The transformer testing instruments can be classified in multiple dimensions based on the test object and purpose. The most commonly used classification method is by test items. The specific categories and corresponding instrument functions are as follows:
1. Insulation characteristic testing instruments
These instruments are mainly used to evaluate the operating conditions of the main insulation and longitudinal insulation of the transformer. The core instruments and functions include:
Insulation resistance tester: Measures the insulation resistance between transformer windings and between windings and ground, to determine if the insulation is damp or if there are penetrating defects.
Dielectric loss factor tester: Measures the dielectric loss factor and capacitance of the transformer bushing and winding. This indicator is a sensitive basis for judging the aging and dampness of the insulation material.
DC resistance tester: Measures the DC resistance of the transformer winding, to check the welding quality of the winding conductors, the contact condition of the tap changer, whether there is a short circuit between the windings, and whether the lead connections are good.
Absorption ratio / Polarization index tester: Often as an advanced function module of the insulation resistance tester, it calculates the ratio of insulation resistances at different time points to more accurately determine the dampness of the insulation.
2. Voltage ratio and voltage vector testing instruments
These instruments are used to verify the core functions of transformer voltage transformation and phase adjustment. The core instruments and functions include:
Voltage ratio tester: Precisely measures the voltage ratio of the transformer, checks if the adjustment of each tap position of the tap changer is accurate, and determines if there is a short circuit problem in the winding.
Connection group tester: Verifies whether the actual connection group of the transformer is consistent with the marking requirements on the nameplate.
3. No-load and load characteristic testing instruments
These instruments are used to measure the basic performance parameters and operating losses of the transformer. The core instruments and functions include:
No-load loss testing system: Under the condition of opening one side of the transformer winding and applying the rated voltage to the other side, measures the no-load current and no-load loss (iron loss) of the transformer.
Load loss testing system: Under the condition of short-circuiting one side of the transformer winding and applying the rated current to the other side, measures the load loss (copper loss) and impedance voltage of the transformer.
Power quality analyzer / Power analyzer: Often as the core measurement unit of the no-load and load loss testing system, used to accurately measure key electrical parameters such as voltage, current, power, and power factor.
4. Winding deformation testing instruments
These instruments are specifically used to diagnose whether the internal windings of the transformer have mechanical displacement, distortion, or deformation problems after short-circuit current impact or transportation vibration. The mainstream instrument is the frequency response analysis method winding deformation tester, which determines whether the winding has deformed by comparing the response curves of the winding at different frequencies.
5. Oil testing instruments
These instruments are applicable to oil-immersed transformers and are used to conduct tests on the performance of the transformer’s insulating oil. The core instruments and functions include:
Oil dielectric strength tester: Measures the breakdown voltage of the insulating oil to determine if the insulation strength of the insulating oil meets the standard.
Microscopic moisture tester: Precisely measures the trace moisture content in the insulating oil to assess the degree of oil dampness.
Gas chromatography analyzer: Analyzes the composition and content of dissolved gases in the insulating oil, which is an effective means to diagnose latent faults in the transformer (such as overheating and local discharge).
6. Comprehensive and high-voltage testing instruments
These instruments are mainly used for the final insulation strength assessment of the transformer and integrate multiple testing functions to improve the detection efficiency. The core instruments and functions include:
Ultra-low frequency high-voltage generator / AC withstand voltage testing system: Applies a higher-than-rated voltage of power frequency AC voltage to the transformer to test the withstand strength of the main insulation.
DC high-voltage generator: Conducts transformer DC withstand voltage tests and leakage current tests to evaluate the insulation performance.
Integrated test bench: Integrates various testing functions such as voltage ratio, DC resistance, and winding insulation detection to achieve integrated testing of multiple items of the transformer and improve the automation level and detection efficiency of the test.
Post time: Feb-02-2026