JPS5821707B2 - Insulation monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an insulation monitoring device that monitors insulation deterioration of a system or equipment in a live line state in an ungrounded system.

In principle, to measure the insulation resistance of a system or equipment, it is sufficient to insert an auxiliary power supply into the object to be measured and detect the leakage current. To do this, various considerations are necessary.

In order to be able to extract the current flowed by the auxiliary power source separately from the system frequency component during current detection, the frequency of the auxiliary power source may be selected to be a specific frequency different from the system frequency.

When attempting to measure insulation resistance in a live wire state, how to insert such an auxiliary power supply into the measurement target is an important point.

In the case of a completely ungrounded system, it is sufficient to connect an auxiliary power supply between one line and the earth to detect leakage current. In such a case, it is impossible to measure the insulation resistance just by making such a simple connection.

This is because, from the perspective of the grid, such a connection would result in a ground fault condition via the auxiliary power supply.

Such ground fault conditions may be avoided by connecting the auxiliary power supply through a filter that has a high impedance at the grid frequency, but such filters are very expensive and even However, the following problems remain.

In other words, when the auxiliary power source is connected as described above, when viewed from the auxiliary power source side, the equivalent ground resistance due to the grounded instrument transformer is connected in parallel with the insulation resistance to be measured, so the auxiliary power source The current that flows out includes a current component that flows through the equivalent ground resistance, and since the equivalent ground resistance is generally extremely small compared to the insulation resistance to be measured, most of the current that flows out from the auxiliary power source flows through the equivalent ground resistance. Therefore, it is virtually impossible to separate and extract the current component flowing through the insulation resistance to be measured.

SUMMARY OF THE INVENTION The object of the present invention is to provide a device as simple as possible, which makes it possible to monitor insulation in live conditions in ungrounded systems with grounded voltage transformers without the above-mentioned problems.

This object is achieved according to the invention by the features described in the claims.

Hereinafter, the present invention will be described in detail with reference to illustrated embodiments.

The figure shows a grounded potential transformer GPTI grounded to an ungrounded three-phase system R, S, T.

This transformer GPTI has a star-connected primary winding whose neutral point is grounded, and a star-connected winding on the secondary side for extracting each phase voltage and a zero-phase voltage. It has an open triangular connected winding for taking out.

A limiting resistor CLR is connected to the open triangularly connected winding.

The zero-sequence voltage appearing across the limiting resistor CLR is guided to a ground fault protection relay device (not shown) including, for example, an overvoltage relay.

The auxiliary power supply G included in the insulation monitoring device according to the present invention has a frequency (for example, 50Hz) that is sufficiently lower than the system frequency (50Hz).
For example, 10Hz).

This auxiliary power supply G can be connected via the normally open contact xA of the relay X to the open triangular winding of the transformer GPTI.

Further, the winding can be separated from the circuit device including the limiting resistor CLR by a normally closed contact xB of the relay X.

Relay X can be connected to power sources P and N via, for example, a pushbutton switch BS.

A monitoring command is issued by turning on switch BS.

Relay X is energized by turning on switch BS.

This opens contact xB and closes contact xA.

In other words, the open triangularly connected winding of GPT■ is disconnected from the circuit device including the limiting resistor CLR and connected to the auxiliary power supply G.

As a result, the auxiliary power supply G is inserted into the object to be measured via the transformer GPTI, and a current flows from the auxiliary power supply G through the insulation resistor.

This current is detected by the monitoring circuit SV.

For this current detection, the monitoring circuit S2 has a current detection resistor inserted in series with the auxiliary power supply G.

If the current detected by this current detection resistor includes a current component flowing through a non-negligible stray capacitance, it is possible to extract only the effective component for the auxiliary power supply voltage from the current detected by this current detection resistor. Yo G
).

This makes it possible to extract a current component that depends only on the insulation resistance to be measured, that is, a signal that is inversely proportional to the insulation resistance.

For example, the monitoring circuit S■ is equipped with a meter relay that directs the signal extracted in this way, and the meter can measure the insulation resistance, and furthermore, when the signal exceeds the specified value, the insulation decreases. Generates an alarm signal to notify.

For example, the alarm contact SVA is closed by this alarm signal, and an optical sound display is performed.

Furthermore, according to the present invention, if a grounding instrument transformer is provided in addition to the grounding instrument transformer GPTI to which the auxiliary power supply G is connected, the remaining grounding instrument transformer GPTI is connected to the grounding instrument transformer GPTI. For example GPT2, the open triangular connected winding is disconnected from the limiting resistor.

This is relay X (or auxiliary relay) as shown.
Normally closed contact y! carried out by B.

Or such a contact yB on the ground wire of transformer GPT2
may be inserted.

By doing so, the equivalent ground resistance of the remaining grounded potential transformer can be avoided from interfering with the measurement of insulation resistance.

As described above, the insulation resistance can be monitored or measured at any time during the live line state.

Turning on the switch BS, which gives the monitoring command, for a long period of time should be avoided.

This is because the earth fault protection relay device is disconnected from the grounded instrument transformer while the switch BS is turned on, so if a ground fault occurs, the earth fault protection relay device cannot respond. be.

Regarding this problem, if a ground fault occurs while a monitoring command is being issued, the ground fault can be detected by the monitoring circuit SV as a drop in insulation resistance. ■ generates an alarm signal in such a case, so
The monitoring command may be forcibly canceled based on this alarm signal.

This can be done, for example, by inserting a contact SVB in series with the switch BS, which is opened by the alarm signal, as shown.

[Brief explanation of the drawing]

The figure is a circuit diagram showing one embodiment of the present invention. GPT I, GPT 2... Grounded instrument transformer, CLR... Limiting resistor, G...
・Auxiliary power supply, BS...Switch for monitoring command generation, X, XA t XB,
...Alarm contact.

Claims (1)

[Claims] 1. In an ungrounded system equipped with a grounded instrument transformer having open triangularly connected windings for extracting zero-sequence current, insulation degradation of systems and equipment is prevented in a live line state. In order to monitor in a live line state, an auxiliary power supply having a frequency different from the grid frequency and the open triangularly connected windings based on the monitoring command are separated from the circuit device to which the zero-sequence voltage is to be guided. It is equipped with a switching opening/closing means connected to an auxiliary power source, and a monitoring circuit that detects a current generated when the open triangularly connected winding is connected to the auxiliary power source and generates an output signal in accordance with the detected current. An insulation monitoring device characterized by: 2. In claim 1, if there is a grounded instrument transformer other than the grounded instrument transformer, the switching means switches between the two on the basis of a monitoring command. An insulation monitoring device characterized in that the open triangularly connected windings of grounded instrument transformers are cut off or the primary grounding wires of those transformers are cut off. 3. An insulation monitoring device according to claim 1 or 2, wherein the monitoring circuit includes means for forcibly canceling the monitoring command when an abnormal decrease in insulation resistance is detected.