JPS6230444Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a ground fault detection device for a field circuit of a generator, and more particularly to a field ground fault detection device for detecting a transition state of a ground fault fault.

As shown in FIGS. 1 and 2, some conventional devices of this type are of the bridge type, in which a bridge circuit is constructed of a field circuit and a ground fault relay. That is, both ends of the field circuit 2 of the generator 1 are connected between the field power supplies P and N, and similarly, between the power supplies P and N, a series circuit of a varistor 3, resistors 4 and 5, and both low resistors 4, A field ground fault relay 7 configured to ground the auxiliary relay 6 from a common portion of the relays 5 is provided. Therefore, since such a configuration is adopted, when a ground fault occurs at any point in the field circuit 2, for example, at point P in the figure, a bridge circuit is formed via the ground as shown in FIG. . 8 and 9 shown in FIG. 2 are field circuits 2
This is a resistor consisting of windings, connecting wires, etc., and can be thought of as a variable resistor whose resistance value changes depending on the location where the ground fault occurs. Therefore, the bridge circuit maintains balance due to the relationship between the variable resistors 8 and 9, and when the balance is lost, current flows and the auxiliary relay 6 detects a ground fault. The varistor 3 shown in FIG. 1 has a characteristic of changing its resistance in a direction that disturbs the balance of the bridge circuit, thereby narrowing the range in which ground faults cannot be detected.

By the way, if a ground fault actually occurs at point P shown in FIG. 1, the resistance value of the variable resistor 8 will be small and the resistance value of the variable resistor 9 will be large, so that the auxiliary relay 6 will receive a current I ₁ in the direction shown in the figure. flows.

Conversely, if a ground fault occurs at point N shown in Figure 1,
Since the resistance value of the variable resistor 8 is large and the resistance value of the variable resistor 9 is small, a current I ₂ flows in the auxiliary relay 6 in the opposite direction to I ₁ . Since the auxiliary relay 6 closes different contacts depending on the current direction, it is difficult to determine whether a ground fault has occurred on the positive side of the field circuit 2.
It is possible to determine whether a ground fault has occurred on the negative polarity side.

By the way, the field circuit 2 of the generator 1 is of a non-grounded type, so even if a ground fault occurs, as long as it is a high-resistance ground fault, the fault current flowing through the field circuit 2 will be small. Yes, it's not that big of a problem. Therefore, in such a high resistance ground fault, since the current is small, operation is often continued while monitoring the ground fault current. From this point of view, conventional devices are designed to detect the occurrence of high-resistance ground faults, and are only used to detect ground faults with large fault currents, such as those that shift to low resistance or that expand to two-point ground faults. The structure is not suitable for this purpose, and it does not have a function to detect the expansion of ground faults.

The purpose of this invention is to reliably detect the state in which a ground fault fault in a field circuit progresses from high resistance to low resistance, and the state in which it progresses from a 1-point ground fault to a 2-point ground fault. It is an object of the present invention to provide a field ground fault detection device capable of preventing winding burnout and the like.

