Basic Electrical & Electronics Engineering (BT-104)
EXPERIMENT NO. 5
OBJECTIVE: Study Name plate specification of single phase transformer and perform Ratio
and Polarity test on single phase Transformer.
APPARATUS REQUIRED:
Sr. No. Apparatus Type Range Qty.
1. Transformer 1 - Phase 230 V / 146 V 1
2. Auto transformer 1-Phase -270 V 1
3. Voltmeter MI 0 – 300 V 2
4. Voltmeter MI 0 – 600 V 1
THEORY:
(A). Theoretically it may seem that transformers may be built to handle any voltage or current. But in
reality there are limit to both the voltage & the current. The nameplate rating of a power transformer
usually contains
1. Volt-amperes KVA
2. Voltage Ratio Rated Primary voltage / secondary voltage = V2/ V1 volt or kV.
3. Frequency 50 Hz
4. Type 1 or 3
5. Equivalent Impedance
(B) Transformation Ratio:
The induced e.m.f per phase in primary & secondary windings of a transformer is given by e.m.f in
primary E1 = 4.44 f N1. Induced e.m.f in secondary E2 = V1 & E2 = V2.
Hence the transformation Ratio ( K ) = V2/ V1 = T2 / T1.
(C) Polarity Test:
Each of the terminals of primary as well as secondary winding of a transformer is alternatively
positive & negative with respect to each other. It is essential to know the relative polarities at any
instant of the primary & secondary terminals for making correct connections if the transformers are to
be opened in parallel or are to be used in a 3 circuit.
When viewed from the primary side the terminals are marked A1 & A2. Now terminals A1 is
connected to one end of secondary winding & a voltmeter is connected between A2 & other end of
secondary winding. When voltmeter reads the difference
(V1 –V2), the transformer is said to posses a subtractive polarity & when voltmeter reads
(Exp. no. 5)1
Department of Electrical and Electronics Engineering / Department of Electrical Engineering
EXPERIMENT NO. 5
OBJECTIVE: Study Name plate specification of single phase transformer and perform Ratio
and Polarity test on single phase Transformer.
APPARATUS REQUIRED:
Sr. No. Apparatus Type Range Qty.
1. Transformer 1 - Phase 230 V / 146 V 1
2. Auto transformer 1-Phase -270 V 1
3. Voltmeter MI 0 – 300 V 2
4. Voltmeter MI 0 – 600 V 1
THEORY:
(A). Theoretically it may seem that transformers may be built to handle any voltage or current. But in
reality there are limit to both the voltage & the current. The nameplate rating of a power transformer
usually contains
1. Volt-amperes KVA
2. Voltage Ratio Rated Primary voltage / secondary voltage = V2/ V1 volt or kV.
3. Frequency 50 Hz
4. Type 1 or 3
5. Equivalent Impedance
(B) Transformation Ratio:
The induced e.m.f per phase in primary & secondary windings of a transformer is given by e.m.f in
primary E1 = 4.44 f N1. Induced e.m.f in secondary E2 = V1 & E2 = V2.
Hence the transformation Ratio ( K ) = V2/ V1 = T2 / T1.
(C) Polarity Test:
Each of the terminals of primary as well as secondary winding of a transformer is alternatively
positive & negative with respect to each other. It is essential to know the relative polarities at any
instant of the primary & secondary terminals for making correct connections if the transformers are to
be opened in parallel or are to be used in a 3 circuit.
When viewed from the primary side the terminals are marked A1 & A2. Now terminals A1 is
connected to one end of secondary winding & a voltmeter is connected between A2 & other end of
secondary winding. When voltmeter reads the difference
(V1 –V2), the transformer is said to posses a subtractive polarity & when voltmeter reads
(Exp. no. 5)1
Department of Electrical and Electronics Engineering / Department of Electrical Engineering
