High-voltage side open or connected to measuring voltage divider and PD coupling capacitor

Wiring: Connect the triple-frequency power output to the low-voltage side of the transformer under test (e.g., 10kV side), with the high-voltage side open or connected to a measuring voltage divider and PD coupling capacitor.

Calibration: Check the wiring, set the frequency (e.g., 150Hz), and perform a no-load verification.

Voltage increase:

Quickly raise to 40% of the test voltage.

Uniformly increase at a rate of 3% per second to 100% (or first raise to 1.5 times for PD background measurement, then to 2 times for withstand voltage).

Timing: Start timing after reaching the target voltage (e.g., at 150Hz, maintain for 40 seconds).

Voltage decrease: After the time is up, quickly and uniformly reduce the voltage to zero, and cut off the power.

Discharge: Fully discharge the test object.

6. Safety and precautions

Core heating: Although triple frequency is used, prolonged high-voltage operation can still cause heating of the core and windings, so the test time must be strictly controlled.

Resonance risk: At certain specific frequencies, the transformer inductance may resonate with stray capacitance, causing abnormal voltage rise; the voltage waveform must be closely monitored.

Neutral point insulation: For graded insulated transformers (e.g., 110kV and above), the neutral point insulation level is lower. During induced voltage withstand test, the neutral point must be grounded (or grounded through a protective gap); otherwise, the neutral point may break down due to excessive potential.

PD interference: If PD testing is performed simultaneously, the noise of the triple-frequency power source itself must be extremely low, and the on-site grounding system must be very well designed.

7. Selection recommendations

If you need to purchase or rent an induced voltage withstand device:

Capacity matching: Calculate the required power capacity (kVA) based on the capacity and no-load current of the transformer under test.

Frequency range: Choose a variable-frequency generator with continuous adjustment from 100-300Hz to meet different standard requirements.

Integrated design: It is recommended to choose a portable device that integrates the "triple-frequency source + control box + measurement unit" for easy on-site movement.

PD support: For high-end tests, confirm whether the device has reserved low-noise PD measurement interfaces and shielding measures.

Are you interested in learning how to calculate the required device capacity, or do you need a wiring scheme for a specific transformer (e.g., 110kV main transformer)?