JPH0636646B2 - Ground fault direction relay - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault direction relay device for detecting a ground fault such as a high voltage distribution line, and more particularly to a current transformer for detecting a zero phase voltage signal and a zero phase current. The thing using the floating capacitance of.

2. Description of the Related Art A ground fault direction relay device detects a zero-phase voltage and a zero-phase current when a ground fault occurs and compares the phases of these voltages and currents to determine that the fault is a zero-phase current transformer. It is a relay device that discriminates the direction of the power supply side or the load side with the vessel as a boundary, and performs a protective operation in case of a ground fault accident on the load side.

FIG. 5 shows a circuit diagram of such a conventional ground fault direction relay device.

In Fig. 5, DG is a ground fault direction relay, ZCT is a zero-phase current.
The zero-phase current transformer for detecting I ₀ , ZPD indicates a zero-phase voltage detecting device for detecting the zero-phase voltage E ₀ . The ground fault direction relay DG receives the zero-phase voltage E ₀ and the zero-phase current I ₀ as inputs, internally detects the levels of the voltage E ₀ and the current I ₀ , and shapes the waveform when the set level is reached. A phase detection circuit that introduces the output signals of the level detection circuit that outputs a signal and the waveform-shaped level detection circuit and compares the phases to determine whether the ground fault is on the load side or the power supply side with the current transformer as the boundary. Have. When a ground fault occurs on the load side, the ground fault direction relay DG
The signals of the zero-phase current I ₀ and the zero-phase voltage E ₀ are input to, and when these signals reach the set level, the rectangular wave pulse and the signal converted into the narrow pulse are input to the phase determination circuit. The lever discriminating circuit outputs an output only when the zero-phase current signal and the zero-phase voltage signal are temporally overlapped with each other, and the auxiliary relay is operated through the time limit circuit. When the ground fault is on the power supply side of the zero-phase current transformer ZCT, the phases of the zero-phase currents differ by 180 degrees, so the waveforms of the zero-phase current signal and zero-phase voltage signal do not overlap in time, so phase discrimination No output signal is output from the circuit.

Problems to be Solved by the Invention In the above ground fault relay device, a capacitor is used for the zero-phase voltage detection device ZPD for obtaining the zero-phase voltage signal, but this capacitor is directly connected to the high voltage line. Therefore, it is necessary to take measures for insulation, and it is generally built in a high voltage insulator. Therefore, the cost is high, and even when the equipment is installed in a switchboard, it is necessary to secure an insulation distance between the phases or other devices, resulting in a large mounting space and high construction cost.
In addition, since there is an imbalance in the electrostatic capacity of the high-voltage line of each phase and a residual voltage (apparent zero-phase voltage) is always generated at the zero-phase voltage output terminal t, the sensitivity of the ground fault direction relay DG is high. If the output signal of the zero-phase voltage output terminal t is increased in order to increase the voltage, the ground fault direction relay DG may malfunction. Therefore, there is a drawback that the sensitivity cannot be increased and it is necessary to reduce the sensitivity to prevent malfunction.

The present invention has been made in view of such problems, without requiring a special capacitor for zero-phase voltage detection,
Moreover, the purpose is to obtain this type of relay device that is free from the risk of malfunction.

Means for Solving the Problems In the present invention, a means for solving the above problems is to detect a zero-phase current and a zero-phase voltage that occur at the time of a ground fault due to a line fault and to detect a zero-phase current signal and a zero-phase current signal. The phase voltage signal is obtained, and when the zero phase current signal and the zero phase voltage signal reach the set level, their phases are compared to each other, and a ground fault occurs at the power source side or the load with the current transformer for detecting the zero phase current as a boundary. In the ground fault direction relay device which is operated when it is the load side by discriminating the direction of the side, the zero-phase voltage signal is detected by using the stray capacitance of the current transformer, In addition, the residual voltage based on the imbalance of the floating capacitance and the zero-phase voltage generated at the time of the ground fault are combined to obtain the difference.

Action In a normal state where there is no ground fault accident, neither zero-phase current nor zero-phase voltage is generated, so the ground fault direction relay device does not operate. The stray capacitances of the three phases of the current transformer are not always the same, so residual voltage is generated due to unbalance, but since zero-phase voltage is not generated, the difference due to their combination is generated. Since the signal of does not appear, there is no risk of malfunction.

A ground fault occurred, the zero-phase current signal reached the set level,
Also, when the difference between the zero-phase voltage and the residual voltage reaches the set level, the phases of the zero-phase current signal and the zero-phase voltage signal are compared, and if the ground fault is on the load side, the ground fault direction relay device. Works.

