Pulse Current Method for Measuring Partial Discharge: How Does the Signal Go from Bubble Discharge to Picometer Reading?

HZJF-9041D adopts the pulse current method (compliant with IEC 60270 standard), which is currently the most classic, accurate, and only quantitative measurement method with international standards in partial discharge detection. By understanding the path of transmitting signals from the inside of the test sample to the pC reading on the instrument screen, one can truly understand why the selection of wiring methods and input units is so important.

Signal generation

The test sample (CX) undergoes partial discharge internally under high voltage, producing an extremely short current pulse (ranging from nanoseconds to microseconds) with each discharge, which propagates outward through the capacitance of the test sample.

Coupling capacitance pickup

The coupling capacitor (CK) is connected in parallel at both ends of the test sample and serves as the "channel" for the transmission of partial discharge pulses. Partial discharge current pulses flow through CK, generating measurable voltage signals in the detection circuit. The capacity of CK is usually on the order of magnitude of the sample capacitance to ensure sufficient signal coupling efficiency.

Input unit frequency selection

The signal enters the input unit (tuned matching converter), which forms a frequency selection network through tuning capacitors and detection impedances to transmit the signal in the desired frequency band (10kHz-300kHz) to the amplifier, while impedance matching reduces signal reflection loss. HZJF-9041D is equipped with 13 input units of 12+7R specifications, covering a capacitance range of 6pF to 250 µ F. The appropriate serial number should be selected based on the equivalent capacitance of the test sample and coupling capacitor.

Third level amplification

The signal is sequentially passed through a low-noise preamplifier (to protect sensitivity), a frequency selective filtering amplifier (to select the desired frequency band, with nine combinations of fL and fH), and a main amplifier (to achieve the desired amplitude for display), and finally displayed as a visible discharge pulse on the touch screen elliptical scanning baseline, and read directly as pC digital.