Safety meets competence

With the partial discharge tester from SPS electronic you can uncover quality defects in windings that are not recognisable with a conventional surge tester alone. The partial discharge tester PD 4000B is always the first choice to ensure the quality of your winding goods.

In short: What is a partial discharge measurement?

Although there is no complete breakthrough of the insulation, parts of the insulation already show partial breakthrough. This partial discharge needs to be measured. Partial discharge is measured using a partial discharge antenna or one in the line coupler integrated into the test line. The high frequency measurement and filter technology makes the system extremely resistant to disruptions. The partial discharge test or pd measurement is therefore perfectly suited to application in manufacturing. The partial discharge testing of a stator winding is carried out using an active microwave antenna. For the partial discharge testing of a fully enclosed motor, a special line coupler is used. Both measurement variants can be used individually or in combination.

The partial discharge tester PD 4000B from SPS electronic with an active microwave antenna.

Technical background

It has been state of the art for some years that electrical machines are operated with PWM inverters. With this technology there are higher voltage spikes, which can lead to partial discharges and the service life of the machines is shortened significantly.

Partial discharge is not a continuous process. The discharges occur only above a certain voltage (inception voltage = PDIV) and after a hysteresis, at reduced voltage, the effect is cancelled again (extinction voltage = PDEV). These voltage values are typical and can therefore be used as a quality feature. The discharges with very steep voltage spikes generate interferences in the broadband frequency band from 50 MHz to 3 GHz and higher. It is possible to decouple these signals capacitively or inductively by cable (test lines). The useful signals are dampened through the test lines and the decoupling. At frequencies above 400 MHz, the metrological limits have been reached. The advantage of this wired signal acquisition is that even enclosed DUT (such as finished motors) can be tested and the pd measurement signal is not influenced by external influences.

A better way is to detect the partial discharge with a microwave antenna. This antenna must be active, as the high frequency signals must be prepared directly on the antenna in order to reach the evaluation unit via cable. In order to mask out disturbances that are not useful signals, this concept must have a narrow band bandpass filter. For open DUT (coils, stators, rotors etc.) this concept provides better results.

Also combinations of the two concepts for signal extraction are possible and improve the suppression of the interference signals that are present in all production lines. The measurements are applicable for both hipot tests and surge tests.

The concept

The partial discharge tester PD 4000B can be used standalone. The existing hardware and software interfaces allow direct operation with high voltage testers and surge testers. The PD 4000B built in high voltage tester complements systems with true 4-wire technology. The high voltage is measured potential free directly at the DUT and is available both as a measured value and for the phase of the signal. The combination of devices provides a complete system for measuring partial discharges in high voltage test and surge test, high voltage test, insulation measurement and surge test. Of course, all components are fully electronic and can be used worldwide thanks to the wide range voltage supply.

Another decisive advantage of the PD 4000B is its two independent measuring channels. This allows the combination of different concepts for the measurement signal acquisition. The channels can also be used for the dynamic measurement of the voltage applied to the DUT. The microwave flat antenna MW 40 has an active, extremely narrow band filter with a centre frequency of 1.57 GHz. This concept has the advantage that at this frequency there are no other interfering signals, as these are reserved for worldwide GPS frequencies. Furthermore, excellent components are available at low cost. All active sensors are supplied via the coaxial cable to the tester. The cable length does not present any problem here.