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TEMPORARY PD MONITORING IN GIS: A CASE STUDY BY ALTANOVA GROUP

21 Feb 2020

In order to assess the condition or health of an insulation system, it is recommended to go for at least temporary monitoring of partial discharge along with spot measurement in high voltage electrical assets, if not the permanent monitoring. This is required to know the trend of any partial discharge occurring in the insulation with time, which ultimately, may lead to failure of the electrical system.

At one of the 400 kV GIS substation in UP, there was option of spot measurement as well as temporary monitoring. Since the acquisition unit can do both – spot as well as temporary monitoring, we went for both the option and one bay was kept in temporary monitoring for four days. Before going for temporary monitoring, the particular bay was spot tested to know the condition of all the phases. It was found that there is some discharge occurring in the Yellow phase, and it was decided to go for temporary

The monitoring equipment AQUILA was connected to the internal UHF sensor of Yellow phase with the acquisition interval of 30 minutes (which can be set to a lower or higher value of interval). Corresponding to each acquisition, a PRPD (Phase Resolved Partial Discharge) pattern and T-F map is recorded and also amplitude-time trend (other trends like number of pulses, repetition rate, applied voltage, etc. with respect to time can also be obtained) is obtained from the recorded data.

The advantage of patented T-F map®technology of TECHIMP is that it is able to diagnose the insulation defects at an early stage. This will help in the optimization of the energy productivity and maintenance and increase the reliability and life cycle of the assets. With no interruption of energy required, easy to install and configure, this equipment is a one-stop solution for Portable PD monitoring of all electrical assets, viz. transformers, cables, rotating machines, switchgears, etc.

On analysing the acquired data, it was observed that there is floating electrode phenomenon occurring in SF6gas chamber. The amplitude, Qmax 95% (95th percentile) showed an increasing trend with respect to time and it goes from 35 mV to 354 mV in four days.

It is recommended that the gas chamber should be visually inspected and looked for the floating electrode as shown by the PRPD pattern. Since the amplitude of the PD pulses shows an increasing trend with time, it is necessary to go for inspection at the earliest to avoid any possibility of system failure in the near future

ALTANOVA GROUP (ISA & TECHIMP) have in-built temporary monitoring system in their portable PD monitoring equipment, AQUILA and MicroAQUILA; and can be used for both options of

spot measurement as well as of temporary monitoring.

AQUILA and MicroAQUILA come with complete in-built software and data storage which is required for temporary monitoring for a number of days depending on acquisition interval.

With a sampling speed of 100 MS/s and resolution of 10 bits, this three-channel equipment acquire data for analysis after a fixed time-interval (which can be changed in the setting), and having both automatic as well as manual full-scale and amplitude-trigger adjustment for acquisition.

It can be used as an option to temporary monitor along with spot testing the electrical assets where no permanent PD monitoring system is installed. Hence, this product from ALTANOVA GROUP can be highly beneficial for utilities who are in quest of a portable PD monitoring solution of electrical assets along with spot tester in order to achieve a reliable, efficient and economical solution.

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