That is, the field ground fault detection device of the present invention detects whether a ground fault in the field circuit of a generator has occurred on either the positive or negative polarity side by closing the output contact of the field ground fault relay. A keep circuit that operates to maintain the ground fault state, a current circuit that is connected to the ground fault polarity side of the field circuit and extracts the ground fault current due to the operation of this keep circuit, and a current circuit that extracts the ground fault current from this current circuit. A current change rate detection circuit that introduces a ground fault current from a current circuit and detects the ground fault current as a current change rate, and a current absolute value detection circuit that introduces a ground fault current from a current circuit and detects the ground fault current as a current absolute value. , a first system that sends out an alarm or a trip command on the condition that the rate of change of the ground fault current detected by the current change rate detection circuit continues for a period of time necessary to determine the transition to a ground fault fault. An alarm or trip command is issued on the condition that the absolute value of the ground fault current detected by the output circuit of the and a second output circuit for sending out data.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a diagram showing the overall configuration of the device of the present invention, which shows a bridge type field ground fault relay 7 provided in the field circuit 2 of the generator 1 as in the conventional case.
The normally closed contacts 11 _b1 and 12 b1 of the keep relays 11 and ₁₂ are connected to the other end of the auxiliary relay 6 (see Fig. 1) of the field ground fault relay 7, and the other end of the contact 12 _b1 is grounded. . This keep relay 11 has an operation coil _11c1 , a return coil _11c2 , a switching contact _11s , etc., and the movable terminal side of the switching contact _11s is connected to the negative polarity power supply N1 side, and the fixed terminal side of the switching contact _11s is connected to the negative polarity power supply N1 side. The other end of the operating coil _11c1 and return coil _11c2 connected to the normally open contact 7 of the field ground fault relay 7
_a1 and a push button switch 13 for resetting the device after the accident has been removed, respectively, are connected to the positive polarity power source P1 side. Moreover, a time relay 14 and a keep relay 11, 1 are connected between the positive and negative polarity power supplies P1 and N1.
A series circuit of two parallel normally open contacts 11 _a1 and 12 _a1 is inserted. Here, the set value of the time-limited operation time limit of the time-limited relay 14 is set to correspond to the time required to determine the transition of a ground fault. On the other hand, 15 is a DC power supply whose positive polarity side is grounded, and whose negative polarity side is commonly connected to a current limiting resistor 16 and one end to the other end of the same resistor 16, respectively.
It is connected to field power supplies P and N via twelve normally open contacts 11 _a2 and 12 _a2 . The other end of the resistor 16 is connected to the input section of a differentiator 17 as a current change rate detection circuit that detects changes in ground fault current as a voltage input, and an absolute value detector 18 as an absolute current value detection circuit. There is. The output parts of the differentiator 17 and the absolute value detector 18 are the normally open contacts 14 _a1 and 14 _a2 of the time-limiting relay 14 and the auxiliary relays 19 and 20, respectively.
It is connected to a negative polarity power supply N1 via a series circuit. Further, the differentiator 17 and the absolute value detector 18 are configured to be inserted and supplied between the positive and negative polarity power supplies P1 and N1.

On the other hand, the keep relay 12 similarly operates the operating coil 1.
2 _c1 , a return coil 12 _c2 , a switching contact 12 _s , etc., the movable terminal of the switching contact 12 _c is connected to the negative polarity power supply N1 side, and the operating coil is connected to the two fixed terminals of the switching contact 12 _c , respectively. 12 _c1 and the other end of the return coil 12 _c2 are connected to the positive polarity power supply P1 side through the normally open contact 7 _a2 of the field ground fault relay 7 and the push button switch 21 for resetting the device after the fault has been removed. .

Next, the operation of the field ground fault detection device shown in FIG. 3 will be explained. Now, if a ground fault occurs at point P on the positive polarity side of the field circuit 2, the field ground fault relay 7 detects that a ground fault has occurred in the positive polarity, and operates with a positive polarity ground fault. Contact 7 _a1 is closed. When this contact 7 _a1 closes, power is supplied to the keep relay 11, which energizes the operating coil 11 _c1 and switches the switching contact 11 _s.
At the same time, the normally open contact 11 of the relay 11
Close _a2 . Therefore, the positive polarity side of the field power supply is grounded through a series circuit of the normally open contact _11a2 , the resistor 16, and the DC power supply 15, forming a current circuit as shown in FIG. 4a. At this time, the normally closed contact 11 _b1 of the keep relay 11 is opened, and the field ground fault relay 7 is disconnected from the ground. Therefore, the current flowing through the ground fault point P of the field circuit 2 is only the current shown in FIG. 4a. When this field-ground fault occurs, the current changes exhibit time-current characteristics as shown in FIGS. 5a, b, and c. Figure 5a shows the case where the grounding resistance suddenly changes from high resistance grounding to low resistance grounding as soon as a ground fault occurs, and Figure 5b shows the case where the grounding resistance changes from high resistance grounding to low resistance grounding after a certain amount of time has passed. In this case, Figure c shows a case where the ground resistance does not change abruptly and the resistance value gradually decreases.

First, consider the case where a ground fault as shown in FIG. 5a occurs at point P of the magnetic circuit 2 shown in FIG.
Since _a1 is closed, the time-limiting relay 14 is energized, and by closing the normally open contact _11a2 of the relay 11, the current circuit of FIG. 4a is formed as described above. At this time, since there is a capacitance between the field circuit 2 and the ground, a rush current flows through the current circuit shown in FIG. 4a. Due to this rush current, there is a possibility that a signal higher than the set value will be output to the output section of the differentiator 17 connected to the resistor 16, so the differentiator 17 and the auxiliary relay 19 that operates based on this differentiator output signal A time-limited operation contact 14 _a1 of the time-limited relay 14 is provided between
The auxiliary relay 19 is kept in an open state while the rush current settles down, thereby preventing the auxiliary relay 19 from malfunctioning.

