The type tests of a power transformer are conducted on a prototype to validate its design and ensure compliance with specified standards. These tests are distinct from routine tests, which are performed on every unit. Here is a comprehensive list of the primary type tests:
Temperature Rise Test:
Evaluates the transformer's ability to dissipate heat under continuous full-load conditions, ensuring that temperature limits for windings and oil are not exceeded.
Dielectric Tests:
Separate Source Voltage Withstand Test: Applies high voltage to windings to verify insulation integrity against external overvoltages.
Induced Voltage Withstand Test (AC Overvoltage Test): Checks inter-turn and phase insulation by inducing elevated voltages at higher frequencies.
Lightning Impulse Test: Simulates lightning surges to assess insulation resilience against transient overvoltages.
Switching Impulse Test: For high-voltage transformers, tests insulation response to switching-induced surges.
Short-Circuit Withstand Test:
Validates the transformer's mechanical and thermal resilience during a short-circuit fault, ensuring no damage to windings or core.
Measurement of Zero-Sequence Impedance:
Determines impedance under unbalanced load conditions, critical for grounding and protection system design.
Noise Level Test:
Measures audible noise to ensure compliance with environmental and regulatory standards.
Tests on On-Load Tap Changer (OLTC):
If equipped, assesses the OLTC's performance under load, including contact endurance and switching capability.
Insulation Resistance Tests:
Part of dielectric validation, measuring resistance to identify potential insulation degradation (often included in dielectric tests).
Pressure Test (for Tank and Radiators):
Ensures mechanical integrity and leak-tightness of the transformer tank under pressurized conditions.