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SUBSTATION COMMISSIONING COURSE
SUBSTATION COMMISSIONING
COURSE
MODULE SIX
COMMISSIONING
DRY-TYPE POWER
TRANSFORMERS
Written by:
Raymond Lee, Technical Trainer
Copyright ©2011
Electrical Industry Training Centre of Alberta
4234 – 93 Street
Edmonton, Alberta, Canada
Phone: (780) 462-5729
Fax: (780) 437-0248
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TABLE OF CONTENT
Headings Page
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Introduction
This module will detail the requirements for performing electrical and mechanical
tests on the MV dry-type power transformers. The purpose of the tests, testing
requirements and procedures are presented. Future module will be written on the
liquid-immersed transformers.
This module will introduce the NETA acceptance testing procedures for
transformer comprising of mechanical and visual inspections, electrical testing and
test data analysis. General guidelines for acceptance testing will be presented.
When equipment specific instructions are required the equipment
manufacturers/manuals should be consulted.
An understanding on the theory of operations, functions, types and ratings are
discussed and this information will be useful when performing acceptance tests.
The discussion will be applicable to the substation medium voltage class power
transformers. Generation step-up transformers and overhead type distribution
transformers are excluded from this discussion.
Objectives
By the end of this module the participants will have the basic skills to perform
acceptance testing on dry-type transformers, conduct visual and mechanical
inspections, perform insulation resistance tests, polarizing index test, applied
voltage tests, winding resistance tests, ratio test, polarity test, power factor test,
capacitance and dissipation test and completing the inspection / test forms andconducting an assessment of the test data.
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1. North American Dry-type Transformer Standards
Power transformers are used to convert and/or isolate power from one voltage level
to other voltage level(s). Power transformers are classified as having a rating
greater that 501 kVA for three-phase transformer and larger than 168 kVA for single-phase transformer as per NETA standards and design for step-down
operation.
1.1 Canadian Standards
Dry-type transformers for use in Canada must comply with Canadian standards.
The CSA standards contain information on applications and testing requirements.
These standards include but are not limited to:
• CAN/CSA-C2 Single Phase and Three Phase Distribution
Transformers• CAN/CSA-C88 Power transformers and Reactors
• CAN/CSA-C227.3 Low Profile, Single Phase, Dead Front Pad-mounted
Distribution Transformers
• CAN/CSA-C227.4 Three Phase, Dead Front Pad Mounted, Distribution
Transformers
• CSA C9-02 Dry-Type Transformer
• CSA C802.2-06 Minimum Efficiency Values for Dry-type
Transformers
CSA C9-02 is the predominant standard for the design requirements of dry-type
transformers and reference the IEEE C57.12.91 for the testing requirement that is
not specifically noted within the document and also reference IEEE C57.96 for the
loading guidelines.
When transformers are not made to Canadian standards, the manufacturer must
declare that the unit has the equivalent safety performance as one made to
Canadian standards.
The Canadian CAN/CSA-C802.2 standard is an efficiency standard for dry-type
transformers that imposes maximum losses for dry-type single-phase and three-
phase self-contained units or components of larger assemblies, 60 Hz, ANN, rated
15 to 833 kVA for single phase and 15 to 7500 kVA for three phase.
CAN/CSA-802.1 covers the efficiency requirements for liquid filled transformers
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Testing based on CSA standards.
Liquid filed transformers shall be tested as per IEEE C57.12.90 as specified in
CAN/CSA C88-M90 for Power Transformers and Reactors.
Dry type transformers shall be tested as per IEEE C57.12.91 as specified in CSA
C9-2002 for Dry Type Transformer.
1.2 US Standards
The ANSI/IEEE standards which contain information on design and testing
requirements include but are not limited to:
• IEEE C57.12.00 Standard General Requirements for Liquid- Immerse
Distribution, Power and Regulating Transformers
• IEEE C57.12.01 Standard General requirements for Dry-Type Distributionand Power Transformers Including Those with Solid-
cast and/or Resin Encapsulated Windings
• IEEE C57.12.90 Standard Test Code for Liquid-Immersed Distribution,
Power and Regulating Transformers
• IEEE C57.12.91 Standard Test Code for Dry-Type Distribution and Power
Transformers
NEMA standard publication TR1-2000 for Transformers, Regulators and Reactors
has adopted the majority of the ANSI/IEEE C57 families of transformer standardswhich then becomes part of the NEMA standard.
