The Circuit Diagram of DC Insulation Monitoring

The DC system has an important location in the substation. To ensure the long-term safe operation of a substation, its factors are various, among which the insulation problem of the DC system cannot be ignored.

The DC system of the substation is relatively complex. It is connected to the terminal row, terminal box and operating mechanism box of the outdoor distribution device through the cable trench. There is more possibility of grounding due to cable damage, insulation aging, damp, etc.

When one pole grounding occurs, the fuse is no short circuit current and can continue to operate, but it must also be found and eliminated in time.

Generally, the insulation resistance of various small buses, terminal circuits, and secondary cables of the DC system, measured with a 500V shaking meter, shall not be less than 0.5MΩ. The insulation of the DC circuit must be regularly monitored. Otherwise, it will bring many unsafe factors to the operation.

Fig. 1 now illustrates the hazards of DC grounding. When the A point and the C point are grounded simultaneously. Equequal to + WC, -WC forming a short circuit loop through the earth, which may fuse fuses FU1 and FU2 and lose protective power;

When the B point and the C point have ground at the same time, the tripping coil will be short circuit. Even if the normal action is protected, the YT tripping coil is short circuit, even if the normal action is protected, the YT tripping coil will not start, and the circuit breaker will not trip, so in the case of failure

When the A point and B point or A point and D point, the protection will causes circuit breaker tripping. The harm of DC grounding is not only the above, but many, not described here.

Because DC grounding will cause many harm, a device is specially designed to monitor the DC system, allowing it to prompt the fault to the DC system on duty in time for quick inspection and processing.