JPH0638690B2 - Ground fault relay - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relay device that detects a ground fault current in the event of a ground fault such as a high-voltage line and performs a protective operation, and particularly, this ground fault current is changed into three. It relates to what is detected by a sink.

2. Description of the Related Art A ground fault relay device detects a ground fault current when a ground fault occurs on a line and issues an alarm or disconnects or disconnects the fault line when the ground fault current flows above a certain level. It is a relay device that performs certain protection operations such as.

A through-type zero-phase current transformer is widely used for detecting this ground fault current. The through-type zero-phase current transformer has a secondary winding distributed and wound around an iron core having a through hole passing through a three-phase primary conductor, and the primary conductor is passed through the through hole to cause a ground fault in the primary circuit. When an accident occurs, the secondary winding outputs an output proportional to the ground fault current.

When this through-type zero-phase current transformer is installed in a high-voltage switchboard, the through-hole of the zero-phase current transformer has a relatively small diameter. Therefore, when the three-phase high-voltage primary conductor is passed through this through-hole, , It is necessary to strictly insulate between the conductors and between the conductor and the iron core or the secondary winding, and before and after the penetration, it is necessary to separate the conductors of the three phases by a constant distance, which is not easy. It also requires space.

Therefore, a method (hereinafter referred to as 3CT method) in which a separate current transformer is provided for each high-voltage primary conductor of each phase and the secondary sides thereof are connected in parallel to obtain a zero-phase current output from both ends has been attempted. Fig. 2 shows a block connection diagram of the ground fault relay by the 3CT method, in which the current transformers CT ₁ , CT ₂ and CT ₃ provided in the R, S and T phases of the high voltage distribution line are connected to the secondary side. Zero-phase current by connecting in parallel
_Io is obtained, this is widened with the amplifier 1 and rectified with the rectifier 2,
This rectified output is introduced into the level detection circuit 3, and when the set level is reached, an output signal is output to drive the timed device, and after the set time, the auxiliary relay R _y is operated, and a broken wire, a breaker, or the like (not shown) is operated. Protective action is performed by, for example, turning off or issuing an alarm.

Problems to be Solved by the Invention The ground fault relay device using the 3CT method requires less installation area for the switchboard and is easy to install, as compared with the case of using a through-type zero-phase current transformer. Although there is an advantage, there is a case where the load current suddenly increases, for example, a residual current output appears when the switch or the like is turned on and the ground fault protection relay malfunctions.

FIG. 3 is an oscillograph for explaining the operation when a rush current flows through such a load, and shows an embodiment when the load current 300A is opened and closed. In the figure, (a) is the operation signal of the auxiliary relay R _y , (b) is the ground fault relay GR
Residual current output appearing at input terminals z ₁ and z ₂ of (1), (c) indicates load current, residual current output when the same load current is opened and closed 1 to 4 times, and operating condition of auxiliary relay is checked Is. The residual current output is different even with the same load current. This residual current hardly appears when the load is turned on or off, but is output when the load is turned on. In the case of Fig. 3 (1) and (4)
The auxiliary relay R _y operates as shown in (a), but does not operate in (2) and (3).

This means that even if there is no zero-phase current due to the ground fault, the ground fault relay device operates due to the residual current due to the rapid increase in the load current.

The reason for this is that when a current higher than the rated current flows through each current transformer, the saturation point of the iron core of each current transformer is not the same as that of each current transformer, so that imbalance occurs in the secondary output or It is considered that the residual current, which is an apparent zero-phase current, is output depending on the voltage phase relationship and other load conditions. Since this output cannot be distinguished from the zero-phase current due to the ground fault, there is a drawback that the ground fault relay malfunctions.

The present invention has been made in view of the above points. In the 3CT method in which the installation area of the switchboard is small and the installation work is simple, the detected current is due to the sudden increase in the load current, but the Therefore, it is intended to provide a ground fault relay device which is capable of discriminating whether or not it is a malfunction.

Means for solving the problem 3CT method detects the zero-phase current, and when this zero-phase current reaches the set level, it outputs a zero-phase current output signal to operate the auxiliary relay. In the device,
A means for detecting the load current, an increase detecting means for detecting a sudden increase in the load current signal detected by the detecting means,
The load current is provided with level detection means for outputting an output signal when the output signal of the increase detection means reaches a set level, and holding means for keeping the auxiliary relay inoperative for a set time by the output signal of the level detection means. The hold means suppresses the operation of the auxiliary relay during a rapid increase in

Action If a ground fault occurs in any of the high voltage distribution lines R, S, T, a zero-phase current is detected on the secondary side of the current transformer connected in parallel, and when the zero-phase current reaches the set level, it is assisted. The relay works. Next, when the load switch is turned on and an inrush current flows to the load side, the load current signal proportional to the current is detected by the increase detection means, and when the output reaches the set level, the inrush current is output. A signal is output to hold the operation of the auxiliary relay for a certain time when the current is settled, and the operation of the auxiliary relay is suppressed to prevent malfunction.

