The VoltageAnalyzer can measure high voltages of all kinds. Its frequency response covers the range from DC to very high pulse frequencies in the MHz range, making it ideal for high-voltage, surge voltage, and partial discharge measurements.

The active probe measures voltages and voltage spikes where they occur, e.g., directly at the motor terminal block in an electric motor. These voltage spikes can be caused by a frequency converter. During a surge voltage test, the spikes can be caused by overshoots in the supply line.

Voltage Measurement for Surge Voltage and Partial Discharge

It can happen that the voltage measured internally in the impulse voltage tester does not exactly match the voltage at the test object. This is because the unavoidable inductances and capacitances in the test leads can alter the voltage waveform of the impulse signal on its way to the test object. The steeper the impulse rise, the more pronounced this difference.

In order to accurately measure the actual partial discharge inception voltage at the motor terminal block, for example during a partial discharge test, a measurement via the active probe directly at the terminal block is required.

The VoltageAnalyzer was developed precisely for this purpose: The voltage measurement takes place between the phases between which the impulse voltage test also takes place.

To enable quick testing of a three-phase motor without time-consuming rewiring, the VoltageAnalyzer is equipped with three measuring terminals. These are connected directly to terminals U, V, and W of the device under test using the shortest possible measuring leads. The switching between the three measuring terminals is fully automatic and synchronized with the surge voltage test within the VoltageAnalyzer.

Communication with the test device

The VoltageAnalyzer has a communication link to the surge voltage tester. This link allows for remote control of the VoltageAnalyzer and the transmission of measured values ​​to the surge voltage tester. During the surge voltage test, the VoltageAnalyzer automatically switches to the terminals currently being tested. This remote control is performed by the surge voltage tester.

Measured values

The following voltages are automatically measured by the active probe:

• U _peak : maximum amplitude
• U _peak-to-peak : maximum voltage between the highest positive and negative amplitudes
• Rise time in ns

At the frequency converter output, the switching edges are still very close to the optimal square wave shape. The image shows the voltage pulses between two phases at the converter's output terminals. The voltage pulses, the pulse width modulation, and the negative and positive half-waves of the sine wave are clearly visible.

The voltage level is derived from the AC supply voltage of the frequency converter. Since every frequency converter first rectifies the input voltage, each converter is equipped with a DC link consisting of capacitors charged to the input voltage x √2. For 230 V AC, this results in a value of 320 V DC, and for 400 V AC, a value of approximately 560 V DC. The diagram shows a level of 315 V DC, which corresponds well to the 230 V AC supply.

The electric motor is connected to the frequency converter via cables.

Cables are not ideal electrical components. They consist of resistances, inductances, and coupling capacitances between the conductors. As a result, the ideal square wave pulse, which is still present at the output of the frequency converter, is significantly distorted on its way to the electric motor.

• Active probe with built-in switching between three phases
• Potential-free voltage measurement
• Precise impulse voltage measurement directly at the winding
• Elimination of voltage interference on the measuring line
• Precise measurement of TE voltages – PDIV, RPDIV, PDEV, RPDEV
• Perfect for standard-compliant measurement according to DIN EN 60034-18-41:2021
• Including determination of pulse rise times
• Determination of voltage peaks caused by frequency converters