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Reply To: Transformer Riddle No.38 -Transformer megger test

#1863
Hamid

    The core and its framework represent the largest bulk of metalwork requiring to be bonded to earth. On large, important transformers, connections to core and frames can be individually brought outside the tank via 3.3 kV bushings and then connected to earth externally. This enables the earth connection to be readily accessed at the time of initial installation on site and during subsequent maintenance without lowering the oil level for removal of inspection covers so that core insulation resistance checks can be carried out. There are many schools of thought as to what is considered an acceptable insulation resistance value. High and medium voltage insulation systems are usually designed to withstand large potentials and large quantities of electricity. Because of this, special equipment must be used to perform resistance tests. Ohm