New installation commissioning test: Verify whether CT/PT parameters meet design requirements and whether polarity is correct. Periodic preventive test: Monitor insulation aging and characteristic changes of transformers. Fault troubleshooting: When relay protection malfunctions or refuses to operate, or metering is inaccurate, determine whether CT is saturated or damaged by testing volt-ampere characteristics. Selection verification: Based on the measured 10% error curve, verify whether the existing CT meets the protection requirements under system short-circuit current. 5. Operation precautions Safety isolation: Before testing, disconnect CT/PT from external secondary circuits (such as protection devices, metering meters) to prevent high voltage from entering and damaging precision equipment. Anti-open circuit (CT): Although the tester itself has protection, it is strictly forbidden to open the CT secondary side during wiring to prevent high voltage from injuring people. Anti-short circuit (PT): Short circuit on the secondary side is strictly prohibited during PT testing. Reliable grounding: The instrument casing and the casing of the tested transformer must be reliably grounded. Demagnetization operation: After testing, it is recommended to perform an automatic demagnetization procedure to eliminate residual magnetism in the core and ensure the transformer returns to its optimal working state. 6. Selection suggestions Routine maintenance (110kV and below): Choose a portable model with output voltage within 1000V and automatic calculation of 10% error curve. EHV/UHV (220kV and above): Need to choose a high-end model with higher output voltage (1800V+) and support for TP-class transient characteristic testing to meet the high requirements of large generator-transformer units. Metering special: If mainly used for electric energy metering verification, choose a special analyzer with higher accuracy class (0.02 or 0.05) and angle difference testing function.
Voltage Transformer (PT/VT) Testing
- Excitation characteristic: Measure the U-I curve of the PT secondary side.
- Ratio test: Verify the voltage transformation ratio.
- Polarity check: Determine the wiring polarity.
- DC resistance test: Measure the DC resistance of the winding.
- Secondary burden: Measure the load of the secondary circuit.
- Power frequency withstand voltage: Some models have a simple power frequency withstand voltage output function (note the capacity limit).
