PD 101 Series – #02: How to measure Partial Discharge?

15/11/2017
hinh 22

 

Since partial discharge is calculated by integral current over time, data acquisition unit detects the voltage drop across the known resistor (shunt) in the test circuit. This resistor will be R, t1 a

Since partial discharge is calculated by integral current over time, data acquisition unit detects the voltage drop across the known resistor (shunt) in the test circuit. This resistor will be R, t1 and t2, which and defined by the user of the measurement system.

nd t2, which and defined by the user of the measurement system.

For PD charge measurement by Frequency Domain Integration, the time-domain signal is transferred to the frequency-domain by Fourier Transform. The integration into frequency-domain is done by a frequency filter, typically by a band-pass system.

The PD pulse gets pre-amplified and digitized by an analog/digital converter. The digital filters do not change their behavior over time and temperature. Furthermore, the user is able to switch the measuring frequency and alter the bandwidth. The PD impulses are digitized by maintaining their amplitude and point of time when they occurred.

More PD processing functions are included in the hardware, such as thresholds and adjustable preamplifiers. The voltage signal is digitized as well. All of this information is transmitted via fiber optical cables. These fiber optic cables and the battery allow the user to use the measurement system on high voltage. The information about PD and voltage is processed further in the computer. A recording of the entire measurement is possible.

The IEC 62070 recommends 2 different filter settings, wide band measurement and narrow band measurement.

For wide band measurement the recommendation is

  • Left frequency limit below or equal to 100kHz and above or equal to 30kHz Right frequency limit below or equal to 1MHz
  • Bandwidth of 100kHz to 900kHz
  • Polarity detection can be possible

For small band measurement the recommendation is

  • Frequency range between 50kHz and 1MHz Bandwidth of 9kHz to 30kHz
  • Polarity detection is not possible
  • Low PD detection rate

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