**Transformer test**

The performance of transformer can be considered on the source of its corresponding circuit which have four main parameters the corresponding resistance R

_{01}as known to primary (or secondary R_{02}) ,the corresponding leakage reactance X_{01}known to primary (or secondary X_{02}), the core loss conductance G_{0}and the magnetizing susceptance B_{0}.These constants are factors that can be simply calculated by two test.
1. Open circuit test (O.C)

2. Short circuit test (S.C)

**1. Open Circuit (O.C) Test on Transformer**

**Calculation**

Open circuit test is used

• To determine no load constants R

_{0}, X_{0}
• To determine core loss

The connection diagram of O.C. test is shown in the fig. The rated voltage is applied to the primary winding, keeping the secondary is open. The readings of voltmeter, Ammeter and wattmeter are recorded. Let the respect readings are given below.

Ammeter reading = I

_{0}
Voltmeter reading = V

_{0}
Wattmeter reading = W

_{0}
W

_{0}represents the power input to the transformer on no load. It is equal to sum of core loss and copper loss. Since the no load current is small, the copper loss,(I_{20}R_{01}) very small. Hence the copper loss at no load is neglected. Therefore W_{0}reading shows the core loss.
From this reading R

_{0}, X_{0}are calculated as followed,
V

_{0}I_{0}cosӨ_{0}= W_{0}
Power factor, cos Ө

_{0}= W_{0}/ V_{0}I_{0}
Core loss component of no load current I

_{C}= I_{0}cosӨ_{0}
Magnetising component of no load current I

_{m}= I_{0}sin Ө_{0}
No load circuit constants

R

_{0}= V_{0}/ I_{c},
X

_{0}= V_{0}/ I_{m}**2. Short Circuit (S.C ) Test on Transformer Calculation:**

Short circuit test is used to

1 determine load constants R01 (or) R02, X01(or) X02

2 determine copper loss at full load

The connection diagram S.C. test is shown in the fig. A reduced voltage is applied to the primary winding and keeping the secondary short-circuited. The applied voltage is gradually increased until full load current flows through the transformer. The reading of ammeter, voltmeter and wattmeter are recorded. Let the respecting readings are I

_{s},V_{s},W_{s}.
Here the core loss is negligibly small since the applied voltage is very small. So the wattmeter reading (W

_{s}) will give the full load copper loss of the transformer.
V

_{s}I_{s}cosӨ_{s}= W_{s}
Power factor, cosӨ

_{s}= W_{s}/ V_{s}I_{s}
Impedance, Z

_{01}= V_{s}/ I_{s}
Full load copper loss, Ws = I

_{s2}R_{01}
Total resistance, R

_{01}= W_{s}/ I_{s2}( R_{01}is total resistance referred to primary side)
Total reactance is primary side, X

_{01}= √ Z_{01}^{2}- R_{01}^{2}
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