Also, when the load switch is turned on normally during normal operation and the load current changes abruptly, an apparent zero-phase current flows, and when it exceeds the set level, the zero-phase current signal is output, but the zero-phase current signal is output. Since the voltage is not generated, the signal of the difference due to the combination with the residual voltage does not appear, so that the earth relay device does not operate.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a block connection diagram showing an embodiment of the present invention.
I ₀ is a zero-phase current, 1 is an amplifier for increasing the zero-phase current,
2 rectifies the zero-phase current amplified by the rectifier. A level detection circuit 3 outputs a signal when the output of the rectifier 2 reaches a set level. Reference numeral 4 is a waveform shaping circuit, which converts the increased zero-phase current into a rectangular wave pulse. An AND gate 5 outputs an output signal when the output signals of the level detection circuit 3 and the waveform shaping circuit are simultaneously input. V ₀ is the zero-phase voltage,
Reference numerals 6 and 7 denote amplifiers provided in parallel with each other for amplifying the zero-phase voltage, and 8 denotes a delay circuit (or a storage circuit).
Delay the output signal of. Reference numeral 9 is a combining circuit such as a differential amplifier, which combines the output signal of the amplifier 6 and the output signal of the delay circuit 8 which delays this signal to obtain a zero-phase voltage signal of the difference. 10 is a rectifier for rectifying the output signal of the synthesis circuit 9, 11
Is a level detection circuit, 12 is a waveform shaping circuit for converting the output signal of the synthesizing circuit 9 into a pulse signal having a short time width, 13 is an AND gate, and the output signals of the level detection circuit 11 and the waveform shaping circuit 12 are input at the same time. Output signal when given. Reference numeral 14 is a phase discriminating circuit, which receives the output signals of the AND gates 5 and 13 and compares their phases to discriminate whether the ground fault is on the load side or the power source side with the zero-phase current transformer as a boundary. At the same time, it outputs an output signal to drive the timer 15. 16 indicates an auxiliary relay operated by a signal issued after the setting time limit of the timer 15,
The auxiliary relay 15 is used to turn on and off the accident circuit.

FIG. 2 (a) is a circuit diagram for detecting zero-phase current I ₀ and zero-phase voltage V ₀ by three current transformers, where R, S, and T are high-voltage primary conductors for each of the three phases. , CT1, CT2, CT3 are current transformers individually provided in the respective high voltage primary conductors, and their secondary windings are connected in parallel with each other and connected to the resistor r. The zero-phase current signal I ₀ is detected from both ends of this resistance r. ZPD is a zero-phase voltage detection device, and is provided between one of the common connection lines of the current transformers CT1, CT2 and CT3 and the ground E. C _P represents the voltage dividing capacitor, T represents a transformer, and the zero-phase voltage signal V ₀ is detected from the secondary winding side of the transformer T. L _S indicates a load switch.

Fig. 2 (b) shows the zero-phase current I by the through-type zero-phase current transformer ZCT.
_In the circuit diagram for detecting ₀ and zero-phase voltage V ₀ , the through-type zero-phase current transformer ZCT is a three-phase high-pressure primary fluid R, S, T
It is formed by penetrating through 20 and distributing secondary windings 21 around this iron core 20. When a ground current flows in the primary circuit, an output appears in the secondary winding, and the zero-phase current I ₀ is detected from the terminals Z ₁ and Z ₂ . Also, between the high voltage primary conductors R, S and T and the iron core 20,
Since there is a stray capacitance between S and T and the shield iron core (not shown) or the secondary winding 21, if a zero-phase voltage detector ZPD is provided between these and the ground E, the zero-phase voltage V ₀ can get.

Figure 3 shows an equivalent circuit for detecting the zero-phase voltage, C _1,
C ₂ and C ₃ indicate the stray capacitance between each current transformer and the high-voltage primary conductor, and Fig. 4 is for explaining the residual voltage output when the stray capacitance of each current transformer is unbalanced. intended, neutral point N 'next, N' original neutral point N when there is unbalanced due to the stray capacitance → residual voltage V _x of N is always appear.

Next, the operation of the following configuration will be described.

The stray capacitances C ₁ , C ₂ , C ₃ of the current transformers CT1, CT2, CT3 or the zero-phase current transformer ZCT provided in each phase are the shape of each current transformer, the mounting method, or the primary conductor. The difference between the core and the iron core does not result in the same value. Therefore, even if the capacitances are simply combined in normal condition, as shown in FIG.
Residual voltage V _x corresponding to N 'is always outputted. This residual voltage V _x is input as the zero-phase voltage signal V ₀ of FIG. This residual voltage V _X is amplified by the amplifiers 6 and 7, and one of them is inputted to the combining circuit 9 through the delay circuit 8 and the other as it is. Therefore, in a normal condition, the input of the amplifier 6 is also V _x , so that the input signal of the combining circuit 9 has a time difference but V _x.
Since the two are compared with each other and there is no output signal of the difference, the zero-phase voltage output signal from the level detection circuit 11 is not output. Further, since the zero-phase current does not flow in the normal state, the zero-phase current output signal from the level detection circuit 3 is not output, so that the output signal is not output from the AND gate 5 and the auxiliary relay 16 is in the inoperative state.

