Insulator–
Insulation resistance tests are made to determine insulation resistance from individual windings to ground or between individual windings. Insulation resistance tests are commonly measured directly in megohms or may be calculated from measurements of applied voltage and leakage current.
Insulation for Transformers can be divided into two fundamental groups: major insulation and minor insulation. Major insulation separates the high- and low-voltage windings, and the windings to core. Minor insulation may be used between the parts of individual coils or windings depending on construction.
The recommended practice in measuring insulation resistance is to always ground the tank (and the core). Short circuit each winding of the transformer at the bushing terminals. Resistance measurements are then made between each winding and all other windings grounded.
Insulation resistance testing: HV – Earth and HV – LV
Transformer windings are never left floating for insulation resistance measurements. Solidly grounded winding must have the ground removed in order to measure the insulation resistance of the winding grounded. If the ground cannot be removed, as in the case of some windings with solidly grounded neutrals, the insulation resistance of the winding cannot be measured. Treat it as part of the grounded section of the circuit.
We need to test winding to winding and winding to ground ( E ).For three phase transformers, We need to test winding ( L1,L2,L3 ) with substitute Earthing for Delta transformer or winding ( L1,L2,L3 ) with earthing ( E ) and neutral ( N ) for wye transformers.
Our Power and Distribution Transformer Test Laboratory is NABL Accredited & BIS Recognized Laboratory.
Our lab is well equipped, meeting National/ International Standards and accredited by NABL (National Accreditation Board for Testing & Calibration Laboratories) under Dept. of Science & Technology (DST), Govt. of India, New Delhi.
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