Course Notes- Electrical Power Distribution & Utilization (EE-357)

NED University of Engineering and Technology Karachi Department of Electrical Engineering

12

Fault Localization

The most common method used by the UGM for pre-location of fault is the ICE-Method

(Impulse Current Equipment), also known as the transient method. This method is ideal

particularly for fault location in long ground cables and wet splices. This method involves two

central components; a Surge Generator and a Reflectometer (TDR) also known as Teleflex.

Step 1: Pre-location of Fault using Transient Method:

In this method a Surge Generator is connected at the Main Cable (usually from Grid Side). The

Surge generates a DC voltage of 16 KV. The surge wave generator ignites an arc at the fault.

This results in a transient, i.e. a spreading and repeatedly reflected travelling wave between the

fault and the surge wave generator.

A Digital Time Domain Reflectometer known as Teleflex is then used to record the transient

wave generated by the Surge generator. The Teleflex displays this transient wave which indicates

the distance to the fault. The length of one full oscillation wave corresponds to the direct distance

to the fault.

Course Notes- Electrical Power Distribution & Utilization (EE-357)

NED University of Engineering and Technology Karachi Department of Electrical Engineering

13

Step Pinpoint Location of Fault:

For a precise location of the fault it is essential to confirm its position along the cable, because

pre-location with the Teleflex only visualizes the absolute distance. But the position and path of

the cable in the ground, and thus the actual position of the fault, is only relatively inaccurately

known. An absolutely precise pinpointing is necessary to limit expensive excavation work and

resulting surface damage to an absolute minimum.

Here, a device known as Seismic Phone is used to exactly pinpoint the fault location. Since direct

discharge of the surge generator produces an arc at the fault position. The direct connection

means that this discharge takes place very quickly, generating a loud flashover sound which can

be located without any problems using a corresponding acoustic receiver at the surface, such as

the Seismic Phone.

The Seismic Phone has dual functions; it performs acoustic detection as well as electromagnetic

cable route detection. The location of the buried cable can be determined by the direction and

intensity of the magnetic field, produced by the impulse current of a surge generator. With the

bar graph-indicator of the Seismic phone, the intensity of the strength of the magnetic field can

be measured. This has a maximum directly above the cable. The acoustic locating is done by

measuring the flash-over noise. If a loud flash band is heard on the Seismic phone than it is an

indication of the fault location.

Course Notes- Electrical Power Distribution & Utilization (EE-357)

NED University of Engineering and Technology Karachi Department of Electrical Engineering

14

General Procedure for Attending Faults

As mentioned earlier, there are two categories of cable faults namely Main Cable Faults (MCF)

and Linking Cable Faults (LCF). Main Cable is the cable which originates from the grid to the

first Substation. This cable carries the load of the entire feeder i.e. around 300A at full load. The

MCFs are given the highest priority in terms of repairs, as they serve a significantly large area.

LCFs on the other hand affect less area and there is usually a provision to back-feed the area

through the ring.

The underground faults are forwarded by the operations department to the UGM after isolating

the cable and give both ends isolation position. The fault is then given to testing Gang for pin

pointing the fault.

SOP for Main Cable Faults

1.Co-ordination and strong communication with concerned operation centre (DFS) & SBO at

S/D.

2. Physically check both isolating positions at S/D & S/S.

3. By using live line tester & discharging rod cable should be checked and diagnosed.

4. Perform discharge test (Pressure test) on each core of the cable by injecting D.C voltage one

by one (Surge Generator).

5. If cable is found sound in pressure test, clearance is given to DFS operation.

6. If any core of cable is found faulty, different instruments (IRG2000, Teleflex etc) are used to

find the exact distance of the fault.

7. After taking result of fault location again DC voltage is injected with surge generator to

search the area of result for pin pointing the fault with the help of seismic phone.

8. After pin-pointing actual location of fault, location is marked & also sketch of fault location is

drawn.

9. Inform the location of fault to UGM control room for excavation & exposing the cable.

10. Before starting excavation, fault location is once again re-confirmed.

11. Check for the nature of fault e.g. pickaxe, manufacturing fault, dead ground fault, running

fault etc.

12. After exposing the faulty portion, cable is retested by injecting D.C voltage.

13. If cable is found sound in pressure test, the Job is handed over for jointing purpose.

14. After completion of jointing procedure clearance is given to operation control by UGM

control room.