partial discharge testing equipment
Partial Discharge Detection for Transformers
Bushings account for a large proportion of High Voltage (HV) substation failures often causing severe and costly damages. Preventive maintenance, early replacement and regular off-line testing have been employed to address this issue in the past. Now, technology exists that enables asset owners to detect impending failures and reduce their maintenance costs. GE’s IntellixTM BMT 330 is an on-line system that continuously monitors the condition of the bushings and can also detect developing partial discharge (PD) activity in the transformer main tank. It will alert personnel of fault conditions at an early stage and provide vital health information on the bushings and the transformer. The Intellix BMT 330 can be utilized as a standalone system to monitor bushing insulation and partial discharge activity, or as an integrated, one-vendor solution with GE’s KelmanTM TRANSFIX Dissolved Gas Analyzer (DGA) multigas analyzer and PerceptionTM Fleet software providing a more in-depth view of the transformer’s condition and root cause of major transformer failures.
Key Benefits
- Comprehensive monitoring of transformer bushings and PD activity on a 3 phase transformer or a bank of 3 single phase transformers.
- One product combining on-line continuous bushing monitoring and partial discharge activity in the transformer main tank using the same bushing adaptor.
- One diagnostic software, GE’s Perception, used for bushing information, PD activity and DGA data analysis, resulting in familiar easy-to-use information.
- One supplier installing, servicing, ensuring proper communication and minimizing administrative burden in order to lower the total cost of ownership of your transformer.
Applications
Power Utilities
Metals
Petrochemical
Monitoring Transformer Bushings
Monitoring transformer bushings is critical, because bushings are constantly under high stress due to the line voltage and heat effect of current flow. These stresses can be further aggravated by the presence of micro cracks from manufacturing, loss of mechanical strength due to ageing, repeated thermal cycling (load + sun), pollution and external flash over melting the porcelain, sludge and moisture in the insulating oil, and by the fact that new bushings have been made closer to design limits in order to reduce cost, size and weight. These stresses can cause the insulation of the bushing to deteriorate. If left undetected, this can lead to catastrophic failure in more than half the cases,with violent explosions, large oil fires and broken shards of porcelain flying about. This can result in the total loss of the transformer, collateral damage to nearby equipment, human injuries, environmental claims and fines or contractual penalties. For years, testing bushings meant taking a transformer off-line on a regular basis and closely inspecting the bushings for cracks or imperfections, monitoring the internal oil levels, measuring capacitance within the bushing itself (C1) or measuring the power factor (or tan-delta). Taking a transformer off-line makes this approach impractical, thus minimizing the frequency of testing to once every few years. A critical problem can easily develop in between checks. With modern fast electronics, continuous monitoring of transformer bushings can now be technically achieved. Remote access to the data allows for continuous on-line monitoring of bushings and is now regarded as “best practice” to better guard against catastrophic bushing failure.
The Intellix BMT 330 Bushing Solution
The Intellix BMT 330 continuously monitors the condition of bushings in real time and provides end users with the information they are used to receiving from off-line tests, namely changes in capacitance and power factor (tan delta), to assess the bushing dielectric efficiency and insulation integrity. Using state of the art custom made adaptors connected at the bushing tapping points, the Intellix BMT 330 measures:
• The change in bushing leakage current compared with the original values calculated from the bushing nameplate information and transformer operational voltage. As the change in current is proportional to the change in capacitance, the Intellix BMT 330 calculates the change in capacitance C1 of the bushing compared with when the bushing was installed, to gauge its dielectric capability and layer integrity.
• The timing differences between the 3 bushing current phases, which translate to phase angle differences relative to each other. Since a change of phase delay equates to a change in power factor, we can determine for each bushing the relative (compared to the others) change of power factor as a percentage of the nameplate value. This is used to gauge small deterioration of the bushing insulation.
The Intellix BMT 330 measures ambient temperature, humidity and the temperature of the main tank. It correlates capacitance changes linked to thermal expansion of the bushing and compensates for the measurements being made at actual bushing operating temperature compared with nameplate values obtained off-line at 20°C.
Partial Discharge Detection
PD is a localized breakdown of a small portion of a solid or fluid electrical insulation system that is under high voltage stress, which does not completely bridge the space between two conductors. PD on solid dielectrics results in localized gradual erosion of the insulation system that eventually leads to failure of critical insulation. Using the same bushing adaptors, the Intellix BMT 330 offers the added advantage of measuring high frequency signals in order to monitor PD activity, giving an added level of protection for the main tank of the transformer. The amplitude of the PD pulses are recorded and used to calculate an overall measure of PD activity. Several methods are used to discriminate between internal PD and external noise (corona discharge). The BMT 330 also provides Partial Discharge Phase Resolve (PDPR) diagnostics.
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