Cable fault detection

Table 12.2 Cable fault detection times for methods A and B...

C.-S. Chen and L.E. Roemer, The apphcation of cepstrum technique in power cable fault detection, in Acoustics, Speech, and Signal Processing, IEEE International Conference on ICASSP 76., IEEE, vol. 1, 1976, pp. 764-767. 

Q. Shi, U. Troeltzsch, and O. Kanoun, Detection and localization of cable faults by time and frequency domain measurements, in 7th International Multi-Conference on Systems Signals and Devices (SSD), IEEE, 2010, pp. 1-6. 

Both differential and ground relaying detect ground faults. Ground-fault protection is located at the starter and protects the cable and the motor differential CTs are located at the motor and protect the motor only. Economic priorities indicate ground-fault protec tion first, adding differential protection when justified by potential savings in downtime and repair costs. 

These considerations can be summarized as a protective device for power cables in coal mines, low voltage switchgear, rectifiers and frequency convertors shall respond within one millisecond. To respond means to detect faults and subsequent fault current cut-off with isolation of network areas to be protected. The maximum load integral shall be limited to 103A2s (as an order of magnitude). 

Two basic requirements apply to feeder cables, firstly to protect the cable from overcurrents, which may be related to the connected load, and secondly to detect faults along the length of the cable. 

Short circuits that do not involve earth, and which are within the length of the cable, can be detected by setting the instantaneous elements of the overcnrrent relays to a value of current calculated at the receiving end of the cable that flows into a zero-impedance fault. Customarily this fault is a three-phase fault for which the calculations are straightforward. If the fault is beyond the cable for example in a consumer then the fault current will be less and shonld be cleared by the consnmer protective device. The feeder cable relays will then act as a back np to the consumer relays. 

On 23 November 1985, a helicopter search was initiated to detect the line fault This fault was due to the accumulation of frost on the cables (one phase in contact with a tree)... 

Whatever type of tire alarm sysfem is installed the integrity of the control circuit is crucial to its effectiveness and the condition of the wiring plays a vital part in ensuring that the system maintains its reliability. TTie cable used must be of a type that is not susceptible to mechanical damage or is suitably protected in metal conduit. The circuit should be monitored by the control equipment so that any fault, deterioration or damage in it is detected and the alarm is tripped. 

Residual current devices - detect earth faults and cut off the supply to the circuit. Their use should be considered a requirement on all temporary power circuits, because they will offer improved protection where, for example, connectors and cables downstream have been damaged and not detected. 

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