How do you test a transformer ratio?
Procedure of Transformer Ratio Test
- First, the tap changer of transformer is kept in the lowest position and LV terminals are kept open.
- Then apply 3-phase 415 V supply on HV terminals.
- After measuring the voltages at HV and LV terminals, the tap changer of transformer should be raised by one position and repeat test.
What is the purpose of ratio test in transformer?
Power transformer turns ratio test is an AC low voltage test which determines the ratio of the high voltage winding to all other windings at no-load. The turns ratio test is performed on all taps of every winding.
What is ratio of transformer?
The turns ratio of a transformer is defined as the number of turns on its secondary divided by the number of turns on its primary.
How do you calculate CT to Pt ratio?
The installed CT has a ratio of 400:5 and the PT has a 4:1 ratio. The CT multiplier would be 80 and the PT multiplier is 4. Since a watt = amps x volts, the watthour meter multiplier, in this case, would be 80 x 4 or 320.
What is magnetic balance test of transformer?
Magnetic balance test is conducted only on three-phase transformers to check the imbalance in the magnetic circuit. Result of this test indicates uniform distribution of flux insulation. This test is carried out by applying 3 phase 400V AC to one winding, measured induced voltages on other two winding on same side.
What is the transformer formula?
Vp=−NpΔΦΔt V p = − N p Δ Φ Δ t . This is known as the transformer equation, and it simply states that the ratio of the secondary to primary voltages in a transformer equals the ratio of the number of loops in their coils.
How is voltage ratio calculated?
According to Faraday’s Law, you can calculate the voltage induced in the primary or secondary windings of the transformer by calculating N x dΦ/dt. This also explains why the transformer turns ratio of the voltage of one part of the transformer to the other is equal to the number of coils of one to the other.
What is CT and PT ratio?
Voltage transformers work on the same premise as CTs in that they step down higher voltages to usable levels. Most PTs have a secondary voltage of 120 volts. A PT with a ratio of 4:1 would step down 480 volts to 120 volts. The installed CT has a ratio of 400:5 and the PT has a 4:1 ratio.
What is CT burden?
The burden of the CT is the resistive load used to create the voltage on the output. It varies with turns ratio, desired output and current rating of the primary.
What is tan delta test in transformer?
Tan Delta, also called Loss Angle or Dielectric Dissipation Factor (DDF) or Power Factor (PF) testing, is an electrical dielectric test on the insulating oil used to determine its quality. The test is performed at two temperatures.
What is TTR testing?
Transformer Turns Ratio (TTR) testing is one of the most common ways of assessing the condition of a transformer’s windings and core. Throughout the life of a transformer, TTR results are compared against the nameplate ratings to reveal insulation deterioration, shorted turns, core heating or other abnormalities.
What is KVA formula?
Use the formula: P(KVA) = VA/1000 where P(KVA) is power in KVA, V is voltage and A is current in amperes. For example, if V is 120 volts and A is 10 amperes, P(KVA) = VA/1000 = (120)(10)/1000 = 1.2 KVA. Use the formula: P (KVA) = P (watts)/pf where pf is the power factor of the power supply.
How do you calculate transformer voltage ratio test?
Ratio measurements are conducted on all tap positions and calculated by dividing the induced voltage reading into the applied voltage value . When ratio tests are being made on three-phase transformers, the ratio is taken on one phase at a time with a three-phase TTR until the ratio measurements of all three phases are completed.
Why is the transformer turns ratio test needed?
A transformer turns ratio test confirms ratio accuracy of a transformer. The test ensures the correct ratio of both primary turns and secondary turns. It can also help to identify issues related to tap-changer performance, shorted turns, incorrect winding connections, and open windings.
What determines the transformer ratio?
As the transformer is basically a linear device, a ratio now exists between the number of turns of the primary coil divided by the number of turns of the secondary coil. This ratio, called the ratio of transformation, more commonly known as a transformers “turns ratio”, ( TR ).
What are the tests conducted on transformer?
8 Common Testing Procedures for Electrical Transformers Turns Ratio Testing. The transformer turns ratio test is used to make sure that the ratio between the windings of the primary and secondary coils follow the proper specifications. Insulation Resistance Testing. Power Factor Testing. Resistance Testing. Polarity Testing. Phase Relation Testing. Oil Tests. Visual Inspection.
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