In such a normal state, if the load switch L _s is turned on and a rush current larger than the rated current instantaneously flows through the primary conductors R, S, T in FIG.
Since the saturation points of the iron cores of CT1, CT2, and CT3 are not necessarily the same, imbalance occurs in their output currents, and an apparent zero-phase current I ₀ is generated at both ends of the resistor r, so that the level detection circuit 3 is set. When the level is exceeded, a zero-phase current output signal may be output to the AND gate 5. However, in this case, the zero-phase voltage V ₀ is the residual voltage V _x only and remains unchanged from the normal state.
Since no output signal is output from the AND gate 13, an output signal is not output from the AND gate 13.

Next, a ground fault occurs at a point g (not shown) on the first line of the primary conductors R, S, and T, and the zero-phase current I ₀ is generated by the level detection circuit 3.
When it reaches the set level of, the output signal is output to the AND gate 5, and when the AND condition with the output signal of the waveform shaping circuit 4 is satisfied, a rectangular pulse signal is introduced to the phase determination circuit 14 via the AND gate 5. To be done. At the same time, the zero-phase voltage E _{0 is} also generated and the voltage of N ′ → g in FIG. 4 appears and is input to the synthesis circuit 9. When a voltage of N ′ → g is input to the synthesizing circuit 9, the voltage of N ′ → g and the residual voltage of N ′ → N delayed by the delay circuit 8 are synthesized, and the zero-phase voltage signal N originally desired to be obtained. →
g is obtained and input to the level detection circuit 11. When the output signal of the level detection circuit 11 reaches the set level, the AND gate 13 outputs the output signal and when the AND condition with the output signal of the waveform shaping circuit 12 is satisfied, the AND gate 13
A pulse signal having a narrow time width is introduced into the phase determination circuit 14 via. The phase determination circuit 14 outputs an output only when the pulse-shaped zero-phase voltage signal and the rectangular-wave pulse-shaped zero-phase current signal overlap each other in time, and drives the auxiliary relay 16 via the timer 15 and disconnects it. Protective action is carried out by turning off or disconnecting or issuing an alarm.

When the ground fault is on the power supply side, the phase of the zero-phase current is 18
Since they differ by 0 degrees, the phase discriminating circuit 14 eliminates the temporal overlapping of the waveforms and the auxiliary relay 15 does not operate.

Effects As described above, the conventional three-current transformer method for detecting zero-phase current has a large residual current, which is particularly noticeable when there is a momentary overcurrent during load inrush, so it is used in a ground fault relay. Then, it causes a malfunction, which has been regarded as difficult to put into practical use.

Also, it has been attempted to detect the zero-phase voltage by using the floating capacitance of a current transformer or a through-type zero-phase current transformer.
The stray capacitance could not be used as a zero-phase voltage detector as it is because the capacitance of each phase becomes unbalanced and a residual voltage is always generated.

In the present invention, when the zero-phase voltage is detected by utilizing the floating capacitance between the current transformer and the high voltage primary conductor, the residual voltage signal due to the imbalance of the floating capacitance is stored in advance, If the original zero-phase voltage signal obtained by combining this and the zero-phase voltage signal generated at the time of the ground fault and subtracting the residual voltage is obtained, and this zero-phase voltage signal does not reach the set level,
Since the ground fault direction relay does not operate at all, there is no risk of malfunction, and zero-phase voltage detection does not require the purpose of installing an expensive high-voltage capacitor as in the past.
It is extremely inexpensive because it is detected by using the stray capacitance of current transformers and zero-phase current transformers that are generally installed, and when installed in a switchboard, high-voltage capacitors are not required. The area is drastically reduced and the distribution board can be downsized, and the installation and wiring work is extremely easy, resulting in extremely excellent effects.

[Brief description of drawings]

FIG. 1 is a block connection diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a circuit diagram for detecting zero-phase current and zero-phase voltage of the present invention, FIG. 3 is an equivalent circuit diagram of FIG. 2, FIG. 4 is a vector diagram of zero-phase voltage and residual voltage, and FIG. FIG. 3 shows a circuit diagram of a conventional ground fault direction relay device. 1,6,7 …… Amplifier, 2,10 …… Rectifier, 3,11 ……
Level detection circuit, 4, 12 ... waveform shaping circuit, 8 ... delay circuit, 9 ... synthesis circuit, 5, 13 ... AND gate, 14 ...
… Phase discrimination circuit, 15 …… Timer, 16 …… Auxiliary relay,
ZPD: Zero-phase voltage detector.

Claims (1)

[Claims] 1. A zero-phase current and a zero-phase voltage generated at the time of a ground fault of a line are detected, and the phase of the signal of the zero-phase voltage and the phase of the signal of the zero-phase current are compared to detect the ground fault. In a ground fault direction relay device in which the direction of the power supply side or the load side is discriminated with the current transformer for detection as a boundary and the device is operated when it is on the load side, the zero-phase voltage signal Detected by utilizing the floating capacitance of the current transformer, the residual voltage based on the imbalance of the floating capacitance and the zero-phase voltage generated at the time of the ground fault were combined and obtained by the difference. A ground fault direction relay device characterized by the above.