Partial discharge test devices with surge test

SCHLEICH partial discharge test devices combine the surge test with partial discharge analysis in a powerful test concept, allowing the insulation quality of electrical windings to be assessed – particularly in Motors, generators, transformers, and coils.

The surge test simulates electrical stresses, such as those arising from converter operation, switching operations, or voltage peaks. For this purpose, a charged surge capacitor with a very short voltage rise time is switched to the device under test (DUT). The objective is to detect insulation weaknesses, turn-to-turn faults, or manufacturing defects early.

In parallel, partial discharge (PD) is detected and evaluated. Partial discharges are localized insulation breakdowns that do not immediately lead to a complete short circuit but damage the insulation long-term. The measurement is standard-compliant, highly sensitive, and frequency-selective.

The PD test, also known as "TE-Prüfung" or "PD-Test" in English, along with the surge test, is one of today's most important and informative test methods for reliably detecting problems in windings. It unsparingly reveals a variety of insulation, material, and production defects.

Why the PD test is so important.

Electric motors, generators, rotors, stators, transformers, valve coils, winding goods of all kinds, and much more can only be operated safely and durably if they exhibit high electrical insulation strength, good material quality, and flawless manufacturing. Poor insulation can quickly lead to total failure.

Using the PD test in combination with the surge test, you can determine the quality of the winding and the insulation system both within the winding and towards the laminated core.

To cover almost all spaces of the Test of winding goods, SCHLEICH has developed an extensive portfolio of test devices from 1,000 to 15,000 V.

However, the PD test cannot replace all known test methods. Therefore, a test device or automatic test device, in most cases, consists of a combination of different test methods. The starting point is always the surge test, ideally in combination with the PD test.

Where testing is performed on the device under test.

The surge test is the »Deep Look into the Winding«:

• within the winding from turn to turn
• from winding to winding
• from phase to phase
• from winding to the laminated core

This does not work with a high voltage test.

A high voltage test cannot achieve such a high test depth. The ultimate solution is the combination of surge test and PD test.

The PD test uncovers these defects in addition to the surge test.

• Inadequate frequency converter suitability
• Insufficient insulation clearances
• poorly placed phase separators
• insulation weaknesses
• enameled copper wire defects
• spacing issues between turns with high potential differences
• spacing issues between phases
• spacing issues to the laminated core
• spacing issues between layers
• …

How does the PD test technically work?

The surge tester fundamentally generates a high voltage pulse with a very high rise time.

For this purpose, the built-in surge capacitor in the device is charged to the desired voltage. As soon as the TEST VOLTAGE is reached, the test device switches the charged capacitor through a very fast semiconductor switch to the winding to be tested. This results in a resonant circuit consisting of the inductance of the device under test and the charged capacitor. The impulse response at the resonant circuit is initially a very steep voltage rise, followed by the typical voltage waveform in the form of a damped oscillation.

If defects of the type described above are present, the application of higher test voltages does not necessarily lead to a high-energy flashover discharge. However, at the damaged area, when the partial discharge inception voltage is exceeded, partial, low-energy discharges can occur. These are neither visible nor audible. Nevertheless, they often lead to complete insulation failure in a short time.

Partial discharge is also referred to as pre-discharge, as it already occurs at low test voltages. They are therefore a kind of 'harbinger' for impending damage.
This is precisely what makes partial discharge testing so interesting and significant.

This is how partial discharge testing is performed.

Partial discharge is an accompanying phenomenon of the high voltage test with alternating current (AC) and/or the surge test.

Since every electric discharge If an electromagnetic wave is emitted, the partial discharge can be received well with an antenna. This is ideally possible with open windings. That is, whenever the winding is not, as in a completely assembled Motor or generator, is encased in metal.

Since partial discharge also propagates on the Connection lines of the device under test, for windings completely shielded with metal, partial discharge can alternatively be measured with a coupling module.

The requirements for a partial discharge test device for winding systems.

SCHLEICH partial discharge test devices feature the following characteristics:

• standard-compliant testing
• Surge voltage pulses with high voltage steepness
• very fast measurement technology with high resolution
• Determination of the
  • Inception voltage
  • repetitive inception voltage
  • repetitive extinction voltage
  • Extinction voltage
• fully automatic analysis
• fully automatic switch-over between the various winding Connections of the device under test
• Development, Production, and Service – Made in Germany

SCHLEICH surge test/partial discharge test devices are based on over 30 years of experience and pioneering work. From the very beginning, the measurement technology was not analog but always designed digitally. Fundamentally, the latest technologies are always applied.

This is how you find the suitable partial discharge test device.

If you exclusively wish to run partial discharge tests on your device under test, a single test device is the right choice. This includes the surge test as a basis for determining partial discharge.

If the device under test requires further tests, we recommend our combination test devices/multifunction testers. Here, additional test methods such as partial discharge, AC high voltage test (plus partial discharge if required), ohmic Resistance test, rotating field test, etc., can be integrated. The fully automatic test method switch-over ensures that no measurement leads need to be manually reconnected to the device under test during the test.

Thanks to the intuitive and convenient operation of our surge testers, every test is run quickly, precisely, and cost-effectively.