JPS5832457Y2 - Protective device for capacitor equipment - Google Patents

Description

[Detailed explanation of the idea] This invention relates to a protection device for capacitor equipment.

Generally, this type of capacitor equipment is used for purposes such as improving the power factor of a load connected to an AC power supply, or absorbing harmonic components generated from this load or a reactive power compensator attached to the load. It is constructed by connecting a capacitor or a capacitor handler in parallel with the load.

By the way, since it is necessary to protect the capacitor from transient phenomena, for example, when looking at a capacitor installed in AC filter equipment, as shown in FIG.
Connect the harmonic branch F2 to the busbar via the switching device S2,
Further, this shunt F2 is provided with a current transformer CT2 and a harmonic overcurrent relay R2.

In the figure, DC2 is a discharge coil, 1 is an AC power source, 11 is a power transformer, 2 is a load such as an electric furnace, 21 is a furnace transformer, 22 is a furnace switchgear, and 3 is a reactive power compensator. It is.

Therefore, in order to prevent the harmonic overcurrent relay R2 from malfunctioning due to the transient current (up to about three times the rated current) that normally flows in when the second harmonic shunt F2 is turned on,
In the past, when this transient phenomenon had subsided, it was supposed to be locked by a fixed timer (about 1 to 2 seconds), so if you want to operate one of the furnaces 2, which is connected to the busbar, the switchgear 22 is closed, the harmonic component (second harmonic in the illustrated example) in the excitation inrush current when the furnace transformer 21 of the circuit of the furnace 2 is turned on flows into the shunt F2, and the circuit continues for a certain period of time. During this time, capacitor C2 has this transient overvoltage (usually 1.5 V to 3
．． OV, about 0.5 to 1 second) will be applied,
This overvoltage generates a partial discharge inside the capacitor C2, and this partial discharge does not disappear even when the voltage reaches a steady state (partial discharge start voltage > partial discharge extinction voltage), which may lead to dielectric breakdown of the capacitor C2. Ta.

In particular, this concern arises when reclosing protection is adopted as a protection method for loads, etc., because the sum of harmonic components in the excitation inrush current due to the transformation gain provided in the circuit to be reclosed is This will be applied to the capacitor.

This idea was proposed in view of the above-mentioned issues, and it connects a discharge coil between the terminals of a capacitor, and does not operate under the transient overvoltage caused by the overcurrent that flows to the secondary side of the discharge coil when the capacitor is turned on. An instantaneous overvoltage relay that is set to operate instantaneously with a voltage slightly higher than this is connected, and the operation of this relay isolates the capacitor from the AC power supply, and after a certain period of time, the capacitor is disconnected. By reinserting the capacitor, the occurrence of partial discharge in the capacitor is instantly extinguished, preventing its dielectric breakdown, minimizing the time the capacitor is removed from the bus bar, and improving the power factor or suppressing harmonic components by using the capacitor. This allows for rapid absorption.

An embodiment of this invention will be explained below with reference to FIG. 2.

In Figure 2, the same symbols as in Figure 1 are approximately the same.
Show things.

According to this idea, Ry2 is a discharge coil DC2.
An instantaneous overvoltage relay connected to the next side is set to a value corresponding to the partial discharge voltage of the capacitor C2 connected to this relay R3'2, and the operation of this relay Ry2 controls a control circuit (not shown). is operated to open the switching device S2 and isolate the capacitor C2 from the AC power supply 1.

Here, the capacitor C2 usually has an IV-T characteristic (a characteristic indicating the relationship between the applied voltage and the voltage application time in the case leading to the occurrence of partial discharge) as shown in FIG. R3'2 does not operate at a transient voltage of 2V based on the transient current flowing when the capacitor C2 is turned on, but must be set to a value such that it operates instantaneously at a voltage slightly higher than this.

That is, it is configured to operate within the range shown by diagonal lines in FIG.

Note that 11 is a power transformer.

In the above configuration, if for some reason the switchgear 22 is closed in order to operate one of the furnaces 2 which has been disconnected from the busbar, the furnace transformer 21 of the circuit of this furnace 2 is turned on. As a result, the second harmonic component in the excitation inrush current flows into the shunt F2, and as a result, a transient overvoltage is applied to the capacitor C2, causing a partial discharge inside the capacitor C2. teeth,
Instantaneous overvoltage relay Ry via discharge coil DC2
2, the relay RV2 operates instantly when the operating set value is exceeded, operates the control circuit (not shown), opens the switchgear S2, and connects the capacitor C2 to the bus line in about a few cycles. It will be separated from

Therefore, the partial discharge that had occurred inside the capacitor C2 disappears, and dielectric breakdown of the capacitor C2 is prevented.The above transient overvoltage disappears in about 0.5 to 1 second as described above, and the normal state Therefore, the switching device S2 is automatically or manually closed after a certain period of time (several minutes), and the shunt F2 is connected to the bus line.

In this case, since the shunt F2 is connected to the bus line, the transient current that flows into the capacitor c2 when the circuit is turned on flows into the capacitor c2, but this does not cause the relay Ry2 to operate, and of course the capacitor C2 does not cause partial discharge. , it will operate normally thereafter.

As detailed above, according to this invention, in a capacitor equipment in which a capacitor is connected in parallel with a load connected to an AC power source via a transformer, when the transformer is connected to the capacitor, Even if a transient overvoltage is applied due to the harmonic component of the excitation inrush current generated by a capacitor, and as a result, a partial discharge occurs inside the capacitor, the capacitor will be instantly disconnected from its circuit, and the said portion will be disconnected. The discharge is quickly extinguished.

Therefore, in addition to preventing dielectric breakdown of this type of capacitor, the occurrence of partial discharge is extremely short, so the insulation properties of this type of capacitor are not impaired, and this type of capacitor can be used for a long period of time. can.

Furthermore, since the time the capacitor is removed from the busbar is minimal, the purpose of installing the capacitor is to improve the power factor. It also has practical effects such as rapid absorption of harmonic components.

[Brief explanation of drawings]

Fig. 1 is an electric circuit diagram showing a conventional example, Fig. 2 is an electric circuit diagram showing an embodiment of this invention, and Fig. 3 shows the relationship between the applied voltage to the capacitor and the voltage application time until partial discharge occurs. FIG. 3 is a diagram showing characteristics (DIV-T characteristics) showing the relationship and the operating range of the instantaneous overvoltage relay. 1... AC power supply, 2... Load, 11...
...Power transformer, 21 ...Transformer, 22
and Sa...Switching device, L...Bus bar, C2...Capacitor, DC2...Discharge coil, L2...Reactor, Ry2...・・・
... Instantaneous overvoltage relay CT2 ... Current transformer.

Claims (1)

[Scope of utility model registration request] In a capacitor installation in which a capacitor is connected in parallel with a load connected to an AC power source and provided with reclosing protection via a transformer, a discharge coil is connected between the terminals of the capacitor, and the discharge coil An instantaneous overvoltage relay is connected to the secondary side of the capacitor, which does not operate due to the transient overvoltage caused by the overcurrent that flows when the capacitor is turned on, but is set to operate instantaneously at a slightly higher voltage. 1. A protection device for capacitor equipment, characterized in that the capacitor is separated from the AC power source by the operation of a relay, and the capacitor is turned on again after a certain period of time has elapsed.