ABSTRACT

This lab consist of two experiments, the first experiment is measuring coil resistance of

transformer. The structure of transformer should be checked up before experimenting and

measuring method of primary and secondary coil resistance by using Transformer Trainer

(WSM-24). Since the primary and secondary coil resistance of transformer is different according

to the temperature, measuring is usually being done in the normal temperature. It is simple and

correct to measure resistances by the voltage drop method using DC variable power supply

devices. If too much current is flowed so that temperature increases, it becomes difficult to

measure the exact resistance.

The second experiment is impedance transformer, consider an ideal transformer. It should

be proved that the resistance and reactance value of transformer can be changed by capacitance.

In this experiment also use Transformer Trainer (WSM-24). Impedance between both terminals

of primary coil is the value to multiply resistance connected to between both ends of secondary

coil, to the square of turn ratio.

INTRODUCTION

A transformer is an electrical device that transfers energy between two or more circuits

through electromagnetic induction. A varying current in the transformer's primary winding

creates a varying magnetic flux in the core and a varying magnetic field impinging on the

secondary winding. This varying magnetic field at the secondary induces a varying electromotive

force (EMF) or voltage in the secondary winding. Making use of Faraday's Law in conjunction

with high magnetic permeability core properties, transformers can thus be designed to efficiently

change AC voltages from one voltage level to another within power networks.

Transformer Trainer (WSM-24)

This equipment contains three single transformers.

The equipment can be experiment of principal, current ratio, polarity, parallel connection

etc.

Also voltmeter & ampere meter attached in outside for convenient experiment.

A coil constructed for the purpose of offering a certain resistance to a steady current. This

resistance may be for the purpose of carrying out quantitative tests, as in Wheatstone bridge

work (see Wheatstone's Bridge), or simply to reduce the intensity of a current. For the first class

of work the coils are wound so as to prevent the creation of a magnetic field. This is affected by

first doubling the wire without breaking it, and then starting at the bend the doubled wire, which

is insulated, is wound on a bobbin or otherwise until a proper resistance is shown by actual

measurement. The coils are generally contained or set in closed boxes with ebonite tops. Blocks

of brass are placed on the top, and one end from one coil and one end from the next connect with

the same block. By inserting a plug, P, so as to connect any two blocks, which have grooves

reamed out for the purpose, the coil beneath will be short circuited. German silver, platinoid or

other alloy, q. v., is generally the material of the wire. A great object is to have a wire whose

resistance will be unaffected by heat.

An impedance transformer is a device which makes impedance at its output port appears

as different impedance at its input port. In waveguide, this device is simply a short length of

waveguide. Especially useful is the quarter-wave impedance transformer which has a length of

g/4. This device can turn capacitances into inductances and vice versa. It also has the useful

property of turning shunt-connected elements into series-connected elements and vice versa.

Series-connected .elements are otherwise difficult to implement in waveguide.

Results

Exercise 1

Figure 1: Current 0.1A

Figure 2: Current 0.2A

Figure 3: Current 0.3A

Figure 4: Current 0.4A

Figure 5: Current 0.4A

Primary Coil Secondary Coil

Voltage (V) Current (A) Coil

Resistance, R

()

Voltage (V) Current (A) Coil

Resistance, R

()

0.6 0.1 6 0.5 0.1 5

1.1 0.2 5.5 0.9 0.2 4.5

1.7 0.3 5.7 1.4 0.3 4.7

2.2 0.4 5.5 1.9 0.4 4.8

2.8 0.5 5.6 2.3 0.5 4.6

Average Resistance Value = 5.66 Average Resistance Value = 4.72

Table 1: Result table for each current value

Exercise 2

Figure 6: Measurement for 110V

Figure 7: Measurement for 220V

Input Voltage, E1

(V)

Primary Current, I 1

(A)

Primary Impedance, Z1

()

Load 110 0.114 964.9

Resistance load () 220 0.286 769.2

Average Impedance 867.05

Table 2: Result for exercise 2

Discussion

1. What are the ways to reduce error in measuring coil resistance of transformer?

The resistance should be measured in ideal temperature to reduce losses in the coil

resistance

2. What is rated load current of transformer to experiment with?

The current increase due to increase of voltage in the experiment

3. Is the impedance conversion of a transformer related to turn ratio?

Yes, where2

1

2

1

V

V

N

NZ

4. There is a transformer of voltage ratio, 2400/120 [V].

Resistor of 3[] is connected to the lower-voltage side transformer.

Calculate resistance value being generated between both terminals of higher-voltage side.

603

120

2400

1

2 RN

NZ

5. a) There is a transformer coupled completely. When the number of primary coil turns is

550, and that of secondary transformer coil turns is 220, a condenser of 10F is

connected to between both terminals of primary coil side. Calculate condenser value

being generated in the coil of 220 turns.

6.1

10*550

220

*

2

2

2

1

2

1

22

Xc

Xc

XcN

NXc

b) If it is an ideal transformer, is the value of condenser affected by the magnitude of

frequency?

No.

6. There is transformer primary sides are inductance of 2.5[mH] and secondary side are

inductance of 2.2[H].What is the turn ratio of this transformer?

30

2

1

2

1

2

N

N

C

C

Conclusion

To get ideal measurement of resistance for a transformer winding, the measurement should be

taken at low temperature. This is because the resistance will increase as the temperature of the

winding increases.