Partial discharge testers with impulse voltage

SCHLEICH’s partial discharge testers combine impulse voltage testing with partial discharge analysis in a powerful testing concept that enables the assessment of the insulation quality of electrical windings—particularly in motors, generators, transformers, and coils.

The surge voltage test simulates electrical stresses such as those caused by inverter operation, switching operations, or voltage spikes. To do this, a charged surge capacitor with a very short voltage rise time is connected to the device under test (DUT). The goal is to detect insulation weaknesses, short circuits, or manufacturing defects at an early stage.

At the same time, partial discharges (PD) are detected and analyzed. Partial discharges are localized insulation breakdowns that do not immediately result in a complete short circuit but cause long-term damage to the insulation. The measurement is performed in accordance with standards, with high sensitivity and frequency selectivity.

Partial discharge testing, also known as “PD testing,” is, along with impulse voltage testing, one of the most important and reliable testing methods available today for reliably detecting problems in windings. It ruthlessly uncovers a wide range of insulation, material, and manufacturing defects.

Why partial discharge testing is so important.

Electric motors, generators, rotors, stators, transformers, valve coils, all types of wound components, and much more can only be operated safely and reliably if they feature high electrical insulation strength, high-quality materials, and flawless manufacturing. Poor insulation can quickly lead to total failure.

By combining partial discharge testing with impulse voltage testing, you can assess the quality of the winding and the insulation system, both within the winding itself and in relation to the laminated core.

To cover virtually all aspects of testing wound products, SCHLEICH has developed a comprehensive portfolio of testers ranging from 1,000 to 15,000 V.

However, partial discharge testing cannot replace all known testing methods. For this reason, a testing device or automated testing system typically combines various testing methods. The starting point is always surge voltage testing, ideally in combination with partial discharge testing.

Where testing is performed on the test object.

The surge voltage test provides a"deep look into the winding":

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

That won't work with a high-voltage test.

High-voltage testing cannot achieve such a high test depth. The ultimate solution is a combination of impulse voltage and partial discharge testing.

This test detects these faults in addition to the impulse voltage test.

• Inadequatecompatibility with frequency converters
• Insulation clearances are too small
• poorly positioned phase splitters
• Weaknesses in insulation
• Defects in enameled copper wire
• Spacing issues between coils with high potential differences
• Phase-to-phase spacing issues
• Clearance issues with the laminated core
• Spacing issues between layers
• …

How does partial discharge testing work from a technical standpoint?

The surge voltage tester generally generates a high-voltage pulse with a very steep rise time.

To do this, the surge capacitor built into the device is charged to the desired voltage. As soon as the test voltage is reached, the tester connects the charged capacitor to the winding under test via a very fast semiconductor switch. This creates 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, applying higher test voltages does not necessarily result in a high-energy flash discharge. However, when the partial discharge threshold voltage is exceeded, partial, low-energy discharges may occur at the defective location. These are neither visible nor audible. However, they often lead to complete insulation failure within a short period of time.

Partial discharge is also referred to as pre-discharge because it occurs even at low test voltages. It is therefore a kind of “warning sign” of impending damage.
This is precisely what makes partial discharge testing so interesting and important.

This is how the partial discharge test is performed.

Partial discharge is a phenomenon associated with high-voltage testing using alternating current (AC) and/or impulse voltage testing.

Since an electromagnetic wave is emitted with each electrical discharge, 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 along the connecting leads of the test object, partial discharge can alternatively be measured using a coupling module in the case of windings that are completely shielded with metal.

Requirements for a partial discharge tester for winding systems.

SCHLEICH partial discharge testers have the following features:

• standard-compliant testing
• Surge voltage pulses with high voltage rise
• High-speed, high-resolution measurement technology
• Determination of the
  • Operating voltage
  • repeating application voltage
  • recurring dropout voltage
  • Cut-off voltage
• fully automated analysis
• Fully automatic switching between the various winding terminals of the test object
• Development, Production, and Service – Made in Germany

SCHLEICH surge voltage and partial discharge testers are based on over 30 years of experience and pioneering work. From the very beginning, the measurement technology has been digital rather than analog. We always use state-of-the-art technologies.

Here's how to find the right partial discharge tester.

If you wish to perform only partial discharge tests on your test object, a single-unit tester is the right choice. This device includes a surge voltage test as a baseline for determining partial discharge.

If the test object requires additional tests, we recommend our combination testers/multifunction testers. These allow for the integration of supplementary test methods such as partial discharge testing, AC high-voltage testing (with partial discharge testing if required), ohmic resistance testing, rotating-field testing, and more. The fully automatic test method switching ensures that no test leads need to be manually reconnected to the test object during the test.

Thanks to the intuitive and user-friendly operation of our surge voltage testers, every test is performed quickly, accurately, and cost-effectively.