JPH0532972B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground fault protection system for high resistance grounding parallel multi-circuit lines, and particularly provides an excellent system for three-terminal systems.

In a parallel multi-circuit system, for example, two lines or four lines, depending on the system configuration, the mutual inductance between each phase of the system may become unbalanced, causing an induced current (hereinafter referred to as circulating current) that circulates between lines due to load current.
occurs. In particular, 1 line outage, 2 line outage, 1 line outage,
The circulating current generated when the terminal is open is significant and cannot be ignored compared to the fault current supplied from the neutral point resistor during a one-line ground fault. For this reason, the relay tap value is increased so that the ground fault protection relay does not malfunction due to the zero-sequence portion of the circulating current (hereinafter referred to as zero-sequence circulating current). Therefore, there is a problem in that highly sensitive protection cannot be achieved as the zero-phase circulating current increases. Also,
This poses a number of problems, such as a drop in the reliability of power supply due to opening one terminal, and troublesome maintenance due to the installation of a prohibited system.

In order to solve the above-mentioned problem, there has been a method in which the constant zero-sequence current is stored and a faulty line is determined based on the amount of change in the zero-sequence current at the time of a fault. However, in principle, this method responds to the change in zero-sequence current before and after a failure, so if an internal failure occurs near the other end, the other end may suddenly break (series strip).
In this case, the zero-phase circulating current changes, making it difficult to identify the faulty line. For this reason, in a two-terminal system, a system is adopted in which the faulty line is determined by switching to a conventional line selection relay after a certain period of time (time before the other end precedes or breaks) after the failure occurs.
In a three-terminal system, the above method cannot be expected to be sufficiently effective because faults are eliminated by a three-stage series strip in which the other end experiences leading and breaking twice.

The circulating current generated in a shared multiline is theoretically proportional to the load current that induces it. Its properties can be summarized as follows.

Property 1 The circulating currents of the a, b, and c phases and the zero-phase circulating currents I· _ac , I· _bc , I· _cc , and I· _pc are proportional to the load current that induces them.

Property 2 The proportionality constant is determined by the operating status of the system, wire arrangement, and load current distribution.

Property 3 From Properties 1 and 2, the vector ratio between the zero-sequence circulating current I・_pc and the amount obtained by excluding the positive-sequence component from the two phase currents, defined below, is determined by the operating conditions, wire arrangement, and load current distribution. .

However, a=exp(j2/3π) The present invention has been made based on the above properties (1) to (3).

When a single-wire ground fault occurs in the a phase, the normal phase b and c phase difference currents I· _bd and I· _cd do not include the fault current component and are as follows.

I・_bd = I・_bc +I・_bL ……(2) I・_cd = I・_cc +I・_cL ……(3) However, I・_bL and I・_cL are the difference current due to branch load, leading or disconnection, etc. The load currents I· _bc and I· _cc appearing in are the b-phase and c-phase circulating currents due to induced currents.

If we advance the c phase difference current by 120 degrees and take the vector difference with the b phase difference current, we get I・_bd −aI・_cd = I・_bc −aI・_cc + (I・_bL −a
I・_cL )
...(4) However, a=exp(j2/3π) Since the load current is almost only the positive phase component,
The load current is eliminated by calculating equation (4). Therefore, I・_bd −aI・_cd = I・_bc −aI・_cc ……(5) As shown in equations (2) to (5), the influence of the load current can be calculated from the healthy difference current of the two phases. You can find the amount removed. Furthermore, the zero-sequence circulating current at the time of the a-phase ground fault can be calculated by vector product calculation of the constant K· _a defined by equation (1) and the amount obtained by excluding the positive-sequence component from the healthy phase-difference current. From equations (1) and (5), the following can be obtained: _I.pc (es) = _K.a x ( _I.bd - _aI.cd )...(6). However, I· _pc (es) is the calculated value of the zero-phase circulating current.

On the other hand, in the line selection relay system, which is generally used as a ground fault protection relay system for two high-resistance lines, I/ _PD
The faulty circuit is selected based on the direction and magnitude of the zero-sequence voltage (zero-sequence portion of the differential current).In a shared multi-circuit system, a zero-sequence circulating current occurs and I/ _pd is at the neutral point. Resistance current component I・_f and zero-sequence circulating current I・_p
c
The composite value is as follows.

_I.pd = _I.f + _I.pc (7) For this reason, conventional relays tend to malfunction, and it is necessary to take countermeasures such as increasing the tap value at the expense of detection sensitivity.

