This document outlines a procedure to determine the efficiency and voltage regulation of a single-phase transformer through direct loading. The apparatus required includes ammeters, voltmeters, a variac, connecting leads, and a 2KVA single-phase transformer. The procedure connects the transformer and variac in a circuit, applies the rated voltage, adjusts the load to the rated current, and records voltage and current readings with no load and full load. These readings are used to calculate efficiency as output over input power, and voltage regulation as the percentage difference between no load and full load voltages. This direct loading test is only suitable for small transformers due to the large energy waste and load requirements for large transformers.

1. Prepared By:
Kevinkumar G.
Raythaththa
Roll No:140310707012
M.E. (Power System)
L.E.COLLEGE, MORBI (GUJARAT)

2. OBJECTIVE : To determine the efficiency and voltage regulation of a
single phase transformer by direct loading.
APPARATUS REQUIRED:
SR.
NO.
NAME OF APPARATUS TYPE RANGE/
RATING
QUANTITY
1. Ammeter MI 0-10 A 01
2. Ammeter MI 0-10 A 01
3. Voltmeter MI 0- 300 V 01
4. Voltmeter MI 0- 300 V 01
5. Single Phase Variac - 230/0-270 V, 8/16
A
01
6. Connecting Leads - - As per
requirement
7. Transformer Single Phase 2KVA,230/115 V 01

3.  THEORY:
Although two chief difficulties which do not warrant the
testing of large
transformers by direct load test are:
• Large amount of energy has to be wasted in such a test.
• It is stupendous (impossible for large transformers) task
to arrange a load large enough for direct loading.
• Yet this test can be performed to find out the efficiency &
voltage regulation of small rating transformers.
• Efficiency η = Output / Input
%η = (V2 x I2) / (V1 x I1) x 100
• Voltage Regulation = (No load voltage – Full load
voltage)
Full load voltage
• % Voltage Regulation =[( E2 – V2)/ V2] x 100

5.  PROCEDURE:
 Connect the circuit as shown in figure.
 Ensure that variac is at its minimum position.
 Switch ON the supply by closing switch S1and apply the
rated voltage slowly by increasing the position of variac.
 Now adjust the load in such a way that rated current
starts to flow in primary side, by closing the switch S2.
 Note down the reading of Ammeters & Voltmeters.
 Now open the switch S2 and take the reading of
voltmeter connected in the secondary side, this voltage
will be the no load secondary voltage E2.
 Now decrease the applied voltage up to zero by
decreasing the position of variac.
 Switch OFF the supply.

7. OBSERVATION TABLE:
SR.N
O
PRIMARY
VOLTAGE
V1 (Volts)
PRIMARY
CURRENT
I1 (Amp)
SECONDARY
VOLTAGE
V2 (Volts)
SECONDARY
CURRENT
I2 (Amp)
1.
2.
3.
4.

9.  CALCULATIONS:
• Efficiency η = Output / Input
%η = (V2 x I2) / (V1 x I1) x 100
• Voltage Regulation = (No load voltage – Full load
voltage)
Full load voltage
• % Voltage Regulation =[( E2 – V2)/ V2] x 100
 RESULTS:
 %η =.................
 % Voltage Regulation =……………

11.  Though two chief difficulties which do not warrant
the testing of large transformers by direct load
test are:
1. Large amount of energy has to be wasted in
such a test.
2. It is stupendous (impossible for large
transformers) task to arrange a load large
enough for direct loading.
 Yet this test can be performed to find out the
efficiency & voltage regulation of small rating
transformers.