engleski

Transient Overvoltage On-Line Monitoring System for Power Transformers

As a part of electrical power systems, transformers may be subjected to various system transients arising from switching operations, atmospheric lightning discharges, shorts-circuits etc. Due to their high voltage and high frequency, transient overvoltages can have a considerable impact on the transformer winding insulation system. Since their amplitude and waveform is usually unknown while the transformer is energized, it is necessary to install an on-line overvoltage transient recorder, with ability to sample, analyze and store transients in order to collect this information. This data could be the basis for the assessment of the transformer insulation condition, especially if combined with the data of an on-line DGA monitor. Since there is an increasing interest in the development of new monitoring techniques for better asset management, team of specialist from Končar – Electrical Engineering Institute redesigned the existing transformer monitoring system Končar TMS and upgraded it with the feature of transient voltage recorder, which is presented in this paper. Advancements in digital instrumentation have enabled the development of sophisticated cost-effective measurement systems. However, it is not an easy task to adapt commercially available digital recorders for application in a high voltage substation. The first step of the development of a new system was to define its features and specifications. List of general requirements that system should fulfill: - It should maintain all the features of the existing monitoring system. - It is necessary that new system record transient overvoltages. - Cost-effective. Requested specifications of the transient recorder are the following: - Sampling rate and bandwidth of the acquisition unit should be high enough to enable reconstruction of the transient shape of a lightning impulse wave. - In order to reduce the error of analog-to-digital conversion, vertical resolution needs to be high enough to cover wide measuring range as it is the case here. - Voltages in all phases and windings must be sampled simultaneously. - Data acquisition unit should provide a temporary data storage of an acquired transient and be able to transfer it to the computer that provides analysis and a long-term archival. Except the above-mentioned requirements, system has to operate in harsh atmospheric, mechanical and electromagnetic hazard environment. After different hardware platforms had been evaluated, industrial computer platform based on PXI standard (Peripheral component interconnect (PCI) eXtensions for Instrumentation) was selected. All other necessary hardware and software have been developed and the system was tested in a HV laboratory. After a successful laboratory testing, the system was installed on the in-service power transformer of Croatian transmission system operator company (HEP-OPS). Experiences and results from the operation of the system have been analyzed and presented in this paper.

transformer; transient overvoltage; monitoring

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