Ph. 64 21 663 491

PO Box 33078, Barrington
Christchurch, New Zealand

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Substation Surveys


How do we test?
If a partial discharge occurs in the phase to earth insulation of an item of high voltage plant, a small quantity of charge is transferred capacitively to the earthed metal cladding. An electromagnetic wave is generated at the discharge site which propagates away in all directions and by escaping through an opening in the metal cladding, such as a gasketed joint, can be detected on the outer surface as a Transient Earth Voltage (TEV). The TEV has a nanosecond rise time and an amplitude which varies widely from millivolts to volts.

In dry termination cable boxes, surface discharges have been found which are less than 50pC and emit very low levels of electromagnetic signal. Provided a direct air passage is available through the skin of the cable box the airborne Ultrasonic signal generated by these surface discharges is detectable with an Ultrasonic detector.

Why test using both TEV and Ultrasonic methods?
Often, but not always, a problem will only be detected by one of the techniques. TEV is successful at identifying when there is a leakage to earth and is suitable for compound and oil insulated components. Generally there will not be any accoustic emissions present. Ultrasonic, on the other hand typically detects problems between phases, terminations and switch tank spouts are likely candidates. Ultrasonic will also show up problems with Air Switches, Insulators and Bushings in Outdoor structures.

TEV Priciple of Operation

Types of Switchgear able to be tested

  • Voltages upto 33kV
  • Indoor Metalclad switchboards
  • Indoor and Outdoor Ring Main Units
  • Partial Discharge Locator and ultrasonic survey recommended every 2 years
  • Partial Discharge Continuous Monitoring recommended every 4 years


The Instruments we use are:

UltraTEV Locator (UTL)

  • Double TEV probes facilitate accurate pinpointing of Electromagnetic 'internal' discharge.
  • Ultrasonic measurement of 'surface' activity including both airbourne & contact probes.
  • RFCT enables identification of PD activity within cables, displayed as pC (pico-Coloumb).
  • Environmental sensors capture Ambient Temp, Relative Humidity & Atmospheric Pressure data.
  • Latest technology Touch Screen interface & integral system function check capability.

Partial Discharge Monitor (PDM03CF) X 3

  • Continuously Monitor 12 Channels simultaneously using full precedence detection technology. 
  • Capture variations caused by changes in the operating environment for up to six months.
  • Record TEV activity at 8 positions while the 4 Aerials effectively screen out external interference.
  • Data stored on Compact Flash card with Analysis / Graphing via a standard PC.
  • Typically deployed for periods of 7 days in duration, cost includes setup, hire, data interpretation and report (travel extra).


UltraTEV Plus+ (UTP)

  • Combines both TEV Amplitude measurement (in dBmV) and pulse discharge rate to calculate Severity rating.
  • Ultrasonic detection of surface PD activity presented as numerical dBuV values & audible signals with provided headphones.
  • Menu driven backlit Colour screen and keypad.
  • Full range of probes available including the UltraDish option for overhead assets.
  • Carried to provide capable back-up redundancy when on site.