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CAN102 Electromagnetism and Electromechanics

Lab 2 Single-phase Transformers

General Information

Operating instructions

(1) Be familiar with equipment used and understand the functions;

(2) Work in groups of 3 people;

(3) Make wiring according to the connection diagrams;

(4) Observe the instruments after switching on the equipment, if there is any abnormal operation or smell, switch off the power immediately and identify the fault;

(5) Measure parameters according to the operating instructions;

(6) Turn off the power supply system when finished a set of measurements, then continue to the next step.

Safety Instructions

(1) Never touch a live circuit.

(2) Only connect or disconnect wires with the power switched off.

(3) Turn on the power supply with instructor’s permission, and switch off the power immediately if a fault occurs.

(4) Check the power meter and ammeter before switching on the power, a short-circuit fault must be avoided.

(5) The main power switch should be operated with instructor’s permission.

1. Objectives

To measure the transformation ratio and parameters of a single-phase transformer.

2. Pre-lab

2.1 What are the features of no load and short circuit tests of a transformer, respectively? To which side should the power supply be connected during each test and why?

2.2 How should the instruments be connected to avoid measurement errors during no load and short circuit tests?  How should the wattmeter W be connected to a circuit?

3. Laboratory exercises

3.1 No load test

Measure the no load characteristics U0  = f(I0), P0 = f(U0), and cosφ0 = f(U0) as the instructions in section 5.1.

3.2 Short circuit test

Measure the short-circuit characteristics UK =f(IK), PK =f(IK), and cosφK =f(IK) as the instructions in section 5.2.

4. Equipment List

The modules in the table below are used in the experiment.

5. Operating instructions

5.1 No load test instructions

The connection diagram is shown in Figure 1.  The transformer is the single-phase transformer of module DJ11 with Low Voltage (LV) winding terminals a and x connected to the power supply, while

High Voltage (HV) winding terminals A and X are open circuit.  Use module D33 for voltmeters V1 and V2.  Use module D32 for ammeter A, and module D34-3 for wattmeter W.  The wattmeter W consists of an ammeter and a voltmeter; be sure to connect those appropriately.

The specifications of the DJ11 transformer are:

PN = 77 V·A

U1N/U2N = 220/55 V

I1N/I2N = 0.35/1.4 A

1) Select appropriate ranges for all meters, and turn the control knob of autotransformer counter

clockwise (CCW) to the end, setting the output voltage to zero (0 volts).

2) Switch on the main power with the key, press the Start button, then turn the autotransformer knob for U0  = 1.2UN.  Measure several sets of U0, I0, P0, UAX while decreasing the regulated voltage from 1.2UN to 0.3UN, recording your results in Table 1.  Be sure to measure U = UN.

3) When finished measurements, press the Stop button, and switch off the main power with the

key.  Disassemble your circuit, removing all cables.

5.2 Short circuit test

1) Connect the circuit as per Figure 2.  The HV winding is connected to the power supply, while the LV winding has the short circuit.  An additional ammeter can be inserted in the path of the short

circuit as optional/advanced work.

2) Select appropriate ranges for all meters, and turn the control knob of autotransformer counter clockwise (CCW) to the end, setting the output voltage to zero (0 volts).

3) Switch on the main power with the key, press the Start button, then turn the autotransformer knob to get IK  = 0.2 IN  on ammeter A.   Measure several sets of UK,   IK,   PK  while increasing the regulated voltage from the value for 0.2 IN  to 1.1 IN,  recording your results in Table 2.   Be sure to measure IK = IN.  Measure Ishort  as optional/advanced work with each set, if of interest.

4) When finished measurements, press the Stop button, and switch off the main power with the

key.  Disassemble your circuit, removing all cables.  Return the cables to the drawer.

Note: Due to the high currents during the short circuit test, the equipment can suffer heating effects which biases results.  It is advisable to make measurements as quickly as possible, and it is acceptable

to only switch on the power during measurements using the Start – Stop buttons.

Comment on your graphs and results!!!

6.5 Conclusion

Briefly describe the experiment as you undertook it, the major findings, any errors or difficulties

that you found, and comment on the relevance to your study.

6.6 Prelab

Give answers to the Prelab questions.

6.7 References

List any textbooks or other reference material you referred to in your write-up.

7. Assessment

Your individual formal report for this experiment should be submitted before the deadline. This report is worth 15% of module CAN102.