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2. Nameplate Data
Industry standards require critical information to be plainly marked, in a permanent
manner on the nameplate(s).
Some of the more important information are:
• Manufacturer’s name, trade name or other recognized symbols
of identification
• Serial, catalogue, style, model or other identifying designation
• Winding temperature class
• Rated temperature rise in degree Celcius
• Cooling classification
• Rated high and low voltages
• Tap voltages either as actual voltages or as a percentage of the
rated voltages
• Rated Frequency
• Rated kVA capacity
• Number of phases unless clearly indicated on the connection
diagram
• Percent impedance at actual rated ambient temperature plus
rated temperature rise in degrees Celcius
• Weight
• Connection diagram or equivalent information
• Vector diagram for polyphase transformers
• Terminal markings
• Enclosure number type if other then general purpose type
2.1 Serial number
The serial number is required any time the manufacturer must be contacted for
information or parts. It should be recorded on all transformer inspections and tests
record.
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2.2 Winding Temperature Class
There are five temperature classes which indicates the maximum permissible
temperature rise on the windings at rated voltage and kVA output. These are based
on rated ambient temperature between -30 ºC to 30 ºC and that the units be
installed at an elevation above sea level and below 1000 meters in elevation.
Table 1: Transformer Winding Insulation System, °C
Temperature class Average winding rise
measured by rise of
resistance *
Winding hottest-spot
rise
Class 130 75 90
Class 150 90 110
Class 180 115 140
Class 200 130 160
Class 220 150 180* Higher average winding temperature rises by resistance may be permitted if the manufacturer
provides thermal-design test data acceptable to the purchaser supporting that the temperature
limits of the insulation are not exceeded.
Note: The average winding rise and hottest spot are based on an average daily ambient
temperature of 30°C with a maximum ambient of 40 °C at an elevation not exceeding 1000m and
above sea level.
2.3 Temperature rise
Temperature rise is the maximum allowable temperature difference between the
winding temperature at the rated ambient temperature at the rated voltage and kVAoutput that the transformer can operate. Temperature rise limits are also specified
to other parts of the transformer.
Transformer temperature rise limits shall not be exceeded under the following
conditions:
• For transformers with primary taps, delivery rated kVA at rated output
voltage with the primary energized on the lowest tap,
• For any tap delivery rated output kVA at a lagging power factor of 80% or
higher, with 105% output voltage,
• Energized at 110% output voltage, at no-load,
• Operating with approximately sinusoidal load current with a harmonic
content less the .05 per unit.
Metallic parts in contact or adjacent to the insulation shall not attain a temperature
in excess of the figures in column 1 of Table 1.
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Exposed metallic parts shall not exceed a temperature rise of 65 °C.
Field terminations shall not exceed a temperature rise of 55 °C.
2.4 kVA Rating
Then power rating of a transformer is the output that can be delivered for the time
specified, at rated secondary voltage and frequency without exceeding the
temperature rise limits for the transformer design.
Whenever a transformer is provided with taps and connected on taps above or
below rated voltage, the capacity shall be the full rated kVA of the transformer.
Table 2: Standard kVA Ratings for Dry-Type Transformers
Single phase Three-phase Single phase Three-phase2 6 333 1000
3 9 500 1500
5 15 667 2000
10 30 833 2500
15 45 1000 3000
25 75 1250 3750
37 112 1667 5000
50 150 2500 7500
75 225 3333 0pen-ended100 300 5000
----- 450 open-ended
167 500
250 750
Preferred self-cooled kVA capacities are shown in Table 2.
Preferred forced-cooled ratings are 133% of the self-cooled ratings.
Full voltage taps are full-capacity taps and provisioned with two 2.5% taps above
and below rated voltage at rated kVA. Exceptions are for low voltage transformers
and units where the purchaser has specified the tap ratings.
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2.5 Voltage Rating
The voltage rating is the operating voltage for the windings and associated tap
positions.
