electrical-engineering-portal.comhttp://electrical-engineering-portal.com/power-transformer-capacitance-and-dissipation-factor-test

Google+

Power Transformer Capacitance and Dissipation Factor Test

Figure 1 Capacitance and Dissipation Factor Test connection diagram

Transformer insulation systemThe capacitance and dissipation factor test is an AC low voltage maintenance test and is very similar to thepower factor test.

The test as it is termed, measures the capacitance and dissipation factor (or loss factor) of the transformerinsulation system. This test may be required to be performed during the acceptance testing stage to establish abaseline reading for future test comparison.

While the transformer preparation is identical to the power factor test procedure, there is no requiremnts tomake connection changes once the initial test set connections are made. High-voltage winding and low-voltagewinding test set connection changes are made through a selector switch provided on the test set.

Winding capacitance and dissipation factor test values are obtained by balancing a null meter for each variable atevery the measured variable selector switch positions.

Capacitance and Dissipation Factor Test Procedure(Two winding dry-type transformer)

Step 1.Isolate the equipment, apply working grounds to all incoming and outgoing cables and disconnect all incomingand outgoing cables from the transformer bushing terminals. Disconnected cables should have sufficientclearance from the switchgear terminals greater that the phase spacing distance.

MEGGER Semi-Automatic Capacitance and DissipationFactor Test Set (Direct readout of capacitance, dissipation

factor and watts dissipated)

Use nylon rope to hold cable away from incoming and outgoing terminals as required.

Step 2.Isolate the neutral bushing connection if applicable fromthe transformer grounding bar.

Step 3.Short-circuit all high voltage bushing terminals together.

Step 4.Short-circuit all low voltage bushing terminals and the neutralbushing terminal together.

Step 5.Connect the capacitance and dissipation factor test set. Refer to Figure 1 above.

Step 6.Record the capacitance and dissipation factor values once the null meter is balance for both phasing position.Record values for the five test-variable selector switch position.

Power Transformer Testing Measuring capacitance and power factor or dissipation factorThe condition of the bushings and the overall insulation of power transformers can be investigated by measuringthe capacitance and dissipation factor, also known as the tangent delta, or power factor. Aging and decompositionof the insulation, or the ingress of water, increases the losses and thus more energy is turned into heat in theinsulation.

The level of this dissipation is expressed by the dissipation factor or power factor.

Cant see this video? Click here to watch it on Youtube.

Reference: Substation Commissioning Course Raymond Lee, Technical Trainer

Power Transformer Capacitance and Dissipation Factor TestTransformer insulation systemCapacitance and Dissipation Factor Test ProcedureStep 1.Step 2.Step 3.Step 4.Step 5.Step 6.Power Transformer Testing Measuring capacitance and power factor or dissipation factor