JPH023371B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a ground fault detection method for detecting a ground fault in a reactor-grounded electrical line.

Prior Art and Problems When a consumer that normally receives high voltage power from an electric power company has a large ground capacitance, a reactor may be installed within the consumer to cancel out the charging current flowing through the ground capacitance. When installing a reactor, it is common to perform reactor reduction compensation (meaning that the current flowing through the reactor is lower than the current flowing through the ground capacitance).

When a ground fault occurs in a certain line in such a system, the ground fault direction relay installed in the faulty line operates to perform a cutoff operation, and other reactors are grounded. Since the phase relationship between the zero-sequence voltage and the zero-sequence current is within the non-operating range in the line, the earth-fault direction relay provided in the line does not operate. In this way, while the fault line is being cut off after the ground fault occurs, the ground fault direction relay installed on the healthy line connected to the reactor does not operate, but if the ground fault fault disappears naturally or When the faulty line is cut off, a resonance phenomenon occurs between the ground capacitance and the reactor of the healthy line, and the phase relationship between the zero-sequence voltage and the zero-sequence current falls within the operating range. However, there was a drawback that the ground fault direction relay provided in the line could malfunction.

Figure 1 is a configuration diagram of a conventional example, where 1 is the main line, 2
is a reactor, 3 is a zero-phase current transformer, 4 is a zero-phase voltage detector, 5 is a ground fault direction relay, 6 and 7 are ground capacitances of the main line 1, and 8 is a circuit breaker. Note that the value of the reactor 2 is set such that the current flowing through the reactor 2 is smaller than the current flowing through the ground capacitance 7.

For example, if a ground fault occurs on the power supply side, the zero-phase equivalent circuit at that time will be as shown in Figure 2A, and the zero-phase current transformer 3 will contain the current I _L flowing through the reactor 2 and the ground static electricity. The current flowing through capacitor 7 is the sum of I _CL and
I _CL + I _L will flow. Figure 3A is a vector diagram at this time, and the current I _L and current I _CL are shown in Figure 3A.
As shown, the phases are different by 180°, and the current I _L + I _CL output from the zero-sequence current transformer 3 is equal to the zero-sequence voltage −
Since the phase is delayed with respect to V ₀ , the ground fault direction relay 5 does not operate.

However, when the ground fault disappears, the zero-phase equivalent circuit at that time becomes as shown in Figure 2B, a resonance phenomenon occurs between the reactor 2 and the ground capacitances 6 and 7, and the zero-phase current transformer 3 A current I _CK equal to the current I _CK flowing through the ground capacitance 6 flows. The current I _CK is the third
As shown in the vector diagram in Figure B, the zero-sequence voltage −V ₀
Since the phase is advanced relative to the ground fault direction relay 5,
will work. That is, in the conventional example, when the ground fault on the power supply side disappears, the ground fault direction relay 5 malfunctions even though there is no ground fault on the load side.

OBJECT OF THE INVENTION The present invention improves the above-mentioned drawbacks, and its purpose is to prevent malfunctions when a ground fault disappears. Examples will be described in detail below.

Embodiment of the Invention FIG. 4 is a block diagram of an embodiment of the present invention, and the difference from the conventional example shown in FIG. 1 is that the reactor 2
This is the point where the zero-phase current transformer 10 is inserted into the ground wire of , and the zero-phase current transformer 3 and the zero-phase current transformer 10 are connected so that the polarity is opposite, and the same reference numerals as in the other Fig. 1 are used. represent the same part.

Therefore, if a ground fault occurs on the power supply side, the zero-phase equivalent circuit at that time will be as shown in Figure 5A, and the zero-phase current transformer 3 will have the current I _L flowing through the reactor 2 and the ground static electricity. The sum of current I _CL and I _L flowing through capacitor 7
+I _CL flows, and current I _L flows through the zero-phase current transformer 10. Figure 6A is a vector diagram at this time, and the current I _L and current I _CL have a phase difference of 180° as shown in Figure 6 A, and the current I _L + I _CL flows through the zero-phase current transformer. 3 and a zero-phase current transformer 10 through which current I _L flows
Since it is connected so that the polarity is opposite to that of the ground fault direction relay 5, a current _ICL is applied to the ground fault direction relay 5. As shown in Figure A, this current I _CL has a delayed phase with respect to the zero-phase voltage -V ₀ , so if a ground fault occurs on the power supply side, the ground fault direction relay 5 will not operate.

In addition, when the ground fault disappears, the zero-phase equivalent circuit at that time becomes as shown in Figure 5B, and a resonance phenomenon occurs between the reactor 2 and the ground capacitances 6 and 7, and the zero-phase current transformer 3 A current I _CK flows through the zero-phase current transformer 10, and a current I _CK +I _CL flows through the zero-phase current transformer 10. Figure 6B is _a vector diagram at this time.
Since only I _CL is applied, according to this embodiment, the ground fault direction relay 5 will not malfunction when the ground fault disappears.

