open and short circuit test on transformer electrical4u
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Open and Short Circuit Test on Transformer | Electrical4u
http://www.electrical4u.com/open-and-short-circuit-test-on-transformer/[9/24/2014 8:12:07 PM]
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Open and Short Circuit Test on Transformer | Electrical4u
http://www.electrical4u.com/open-and-short-circuit-test-on-transformer/[9/24/2014 8:12:07 PM]
Open Circuit Test on Transformer• Short Circuit Test
These two tests are performed on a transformer to determine (i) equivalent circuit oftransformer (ii) voltage regulation of transformer(iii) efficiency of transformer. Thepower required for these open circuit test and short circuit test on transformer isequal to the power loss occurring in the transformer.
Open Circuit Test on Transformer
The connection diagram for open circuit test on transformer is shown in the figure.A voltmeter, wattmeter, and an ammeter are connected in LV side of the transformeras shown. The voltage at rated frequency is applied to that LV side with the help of avariac of variable ratio auto transformer. The HV side of the transformer is kept open.Now with the help of variac, applied voltage gets slowly increased until the voltmetergives reading equal to the rated voltage of the LV side. After reaching at rated LV sidevoltage, all three instruments reading (Voltmeter, Ammeter and Wattmeter readings)are recorded.
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Open and Short Circuit Test on Transformer | Electrical4u
http://www.electrical4u.com/open-and-short-circuit-test-on-transformer/[9/24/2014 8:12:07 PM]
The ammeter reading gives the no load current I . As no load current I is quite smallcompared to rated electric current of the transformer, the voltage drops due to thiselectric current that can be taken as negligible.
Since, voltmeter reading V can be considered equal to secondary induced voltage ofthe transformer, the input power during test is indicated by watt-meter reading. As thetransformer is open circuited, there is no output, hence the input power here consistsof core losses in transformer and copper loss in transformer during no load condition.But as said earlier, the no load current in the transformer is quite small compared tofull load current, so copper loss due to the small no load current can be neglected.Hence, the wattmeter reading can be taken as equal to core losses in transformer. Letus consider wattmeter reading is P .
Where R is shunt branch resistance of transformer.
If, Z is shunt branch impedance of transformer.
Therefore, if shunt branch reactance of transformer is X ,
These values are referred to the LV side of transformer as because the test isconduced on LV side of transformer. These values could easily be referred to HV sideby multiplying these values with square of transformation ratio.
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Open and Short Circuit Test on Transformer | Electrical4u
http://www.electrical4u.com/open-and-short-circuit-test-on-transformer/[9/24/2014 8:12:07 PM]
Therefore it is seen that the open circuit test on transformer is used to determinecore losses in transformer and parameters of shunt branch of the equivalent circuit oftransformer.
Short Circuit Test on Transformer
The connection diagram for short circuit test on transformer is shown in the figure.A voltmeter, wattmeter, and an ammeter are connected in HV side of the transformeras shown. The voltage at rated frequency is applied to that HV side with the help of avariac of variable ratio auto transformer.
The LV side of the transformer is short circuited. Now with the help of variac appliedvoltage is slowly increased until the ammeter gives reading equal to the rated electriccurrent of the HV side. After reaching at rated electric current of HV side, all threeinstruments reading (Voltmeter, Ammeter and Watt-meter readings) are recorded. Theammeter reading gives the primary equivalent of full load current I . As the voltageapplied for full load current in short circuit test on transformer is quite small comparedto the rated primary voltage of the transformer, the core losses in transformer can betaken as negligible here.
Let’s say, voltmeter reading is V . The input power during test is indicated by watt-meter reading. As the transformer is short circuited, there is no output; hence the inputpower here consists of copper losses in transformer. Since, the applied voltage V isshort circuit voltage in the transformer and hence it is quite small compared to ratedvoltage, so core loss due to the small applied voltage can be neglected. Hence thewattmeter reading can be taken as equal to copper losses in transformer. Let usconsider wattmeter reading is P .
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Open and Short Circuit Test on Transformer | Electrical4u
http://www.electrical4u.com/open-and-short-circuit-test-on-transformer/[9/24/2014 8:12:07 PM]
Where R is equivalent resistance of transformer.If, Z is equivalent impedance of transformer.
Therefore, if equivalent reactance of transformer is X
These values are referred to the HV side of transformer as because the test isconduced on HV side of transformer. These values could easily be referred to LV sideby dividing these values with square of transformation ratio.
Therefore it is seen that the short circuit test on transformer is used to determinecopper loss in transformer at full load and parameters of approximate equivalent circuitof transformer.
Objective Questions on Transformer (MCQs)
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Open and Short Circuit Test on Transformer | Electrical4u
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