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SWITCHGEAR
On-Line PD monitoring of medium voltage switchgear will diagnose insulation faults before they happen, determine the safety of existing switchgear and provide valuable information when considering replacement or retrofitting.
The ultimate benefits from On-Line PD testing switchgear are:
Testing is done using Transient Earth Voltage (TEV) sensors, High Frequency Current Transformers (HFCT) and Acoustic detectors. These sensors are all non-invasive and no shutdown time is required.
Waveforms are captured from the sensors with an oscilloscope at a sampling rate of up to 500 MS/s. Software is used to classify the discharges by examining the waveform shape and frequency. By studying the waveforms from multiple TEV sensors it is possible for LIVE HV test engineers to not only read the level of PD but accurately locate the site where the PD is emanating from.
The likelihood of dangerous PD increases as switchgear ages and the majority of aging switchgear was not designed to withstand an internal arc fault. This means that operators may be placing themselves at great risk when operating aged switchgear.
Where on-site work or modification of switchgear has taken place a PD test is always advisable. If cables have been installed in unsuitable cable boxes PD is often detected.
When considering switchgear replacement, PD testing can quickly and easily direct you to the switchboards that impose the greatest risk to your network. PD testing can also be used to determine the feasibility of retrofitting new circuit breakers into an existing switchboard.
Switchgear is tested for partial discharge at the time of manufacture but the Australian Switchgear Maintenance Standard AS2467 recommends that switchgear insulation is also routinely assessed throughout its lifetime. The latest in PD testing equipment can provide an accurate assessment of insulation and locate any PD sites, all while the switchgear remains live. |
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