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ABSTRACT:

One of the tests performed in transformer is the open-

circuit test. This test is necessary in the determination

of the core loss of the transformer........

INTRODUCTION:

When one side of a transformer is left open-circuited

and the other side is connected to an AC source

whose voltage is the rated value, the current will be

extremely low, about 2 to 10% of the rated loadcurrent. This no-load current or the exciting current

Io has two components, one producing the normal

mutual flux, and the other taking care of the

hysteresis and eddy-current losses in the core. Sincethe current is very low, the copper loss will be

negligible. For all practical purposes, therefore, the

 power measured by the instrument under condition of

the open circuit will register the core loss.

OBJECTIVES:

To determine the amount of power lost in hysteresis

and eddy-current in the iron core of the single-phase

transformer.

MATERIALS AND EQUIPMENT USED:Transformer, Digital Power Meter, Variac, Multi-

Tester, Connecting Wires

METHODOLOGYConnect the circuit as shown in Figure1. Connect the

220 volt AC source to the variable autotransformer so

as to vary the input voltage in the circuit. Starting

from zero, gradually increase the input voltage step-

 by-step up to ten per cent above the rated voltage ofthe transformer which is in this case equal to 220-

volts. For each of the voltage variation, record the

input current, input power and voltage.:

:

The circuit diagram is reconnected for a 220/440

volts configuration. As before, the input voltage...:

:

DATA and RESULTS

Table1: Tabulated results on the OCT of

Transformer with 220:220 configuration

Voltage

Input

Vin 

Current

Input

IO 

Power

Input

PC 

Wattful

Current

Ih+e 

Wattless

Current

Im 

Table2: Tabulated results on the OCT of

Transformer with 220:440 configuration

Voltage

Input

Vin 

Current

Input

IO 

Power

Input

PC 

Wattful

Current

Ih+e 

Wattless

Current

Im 

:

:

:

University of San Carlos

Department of Electrical and Electronics EngineeringEE421NL-EE Machines 1 Lab

7:30-10:30, Monday, 2nd Semester AY2015-16

Open Circuit Test of Transformer

Rafael D. Seva, Jr .

CIRCUIT DIAGRAM: 

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SAMPLE CALCULATIONS:

[1] Ih+e = Pc/Vin

[2] Im = √Io2 − Ih+e2  

::

:

ANSWERS to QUESTIONS:

1. 

Plot, with applied voltage as abscissa, the values

of the input watts, and total current Io. Taking the

magnetizing current Im versus the input voltage.

2.  Draw a typical vector diagram of the transformer

on open-circuit test showing the phase

relationship between flux, primary voltage, no-

load current, and the wattful and wattless

components of the current Io.3.  Explain the primary and secondary winding

connection.

GRAPHS

It can be seen from Figure1 that when the inputvoltage is varied, the input current varies

exponentially. It could be deduced that when thevoltage is increased beyond its rated value, the

increase in the input current is very dramatic. This isan indication that a transformer should not be

operated beyond its rated voltage because by doing

so the ........

[There should be an analysis of every graphs

 presented ]

:

:

:

:

CONCLUSION:

[Must be based upon (1) Objective, (2) Graphs]

REFERENCES:

[ Books, Articles, PDF files, internet web-site, etc]

REFLECTION:

[ How the experiment/lab activity affected you

 personally in preparation for your career, etc....

 Maximum of 5 sentences only .]

CERTIFICATION:I hereby certify that this report is ........

 ________________________

Rafael D. Seva, Jr.[ Signature above name ]

Figure1: Graph of Vin and Iin