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Tan Delta & Capacitance

Every Power electrical appliances in use, undergo stress from Operating Voltage, Mechanical Vibration, Temperature, Gaseous and Solid Metallic Impurities. Under these stress, the degradation of the insulation takes place, in the Electrical equipment. This  stress lead to the continuous ageing of the appliance, with regard to its Electrical Properties. Sometimes there will be an avalanche of Insulation breakdown.  In the total complex network of Power Generation, Transmission, Distribution System ageing of a simple insulation may lead to a disastrous breakdown of the system, causing heavy loss.

To avoid such unexpected breakdowns and for the un-interrupted service, from electrical power  it is very essential to know the insulation quality of the equipment that is going to be used in the power system. And it is also essential to periodically monitor the Insulation property of equipment, that in use in this Power Network.

In Electrical AC System the Dissipation Factor Tan ? or Power Factor Cos ø is considered as the indicator of quality of insulation.

Applications

• Transformers
• Generators
• CT/CVT
• Motors
• Breakers
• Cables

Insulation Resistance

It is desirable to have Insulation Resistance as high as possible consistent with acceptable mechanical, chemical and heat resisting properties.

This test is to detect the conductive impurities or mechanical imperfections in the dielectric which affect the quality of insulation which may be developed in the dielectric during the manufacturing process.

The insulation resistance test can detect if this connection is loose. It can also detect whether there are other, undesired and inadvertent, grounds. If the intentional core ground is intact, the resultant resistance should be very low. To check for unintentional core grounds, remove the intentional ground and Megger between the core and the grounded transformer tank. This test should produce very high resistance indicating that an unintentional ground is not present. This test is to supplement DGA that shows generation of hot metal gases (methane, ethane, and ethylene) and to indicate if a spurious, unintentional core ground is the problem. Experience can help locate the source of the problem.

Polarization Index

Polarization Index test that it can provide an indication of insulation quality in ten minutes for very large equipment that might take very long time to get fully charged.

DC Absorption

DC Absorption Test indicates the insulation Condition of the Winding and Supplements to to various other Insulation measurements, therefore, if analyzed, based upon its trend over a period of Time, helps in making decisions better.

Ratio, Burden & Polarity

Phase & Magnitude Error

Excitation Curve

Winding Resistance

Winding resistances are tested in the field to check for loose connections on bushings or tap changers, broken strands, and high contact resistance in tap changers.

Results are compared to other phases in wye connected transformers or between pairs of terminals on a delta-connected winding to determine if a resistance is too high. Resistances can also be compared to the original factory measurements or to sister transformers.

Secondary Burden

CT Circuit Continuity