With instruments placed on the high-voltage side and the low-voltage side short-circuited, the short-circuit test readings for a 120 kVA, 2,400: 240 V single-phase transformer are 160 V, 50 A and 1 KW. An open circuit test in which the low voltage
instrument readings on this side of 240 V, 12 A and 480 W. Calculate:
a) Determine the efficiency of this transformer at full load with a unit power factor.
b) Determine the efficiency of this transformer at full load with an inductive power factor of 0.80.
c) Determine the voltage regulation at full load for an inductive power factor of 0.80.
d) Determine the voltage regulation at half load for a capacitive power factor of 0.60.
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Why is a short-circuit test, in the case of transformers, done with the high-voltage side only?
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Jim Phipps, Power systems engineer (30 yrs in the T&D industry)
Answered Jul 7, 2017 · Author has 879 answers and 681.1k answer views
Originally Answered: Why is a short circuit test in a transformer done on the high voltage side only?
The reason that a power transformer short circuit test is performed on the HV side is mostly due to the limitations of the power supply used to perform the test. Let us review:
The purpose for performing a short circuit test in the first place is to measure the positive-sequence impedance of the transformer ZZ. It is expressed as a percentage of the rated voltage applied to the transformer that results in rated current when the output is short circuited. It is measured at the factory using a balanced short circuit test as shown in the following single-phase equivalent circuit:
The low-voltage (LV) winding is shorted. A balanced three-phase, alternating current (AC), variable voltage source is used to excite the high-voltage (HV) winding. The voltage source is increased from zero until rated current is measured in the HV winding using an ammeter (A). Once this operating point is reached, the HV voltage is measured with a voltmeter (V). The impedance-voltage is then expressed as a percent of the rated voltage of the transformer Z=V/Vrated×100Z=V/Vrated×100. Since the full-load current of the HV winding is typically only in the 100’s of amps range, the power supply capability can be reduced (e.g., a less expensive power supply).
If the test was performed on the LV winding, the power supply would need to have the capability of producing 1000’s of amps since the full load current of the LV winding is greater by the voltage ratio HV/LVHV/LV of the transformer.
Thus, all short circuit tests are performed on the HV side because the power supply capabilities (and cost) are reduced.
Consider a 1 MVA 415V/ 11,000 V transformer
If you were to perform SC test on LV side the current would be (1 x 10^6)/(1.732 x 415) = 1391.2 A
Whereas if you were to perform the Test on HV side the Current Would be (1 x 10^6)/ (1.732 x 11000) =52.48 A
as you can see the Current on the HV side is much lower so SC test is conducted on the HV side S.C
The Problem with LV side is that for test purposes getting a source for delivering 1391 A is very difficult .
Just imagine the size of variac needed to deliver the same . It will be huge Uneconomical & Impractical
Imagine the current needed for higher rated transformers
Short circuit test is conducted to find the copper loss. It is calculated under the assumption that core loss are neglected. When SC test is conducted on the LV side it would require a larger voltage to get the rated current. Hence core loss cannot be neglected in this case and wattmeter dosen't give the copper loss alone. It is to get accurate results that test is done on HV side
First of all, you need to realise that the SC test is performed at rated current, so that the voltage drop seen at the secondary is same as that when the transformer is actually operated at rated values.
Now, rated current on the LV side is higher as compared to the HV side. Thus, we prefer working with a lower rated current (HV side) so that the apparatus (ammeter, supply) etc. with high current rating (implying higher cost) are not needed.
In the SC test, we focus on calculating the copper losses and thus intend on minimising the core losses (proportional to square of applied voltage). HV rated current is small and is achieved at a much lower voltage. Thus, core losses are also brought down.
Larger current flowing in the coils implies larger copper losses. Thus, lower current is desirable.
the high voltage side has lower rated current. The SC test requires rated current to flow through the winding. As for very high rating transformers the difference in rated current of HV and LV side could be huge, it is easier to conduct test at lower current
In a short circuit test, our purpose is to find cu losses of T/F and series branch parameters of equivalent circuit.
Short circuit test of T/F is conducted at its rated current and can be easily obtained by applying 5-6% of normal voltage. We normally short lv windings and test is performed from hv side.
