Off Line Electrical Testing

ENGIS offers Offline Condition Assessment of transformers when showing unusual oil test results that requires further investigation.  Our Off-line Condition Assessment Services

Includes  performance of full suite of outage tests to assess the condition of the transformers.  With emphasis at determining the Dielectric, Thermal and Mechanical condition of the core and windings.

Mechanical Integrity from SFRA

A very sensitive means of detecting winding movement before it causes failures.  Any winding movement results in changes in capacitances and inductances which affect the characteristic ‘fingerprint’ response of the winding.

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The M5400 measures responses with excellent repeatability by injecting a 10v AC wave of varying frequency into one end of one winding and measuring the signal transferred through the winding.

Mechanical & Thermal Integrity from Excitation Current

When an AC Voltage Source, such as a Doble M4000, is placed on a transformer, a small current will flow.  This small current is the Magnetizing Current: the current required to magnetize the Transformer core with the Magnetic Flux.  If a fault develops in the secondary windings, this fault will act as a load across the faulted windings drawing a current- thus indicating a fault.

Dielectric Integrity from Power Factor

For a new unit, it is important to have measures to indicate adequate drying.  For older units, the need is to quantify the existence of degradation products on the winding and other insulating surfaces.  These include moisture, products of oxidation of the mineral oil, and conducting materials.

Thermal Integrity Winding Resistance to Detect Connection Issues

Winding resistance will indicate if any connections have worked loose, or have developed high contact resistance from overheating, for example.

Thermal Integrity Unintentional Earths from Insulation Resistance

Where the core earth is brought out and connected externally, this connection can be broken and the core checked for spurious earth and frame connections. If there is a poor IR, this could lead to circulating current heating.

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Transformer Bushing Integrity

Power factor/ capacitance are checked to identify degradation.  An oil sample can also be tested at this time.

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