Partial discharge diagnostic system aims at partial discharge detection, monitoring and partial discharge measurement. ASD developed a state-of-the-art partial discharge test system that is a complete, self-contained, multiple-channel phase system that will replace the old selection switch PD technology. The partial discharge detection system can simultaneously measure and analyze up to seven different channels. Both the measurement and analysis parts offer full diagnosis regarding partial discharges in your transformer and cables. In addition, the system offers users full control through an hierarchical and well-organized configuration menu.

A transformer under test, it is connected at its both sides. The low voltage side is connected to the power supply through step up transformer and reactors. The high voltage side is connected to the PC via calibration coupler, impedances boxes and signal conditioner filter. Before applying power to the TUT, users should operate the software, define some configurable parameters and define the TUT ID number and specifications. Users then access the measurement panel from software and start PD Calibration. The calibration coupler should be connected to each of the three TUT bushings respectively while each phase is PD calibrated. Via software, user can check noise and linearity.
 

Partial Discharge Facts:

When a high voltage is applied to an insulation material, partial discharges (PDs) can occur in the voids in that material. The magnitude of such discharges indicates the level of ageing of the material. Few and weak discharges normally indicate a healthy material while many and strong discharges indicate an aged insulation. Therefore, partial discharge measurement is essential. Possible PD sources include:

▪ Turn-to-turn faults in power transformers
▪ High voltage underground cable
▪ Electrodes at floating potential
▪ Voids in insulation material
▪ Free particles in gas-insulated switchgear
▪ Surface discharge
▪ Contamination of foreign particles in the insulation system
 

SYSTEM HARDWARE

▪ Multi-Channel Filter/ Peak Detector
▪ Switching AC Power Supply
▪ Power Supply Controller
▪ Impedance Box
▪ Control Panel
▪ Calibration Coupler
▪ 240V/24KV Step Up Transformer
▪ Current Transformers
▪ Reactors

- Krohn-Hite Filter
A programmable multi channel filter system. Three Butterworth configured filter cards are used forming three channels. The high pass frequency, low pass frequency and filter amplifier gain can be programmed as desired. After filtering, the signal enters a peak detector of a discharge time of 500 ms inside the Krohn-Hite.  

- Pacific Power Supply and Controller
It’s an MS-series three phase switching power supply with selectable frequencies of 50, 60 or 400 Hz and a variable oscillator range of 47to 500 Hz. It ensures flexible and reliable AC power ranging from 62.5 to 625 kVA for each 3060MS.
Pacific Controller reads the power supply status throughout operation and generates signals that control frequency and voltage. Output Voltage, Current, Active Power, Reactive Power, etc are displayed; in addition to many other available features. 

- Impedance Box
Three ASD designed impedance boxes are utilized in the system. Each box is connected to one of the channels (filter card) at one end, while connected to the required transformer bushing (phase) at the other. The impedance box contains circuitry to separate the PD and AC signals, as well as an amplification stage.

- Control Panel
ASD designed control panel, fixed to the consul, includes visual indicators and push buttons to help control and monitor system’s functions. A power factor meter displays the output power factor of power supply. An emergency button is pressed in case of overheating or unexpected behavior. High voltage ON and interlock indicators are available in addition to a reset button to be pressed when interlock is fixed. Reactors are fully controlled through monitoring the current displays at each phase and using the raise / lower buttons to increase or decrease the reactance’s inductance.