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
UltraTEV Plus2 (UTP2) Kit 3
- TEV and Ultrasonic detection including PRPD (phase resolved plots) and inbuilt classification algorithms.
- Locator probe enables pinpointing of Electromagnetic ‘internal’ discharge through time of flight measurement.
- Ultrasonic measurement of ‘surface’ activity including both Airborne & Contact probes.
- RFCT enables identification of PD activity within cables, displayed as pC (pico-Coloumb).
- UltraDish allows assessment of Surface discharge on unapproachable Overhead Assets.
- Environmental sensor capture Ambient Temp, Relative Humidity data.
- Survey Mode, NFC tags and the ability to save screenshots onto Micro SD card.
- 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).