Also, if a ground fault occurs on the load side,
The zero-phase equivalent circuit at that time is shown in Figure 5C, and the current flows to the ground capacitance 6 in the zero-phase current transformer 3.
I _CK flows, and I _L flowing through the reactor 2 flows to the zero-phase current transformer 10. FIG _{. 6C} is a vector diagram at this time _.
Therefore, the ground fault direction relay 5 operates normally.

Furthermore, when the ground fault disappears, the zero-phase equivalent circuit at that time becomes as shown in Figure 5D, and a resonance phenomenon occurs between the reactor 2 and the ground capacitances 6 and 7, and the zero-phase current transformer 3 A current I _CK flows through the zero-phase current transformer 10, and a current I _CK +I _CL flows through the zero-phase current transformer 10. FIG. 6D is a vector diagram _at this time _.
Therefore, the earth fault direction relay will not malfunction. However, since the load is cut off when the ground fault directional relay 5 operates, it is generally not necessary to consider the resonance phenomenon after the ground fault disappears.

FIG. 7 is a configuration diagram of another embodiment of the present invention,
The difference from the conventional example shown in FIG. 1 is that the ground wire of the reactor 2 is passed through the zero-phase current transformer 3 from the load side to the power supply side and then grounded.
The same reference numerals as in other FIG. 1 represent the same parts.

As described above, in this embodiment, the ground wire of the reactor 2 is passed through the zero-phase current transformer 3 from the load side to the power supply side. This means that the flow device 3 is installed on the load side. Therefore, if a ground fault occurs on the power supply side, the zero-phase equivalent circuit at that time will be as shown in Figure 8A, and the zero-phase current transformer 3 will have a zero-phase circuit as shown in the vector diagram of Figure 9A. Since the current I _CL having a delayed phase with respect to the voltage −V ₀ flows, the earth fault direction relay 5 does not operate.

Moreover, when the ground fault disappears, the zero-phase equivalent circuit at that time becomes as shown in FIG. Since the current I _CL having a delayed phase with respect to the zero-phase voltage −V ₀ shown in the vector diagram of FIG. B flows, the earth fault direction relay 5 will not operate when the earth fault fault disappears.

Also, if a ground fault occurs on the load side,
The zero-sequence equivalent circuit at that time is shown in Figure 8C, and the zero-phase current transformer 3 has a current that has a leading phase with respect to the zero-sequence voltage -V ₀ shown in the vector diagram in Figure 9C.
Since I _CK +I _L flows, the earth fault direction relay 5 operates.

Furthermore, when the ground fault disappears, the zero-phase equivalent circuit at that time becomes as shown in Figure 8D, and the reactor 2
Due to the resonance phenomenon between the ground capacitances 6 and 7, a current I _CL having a lagging phase with respect to the zero-sequence voltage −V ₀ shown in the vector diagram of FIG. 9D flows through the zero-phase current transformer 3. Therefore, the ground fault directional relay 5 will not operate when the ground fault disappears. However, since the load is cut off when the ground fault directional relay 5 operates, it is generally not necessary to consider the resonance phenomenon after the ground fault disappears.

Effects of the Invention As explained above, when detecting a ground fault in an electric line where the load side is grounded by a reactor, the present invention provides a detection means ( In the embodiment, a zero-phase current transformer 3, 10 or zero-phase current transformer 3, consisting of a ground wire of the reactor 2) is provided, and a zero-phase current transformer 3, 10, or a zero-phase current transformer 3, and a zero-phase current transformer 3, and a zero-phase current transformer 3, and a ground wire of the reactor 2 are provided to detect the detection result of the detection means and the zero-phase voltage of the electric circuit. Since ground faults on the load side are detected based on the detection results of the phase voltage detector, there is an advantage that malfunctions due to resonance phenomena that occur when a ground fault fault disappears can be prevented.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional example, Figure 2 is a zero-phase equivalent circuit when a ground fault occurs in Figure 1, and Figure 3 is a diagram when a ground fault occurs in Figure 1. 4 and 7 are configuration diagrams of different embodiments of the present invention, and FIGS. 5 and 8 are vector diagrams of the cases in which a ground fault occurs in FIGS. 4 and 7, respectively. Zero-phase equivalent circuits, FIGS. 6 and 9 are vector diagrams when a ground fault occurs in FIGS. 4 and 7, respectively. 1 is a main line, 2 is a reactor, 3 and 10 are zero-sequence current transformers, 4 is a zero-sequence voltage detector, 5 is a ground fault direction relay, 6 and 7 are ground capacitances, and 8 is a circuit breaker.

Claims (1)

[Claims] 1 Ground fault detection is performed based on the detection results of a zero-sequence current transformer that detects the zero-sequence current of an electrical line whose load side is grounded by a reactor, and the detection result of a zero-sequence voltage detector that detects the zero-sequence voltage of the electrical line. In the method,
A detection means for detecting the difference between the zero-sequence current in the electric circuit and the zero-sequence current flowing through the reactor is provided, and based on the detection result of the detection means and the detection result of the zero-sequence voltage detection means, a ground voltage is applied to the load side. A ground fault detection method that detects a ground fault only when a fault occurs.