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Which test is a special type of test performed on the transformers?
Switching impulse test
Temperature rise test
Ratio and polarity test
Noise level test
Switching impulse test
The switching impulse test is classified as a special test for power transformers, as defined by standards like IS 2026 or IEC 60076. These tests are performed to verify the ability of the transformer insulation to withstand switching surges, which are transient overvoltages occurring during switching operations in a power network.
The switching impulse test is classified as a special test for power transformers, as defined by standards like IS 2026 or IEC 60076. These tests are performed to verify the ability of the transformer insulation to withstand switching surges, which are transient overvoltages occurring during switching operations in a power network.
VsтАЛ=VpeakтАЛтЛЕ(eтИТ╬▒tтИТeтИТ╬▓t) тАФ Basic representation of a switching impulse voltage waveform
The test involves applying a standard switching impulse voltage wave to the transformer windings. This wave typically has a front time of 250 ╬╝sand a time to half-value of 2500 ╬╝s.It checks the dielectric strength of the insulation system under slow-front transient conditions that mimic real-world switching transients.
Special tests are performed only when agreed upon by the manufacturer and the purchaser.
Switching impulse tests are mandatory for transformers with a rated voltage of 300 kV and above.
The test is essential for high-voltage and extra-high-voltage (EHV) transformer insulation coordination.
Unlike routine tests, special tests are performed on a sample basis or upon specific request.
Ensures safety against transient overvoltages during system switching.
Verifies the insulation design adequacy for EHV levels.
Requires expensive and sophisticated impulse voltage generator equipment.
High cost and time-consuming procedure.
High Voltage Transformer testing
Extra High Voltage (EHV) insulation coordination
Design validation of Power Transformers
Standard: IS 2026 / IEC 60076.
Routine tests include: Resistance measurement, Ratio test, Vector group check, Impedance voltage, Load loss, No-load loss, and Induced/Separate source voltage withstand.
Option B (Temperature rise) is a Type test, not a Special test.
A is correct тАФ The switching impulse test is categorized as a special test because it is performed to verify insulation performance specifically under switching surge conditions, often required for high-voltage apparatus.
Always distinguish between Routine, Type, and Special tests; Routine tests are for every unit, Type tests for design validation, and Special tests are case-specific agreements.