JPS6055824A - Ground-fault protecting system of high voltage distributing system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground fault protection system for a high voltage power distribution system in which each power distribution line drawn out from a busbar is provided with a ground fault direction relay.

If the ground capacitance is large, an abnormal voltage phenomenon will occur in a non-grounded system at the time of a ground fault, or a secondary abnormal phenomenon will occur due to saturation of a grounding transformer, etc. In order to prevent this, a method is generally adopted in which a grounding effective current is supplied by a current limiting resistor or a neutral point resistor of a grounding transformer. However, in this case, it has been found that when an intermittent ground fault continues in a cable system or the like, the ground fault protection relay of a healthy power distribution line may perform an unnecessary operation, that is, malfunction.

As a result of various investigations and examinations regarding this issue, we found that while an intermittent ground fault continues, the charge in the ground capacitance is discharged immediately after the ground fault disappears, and the discharge current is a component in the operating direction of the ground fault direction relay. It was determined that this was the cause of the malfunction.

Therefore, an object of the present invention is to prevent malfunction of a ground fault direction relay of a healthy power distribution line when an intermittent ground fault occurs in a high voltage power distribution system.

This purpose, according to the invention, is to reduce the zero-sequence current detected by the zero-sequence current transformer provided on each distribution line leading out from the bus and the grounding transformer provided on the bus side. It is equipped with a ground fault directional relay that determines ground faults in the relevant distribution line based on the zero-sequence voltage generated, and supplies a grounding active current via the current limiting resistor or neutral point resistor of the grounding transformer. In a ground fault protection system for a high-voltage power distribution system, when the first half wave of the zero-sequence current rises in the opposite phase to the zero-sequence voltage in each fundamental wave half-wave, the remaining period of the zero-sequence voltage half-wave This is accomplished by providing each fault direction relay with a locking means that prevents the operation of the ground fault direction relay.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a system diagram showing a general high voltage power distribution system.

A breaker CDI is connected to each bus bar connected to the receiving transformer MTr via a breaker CBQ.

' Distribution lines are drawn out via CBz,...CBn.

Ground capacitance in individual distribution lines c, l c21 ”
"" tCn is shown isometrically with the distributed inductance. The grounding transformer GPT connected to the busbar and taking out the zero-sequence voltage has a current limiting resistor CRT connected to its open delta winding. Lost ZCT2 at complete ground fault
, . The zero-sequence voltage detected via the grounding transformer GPT is input to these ground fault direction relays.

Ground fault phenomena in ungrounded high-voltage distribution systems exhibit complex behavior depending on the ground capacitance of the distribution lines. This is especially severe when intermittent ground faults occur in cable systems.

Figure 2 shows the ground fault phase cause and pressure (a) when an intermittent ground fault occurs.
), the waveforms of the zero-sequence current (b) of the grounded distribution line, the zero-sequence current (C) of the healthy distribution line, and the zero-sequence voltage (d) are illustrated.

The behavior of zero-sequence current 1° and zero-sequence voltage when such a ground fault occurs is explained as follows.

1o==Aosin (ω.t-1-ψ.)+A1e
−α, t Sin (ωt'+ψs)+A2e ”2
” sin (ω2t-1-ψ2) −−−−−・−・
(1) However, ω1-2πf1 fo - fundamental frequency f, - positive, negative phase circuit natural resonance frequency (2 = = zero-phase circuit natural resonance frequency ψj = earth fault occurrence phase τ0 = earth fault occurrence time Δτ = earth Fault duration time This is an example of a ground fault that occurs Δτ/2 before the peak value phase of the basic voltage waveform at the fault point and disappears after 21 hours, as shown in Figure 2 t. This is the time equivalent to a half-wave of the natural resonance frequency of the zero-phase circuit.In other words, an intermittent fault occurs in the cable of the power distribution system, a half-wave of inrush ground fault current based on the resonant current flows, and the insulation is restored by an arc. The case is shown in which the ground fault disappears, and then the ground fault continues to occur just before the peak value of successive half waves based on the fundamental frequency.

FIG. 3 is an equivalent circuit diagram in the case where an intermittent ground fault occurs at point A in the system shown in FIG. 1.

E corresponds to the normal power supply phase voltage, Z represents positive and negative phase impedance/phase, and S is a ground fault simulating switch. 1st
The current limiting resistor CLR in FIG. 1 is shown here as a resistor equivalent to l.

