discrimination based on DC component locking, it is characterised in that: bag Include following steps,

Step 1, the maximum circuitry number of definition is M；

Step 2, defines X=1；

Step 3, read X article of branch road malfunctioning open into；

Step 4, calculates malfunctioning current condition；

Step 5, calculates phase current first-harmonic virtual value I of the previous cycle of X article of branch road；

Step 6, if I is < NI_n, then go to step 7, if I >=NI_n, the differentiation of the most malfunctioning tail currents is opened Dynamic, go to step 8；

Wherein, I_nFor rated current, N is the rated current multiple that can arrange；

Step 7, it is judged that X, whether less than M, if it is, X=X+1, goes to step 3, if it is not, Then go to step 2；

Step 8, calculates DC component I in phase current_z；

Step 9, it is judged that I_z/I≥K1_setAnd I_z/I_rms≥K2_setWhether setting up, if set up, then being judged to lose Spirit tail currents, locking correspondence phase failure protection, flow process terminates；If be false, flow process terminates；

Wherein, K1_setAnd K2_setFor threshold value, I_rmsFor phase current real effective.

A kind of failure protection current tail based on DC component locking the most according to claim 1 differentiates Method, it is characterised in that: same branch road is by differentiating the most respectively, if A phase meets a rear locking malfunctioning guarantor of A phase Protect, B phase or C phase or the malfunctioning not locking of three-phase；Between a plurality of branch road separate, each differentiate.