It aims to measure the partial discharges which may occur in the transformer insulation structure during test.
Partial-discharges are electrical arks which form the surges between electrodes of any area of the insulating media of a transformer between the conductors. These discharges may occur in air bubbles left in the insulating media, gaps in the solid materials or at the surfaces of two different insulators. Although these discharges have small (weak) energy, the thermal energies due to these discharges can cause aging, deformation and tear of the insulating material.The following conditions can be determined during partial-discharge measurement;
- To determine whether a partial-discharge above a certain value has occurred in the transformer at a pre-defined voltage
- To define the voltage values where the partial-discharge starts by increasing the applied voltage
(partial-discharge start voltage) and the value where the partial-discharge ceases by decreasing
the applied voltage (partial-discharge cease voltage).
- To define the partial-discharge strength at a pre-defined voltage
How Partial-Discharge occurs and measured magnitudes :
The structure where a partial discharge occurred in an insulating media is shown in the simplified. As seen on the simpliified diagram, the impulses forming on the discharge point cause a U voltage drop at the transformer line terminals. This forms a measurable "q" load at the measuring
impedance. This load is called apparent load and is given in pC (Pico-Coulomb) units.
During measurements; U voltage drop, average value of apparent partial-discharge current, partial discharge power, impulse count within a time unit, partial-discharge start, and cease voltages can also be determined.
To measure the partial discharge value, Wuhan huayi company makes the HYJF-2000 Dual channel digital PD Tester. It uses the worldwide standard Windows operating system and an intuitive control and display panel to allow even inexperienced operators to learn quickly with minimal training. In addition, advanced features such as higher accuracy, automated calibration, data analysis, and customized test
recording, are standard. It has full program-controlled automatic calibration, automatic synchronization, automatic voltage recording, automatic measurement & save & playback features. Comply with IEC-270 such as the discharge repetition rate n, the average discharge current I. Various
display styles of the PD waveform such as sine map, dot matrix, and so on, make it easier to get the result. New digital filtering and interference suppression combined with a rich and dynamic statistical analysis of patterns. The detection method, measurement loop, and technical performance parameters comply with the latest GB7354 and IEC-270 "partial discharge measurement" standards.