According to the present invention, the zero-sequence circulating current I・_pc included in the zero-sequence difference current in equation (7) is calculated as follows using the calculated value I・_pc (es) of the zero-sequence circulating current obtained by the above method. cancel out

I・_pd (es)=I・_pd −I・_pc (es)=I・_f +I・_p
c −I・_pc
(es) ...(8) If the compensation by I・_pc (es) is complete, I・oL=
I·oc(es), and the neutral point resistor current component I· _f can be obtained.

Therefore, earth fault protection can be performed without being affected by zero-phase circulating current. Although we have explained the a-phase one-wire ground fault, the zero-phase can also be detected in the case of a one-wire ground fault in the b and c phases by using the same concept and using two healthy phases and the constants K・_b and K・_c in equation (1). Can compensate for circulating current.

The constants K・_a , K・_b , and K・_c take different values depending on the operating status of the system in parallel three-circuit and four-circuit systems, but
If this value differs from the values of K・_a , K・_b , and K・_c set in the relay, it becomes a compensation error and deteriorates the ground fault protection accuracy. In the present invention, in order to correct this problem, information on the line break in the protected system is obtained using transmission means such as optical fiber or communication cable, and the system status is determined based on the condition of each line and line break. Constant K to be used
It is characterized by selecting _a , K・_b , and K・_c .

In this case, constant K・_a ,
There is no need to have _K.b and _K.c separately. In other words, by collecting similar operating states of constants into one pattern, several types of constants K・_a , K・_b , K・_c
, and this value can be found through simulation.

A parallel multi-line ground fault protection system according to an embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows a parallel four-line power transmission system to which the present invention is applied. For simplicity, the power transmission line has a two-terminal configuration, but there is no difference between the embodiments even if the power transmission line has a three-terminal configuration. The earth fault protection relay according to the present invention is
installed at the end. In Figure 1, 1a-1c is 3
Phase power supply, 2 is neutral point grounding resistor NGR, 11a-
11c and 12a-12c are busbars, 21a-24
c indicates the power transmission line, of which 21, 21a to 21
c, 22, 22a-22c, 23, 23a-23
c, 24, 24a to 24c are No. 1 1L, respectively.
No. 2 2L, No. 3 3L, and No. 4 4L lines. In addition, 3 indicates a voltage detection transformer, and bus bars a, b,
Detect c-phase voltages E ₁ , Ea, Eb, Ec and zero-sequence voltage E ₀ . 41a-44c and 61-64 show the breakers and disconnectors. 51a-54c indicate current transformers for current detection, and a, b,
c and zero-sequence current I ^1L (I ^1L _a , I ^1L _b , I ^1L _c , I ^1L _p ), I ^2L (
I ^2L _a ,
I ^2L _b , I ^2L _c , I ^2L _p ), I ^3L (I ^3L _a , I ^3L _b , I ^3L _c , I ^3L _p )
, I ^4L (I ^4L _a ,
I ^4L _b , I ^4L _c , I ^4L _p ) are detected. B is the other end electric station,
7 indicates a three-phase load.

FIG. 2 shows a protection processing unit that executes a parallel multi-line protection system according to an embodiment of the present invention, in which 13 indicates a first data conversion unit, and current transformers 51a-54
Each phase current of each line I ^1L , I ^2L , detected by c
It inputs I ^3L and I ^4L , samples them at regular intervals, converts them into digital quantities, and outputs these quantities S ₁ . Reference numeral 14 denotes a second data conversion section, which inputs the bus voltages E ₁ and E ₀ detected by the transformer 3, converts them into digital quantities in the same manner as above, and converts these quantities S ₂ into digital quantities. Output. Reference numeral 15 denotes a ground fault phase detecting section which inputs each phase voltage _S2 which is the output of the second data converting section 14, detects a ground fault phase therefrom, and outputs the signal _S3 .

Reference numeral 16 denotes a system operation pattern detection unit, which transmits the opening/closing information of the opposite end and disconnectors 61 to 64 obtained using transmission means such as communication cables and optical fibers to the transmission terminal unit 7.
Receive from 0, self-end and disconnector 43, 43a-4
The information of 3c, 44, 44a to 44c is directly received from the pallet contact, etc., and it is detected which pattern it belongs to among the grid operation patterns classified in advance according to the breakage and disconnection conditions, and the detected pattern is indicated. Output signal S ₄ . Reference numeral 17 denotes a constant output unit, which inputs the detected grid operation pattern _S4 , which is the output of the grid pattern operation detection unit 16, and calculates the zero-phase circulating current for each of the aforementioned patterns obtained in advance by grid simulation. Constants K· ^set _a , K· ^set _b , and K· ^set _c that minimize the error are stored, and a constant S ₅ for the detected pattern is output.

