Test on a Tranformer

8/6/2019 Test on a Tranformer

http://slidepdf.com/reader/full/test-on-a-tranformer 1/7

OBJECTIVES

• To study variation of core loss an no load current with applied voltage

• To determine the parameters of a transformer by open circuit and closed circuit tests

• To determine the efficiency

• To study the voltage regulation of a transistor

APPARATUS

• Single phase transformer 400/230V, 4kVA, 50Hz

• Auto transformer (input 400V output 0-400V)

• 1 no. Voltmeter 0-600V a.c



• 1 no. Ammeter 0-25A a.c

• 1 no. Ammeter 0-5A a.c

• 1 no. Wattmeter

• Resistive load units (230V, 10A)

• Power Factor meter



INTRODUCTION AND THEORY

A transformer, operated on AC voltage can be categorized into two main categories, namely, step up

transformers and step down transformers. When the device is supplied with the AC voltage to the primary winding, a higher or a lower voltage depending on the category of the transformer will be

given out in the secondary winding which is connected through a magnetic core.

When it comes to an Engineering point of view consideration of losses of an electrical machine is of great importance due to reasons such as determination of efficiency which influences the operating

cost, determination of heating of the machine which places an upper limit for output which can be

obtained without any deterioration of the insulation, etc.

Considering a transformer, losses which occur can be stated as,

• Copper loss in the windings, which vary the current

• Hysterisis and eddy current losses in the laminated iron-core constant in the

neighbourhood of a normal operating voltage

• Dielectric losses in the insulation material (appreciable only in case of high voltagetransformer)

•Leakage flux in the magnetic circuit

(P. T.O.)



For steady state operation of the equivalent circuit of a two winding transformer is shown in

Figure 1.

The equivalent circuit in Figure 1 can be simplified further and is shown in Figure 2.

The phasor diagram is shown in Figure 3.

Voltage regulation = open cct voltage – load voltage

open cct voltage

= V1-V’2

V1

From the phasor diagram (figure 3)

V1-V’2 = I’2.r.Cosθ + I’2.x.Sinθ

V1-V’2 = I’2.r.Cosθ + I’2.x.Sinθ

V1 V1

Since Io is negligible compared to I’2

Approximate Voltage Regulation = I2.r.Cosθ + I2.x.SinθV1

Considering only the hysterisis, eddy current and copper losses,

Efficiency = output power *100%

input power

= 1 – losses * 100%input

= 1 – losses * 100%output + losses

= V2. I2.Cosθ * 100%V2. I2.Cosθ + I’2 + PC

(PC = core loss, I2 = I’2)



r 1 x1 x2 r 2

V1 r c R L

Figure 1

r 1 – Primary winding resistance

r 2 – Secondary winding resistancex1 – Primary winding leakage reactance

x2 – Secondary winding leakage reactance

xm – Magnetizing reactancer c –Core loss resistance N2/N1 – Turns ratio

I1 I2’ r x I2

I0

V1 r c V1 V2

Figure2

V1

I2’x

I2’ V2’ I2’r

Figure 3

xm

xm



TEST ON A TRANSFORMER

INSTRUCTED BY : NAME : Roshan L. Peiris

Ms. K. R. S. Dematagolla

FIELD : Electrical Engineering

INDEX NO : 020280

DATE PERFORMED: 08 – 09 – 2003

DATE SUBMITTED: 15 – 09 – 2003



DISCUSSION

The transformer is a device, which works on AC supplies. It has two windings, which are connectedthrough a magnetic core. The two windings are named as the primary to which the AC voltage is

supplied and the secondary from which the output voltage is taken.

This device can mainly be categorized into two parts in accordance to its function. They are the stepup transformer in which a higher voltage is achieved through the secondary and the step down

transformer in which a lower voltage is achieved similarly.

When it comes to transformers role in electrical power systems it could be mentioned as one of the

most important devices. In an electrical power systems power transmission is a very important area.

Power = I2R

As shown in the equation above if the current is increased power generated due to resistance inincreased. Therefore when it comes to power transmission in an electrical system it might be

necessary for the power to be transmitted to hundreds of kilometres. So if a high current is used for

the transmission the power loss along the lines is high as shown in the above equation. To minimizethis power loss a higher voltage rather than a higher current is needed. Since it is not easy to

generate a high voltage at generating stations itself, the role of the transformer is brought in. I.e. the

step up transformers, which have the capability of producing a higher voltage and a lower current

output than the input, are used. These transformers output voltages as high as 33,000 volts (evenhigher than that) for long distance transmission.

When it comes down to distributing power to the consumer again the transformers are brought in asthe voltages have to be brought down to the usage levels such as 230 V, 400 V etc. For this purpose

step down transformers are used which produce lower voltages than the input. Sometimes this is

done in steps requiring the usage of the transformer even more.

So considering the above points which mainly involve transformers’ role in power transmission

could be mentioned as one of the most important aspects in a electrical power system. In conclusion

the transformer plays a very big role in an electrical power system.



RESULTS

Test on a Tranformer

Documents

Transcript of Test on a Tranformer