When such a ground fault phenomenon occurs and the faulty distribution line is cleared, or the intermittent ground fault phenomenon disappears, a charge remains in the ground capacitance of the healthy distribution line, and the above equation (2) The zero-sequence voltage V as shown by remains. This zero-sequence voltage■. is the third
As shown by the broken line arrow ('dt to 1dn) in the equivalent circuit of the figure, the photoelectric charge of the ground capacitance is attenuated as it is discharged through the current limiting resistor.

The discharge time constant T, when the total ground capacitance ΣC, is expressed as T-ΣC-i(,... Song... Song (3). Here, the discharge time constant is the system fundamental frequency If it is several cycles or more based on drawn into the abnormal phenomenon and transferred to a new transient phenomenon.Furthermore, in such conditions the earthing transformer no longer has the ability to supply the normal zero-sequence voltage V. to the earth fault directional relay, as a result of which the protection system It becomes an incomplete state.

In order to suppress these abnormal voltage phenomena and the saturation phenomenon caused by DC excitation of grounding transformers, etc., the effective portion of the ground fault current by the current limiting resistor of the grounding transformer or the grounding resistor installed at the neutral point is diverted from the ground to the distribution line. Generally, a method of raising the current to a value around the charging current value, which is related to the capacitance, is adopted. That is,
Effective current ioR due to current limiting resistor and line charging current 1o
The ratio γ with ΣC may be used. In other words, the above-mentioned disadvantages are avoided by appropriately reducing the discharge time constant T to speed up the attenuation of the residual zero-sequence voltage.

However, in this case, the ground fault direction relay of the healthy distribution line may malfunction. The cause of this will be explained with reference to the equivalent circuit diagram of FIG. 3 and the waveform diagram of FIG. 4.

flows. Zero-sequence voltage V. Hato becomes. Figure 4 shows the current '0' at each part in Figure 3.
OI+ 101 s 102 and zero-sequence voltage v. The waveform of is shown.

If the intermittent ground fault current disappears in Δτ time (equivalent to a half-wave of the natural resonance frequency of io) as shown in Fig. 4, the current limiting resistor will be activated immediately after that. The charge of each ground capacitance is discharged through the ground capacitance. These discharge currents are shown in FIG. 3 by dashed arrows 'ti1 to Idn.

In this case, the zero-sequence current 9 of the healthy distribution line, for example i shown in FIG. As can be seen from the waveform No. 2, the discharge current L12 becomes a zero-sequence current component in the operating direction for the ground fault direction relay of the distribution line. For this reason, if such an intermittent ground fault continues, there is a possibility that the ground fault direction relay of a healthy power distribution line will perform unnecessary operation (malfunction).

In order to prevent the above-mentioned malfunction, the present invention provides that when the first half wave of the zero-sequence current waveform caused by each ground fault has a polarity opposite to the zero-sequence voltage waveform, the zero-sequence voltage waveform at that time During the half-wave period, the ground fault direction relay is locked so that it does not operate.

An embodiment of a ground fault directional relay provided with such locking means according to the invention is shown in FIG. FIG. 6 shows a specific example of the structure of the locking means.

In FIG. 5, 11 is an input terminal for a zero-sequence voltage detected by a grounding transformer, and 12 is an input terminal for a zero-sequence current detected by a zero-sequence current transformer. The zero-sequence voltage input to the input terminal 11 is passed through the filter 13, and the zero-sequence current input to the input terminal 12 is converted by the voltage conversion element 14 into a voltage proportional to the current value, and then passed through the filter 15. The signals are respectively guided to the failure determination calculation circuit 16. The failure determination circuit 16 determines whether the ground fault occurred in the distribution line to which it belongs or in another distribution line, based on the phase relationship between the zero-sequence voltage and the zero-sequence current that occur in the ground fault. The determination is made and a corresponding signal is output to the output terminal 17.

Furthermore, a zero hold command calculation circuit 18 is provided here as a locking means added according to the present invention. The input side of this zero hold command calculation circuit is input terminal 1.
1 and 12, and receives a zero-sequence voltage and a voltage proportional to the current from each. This arithmetic circuit 18 detects that when the zero-sequence current rises with the opposite polarity to the rise of the zero-sequence voltage, an erroneous ground fault detection signal is output until the end of the half-wave of the zero-sequence voltage at that time. It has a function of giving a zero hold command to both input filters 13 and 15 of the failure determination calculation circuit 16 so that the failure determination calculation circuit 16 does not have a zero hold command.

