JPS6225817A - Multi-point ground fault detector for dc circuit - 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 [Field of Industrial Application] The present invention relates to a multi-point ground fault detection device for a DC circuit such as a field winding of a synchronous generator.

[Conventional technology]

FIG. 2 is a circuit diagram of a conventional ground fault detection device. In the figure, 1 is a synchronous generator, 2 is a synchronous generator 1
3 is a field winding of a synchronous generator, and 4 is a field power source. 5 is a ground fault detection device, which includes voltage dividing resistors 6 and 7.
and a current detector 8. As the current detector 8, a bidirectional current relay or a meter relay is used.

Now, as shown in FIG. 3, if a ground fault occurs at point F of the field winding 3, a bridge circuit is formed, and 3a is the part of the field winding 3 on the positive side of the ground fault point F, and 3b indicates the negative side part of the field winding 3 from the ground fault point F, the current detector 8 has the resistance values of the resistors 6 and 7, and the positive side part 3a of the field winding 3 and the above A current determined by the resistance value of the negative electrode side portion 3b flows. The direction of this current changes depending on whether the ground fault point F is on the positive side or the negative side from the center point of the field winding 3.
When it is on the positive side from the midpoint, it flows in the direction shown by the dotted line arrow, and when it is on the negative side from the midpoint, it flows in the direction shown by the solid line arrow. Therefore, by using the contact output of the current detector 8 to drive an alarm device (not shown), it is possible to notify the operator of a ground fault in the field circuit.

[Problem that the invention seeks to solve]

In this way, the conventional ground fault detection device uses a current relay or a meter relay as the current detector 8, so once a ground fault is detected, the operating state is maintained, and if a ground fault occurs subsequently. In other words, if a ground fault occurs at two or more points, it will not be possible to detect it. Therefore, if a ground fault occurs in the field circuit, the generator must be stopped for inspection. To do this, load balancing between power plants must be accomplished in a short period of time, which places a heavy burden on the operator and reduces the operational efficiency of the generator.

This invention was made to solve the above problem.
It is an object of the present invention to provide a multi-point ground fault detection device for a DC circuit that can reduce the burden on an operator and increase the operational efficiency of equipment and devices such as generators having a DC circuit, compared to conventional devices.

[Means to solve the problem]

In order to achieve the above object, the present invention uses a variable resistor as a voltage dividing resistor for configuring a ground fault detection bridge circuit, and when a ground fault occurs, the bridge circuit balances the variable resistor using a ground fault detection signal. In addition to controlling the increase/decrease in the direction in which the ground fault detection signal occurs, a counter is provided to count the number of occurrences of the ground fault detection signal.

[Effect]

In this invention, when a ground fault occurs, the ground fault detection bridge circuit shifts to a new equilibrium state, and this equilibrium state is disrupted by a subsequent ground fault, causing a ground fault current to flow to the ground fault current detector. Since the current is flowing, it is possible to detect multi-point ground faults, and by detecting the number of ground fault points with a counter, it is possible to know whether the number of ground fault points is dangerous to equipment/equipment.

〔Example〕

FIG. 1 is a circuit diagram showing one embodiment of the present invention. 6A
and 7A are variable resistors having a slider S, which are inserted in series between both terminals of the field winding 3. The sliders S of the variable resistors 6A and 7A are driven by DC motors 9 and 10 of the resistance control device, respectively. A ground fault current detector 11 outputs a ground fault detection signal having a polarity corresponding to the direction of the input ground fault current and a level corresponding to the magnitude of the ground fault current. This ground fault current detector 11 is inserted between the connection point (voltage division point) of the variable resistors 6A and 7A and the ground, and its ground fault detection signal is supplied to the output relay 12 and at the same time the DC motor 9 It is supplied to the motor drive circuit 13 and the motor drive circuit 14 of the DC motor 10 . The contact output of the output relay 12 is supplied to an alarm relay 14 and a counter 16. When the number of outputs of the contact output reaches [2], the counter 16 is reset at the same time as the output, and the output is supplied to the output relay 17.

Next, the operation of this device will be explained.

