[Ahmed]

Is the megger test necessary for new power transformer and are there any accepted values for measured megohm in insulation resistance test?

Is the megger test necessary for new power transformer and are there any accepted values for measured megohm in insulation resistance test?

Topic

[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

[R K Mohapatra]

The Insulation Resistance is a necesary not sufficient requirement for power transformer – New or Old .Even though there is no binding values as per standards – a value of 2 Mega ohm per kv at 60 C is supposed to be the requirement .However the values should not be less than 1000 mega ohm at room temperature for poweer trnasformers of 132 kV and above . P I value should range from 1.3 to 1.5 under all circumstances . A reduction of P I value is an indication of contamination by moisture or other suspended particles , which must be removed before charging .

[Author]

Replies