Partial discharge testing has become an indispensable part of everyday testing.
The rapidly increasing prevalence of modern electric motors with frequency converters makes partial discharge testing essential —because only this test allows for a reliable assessment of your motors' suitability for frequency converter operation and the detection of critical insulation weaknesses.
With the increasing importance of partial discharge testing, we are hearing two questions more and more often—questions we are happy to answer:
- How exactly does a partial discharge test work?
- And what technological advances are there in this space?
What exactly is partial discharge or a partial discharge test?
A full discharge an electrical breakdown that is often visible and audible breakdown similar to lightning. In contrast, a partial discharge is only a very weak partial breakdown in part of the winding insulation. Over time, this partial discharge leads to increasing damage to the insulation, which in the worst case can extend to total failure. This is exactly what needs to be avoided. This is where partial discharge testing comes in. It helps you to identify potential total failures in advance.
Partial discharge testing according to IEC 61934 and DIN EN 60034-18-41
Partial discharge testing is used to check the winding quality of wound products. The test can surge test in conjunction with both the high voltage test sine) and the surge test . The main purpose is to detect quality defects in windings that cannot be identified using the conventional high voltage test surge test .
The measurement technology, combined with high-frequency filter technology, makes the system extremely resistant to interference. This makes the system ideal for use in the field or in manufacturing.
Partial discharge measurement (filtering and analysis) is fully built-in intothe MTC2/MTC3. Only the decoupling (measurement) of the actual partial discharge signal takes place outside the test device. This is necessary in order to measurement as close as possible to the winding measurement to adapt optimally to the respective measurement situation. The test on an open stator winding is performed using a highly sensitive measuring antenna or on a fully assembled Motor a special coupler. Both the antenna and the special coupler can be connected tothe MTC2/MTC3 as required. This means you are ideally equipped for any measurement task.
Further development of the antenna makes the measuring system even more sensitive than ever before. Any partial discharge that occurs is clearly detectable and has sufficient signal-to-noise ratio.
KEY FACTS
- Determination of the starting and stopping voltage according to IEC 61934
- Very high reproducibility thanks to special filter technology
- Special coupling technology for measuring fully assembled motors
- Extremely interference-free thanks to special high-frequency filter technology
- Shielding of the test area is not mandatory – but can be done optionally.
- Partial discharge testing up to 25 kV
- Qualification of enameled copper wires (twisted pair), enamel insulation, and impregnation process
- Testing for frequency converter compatibility
Partial discharge test on an open stator winding
Partial discharge measurement on an open stator winding is performed using a highly sensitive measuring antenna, which is placed in the device under test in the immediate vicinity of the test object.
Partial discharge testing on a fully assembled Motor
Measurements on a fully assembled Motor performed using an antenna, as the high-frequency signals are shielded by the closed motor housing. In these cases, measurements are performed using a special coupler that is measurement lead into the measurement lead .
Partial discharge testing at surge test
The test is performed either manually or fully automatically. In manual mode, the operator increases operator voltage
Observation of the partial discharge signal.
Automatic operation enables fully automatic analysis of all three phases via a test sequence. The following values are determined for each phase
:
- Phase voltage
- PDIV (application voltage)
- PDEV (breakdown voltage)
- RPDIV (repeated insertion voltage)
- RPDEV (repeating dropout voltage)
Here, too, it is not necessary to drive the entire ramp. If a quick distinction between GO niO must be made in production, a fixed TEST VOLTAGE can be TEST VOLTAGE . In this case, no partial discharge (PD) may TEST VOLTAGE at the TEST VOLTAGE .
The following graph shows the start of the surge test oscillation yellow) and the partial discharge pulses (red).
Partial discharge testing at high voltage AC
The test is performed fully automatically using a preset test sequence. A ramp function is run through,
,
during which the TEST VOLTAGE is increased TEST VOLTAGE . As soon as the first partial discharges occur, this voltage is stored voltage PDIV (Partial Discharge Inception Voltage).
The voltage is then reduced voltage until the partial discharge has completely disappeared. This point is recognized as PDEV
(Partial Discharge ExtinctionVoltage) and is also stored. In order to keep test times as short as possible during production, the intensity of the partial discharge can also be voltage at a fixed voltage . This allows a very quick distinction to be made between "good" and "bad."
It is also possible to perform the measurement manually. In this case, the operator increases operator voltage un
Observation of the partial discharge signal.
The VoltageAnalyzer – measurement accuracy at its finest
The VoltageAnalyzer is used to measure surge voltage signals directly at the motor winding.
The frequency responsespace the space DC to very high pulse frequencies inspace . This makes the VoltageAnalyzer perfect for high-precision surge voltage and partial discharge measurement.
The VoltageAnalyzer measures voltages and voltage peaks directly where they occur. This can be, for example, in Motor motor terminal board directly at the winding connections.
Voltage measurement during surge test partial discharge
It sometimes happens that the voltage surge tester internally in surge tester device under test voltage device under test exactly to the voltage device under test . This is because the unavoidable line inductances and capacitances between the measuring lines can device under test the voltage curve of the surge signal on its way to device under test . The steeper the surge impulse , the more pronounced this effect is.
In order to precisely measurement the partial discharge onset voltage actually motor terminal board to motor terminal board during a partial discharge test, for example, it is therefore terminal board take a measurement using the VoltageAnalyzer directly on terminal board .
KEY FACTS
- Precise surge test on the winding or motor terminal board
- Active probe with integrated switch-over three phases
- Potential-free voltage measurement
- Signal response influence by the measurement lead eliminated
- Precise measurement of TEvoltage PDIV, RPDIV, PDEV, RPDEV
- Perfect for standard-compliant measurement in accordance with DIN EN 60034-18-41:2014
- Determination and recording of pulse rise times
Partial discharge test on an open stator winding
To stator check a three-phase motor or stator without reconnecting, the VoltageAnalyzer has three measuring connections. These are connected directly to the U, V, and W terminals of the test object using the shortest possible measuring cables. The measuring point is switched between the three measuring connections in the VoltageAnalyzer fully automatically and synchronously with surge test.
The SCHLEICH !
Surge voltage signals measured with the VoltageAnalyzer
- measured directly at the motor terminals
- precise caster measurement
- Accurate peak and peak-to-peak voltage measurement
Surge voltage signals measured without VoltageAnalyzer
- The surge test oscillation not measured directly at the motor terminals, but in the test device.
- high attenuation of the trailing signal
Connection configuration of the VoltageAnalyzer to theMTC2/MTC3 and device under test