Such a function can be realized by the specific configuration of the zero hold command circuit shown in FIG. That is,
Both input voltages derived from input terminals 11, 12 are supplied to comparators 181 and 182, respectively. When the magnitude of each input voltage exceeds a predetermined threshold, the comparators 1B1 and 182 generate an 11" signal at the output terminal Q if the polarity is positive, and at the output terminal Q if the polarity is negative, according to the polarity of each input voltage. Monostable circuits 183, 184, 185,
186 is arranged in succession, and each of these monostable circuits outputs a "1" signal for a certain period of time when a "1" signal is input.The outputs of the monostable circuits 183 and 186 are connected to the The outputs of the circuits 184 and 185 are AND-coupled by an AND gate 188. is the input filter 13゜1 in Fig. 5.
It is connected to the zero hold control terminal of No.5.

FIG. 7 is an explanatory diagram of the operation of the zero hold command circuit of FIG. 6. Figures 7(a) and 7(b) each show input terminal 1.
Input voltages corresponding to the zero-sequence current and zero-sequence voltage input to 1.12 are shown. The positive and negative levels indicated by broken lines are the comparators 1B1 and 18.
2 threshold level. These threshold levels are well above the maximum instantaneous value of zero-sequence current or zero-sequence voltage in a permanent ground fault, but the resonant inrush current in the event of an intermittent ground fault (its frequency is several KHz, its value is ) or it is set to an excessive level that is well below the maximum instantaneous value of the zero-sequence voltage. Comparator 181
The outputs Q, Q of the comparator 182 are shown in FIGS. 7(C) and (d), and the outputs Q, Q of the comparator 182 are shown in FIG. 7(e),
(f) Nisoresore is shown.

The output pulses of these comparators 181 and 182 are guided to monostable circuits 183 to 186, respectively, and are shown in FIG.
The pulses are converted into pulses having a constant time width as shown in 1 to (j) d. When the output pulse of the monostable circuit 183 and the output pulse of the monostable circuit 186 exist simultaneously, the AND gate 1
87 outputs a pulse as shown in FIG. 7(k),
This pulse passes through the OR gate 189 to the monostable circuit 19.
Operate 0. Similarly monostable circuits 184 and 185
AND gate 1 also exists when the output pulses of
A pulse as shown in FIG. Monostable circuits 183 to 186 are monostable circuits 190
This helps ensure that the input pulses of the device have a width that will ensure that it operates. As shown in Fig. 7), the time width of the pulse output by the operation of the monostable circuit 190 is as follows: The time is set to allow sufficient decay.

Of course, this time must not exceed one half cycle of the fundamental wave. During the output pulse period of the monostable circuit 190, a zero hold command is given to the input filter 13.15 of FIG.

In this way, by determining the polarity between the two inputs every half cycle of the fundamental wave, unnecessary input to the failure determination calculation circuit 16 can be cut off, thereby preventing malfunctions.

In order to prevent such malfunctions, in the embodiment shown in Fig. 5, both input filters are held at zero, but if the same result is obtained every half cycle, the locking function is set in the ground fault direction. It can be attached to any part of the relay.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing a high-voltage distribution system, Figure 2 is a waveform diagram to explain the intermittent ground fault phenomenon, and Figures 3 and 4 are ground fault direction relays on healthy distribution lines when an intermittent ground fault occurs. Fig. 5 is a block diagram showing an embodiment of a ground fault directional relay configured according to the present invention, and Fig. 6 is a diagram of the embodiment of Fig. 5. FIG. 7 is a block diagram showing a specific example of the configuration of the main part. FIG. 7 is a waveform diagram for explaining the operation of the circuit shown in FIG. 6. DGRI~DGRn...Ground fault direction relay, ZCT 1
~ZCTn...Zero-phase current transformer, GPT...Grounding transformer, CLR...Current limiting resistor, C1-Cn...Ground capacitance, 11.12...Input terminal, 13. 15... Input filter, 16... Failure determination calculation circuit, 17... Output terminal, 18... Zero hold command calculation circuit, 181, 182... Comparator, 183-186
, 190...monostable circuit. Figure 5 Figure 26

Claims (1)

[Claims] 1) From the zero-sequence current detected by the zero-sequence current transformer installed on each distribution line drawn out from the bus and the zero-sequence voltage detected by the grounding transformer installed on the bus side, Equipped with a ground fault direction relay that detects ground faults in distribution lines, and reduces the capacitance to ground of distribution lines by passing a grounding active current through the current limiting resistor of the grounding transformer or the neutral point grounding resistor in the event of a ground fault. In a ground fault protection system for high-voltage power distribution systems designed to suppress abnormal phenomena caused by On the condition that the first half-wave of current rises in phase opposite to the zero-sequence voltage, locking means is installed in each fault direction to prevent the operation of the relay in the relevant ground-fault direction during the remaining period of the zero-sequence voltage half-wave. A ground fault protection system for high-voltage power distribution systems that is characterized by being installed in a relay.