Power Transformers - Factory Acceptance Tests (FAT)

Transformer Operation, Maintenance,
Diagnosis & Testing
XRS Consulting Engineers and Project
Managers 1
Section 1 XRS Consulting Engineers and Project
Managers 1
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Appendix XRS Consulting Engineers and Project
Managers 1
Section 9
Section 9
Factory Acceptance Tests (FAT)

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Section 9
Test Classification and Conditions
Testing procedures and the acceptance criteria must
follow what is stated at the relevant IEC standards.
Tests must be performed at an ambient temperature
between 10°C and 40°C and with cooling water (if
applicable) at a temperature up to 25°C.
When tests results have to be referred to a reference
temperature, for oil-immerse transformers a
temperature of 75°C must be considered, and for dry
type transformers a temperature above 30°K of those
shown on column 3 of the below table must be
considered.
This document is a partial preview. Full document download can be found on Flevy:
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Section 9
Test Classification and Conditions
According to IEC standard 60076 FAT for oil-immerse
transformers are classified into three categories:
Type tests
Routine tests
Special testsThis document is a partial preview. Full document download can be found on Flevy:

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Section 9
Routine Tests
Routine tests are performed at each transformer, and in
accordance with IEC standard 60076 they comprise:
Measurement of no-load harmonics.
Measurement of impedance voltage drop and resistive
losses.
Measurement of ratio and verification of vector group
(polarity).
Measurement of no-load current and iron (core) losses.
Individual dielectric tests.
Tap changer test (if applicable)

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Section 9
Special Tests
These tests, which must be agreed between the client
and the manufacturer, are also defined at IEC standard
60076, and are:
Special dielectric tests
Determination of the capacitances between windings
and between each winding and the earth.
Determination of the characteristics of zero sequence
voltages transmission.
Measurement of zero sequence impedances.
Short-circuit withstand.

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Section 9
Bushings
Transformer’s bushings failure may be one the main
reasons for a transformer fault.
In transformers with high rated power used in HV and
EHV installations it is recommended to test the bushings
for a rated voltage above 1 kV, in accordance with the
type of bushings and the voltage level, following what is
stated at IEC standard 60137.

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Section 9
Dry Transformers
According to IEC standard 60726 dry type transformers
must be subjected to the following tests:
Measurement of winding resistance (routine test).
Measurement of voltage ratio and check of voltage
relationship (routine test).
Measurement of impedance voltage (principal taping),
short circuit impedance and load loss (routine test).
Measurement of no-load loss and current (routine
test).
Separate-source voltage withstand test (routine test).

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Section 9
Oil Testing
Tests of oil prior to the first fill of the transformer have
the aim to verify the following properties:
Chemical
Physical
ElectricalThis document is a partial preview. Full document download can be found on Flevy:

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Section 9
Oil Testing
Interfacial tension (IFT)
Interfacial tension test is used by to determine the
interfacial tension between the oil sample and distilled
water, with the objective to find any contamination in
the oil.This document is a partial preview. Full document download can be found on Flevy:

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Section 9
Oil Testing
Viscosity
Viscosity that is the resistance of oil to flow, determines
the rate of cooling, and varies with the temperature. A
high viscosity as an obvious disadvantage because of the
sluggish flow through small apertures, which is, entails.
Good oil should have less viscosity so that it offers less
resistance to flow thereby not affecting the cooling of
transformer adversely.

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Section 9
Oil Testing
If oil is exposed to very high temperatures under fault
conditions for long duration lower molecular weight
hydrocarbons may be produced.
These low molecular weight hydrocarbons cause a
lowering in the flash point of oil.This document is a partial preview. Full document download can be found on Flevy:

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Section 9
Oil Testing
Moisture
The existence of moisture in the oil decreases
dielectric strength and IFT, degrades cellulose and is
a failure risk.

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Section 9
Oil Testing
Power factor
The power factor of insulating oil is the ratio of active
power to apparent power.
In a transformer, a high power factor is an indication
of significant dielectric loss in the insulating oil,
usually as a result of polar contaminants such as
water, oxidized oil and cellulose paper degradation.

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Section 9
End of this
Section

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