JPS5825724Y2 - Ground fault relay with power outage compensation - Google Patents

Description

[Detailed explanation of the idea] This invention relates to the improvement of ground fault relays.

In recent power receiving equipment for high voltage consumers, power fuses are installed in power receiving circuit breakers in order to prepare for short-circuit accidents within the power receiving equipment, improve overload protection performance, and simplify equipment. ing.

In this way, when a short circuit (overcurrent) accident occurs in a customer's equipment, the power fuse blows out sooner than the overcurrent relay at the substation, disconnecting the customer where the accident occurred from the distribution line. ing.

Furthermore, if a ground fault occurs alone, the ground fault relay operates and the customer's switch shuts off faster than the substation's ground fault relay, disconnecting the faulty customer from the distribution line.

However, when a ground fault and short circuit accident (when a ground fault and a short circuit accident occur at the same time) occur in a consumer's power receiving equipment, one of the three power fuses connected to each three-phase AC line One or two fuses will melt instantly and the short-circuit accident will be resolved, but the ground fault current will pass through the one or two remaining power fuses and the transformer windings of the load equipment, causing a ground fault current. flow, and the ground fault continues as it is.

However, since the ground fault relay normally receives power from a lighting transformer installed on the load side of the power fuse, the power supply to the ground fault relay stops at the same time as the power fuse blows out.

Therefore, the ground fault relay becomes inoperable and the necessary interrupting operation is not performed.

Therefore, the reclosing operation performed at the substation also ends in failure, resulting in a serious accident in which the entire distribution line including the customer where the accident occurred is out of power.

The present applicant has already filed an application for an invention that basically solves the above-mentioned problems (Japanese patent application filed in 1973).
0-158276), the present invention further improves this basic invention and provides a ground fault relay with an improved power supply section that allows disconnection operation based on ground fault detection even when charging time is extremely short. The purpose is to

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, the primary winding of a power transformer 1 is connected to two predetermined wires on the load side from a power fuse of a three-phase distribution line (not shown).

A secondary winding 1 of this power transformer is connected to a rectifier bridge 2 , and a storage capacitor 3 is connected to an output terminal of the rectifier bridge 2 .

A series circuit consisting of a speed-up capacitor 5, a reverse prevention diode 7, and the energy storage capacitor 3 is connected to both ends of the energy storage capacitor 3.

A Zener diode 6 for voltage clipping is connected in parallel to this series circuit consisting of the diode 7 and the capacitor 8.

A current limiting resistor 4 is connected in parallel to a series circuit of a capacitor 5 and a diode 7.

Power is supplied from both ends of the energy storage capacitor 8 to the main circuit section 9 that detects a ground fault based on the output from the zero-phase current transformer 10.

Next, the operation of the above configuration will be explained with reference to FIGS. 2a and 2c.

If the output voltage of the rectifier bridge 2 is E, then the capacitor 3
The terminal voltage of changes as shown in FIG. 2a.

In this figure, the solid line indicates a long charging time in some cases, and the broken line indicates a short charging time T1.

On the other hand, the voltage across the capacitor 8, that is, the voltage supplied to the main circuit section 9, changes as shown in FIG. 2 during charging and discharging.

That is, when power is applied to the primary winding of the power transformer 1, the capacitors 5 and 8 begin to be charged through a series circuit including the capacitors 5 and 8 and the diode 7.

At this time, the voltage across the capacitor 8 tends to peak transiently (see the dotted line in FIG. 2), but is clipped by the Zener diode 6 and suppressed to the Zener voltage Vz.

At this time, the capacitor 5 is rapidly charged by the current flowing through the Zener diode 6.

Since the capacitors 5 and 8 are thus charged through the series circuit sandwiching the diode 7, their charging time constant is approximately determined by the output impedance of the rectifier bridge 2 and their own capacitance value, and therefore the charging time constant is small and rapid. It will be charged to.

When the capacitors 5 and 8 are fully charged and settled into a steady state, the voltage across the capacitor 8 becomes the resistance value of the resistor 4 by R1,
When the combined resistance value of the main circuit section 9 is R2, it becomes stable.

When the supply of power to the power transformer 1 is stopped and each capacitor is discharged, the charge in the capacitor 3 is discharged via the resistor 4 and the main circuit section 9, and the charge in the capacitor 5 is discharged through the resistor 4 and the main circuit section. 9 and Zener diode 6.

Further, the charge in the capacitor 8 is discharged via the main circuit section 9.

