SHOCK DISCHARGE: BEST WAY TO TROUBLESHOOT UNDERGROUND CABLE FAULT

RMU system Enclosure

The fault recorded was that the supply into into the power house reads 220V, 063V and 115V (L1, L2 & L3) this revealed there is a problem of L2 & L3 which needs to be cleared.

opening the RMU system

Shoot out Fuse inside RMU system

Lets see the full details on rectifying underground cable fault in power distribution cable.

When studying electrical distribution system underground installation is reliable but determining the exalt fault and location of such fault has been the major challenge on system protection.

There are different system in transformer and power house and all this is for control and protection in an electrical system. The functionality of distribution system is to allow electrical transfer from generating station to the consumers.

When the discussion of fault on distribution system occur we categories it into two: Permanent Fault and Transient Fault

During permanent fault the electricity supplied remain off until the fault is been located. On the other hand for transient fault there is what we called intermittent power loss. Now the detection of the exact area of where there is problem is now the major issue here. When this occur there will be series of excavation to trace where exactly problem is which will actually increase the number of downtime in the production of the company or industry that has this fault reported.

Now comes a discharge technique with a performance of surge generator the fault can be traced and clear away the fault along the line or circuit

What is this capacity discharge technique?

Their is an impulse transmitted into faulted power cable to ascertain a faulty cable which been performed by a surge generator and the whole process is cause by a device called thumper. It is also a capacitor discharge system.

Pixage: Block diagram for thumper operation

Thumper consist of four parts which

Single Phase Variac:

This is an auto transformer which has only one winding. According to history of electricity autotransformer portion when dealing with the same winding will always act as both primary and secondary side of transformer.

Signal Conditioner:

It is a device that electronically manipulate an analog signal to meet up the requirement of the next stage for further processing. There is a need to convert AC signal to DC signal signal conditioner serve as a rectifier.

DC Voltage Booster: This is a step up convertor (DC-DC convertor) with the output voltage greater than input voltage.

Power Capacitor: This is a two terminal electrical component which is use to store energy electrostatically in an electric field.

Detailed Explanation

A power capacitor which comes with two terminals are separated with an insulator(dielectric), when there is voltage(potential difference) across the two conductors, an electric field develops across the insulator and this will cause the positive charge to collect on one plate and negative charge to collect on the other plate.

The combination of all four devices mentioned above is called Thumper and the process of action performed by the thumper is called Thumping

In finding out fault in an underground cable we make use of thumper and on this system is a display screen that shows a surge-wave. A surge-wave receiver serves for pinpoint the location of faults in power cables as per the acoustic method. Acoustic method means by sound production.

In conclusion, to ascertain the location of a distance fault occurring in an underground cable thumping is a technique that can be used. This technique is also known as shock discharge method. This method can be used on single phase, three phase or line to line voltage distribution network.

References

1. Underground cable fault location reference manual

2. Boost Converter operation LT1070 Design Manual, Carl Nelson & Jim Williams

3. Cable fault location by the impulse current method (Gail, P.F) IEE, Vol. 122 No 4 pp. 403-408

4. www.mikrozona.hu