AReS

PART1R, L, C Circuit

Experiment 17 :Characteristic of Transformer

Theory

This is a transformer to change single phase AC voltage, and is composed of a core and high and low voltage coils wound to the core. This is used to supply single phase power and sometimes to supply 3 phase power.

A. Principle of Transformer

Faraday’s Law: The size of induced electromotive force changes according to the number of flux lines that cut the coil and the changing speed.

$e _{1} =L {DELTA phi } over {DELTA t}$

Lenz’s Law: The direction of induced electromotive force occurs in direction of deterring the electromotive force.

$e _{2} =L {DELTA phi } over {DELTA t}$

Ampere’s Right-handed Screw Rule: When the current flow through the coil, the magnetic flux occurs in direction of progress of the screw.

B. Induced Electromotive Force

When v₁ = √ 2 V₁ sin ωt[V] is applied to primary terminal, that is, source side, alternate magnetic flux Φ[ωb] occurs among the core, and at the secondary coil which is interlinkaged to this magnetic flux, the induced electromotive force occurs, which is caused by electromagnetic induction and which is proportional to the number of coil.

$e _{1} = {2 pi } over {sqrt {2}} fn _{1} phi =4.44fn _{1} phi$

V₁ : primary terminal voltage (source side)
V₂: secondary terminal voltage (load side)
e₁ : primary electromotive force (self-induced electromotive force)
e₂ : secondary electromotive force (mutual induced electromotive force)
n₁ : primary coil number
n₂ : secondary coil number
Φ : alternate magnetic flux

$e _{2} = {2 pi } over {sqrt {2}} fn _{2} phi =4.44fn _{2} phi$

Voltage Ratio(Turn Ratio) :
전압비= {1차`전압} over {2차`전압}

$a= {V _{1}} over {V _{2}} = {n _{1}} over {n _{2}} (권수비)$

C. Type of Transformer

Core type: the coil is arranged concentrically at both core
Shell type: high/low voltage coils are arranged in turn at inner side of core
Wound core type: this is made by winding silicon steel strip of cold rolling

fig1-27

Fig. 1-27Basic Circuit of Transformer

D. Rating of Transformer

Rated capacity: this is the product of rated secondary voltage and rated secondary current under rated frequency. The unit is [VA], [KVA].
Rated voltage: this is the terminal voltage of secondary coil recorded on the rating plate.
Rated Current: rated secondary current means the value produced by dividing rated capacity with rated secondary voltage.

Experiment Process

fig1-28

Fig. 1-28Transformer Measurement

1. In M01 module, connect as in fig.1-28 using Block g.

2. Measure the resistance value of primary and secondary sides of T1 using digital multimeter. The primary side is the left side(4-5), and the secondary side the right side(1-3). Measure the resistance value of upper parts and lower parts with the middle tap of secondary side as center and record the result in the relevant column of table 1-17.

3. Set up the output wave form of function generator as sine wave, the output frequency as 10kHz, and the output voltage as 20Vpp and connect to the primary side, and measure each voltage of the secondary side and record the result in the relevant column of table 1-17.

tab1

Experiment 1-17.1 In M01, compose a circuit as in fig.1-28.

1.Connection(M01 Module)

1.Connect the measuring module(ARES-EI-M01) to the platform.

2.Power Connection

In M01 module, connect between A+ terminal of Function Generator and terminal 4 of T1 of Block g with red line, and between A- terminal and terminal 5 of T1 with black line.

3.Measuring Instrument Connection

Voltmeter Connection

V1 Measurement: Connect between A+ terminal of Signal Input CH A on front panel and terminal 1 of T1 of Block g with red line, and between A- terminal and terminal 2 of T1 with black line.

V2 Measurement: Connect between B+ terminal of Signal Input CH B on front panel and terminal 2 of T1 of Block g with red line, and between B- terminal and terminal 3 of T1 with black line.

Vt Measurement: Connect between High terminal of Multimeter on front panel and terminal 1 of T1 of Block g with red line, and between Low terminal and terminal 3 of T1 with black line.

2.Wiring Diagram

flash

3.Measurement

<Resistance Measurement>
1VR1 Resistance Measurement
Connect between High terminal of multimeter and terminal 4 of Block g with red line, and connect between Low terminal and terminal 5.

When you choose dmm at left menu of Touch LCD panel, Digital Multimeter window appears, and if you click ohm , the resistance value is indicated.

Measure the resistance value between terminal 1-3, 1-2, 2-3 and record the result in table 1-17.

After the measurement, make a connection as in [Experiment Process].

<Voltage Measurement>
1Choose analog output at left menu of front panel.
In Function Generator window, set up Amplitude as 20vpp , Frequency as 10k , Signal as sine and click on to output 10KHz 20Vp-p.
2Click analog input at left menu of Touch LCD panel, then Oscilloscope window appears, then choose Volt & Ampere Meter tab and click voltage, ac, rms at CH A, and then the voltage value is indicated.
Here, CH A is V1, and CH B is V2 value, so record this value in the relevant column of table 1-17.
3If you click dmm at left menu of Touch LCD panel and click acv , Vt voltage value is indicated. Record the result in the relevant column of table 1-17.
4Input Voltage Measurement
Connect between High terminal of multimeter on front panel and terminal 1 of T1 of Block g with red line, and connect between Low terminal and terminal 3 of T1 with black line.

If you click dmm at left menu of Touch LCD panel and click acv , Vt voltage value is indicated. Record the result in the relevant column of table 1-17.
5Apply the input to the secondary side and measure the output at the primary side
In M01 module, connect between A+ terminal of Function Generator and terminal 1 of T1 of Block g with red line, and between A- terminal and terminal 3 of T1 with black line.
<Voltmeter Connection>

Input Voltage Measurement: Connect between A+ terminal of Signal Input CH A on front panel and terminal 1 of T1 of Block g with red line, and between A- terminal and terminal 3 of T1 with black line.

Output Voltage Measurement: Connect between B+ terminal of Signal Input CH B on front panel and terminal 4 of T1 of Block g with red line, and between B- terminal and terminal 5 of T1 with black line.

Click analog input at left menu of Touch LCD panel, then Oscilloscope window appears, then choose Volt & Ampere Meter tab and click voltage, ac, rms at CH A, and then the voltage value is indicated.

Here, CH A is the input voltage and CH B the output voltage. Record this value in the relevant column of table 1-17.

Wiring Diagram

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6After the measurement, click on red at Analog Output to cut off the output.