Reference numeral 18 denotes a zero-phase circulating current calculation section, which includes the output S ₁ of the first data conversion section 13 and the output of the ground fault phase detection section 15.
S ₃ and the output S ₅ of the constant output section 17 are input. 1L,
For the 2L line selection relay, the healthy phase is known by the input signal _S3 , and for example, if the a phase is grounded, the phase b and c phase difference currents 1L-2L, which are healthy phases between 1L and 2L, are detected. Calculate from S ₁ . Furthermore, the positive phase component is excluded from the current of the two healthy phases, and this amount is multiplied by the constant obtained from the output _S5 of the constant output section 17 (K・^set _a if the a phase is grounded) to calculate the zero phase. Calculates the circulating current and outputs its value _S6 . Calculate equation (6) for the a-phase ground fault. Reference numeral 19 indicates a compensation unit, and zero-phase circulating current calculation unit 1
8 output S ₆ and the output S ₁ of the first data converter 13
(zero phase component only). For the 1L and 2L line selection relays, calculate the zero-sequence difference current 1L-2L between 1L and 2L from _S1 , and calculate the zero-sequence circulating current calculated by the zero-sequence circulating current calculation unit 18 from this calculated value. Derive the neutral point resistor current component due to ground fault by subtracting the value S ₆ and output this value S ₇ .
Perform the calculation of equation (8). Reference numeral 20 indicates a ground fault line selection unit, which inputs the output S ₇ of the compensation unit 19 and the output S ₂ (zero-sequence voltage only) of the second data conversion unit 14, and selects the output of the compensation unit 19 based on the zero-sequence voltage. Select the ground fault line by looking at the direction of the neutral point resistor current signal _S7 , which is
A trip command _S8 is output to the line disconnector.

As explained above, in the present invention, by obtaining information on the faults and disconnections in the protection system, it is possible to completely understand the status of the system, and the accuracy is significantly higher than when the system is known. .

Further, in the present invention, since only the information on the edge and disconnection is transmitted, the transmission can be performed relatively easily.

Furthermore, in the present invention, if information on the other end is obtained, it is possible to reliably detect an advance or a failure, and the reliability of protection is greatly improved.

[Brief explanation of drawings]

FIG. 1 is an electrical connection diagram of a parallel multi-line power transmission system to which the present invention is applied, and FIG. 2 is a block connection diagram of a protection processing unit that executes a parallel multi-line ground fault protection system according to an embodiment of the present invention. 11a-11c, 12a-12c... Bus bar, 1
3...First data conversion unit, 14...Second data conversion unit, 15...Ground fault phase detection unit, 16...System operation pattern detection unit, 17...Constant output unit, 18
... Zero-phase circulating current detection section, 19 ... Compensation section, 20
...Ground fault line selection section, 41a-44c, 61-6
4...Shiya disconnector, 70...Transmission terminal section.

Claims (1)

[Claims] 1. A relay that samples the electrical quantity obtained from the voltage transformer and current transformer of a parallel multi-circuit transmission line at regular intervals, converts it into digital data, and uses this digital quantity to protect against ground faults. System operation pattern detection means obtains disconnection information using transmission means such as communication cables and optical fibers, determines the system operation according to each disconnection condition, and classifies it into several types of patterns, and constant output means for determining and storing a constant that minimizes a calculation error of the zero-phase circulating current for each of the above-mentioned patterns, and outputting the constant in response to a pattern detection signal by the system operation pattern detection means; a ground-fault phase detection means for detecting a ground-fault phase when a one-line ground fault occurs;
zero-sequence circulating current calculation means for calculating a zero-sequence circulating current by multiplying the constant output from the constant output means by a value selected according to the ground fault phase and the amount obtained by removing the positive phase component; Compensating means for calculating an amount obtained by subtracting the calculated value of the zero-sequence circulating current from the zero-sequence of the difference current, and selecting a ground fault line from the direction and magnitude of the amount calculated from the compensating means with respect to the zero-sequence voltage. 1. A parallel multi-line ground fault protection system, comprising a ground fault line selection means, and an output of the ground fault line selection means opens a break or a break in the ground fault line.