Therefore, the differentiator 17 is connected to the keep relay 11.
Since it is connected between the normally open contact _11a2 and the resistor 16 and detects the change in the ground fault current as a voltage signal, if the rate of change in the ground fault current is greater than or equal to the set value even after the time limit operation has elapsed, the differentiator An output signal is output from 17 to operate the subsequent auxiliary relay 19, thereby notifying the transition and expansion of the ground fault by an alarm or trip operation.

In the case of a ground fault as shown in Figure 5a, the time for the ground resistance to shift from high resistance to low resistance is very short;
In some cases, the ground fault current has already changed by the time the time-limited operation contact 14 _a1 closes. However, if the resistance has shifted to low, the absolute value of the current has increased, so an absolute value detector 18 is connected in parallel to the differentiator 17 to detect this. If the current value is greater than or equal to the set value, the absolute value detector 18 operates the subsequent auxiliary relay 20 via the time-limited operation contact 14 _a2 after the time limit has elapsed, in the same way as explained in the case of the differentiator 17. alarm or trip operation.

Even in the case of a ground fault exhibiting the characteristics as shown in FIG. 5b, expansion of the ground fault can be detected by performing signal processing in the same manner as in the case of FIG. 5a.

In addition, when a ground fault occurs at point N of the field circuit 2 shown in Fig. 3, the field ground fault relay 7 detects that a ground fault has occurred with negative polarity and operates with a negative polarity side ground fault. Open contact 7 _a2 is closed and keep relay 12 is operated. Therefore, as the normally open contact 12 _a2 is closed by the operation of this relay 12, a current circuit as shown in FIG. Perform alarm or trip operation.

Next, as shown in FIG. 4c, first the field circuit 2
If a ground fault occurs at point P1 on the positive polarity side _of Although the amount of current flowing through the circuit consisting of P16 and DC power supply 15 does not increase much, P1
Since the current from the field power source flows between the points P1 and P2, there is a possibility that a large ground fault current will flow between the two points P1 and P2.

In such a case, the current changes at the moment the ground fault shifts from one point to two points. Even if the absolute value of this current does not change much, the rate of change itself is quite large, so the differentiator 17 can detect the expansion of the ground fault.

Next, in the case of a ground fault where the ground resistance gradually decreases as shown in Fig. 5c, the absolute value detector 18 shown in Fig. 3 detects the ground fault current at a value that makes it impossible to operate the generator. This is detected when the value increases to .

When the ground fault is recovered, push button switch 13
or 21 to de-energize keep relay 11 or 12 and reset the operation of the device.

Therefore, the device shown in Fig. 3 can accurately detect when a ground fault in a field circuit expands from high resistance to low resistance, and when it transitions from a 1-point ground fault to a 2-point ground fault. can do.

FIG. 6 shows another embodiment of the device of the present invention. This device is a simpler version of the device shown in Figure 3, and uses a meter relay 18a as an absolute value detector to detect when the ground resistance of a ground fault shifts from a high resistance ground to a low resistance ground. , the differentiator 17 itself is omitted.

Although it is difficult for this device to detect a transition from a one-point ground fault to a two-point ground fault, it can detect a transition from a high-resistance ground to a low-resistance ground as described above.

The detection operation in this case is similar to that described in FIG. That is, when a ground fault occurs at point P, the normally open contact 7 _a1 of the field ground fault relay 7 is closed, the keep relay 11 is energized, and the normally open contact 11 _a2 is closed. As a result, the positive polarity side of the field circuit 2 is connected to the meter relay 1.
8a, a resistor 16, and a DC power source 15 are connected to form a current circuit via the ground, and the normally closed contact _18b1 of the meter relay 18a is opened to disconnect the field ground fault relay 7 from the ground. When the current exceeds the set value, the meter relay 18a is activated to issue an alarm or trip operation.

Similarly, when a ground fault occurs at the N point of the field circuit 2, the normally open contact _7a2 closes, the keep relay 12 is energized, the normally open contact _12a2 closes, and the meter relay 18a switches to the negative polarity of the field circuit 2. connected to the side.