The rated current on hv side is much less than lv side(VI = constant), so the rated hv side current is easily achieved(compared to lv side).
and Also because we cannot short-circuit hv side, as, if we short-circuit hv side, Voltage of hv side abruptly falls to zero and since VI(VA power=constant), so the hv current will be very high(compared to low rated current on hv side), and will burn the windi
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25 ANSWERS

Jim Phipps, Power systems engineer (30 yrs in the T&D industry)
Answered Jul 7, 2017 · Author has 879 answers and 681.1k answer views
Originally Answered: Why is a short circuit test in a transformer done on the high voltage side only?
The reason that a power transformer short circuit test is performed on the HV side is mostly due to the limitations of the power supply used to perform the test. Let us review:
The purpose for performing a short circuit test in the first place is to measure the positive-sequence impedance of the transformer ZZ. It is expressed as a percentage of the rated voltage applied to the transformer that results in rated current when the output is short circuited. It is measured at the factory using a balanced short circuit test as shown in the following single-phase equivalent circuit:
The low-voltage (LV) winding is shorted. A balanced three-phase, alternating current (AC), variable voltage source is used to excite the high-voltage (HV) winding. The voltage source is increased from zero until rated current is measured in the HV winding using an ammeter (A). Once this operating point is reached, the HV voltage is measured with a voltmeter (V). The impedance-voltage is then expressed as a percent of the rated voltage of the transformer Z=V/Vrated×100Z=V/Vrated×100. Since the full-load current of the HV winding is typically only in the 100’s of amps range, the power supply capability can be reduced (e.g., a less expensive power supply).
If the test was performed on the LV winding, the power supply would need to have the capability of producing 1000’s of amps since the full load current of the LV winding is greater by the voltage ratio HV/LVHV/LV of the transformer.
Thus, all short circuit tests are performed on the HV side because the power supply capabilities (and cost) are reduced.
Consider a 1 MVA 415V/ 11,000 V transformer
If you were to perform SC test on LV side the current would be (1 x 10^6)/(1.732 x 415) = 1391.2 A
Whereas if you were to perform the Test on HV side the Current Would be (1 x 10^6)/ (1.732 x 11000) =52.48 A
as you can see the Current on the HV side is much lower so SC test is conducted on the HV side S.C
The Problem with LV side is that for test purposes getting a source for delivering 1391 A is very difficult .
Just imagine the size of variac needed to deliver the same . It will be huge Uneconomical & Impractical
Imagine the current needed for higher rated transformers
Short circuit test is conducted to find the copper loss. It is calculated under the assumption that core loss are neglected. When SC test is conducted on the LV side it would require a larger voltage to get the rated current. Hence core loss cannot be neglected in this case and wattmeter dosen't give the copper loss alone. It is to get accurate results that test is done on HV side
First of all, you need to realise that the SC test is performed at rated current, so that the voltage drop seen at the secondary is same as that when the transformer is actually operated at rated values.
Now, rated current on the LV side is higher as compared to the HV side. Thus, we prefer working with a lower rated current (HV side) so that the apparatus (ammeter, supply) etc. with high current rating (implying higher cost) are not needed.
In the SC test, we focus on calculating the copper losses and thus intend on minimising the core losses (proportional to square of applied voltage). HV rated current is small and is achieved at a much lower voltage. Thus, core losses are also brought down.
Larger current flowing in the coils implies larger copper losses. Thus, lower current is desirable.
the high voltage side has lower rated current. The SC test requires rated current to flow through the winding. As for very high rating transformers the difference in rated current of HV and LV side could be huge, it is easier to conduct test at lower current
In a short circuit test, our purpose is to find cu losses of T/F and series branch parameters of equivalent circuit.
Short circuit test of T/F is conducted at its rated current and can be easily obtained by applying 5-6% of normal voltage. We normally short lv windings and test is performed from hv side.
The rated current on hv side is much less than lv side(VI = constant), so the rated hv side current is easily achieved(compared to lv side).
and Also because we cannot short-circuit hv side, as, if we short-circuit hv side, Voltage of hv side abruptly falls to zero and since VI(VA power=constant), so the hv current will be very high(compared to low rated current on hv side), and will burn the windi
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