Embodiment An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block connection diagram showing an embodiment of the present invention, in which the same names as those in FIG.

In FIG. 1, GR indicates a ground fault relay similar to the conventional one,
HS indicates a hold circuit that detects an increase in the load current and outputs a signal for holding the operation of the ground fault relay D _y when the detected signal is at a certain level or higher. The present invention includes the hold circuit HS. It has a feature.

Reference numeral 6 is a current transformer as a load current detecting means, which is a current transformer C.
It is provided on the secondary side of any one of T ₁ , CT ₂ , and CT ₃ . Reference numeral 7 is a widening device, which widens the output signal of the current transformer 6. 8 is a rectifier, which rectifies the output of the amplifier 7 and differential circuit
Enter 12 Reference numeral 9 is a thickener connected in parallel with the thickener 7, and 10 is a delay circuit, which slightly delays the output signal of the thickener 9. A rectifier 11 rectifies the output signal of the delay circuit and inputs it to the differential circuit 12. The differential circuit 12 combines the output signal of the amplifier 8 and the output signal of the delay circuit 10 which delays this signal, and obtains the difference signal. Reference numeral 13 is a level detection circuit, which outputs an output signal when the output signal of the differential circuit 12 reaches a set level and introduces it into the time limit circuit 14. Reference numeral 15 is a note circuit, which sets the output signal to 0 for a certain period of time while the time limit circuit 14 is operating. 5
Is an AND circuit, which outputs an output signal and operates the auxiliary relay Ry only when a signal from the time limit circuit 4 of the ground fault relay GR and a signal from the not circuit 15 are simultaneously input.

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

In a normal condition where a grounding accident or a suddenly increasing load current such as an inrush current does not flow into the load, the hold circuit HS
, The output signal of the current transformer 6 is amplified and rectified, while the delay circuit 10 delays the same signal to create the state before the change of the load current, and the differential circuit 12 compares them. Therefore, no output signal is output from the differential circuit 12. Therefore, since no output signal is output from the level detection circuit 13 and the time limit circuit 14,
A signal is output from the NOT circuit 15 to the AND circuit 5. However, since there is no signal from the time limit circuit 4 of the ground fault relay GR in the AND circuit 5, the AND circuit 5 outputs an auxiliary relay.
No output signal is output to Ry.

In the above normal state, if a ground fault occurs on the distribution line,
When the zero-phase current Io is input to the input terminals Z ₁ and Z ₂ of the ground fault relay GR and the current exceeds the value set by the level detection circuit 3, after a certain time, the output signal is output to the AND circuit 5. The auxiliary relay Ry is operated by the output signal of the AND circuit 5.

Next, if a rush current flows in the distribution line after turning on the load switch, etc., the terminals Z ₁ and Z ₂ of the ground fault relay GR are connected to the terminals shown in FIG.
When the residual current as shown in (b) flows and the change is rapid, a signal may be output to the AND circuit 5. On the other hand, this increase in the load current is detected by the current transformer 6 and the hold circuit H
The differential circuit 12 of S compares the increased current signal with the delayed signal before the increase of the load current, and when the signal of the difference reaches the set level of the level detection circuit 13, the timed circuit 14 outputs a signal for a fixed time. A signal is output to the circuit 15, and the output signal of the not circuit 15 is set to zero. Therefore, since the output signal is not output from the AND circuit 5, the auxiliary relay Ry does not operate.

As shown in FIG. 3 (b), the residual current flows abruptly at the moment when the load is turned on and then settles down. Therefore, the time limit circuit 14 sets the time limit by looking at the time until it settles.

EFFECTS OF THE INVENTION As described above, according to the present invention, the operation of the ground fault relay is held only when the load current changes abruptly.
The advantages of the ground fault relay by the method can be utilized as they are without any damage, and the malfunction due to the residual current which occurs when the load current changes suddenly, which is a drawback of the 3CT method, can be completely prevented.

[Brief description of drawings]

FIG. 1 is a block wiring diagram showing an embodiment of the present invention, FIG. 2 is a block wiring diagram of a conventional ground fault relay, and FIG. 3 is an oscillograph for explaining a conventional ground fault relay. . GR: ground fault relay, HS: hold circuit, 5: AND circuit, 6: current transformer, 1, 7, 9 ... amplifier, 2,
8, 11 ... Rectifier, 10 ... Delay circuit, 12 ... Differential circuit,
3, 13 ... Level detection circuit, 15 ... Not circuit, Ry ...
… Auxiliary relay.

Claims (1)

[Claims] 1. A current transformer provided in each of the three phases is connected in parallel to detect a zero-phase current, and when the zero-phase current reaches a set level, an output signal is output to operate a relay. In the ground fault relay device described above, a detecting means for detecting an increase in load current is provided in at least one phase of the current transformer, and the signal detected by this detecting means sharply increases so that the increase is above a set level. A ground fault relay device, comprising: a hold circuit for outputting an output signal when the relay is turned on and for deactivating the relay by the output signal.