On-Line Partial Discharge (PD) Test Services

TDR - Time Domain Reflectometry Measurement of HV Cables

In the event of a fault on a high voltage cable the first requirement for the cable owner is to make a quick identification of the fault location in order that they can formulate an efficient plan for repairing the faulted cable. The preferred fault location technique for underground cables is the Time Domain Reflectometery technique which is referred to as a 'TDR' test.

TDR testing provides a generalised location of the fault (typically accurate to between 0.5%-1.5% of the cable length) and is carried out prior to pin-pointing the fault at the site location (using a cable test van with a High Voltage 'thumper' and radiodetection).

HVPD provides equipment (100V Portable Pulse Generator and HVPD-Longshot™ Test System) and test services for TDR measurements on High Voltage Cables. This technique involves injecting a very short (0.1-10.0μsec) 100V pulse down the cable which is injected directly onto the conductor at the cable sealing end.

A portion of the pulse is reflected at points where there is a change in the 'surge impedance' of the cable insulation, typically at joints or at the fault itself, along the cable and these reflections are captured and timed by the instrument. The distance from the sending end is then calculated from the 'time of flight' between the sending and the reflected pulses combined with knowledge of the average velocity of propagation of the cable.