Therefore, since the charge in each capacitor is discharged through the main circuit section 9 which is configured to have a relatively high impedance, the discharge time constant thereof is large.

Therefore, the voltage across the main circuit section 9 is maintained for a relatively long time as shown in FIG. 2, and the main circuit section 9 can operate for a certain period of time even after a power outage.

In this way, each capacitor 3, 5, and 8 has a small charging time constant and a large discharging time constant, so for example, a short-circuit/ground fault may occur just before the power is turned on, and the power fuse will melt immediately. In some cases, even if the time T□ is short, such as the time it takes for the power fuse to blow, the
As shown by the broken line, the main circuit section 9 is charged with enough charge to operate, and the charged charge is discharged for a relatively long time, so the relay provided in this ground fault relay is Time longer than operating time T4 (T1+T2)
, an operable voltage is supplied to the main circuit section (see the broken line in Figure 2).

Therefore, the ground fault relay will produce an output signal at the end of the operating time of the relay (ie, from the end of time T4 to the end of time T2).

(See the broken line C in Figure 2). Of course, when the voltage supplied to the primary winding of the power transformer 1 becomes zero after a long charging time, the time T3 is sufficiently longer than the relay operating time T5, as shown by the solid line in Figure 2. Since the power supply voltage is secured, an output signal as shown by the solid line in FIG. 2C can be obtained.

Therefore, for example, if a short-circuit/ground fault occurs at the same time as the switch of the power receiving equipment of a customer that was previously out of power is turned on, or if the switch is turned on and the power is being transmitted from a distribution line that was previously out of power. At the same time, even if a short-circuit/ground fault occurs, the ground fault relay can be activated.

In other words, in these cases, the charging time of the energy storage circuit of the ground fault relay is extremely short, only a half cycle from power-on to the time the power fuse blows out, and the power supply voltage drops significantly due to the short-circuit accident. 30% of the rated voltage
This is because even in such a case, the electric charge necessary for the operation of the relay can be stored.

In addition, in order to cope with the case where the voltage applied to the primary winding of the power transformer 1 is about 30% of the rated voltage, it is necessary to make sure that the terminal voltage of the capacitor 3 is sufficient for the operation of the main circuit even at such a voltage. The transformer 1 should be designed so that

Moreover, since the three capacitors 3, 5, and 8 discharge through the main circuit section 9 when the power is cut off, the capacitance of each of these three capacitors 3, 5, and 8 may be small.

In particular, since only the voltage limited by the Zener diode 6 is applied to both ends of the capacitor 8, the withstand voltage of the capacitor 8 may be small.

As described above with respect to the embodiments, according to the present invention,
Even if a short circuit/ground fault occurs at the same time as the power is turned on,
It is possible to operate the circuit breaker to provide ground fault protection.

In addition, since no batteries are used, the maintenance effort can be saved, which is advantageous in terms of cost.

Since power is consumed for charging only for a short time when the power is turned on, the overall power consumption is low and is equivalent to a normal ground fault relay.

In this way, since the power consumption is low, transformers etc. need only be considered within the limits necessary to ensure a predetermined voltage fluctuation rate in order to keep the voltage drop due to overcurrent when the power is turned on to a certain limit, so they are better than regular types. A hazy or thick riVA one will suffice.

Furthermore, according to the present invention, the capacitors used to achieve the above can be as small as three capacitors, and in particular, one of the capacitors has only a limited voltage applied to it by the constant voltage element, so it has a withstand voltage. A small one is fine.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 a, b,
c is a time chart for explaining the operation of Fig. 1;
a represents the voltage across the capacitor 3, b represents the voltage across the capacitor 8, and C represents the output signal of the relay. 1... Power transformer, 2... Rectifier bridge, 3゜8... Energy storage capacitor, 4...
... Current limiting resistor, 5... Speed-up capacitor, 6... Zener diode for voltage clipping, 7... Diode for reverse current blocking, 9...
...Main circuit section, 10...Zero-phase current transformer.

Claims (1)

[Scope of utility model registration request] A transformer, a rectifier connected to the secondary winding of the transformer, a first capacitor connected across the rectifier, a second capacitor connected across the capacitor, a diode, and a second capacitor connected across the rectifier. 3, a constant voltage element connected in parallel to the series circuit consisting of the diode and the third capacitor, and a resistor connected in parallel to the series circuit of the second capacitor and the diode. A ground fault relay with power outage compensation, wherein power is supplied from both ends of the third capacitor to a main circuit section that detects a ground fault based on the output from a zero-phase current transformer.