Department of Electrical and Computer Engineering

Electrical Machines Laboratory

Experiment 1Single Phase TransformerDr. Tarik Baldawi Objective:

1- To perform open-circuit and short-circuit tests to determine parameters of a transformer.2- To study the effect of loading a three-phase transformers with resistive, inductive, and capacitive loads. Components:

1. Power pack.2. Transformer.3. Switch.

4. Four digital multi-meters.

5. Load resistor.

6. Load reactor.

7. Load capacitor.

Wiring and Procedure:1. The single-phase transformer has 220 V primary voltage and 110 V secondary voltage.2. For open circuit test, connect the primary winding to constant 220 v primary voltage, while open circuit the secondary winding3. Record the reading of wattmeter, voltmeter, and ammeter.4. For short circuit connect the primary winding to variable voltage test, source, while the secondary is short circuited. Start from zero volt up to voltage that cause a rated secondary current to flow in secondary winding. Record the reading of wattmeter, voltmeter, and ammeter.5. For testing of transformer under various types of load, connect the secondary winding of transformer to resistive load, after that to inductive load, and that finally to capacitive load. Record the reading of ammeter and voltmeter while connected to secondary winding. Change the secondary current from zero in steps of one ampere.

Short Circuit Test:

V short circuit = 33 VI short circuit = 4.5 A

P short circuit = 35 Watt

Load Test:

I1 (A)I2 (A)V2 (V)P1 (Watt)P2 (Watt)

1.131.6119212190.488.55%

1.83.23118370381.14103.01%

2.55117530585110.3%

3.26.7116650777.2114%

3.78115800920115%

Questions: What is the ideal transformer?

An Ideal Transformer is an imaginary transformer, which does not have any loss in it, means no core losses, copper losses and any other losses in transformer. Efficiency of this transformer is considered as 100%. Why percent impedance of transformer Z2 is a very important value?1- It decides suitability of transformer to the system.2- It limits Short Circuit Current (Inversely).

3- It causes voltage drop (Directly).

Explain how the efficiency of transformer depend on power factor.

The power factor may reduce if the transformer works under a lighter load. Moreover, the efficiency of the transformer reduces if it is used below or above its load range, but lighter load affects it more. The voltage V=100 sin314t 20 sin1885t, is applied to 100 turn transformer winding. Drive the equation for the flux in the core, neglecting leakage flux and winding resistance.Total winding voltage is:V(t) = n * Vturn = n

= ( 100 cos314 ) ( 20 cos1885 ) = 51.62

V(t) = 100 * 51.62 = 5162 V

What is the condition for the maximum efficiency of a transformer and at which load does it occurs?The maximum operating efficiency occurs at the load where the core losses equal the load losses. Why the efficiency of a transformer higher than that of motor?Transformer is a electromagnetic stationary device which converts electrical energy from one level to another level by keepings its frequency constant. Where as in motors electrical energy is converted to mechanical energy . Now when this conversion of energy is taking place noise and friction comes in existence due to which some loss of input energy takes place and due to which energy output reduces efficiency accordingly.