To conduct Open circuit and Short circuit tests on single phase transformer

AIM:

To conduct Open circuit and Short circuit tests on single phase transformer to pre-determine the efficiency, regulation and equivalent parameters.

Name Plate Details:

Apparatus Required:

Circuit Diagram:

Open Circuit Test:

Short Circuit Test:

Theory:

Transformer is a device which transforms the energy from one circuit to other circuit without change of frequency.

The performance of any transformer calculated by conducting tests .OC and SC tests are conducted on transformer to find the efficiency and regulation of the transformer at any desired power factor.

OC Test:

The objectives of OC test are.

• 1. To find out the constant losses or iron losses of the transformer.
• 2. To find out the no load equivalent parameters.

The objectives of OC test are.

• 1. To find out the variable losses or copper losses of the transformer.
• 2. To find out the short circuit equivalent parameters.

By calculating the losses and equivalent parameters from the above tests the efficiency and regulation can be calculated at any desired power factor.

Procedure (OC Test):

• 1. Connections are made as per the circuit diagram.
• 2. Initially variac should be kept in its minimum position.
• 3. Close the DPST switch.
• 4. By varying Auto transformer bring the voltage to rated voltage.
• 5. When the voltage in the voltmeter is equal to the rated voltage of HV winding note down all the readings of the meters.
• 6. After taking all the readings bring the variac to its minimum position.
• 7. Now switch off the supply by opening the DPST switch.

Procedure (SC Test):

• 1. Connections are made as per the circuit diagram.
• 2. Short the LV side and connect the meters on HV side
• 3. Before taking the single phase, 230 V, 50 Hz supply the variac should be in minimum position.
• 4. Now close the DPST switch so that the supply is given to the transformer.
• 5. By varying the variac when the ammeter shows the rated current (i.e. 13.6A) then note down all the readings.
• 6. Bring the variac to minimum position after taking the readings and switch off the supply.

OC Test Observation:

SC Test Observation:

Calculation:

(a)Calculation of Equivalent circuit parameters:

Let the transformer be the step down transformer.

(i)Parameters Calculation from OC test:

(ii)Parameters Calculation from SC test:

(a)Calculations to find efficiency:

(a)Calculation of Regulation at full load:

Tabular Column:

Tabular Column:

Model Graphs:

1. Efficiency Vs Output

1. Regulation Vs Power Factor

Result:

Viva Questions:

• 1) What is a transformer?
• 2) Draw the equivalent circuit of transformer?
• 3) What is the efficiency and regulation of transformer?