Power Transformer Insulation Resistance Testing

Summary

A substation power transformer's insulation helps it withstand significant electrical stresses. Any weakness in the insulation can lead to transformer failure. Because of its importance, the condition of the insulation is routinely evaluated. One of the field tests used to evaluate a transformer's insulation is the insulation resistance test.

This 37-minute DVD explains the purpose of insulation resistance testing, describes the equipment and procedures used to conduct this type of test, and explains how the test results can be interpreted.

Training Sessions

The Purpose of Insulation Resistance Testing – 4 minutes
Describes the function of power transformer insulation and state the purpose of transformer insulation resistance testing. Identifies factors that can change the resistance of transformer insulation.

Test Equipment – 7 minutes
Describes the principle of insulation resistance testing. Identifies and describes the components of a typical megohmmeter. Describes how a typical megohmmeter works.

Test Connections – 6 minutes
Identifies the connections for testing insulation resistance between the high-voltage winding and ground. Identifies the connections for testing insulation resistance between the low-voltage winding and ground. Identifies the connections for testing insulation resistance between the low-voltage winding and the high-voltage winding. Identifies the connections for testing insulation resistance between the transformer core and ground.

Test Procedures – 10 minutes
Describes safety precautions commonly associated with insulation resistance tests. Identifies transformer and environmental conditions that can affect insulation resistance test results. Describes typical preparations for performing an insulation resistance test. Describes a procedure for performing an insulation resistance test on a typical power transformer.

Evaluating Test Results – 9 minutes
Describes three ways the results of insulation resistance tests can be evaluated.

Support Materials Available

Student workbook, instructor guide.