Transformer Laboratory Exercise Setup Connect the test transformer as a single-p

Question

Transformer Laboratory Exercise

Setup

Connect the test transformer as a single-phase transformer to a variable voltage supply.

Open circuit characteristic

Record the open-circuit characteristic with 10 points from zero or minimum voltage to rated voltage. You can allow yourself to exceed rated voltage by 25%. Record voltage, current, power and the shape of the current using oscilloscope. Describe why the characteristic is linear/non-linear and the current is sinusoidal/non-sinusoidal.

Estimate the equivalent circuit parameters of the transformer: R1, R2’, X1, X2’, Xm and Rc. State all assumptions.

Values obtained

rated current in secondary winding: 5,2 A

We connected everything to secondary instead of primary

V I rms P 44.3 19,4 mA 88,1 36,13 mA 133,6 175 mA 43,7 176,2 555 mA 76 215,2 5.1 A 263 MTX Oscilloscope Trace CH1: 50.0mV-AC CH2: 10.0N-AC. couplings 5,00ms/div tomorrow with you RUN

Explanation / Answer

As the secondary of single phase transformer is connected to variable voltage supply with primary open circuited- that means only exciting current will flow in the core of the transformer to counter the mmf introduced by variable secondary current(as source is variable).

By using the relation - IoN1 = I2N2,where N1,N2 is primary and secondary turns.I2 is secondary current and Io is exciting current.

Following that relationship suggest -

Io = I2*N2/N1 implies the linear function for output current (here exciting current only) or output current profile shall be sinusoidal.

By relation of V1/V2= N1/N2;V1 = V2*N1/N2;

Where V2 = Variable input voltage - I2*(R2+jX2);

So voltage measured will be linear function of secondary voltage(V2).

Power consumed is Io^2*Rc which is linear function.

Table associated with the question comprises open circuit test on the transformer.

Active power loss = Irms^2*Rc- for open circuit condition ...(a)

Considering rated voltage level of 215 V, where Irms = 5.1 A and P = 263 W

Using formula (a) ,Rc = 10.11 A

And V= Irms*Xm; Xm= 42.196 ohm

For other transformer parameters (R1,R2',X1,X2') we need short circuit test .We cannot make any estimation.

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