basic tests for transformers

7/29/2019 Basic Tests for Transformers

1/4

POWER ELECTRONICS

BASIC TESTS FOR TRANSFORMERS

Mario Alejandro Chaparro

Hoosman Monroy

OBJECTIVES:

Understand the operation of a

transformer and introduce in the technical

language used in the rules.

Based on the Colombian technicalregulations do various tests required for

optimal performance and characteristics

of transformers.

As the NTC 380 tests carried out to

demonstrate compliance with specific

requirements that are not covered by

routine tests.

Given the NTC 375: 2000 take the

measurement of the resistance of thewindings in transformers used in practice.

Using the provisions of NTC 471, check

the transformer turns ratio.

I. THEORETICAL

FRAMEWORK.

a. TRANSFORMER

The transformer is an electrical device

using the physical properties of

electromagnetic induction is able to raise

and lower the voltage, convert the

frequency (Hz), balanced or unbalanced

circuits as needed and the specific case.

Transporting electricity from power

generating electricity to domestic

residences, businesses and industries.

Said device is also electrical circuits

capable of isolating circuitry AC current.

b. Measure the resistance of the

windings. NTC375

According to the NTC 375.

Measuring the resistance of the

transformer windings, is used inter alia, to

check the connections and determine if

an open circuit condition or the existence

of a high resistance connection

conductors arranged in parallel.

Applicable to distribution transformers

and power.

This trial is of fundamental importance to

Calculate the losses ^ 2 * R

Control and field maintenance.

Comparison of phases.

Detect problems circuital partial short.


2/4

POWER ELECTRONICS

Check the operation of the tap changer

perfect.

METHOD.

Method voltage ohmmeter or bridge:

The instructions are performed following

the manual instructions in order to select

the most appropriate ranges. Wheatstone

bridge, wherein R, R1 and RX R2son

known resistances and represents the

winding resistance which the

measurement is made.

The resistance of each winding, the

terminals between which is measured

and the temperature of the windings to be

recorded. The measurement is done with

direct current. All resistance

measurements inductive effects should

be minimized.

c. Measurement of the ratio, and

polarity verification phase

relationship. NTC 471

Voltmeter Method

It consists in applying a sinusoidal

alternating voltage of known value to the

higher voltage winding, measuring this

voltage and which appears in the other

winding by means of appropriate

transformers and voltmeters. The ratio ofthe two voltages measured will be the

transformation ratio. The voltmeter

should read simultaneously. It should be

a second reading voltmeters exchange,

will take the average of the two readings

to compensate for instrument error.

Transformer Method pattern

Consists in comparing the voltage of the

transformer under test with the calibrationpattern of a transformer, whose

relationship is adjustable in small steps.

With this method, the transformer and the

test pattern are connected in parallel and

voltage is applied to its high-voltage

windings, while the lower windings are

connected to a sensitive detector which

takes zero indication transformer ratio

adjusting pattern . At this point, the

relationship of both transformers are

equal.

d. PROCEDURE FOR THE

DETERMINATION OF NO LOAD

LOSSES


3/4

POWER ELECTRONICS

The maximum flux density corresponds

to the absolute average value of the

voltage (NAM effective value rms) and

therefore, if the average value of the

voltage is set to quesea equal to the

average value of the sinusoidal wavevoltage and maintains the desired

appropriate frequency, the hysteresis

loss should be corresponding to the

desired sinusoidal waveform.

II. Calculations and operations

Turns ratio

Connecting a laboratory autotransformer

(variac) to the transformer primary, a

voltmeter measuring the voltage at the

primary and secondary induced voltage,

as shown in the circuit of Figure.

Turns ratio of the transformer

a

N

V1 1

N2 V2

V1 V2

119.8 29.9

Table 1. Measurements of the voltage

ratio.

As the turns ratio of the primary to the

secondary of the transformer

corresponds to 4

Number of turns of the primary

The procedure consists of applying the

nominal voltage corresponding to the

winding for measuring the voltage

induced in one or several turns of wire

previously wound on the transformer

windings. The ratio of voltage and power

(s) return (s) sets the number of turns of

winding. This test rolled

four turns through the window of the

transformer.

Number of turns of the primary

V1 V4vueltas

119.8 0.8858

Table 2. Measuring the number of

primary turns.

IDENTIFICATION OF THE POLARITY

To perform this test is fed to the

transformer primary with nominal voltage,

previously connected with one terminal of

the primary side as shown in Figure 10.

Connect a voltmeter between the primary

and secondary terminals that are

available. If the reading obtained is the


4/4

POWER ELECTRONICS

remainder of the primary voltage and

secondary marks are placed on the

terminals where the voltmeter is

connected. If the reading is the sum, the

polarity must be one in the terminal

where the voltmeter and the other in theterminal where he joined the primary and

the secondary.

Identification of the polarity markings.

WINDING RESISTANCES

Measure the resistance of each winding,

previously with a multimeter to be a

reference to its value. Then applied volt-

ammeter method feeding a direct current

source such that the winding rated

current flow. Applying Ohm's law relate

measurements voltmeter and ammeter

and determined resistance. This process

must be performed for both windings.

V I

2.5708 V 0.2588 A

TEST SHORTED

This test is performed at rated current,

connect the low side short and gradually

increased from zero the voltage fed to the

primary. In this test, the core losses are

neglected because the voltage is too low.

Connecting the short circuit test.

V IRetraso de corriente

5.528 V 0.255 A 2.1 ms

Table. Measurements of short-circuit

proof.

CONCLUSIONS

En el presente informe se presenta en forma

integral las etapas de medicin de un

transformador de pequea capacidad,

adems de establecer las pruebas fsicas y

elctricas estndar de los transformadores.

REFERENCES

[1] Mark N. Horesntein. Microelectronics

circuit and processors. 2 edition p. 125 to

130

[2]

http://www.labc.usb.ve/gfernandez/Ec_38

81/webs/Enero_Marzo_2006/diagrama_b

loque.pdf

basic tests for transformers

Documents