If a ground fault occurs at one point in field winding 3,
A ground fault detection bridge circuit similar to that shown in the figure is formed, and a ground fault current flows to the ground fault current detector 11, and the ground fault current detector 11 detects a level according to the magnitude and direction of the ground fault current. Outputs polar ground fault detection signal. When this ground fault detection signal occurs, the alarm relay 14 is activated by the contact output of the output relay 12.
is energized, an alarm device (not shown) is activated, the operator is notified that a ground fault has occurred, and the counter 15 is activated.
counts [1]. At the same time, the ground fault detection signal is supplied to motor drive circuits 13 and 14, and both motor drive circuits 13 and 14 drive DC motors 9 and 10, respectively, while the ground fault detection signal is input. Field winding 3 when a ground fault occurs
The resistance value of the positive electrode side portion 3a from the ground fault point F is R3a, the resistance value of the negative electrode side portion 3b is R3b (>R3a), and the resistance values of the resistors 6A and 7A are R6 and R7 (R6-), respectively.
R7), the motor drive circuit 13 drives the DC motor 9 in the direction of rotation in which the resistance value of the resistor 6A increases, and the motor drive circuit 14 drives the DC motor 10 through the resistor 7.
Drive in the direction of rotation where the resistance value of A becomes smaller. Resistor 6
Due to the resistance change of A and 7A, (R3a/R3b) = (
When R6/R7) is established, the bridge circuit becomes balanced, the ground fault current disappears, and the ground fault detection signal disappears, so the DC motors 9 and 10 stop driving, and the bridge circuit enters a new balanced state. maintained.

If a ground fault occurs in another part of the field winding 3, that is, in one of the parts 3a and 3b of the field winding 3 after the above-mentioned ground fault occurs, there is a ground fault, but in terms of the circuit. Since the resistance value on one side of the balanced bridge circuit has changed,
The balance of the bridge circuit is broken, and the ground fault current detector 11 detects the ground fault current and outputs the ground fault detection signal again. This ground fault detection signal energizes the output relay 12, and the contact output energizes the alarm relay 14 to drive an alarm device (not shown), as in the previous case. At the same time, the counter 16 counts up and outputs an output, which energizes the output relay 17, and its contact output drives an alarm device that notifies that a two-point ground fault has occurred, and stops the synchronous generator. trips will be made.

Generally, synchronous generators are operated without field grounding, and the ground fault current in the event of a ground fault at one point is very small, so it is possible to continue operation until a ground fault occurs at another point. It is possible. In this embodiment, it is possible to reliably detect a two-point ground fault, so even if a one-point ground fault occurs, there is no need to immediately stop the synchronous generator and remove the cause of the ground fault. Since maintenance and inspection can be carried out on days that are convenient for the schedule, holidays, weekends, etc., the limited number of generators can be operated efficiently, which provides immeasurable advantages in terms of system operation.

Although the above embodiment describes the case where the present invention is applied to the field circuit of a synchronous generator, it is clear that the present invention can also be applied to detecting multi-point ground faults in ordinary DC circuits. .

〔Effect of the invention〕

As explained above, the present invention is capable of reliably detecting an increase in the number of ground faults in a DC circuit, thereby preventing the occurrence of multiple ground faults that would make it dangerous to continue operating equipment/equipment having the DC circuit. It is no longer necessary to immediately stop operation every time a ground fault occurs, and work can be carried out to eliminate the cause of the ground fault according to the convenience of the operating schedule, making operation easier than before. It is possible to increase efficiency and reduce the burden on the operator.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a conventional ground fault detection device, and FIG. 3 is a circuit diagram for explaining the operation of the conventional example. In the figure, 2- Field winding of synchronous generator, 6A, 7
A.-variable resistor for voltage division, 9.10-DC motor, 1
1-ground fault current detector, 12-...output relay, 13.
14-・-Motor drive circuit, 16-・Counter, 17-
・Output relay. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A variable resistor for voltage division inserted between the positive and negative poles of a DC circuit,
a ground fault current detector connected to a voltage dividing point of the voltage dividing circuit; a resistance control device that controls the resistance value of the variable resistor to increase or decrease in a direction in which the output disappears based on the output of the ground fault current detector; A multi-point ground fault detection device for a DC circuit, comprising a counter that outputs an output when the number of outputs of a ground fault current detector reaches a predetermined number.