To perform open circuit and short circuit test on a single phase transformer and to pre-determine the efficiency, regulation and equivalent circuit of the transformer.

Aim

To perform open circuit and short circuit test on a single phase transformer and to pre-determine the efficiency, regulation and equivalent circuit of the transformer.

Apparatus Required:

Transformer Specifications:

Transformer Rating :( in KVA) _________

Winding Details:

LV (in Volts): _______________________

LV side current:_____________________

HV (in Volts): _____________________

HV side Current:___________________

Type (Shell/Core):___________________

Auto transformer Specifications:

Input Voltage (in Volts):______________

Output Voltage (in Volts): ____________

frequency (in Hz):____________________

Current rating (in Amp):_____________

Circuit Diagram:

Procedure:-

Open circuit test:

1. Connections are made as per the circuit diagram.
2. Ensure that variac is set to zero output voltage position before starting the experiment.
3. Give the dc supply to the machine by closing the DPST switch and start the motor with the help of three point starter.
4. Switch ON the supply. Now apply the rated voltage to the Primary winding by using Variac.
5. The readings of the Voltmeter, ammeter and wattmeter are noted down in Tabular form.
6. Then Variac is set to zero output position and switch OFF the supply.

Short Circuit Test:

1. Connections are made as per the circuit diagram.
2. Ensure that variac is set to zero output voltage position before starting the experiment.
3. Switch ON the supply. Now apply the rated Current to the Primary winding by using Variac.
4. The readings of the Voltmeter, ammeter and wattmeter are noted down in Tabular form.
5. Then Variac is set to zero output position and switch OFF the supply.
6. Calculate R _o1 and X _o1from the readings.

Observation:

(I) For OC test

Tabular columns:

(II) For SC test

Model Calculation:

R₀=V₁/I_w,where I_w =I₀Cosɸo

X₀= V₁/I_m , where I_m =I ₀Sin ɸ₀

R₀₁= W_SC/ I_SC ²,Z₀₁= V_SC/ I_SC,X₀₁=√Z₀₁²- R ₀₁ ²

K=V₂/V₁, where K=Transformation Ratio

Find the equivalent circuit parameters R₀, X₀, R₀₁, R₀₂, X₀₁ and X₀₂rom the O. C. and S.

C. test results and draw the equivalent circuit referred to L. V. side as well as H. V. side.

Let the transformer be the step-down transformer

Primary is H. V. side.

Calculations to find efficiency and regulation:

For example at ½ full load

Cupper losses = W_SC x (1/2) ² watts, where W_SC = full – load cupper

losses Constant losses = W₀ watts

Output = ½ KVA x cos Φ [cos Φ may be assumed] Input = output + Cu. Loss + constant loss_________

Efficiency =(output /input)*100

Efficiency at different loads and P.f’s

Regulation: From open circuit and Short circuit test

% Voltage Regulation=(I_2rat/V₂)(R₀₂Cosϴ ± X₀₂Sinϴ)*100

‘+’ for lagging power factors

‘-‘ for leading power factor

CosΦ = 1.0

CosΦ = 1.0

Graphs:Plots drawn between

1. % Efficiency Vs output

2. % Regulation Vs Power factor

Precautions:

1. Connections must be made tight.
2. Before making or breaking the circuit, supply must be switched off.

Result:By conducting open circuit and short circuit test of a single phase transformer calculated the efficiency and regulation of the transformer.