Next, FIG. 7 shows another embodiment of the device of the present invention, which further adds a differentiator 31 and an integrator 32 to the circuit of FIG. This is an example in which a new alarm is issued when the ground resistance gradually decreases. Furthermore, the fifth
For ground faults such as those shown in FIGS. b and c, a warning etc. can be issued using a configuration similar to that shown in the device shown in FIG.

By the way, in the case of a ground fault as shown in FIG. 5c, a ground fault current flows through the field circuit 2, so it is not desirable to leave it as it is forever.

Therefore, as shown in FIG. 7, the differentiators 17, 31 and the integrator 32 are combined to provide a second-stage alarm after the first-stage alarm by the field ground fault relay 7 in the case of a ground fault as shown in FIG. 5c. It was designed to send.

Hereinafter, to explain specifically about FIG. 7, the differentiator 17 is connected to the circuit of the differentiator 17 and the absolute value detector
A differentiator 31 with a lower setting value is connected in parallel to detect that the ground resistance gradually decreases even in a ground fault as shown in FIG. 5c. Further, an integrator 32 is connected to the differentiator 17 and the like to detect the total amount of ground fault current.

When the ground fault is gradually expanding, the differentiator 31 uses the inrush current as described in FIG.
The auxiliary relay 34 is operated via the time-limited operation contact _14a3 of the time-limited relay 14 in order to prevent malfunction of the time-limited relay 14. The integrator 32 operates the subsequent auxiliary relay 34 when the total amount of ground fault current exceeds a set value. Then, the output signals of the auxiliary relays 33 and 34 close the normally open contacts 33 _a1 and 34 _a1 , which have an AND configuration, for example, and send out a second-stage alarm for the expansion of the ground fault.

In the above embodiment, the case of expansion from high resistance ground to low resistance ground has been described, but conversely, the case of transition from low resistance ground to high resistance ground can also be detected by similar means.

As described in detail above, according to the present invention, the ground fault current is extracted by the current circuit connected to the field circuit by energizing the field ground fault relay, and this ground fault current is Each is detected as an absolute value, and an alarm or trip command is sent on the condition that the rate of change or absolute value of these ground fault currents continues for a period of time necessary to determine the transition to a ground fault fault. As a result, the ground fault in the field circuit expands from high resistance to low resistance, and 1.
It is possible to provide a field ground fault detection device that can reliably detect the transition and expansion of a point ground fault to a two point ground fault and thereby prevent burnout of the field winding.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a conventional device, Fig. 2 is an equivalent circuit diagram when a ground fault occurs in the field circuit in the device shown in Fig. 1, and Fig. 3 is a diagram of a field ground fault detection device according to the present invention. A configuration diagram showing one embodiment, FIGS. 4a to 4c are current extraction circuit diagrams of the device shown in FIG. 3 in various ground fault configurations, and FIGS. 6 and 7 are configuration diagrams showing other examples of the device of the present invention. 1... Generator, 2... Field circuit, 7... Field ground fault relay, 11, 12... Keep relay, reset push button switch, 14... Time limit relay, 1
5...DC power supply, 16...Resistor, 17...Differentiator, 18...Absolute value detector, 18a...Meter relay, 19, 20...Auxiliary relay, 31...Differentiator, 32...Integrator , 33, 34...auxiliary relay.

Claims (1)

[Scope of utility model registration request] In a device for detecting a ground fault in a field circuit of a generator, closing of an output contact of a field ground fault relay that detects whether a ground fault in the field circuit has occurred on either the positive or negative polarity side. a keep circuit that operates to maintain the ground fault state, a current circuit that is connected to the ground fault polarity side of the field circuit and extracts the ground fault current by the operation of this keep circuit, and a current circuit that extracts the ground fault current from the current circuit. A current change rate detection circuit that introduces a fault current and detects the ground fault current as a current change rate; and a current absolute value that introduces a ground fault current from the current circuit and detects the ground fault current as a current absolute value. An alarm or trip command is issued on the condition that the rate of change of the ground fault current detected by the detection circuit and the current change rate detection circuit continues for a period of time necessary to determine the transition to a ground fault fault. Provided that the absolute value of the ground fault current detected by the first output circuit and the current absolute value detection circuit continues to be a predetermined value or more for a period of time necessary to determine the transition to a ground fault fault. A field ground fault detection device comprising: a second output circuit that sends out an alarm or a trip command.