Table 3: Preferred Voltage Ratings for Dry-type TransformersPrimary Voltage Secondary Voltage
Single-phase Three-phase Single-phase Three-phase
120 / 240 480 120 / 240 208 Y / 120
480 600 240 / 480 480 Y / 277
2,400 2,400 480 600 Y / 347
4,160 4,160 600 4160 Y / 2400
7,200 12,470 2,400
8,000 13,860 4,160
12,470 24,940
13,860 27,600
14,400 34,500
16,000 46,000
20,000
24,900
34,500
46,000 Notes:
1) If a three-phase transformer is to be applied in a wye-wye configuration, the supplier shall be
so advised at the time of ordering.2) If a three-phase transformer is manufactured for application in a wye-delta configuration, the
supplier shall include a precautionary note on the transformer: “DO NOT CONNECT
PRIMARY SIDE TO SYSTEM NEUTRAL OR TO GROUND”.3) Single-phase transformers with a voltage class of 2.5 kV and below shall be insulated for
possible use within a three-phase wye-connected bank.
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2.6 Cooling Class
Cooling classifications are identified by three-letter designations according to the
cooling characteristics.
The first letter designates the cooling medium surrounding the winding:
• A – for air
• G – for gas other than air
The second letter designates the method of circulating the cooling medium through
the winding:
• N – for natural convection
• F – for forced circulation
The third letter designates the manner of removing the heat from the cooling
medium:
Ventilated type:
• N – for natural circulation of outside air that is in contact with the windings
• F – for forced circulation of outside air that is in contact with the windings
Enclosed type:
• C – for natural convection of outside air that is not in contact with the
winding
• P – for forced circulation of outside air that is in not in contact with thewindings
Cooling class examples:
ANN: Air-filled natural convection with open-ventilated enclosure through
which the ambient air readily enters and leaves the enclosure
GNC: Gas-filled unit cooled by natural convection of the gas within the
enclosure and by natural convection of ambient air outside the enclosure
AFN: Air-filled cooled by forced circulation of the air within the open-
ventilated enclosure and by natural convection of ambient air outside the
enclosure
GNP: gas-filled unit cooled by natural convection of the gas within the
enclosure and forced flow of ambient air over the outside of the enclosure
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ANC / ANP: Air-filled unit cooled by natural convection of the air within the
enclosure and by natural convection of ambient air outside the enclosure and
emergency operation at higher kVA cooled by natural convection of the air
within the enclosure and by forced flow of ambient air over the outside of the
enclosure
2.7 Polarity Markings
Polarity is a designation of the relative instantaneous directions of current in the
leads of a transformer. The primary and secondary leads are said to have the same
polarity on each half cycle. The current enters an indentified or marked primary
lead and leaves the similarly identified or marked secondary lead in the same
direction as if the two leads formed a continuous circuit.
The relative lead polarities are indicated by identification marks on the primaryand secondary leads of like polarity or by other appropriate identification.
All single-phase transformers are of subtractive polarity unless otherwise specified:
2.8 Winding Designations
The windings are distinguished from one another as follows:
• The high voltage winding designated as HV or H and the low voltage
winding designated as LV or X, for a two winding transformer
•
Transformers with more than two winding shall have designations as H, X ,Y and Z
• The highest voltage winding are designated as HV or H
• The other windings are designated in order of decreasing voltage as X, Y
and Z
• If two or more windings have the same voltage rating and different kVA, the
higher kVA winding are designated in order of sequence of X, Y and Z
• If two or more windings have the same kVA and voltage rating, the
designation of the windings can be arbitrarily assigned
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2.9 Terminal markings
External terminals are identified from one another with a capital letter followed by
a subscript number.
For a three-phase 2 winding transformer, the terminals of the H windings would be
marked H1, H2 and H3 and the terminals of the X winding would be marked X1, X2
and X3.
The highest voltage winding are identified in phase sequence order by H1, H2, H3
and the other winding in order of voltage rating by X1, X2, X3 and Y1, Y2, Y3, etc.
The neutral terminals of a three-phase transformer are marked by the subscript 0
(e.g. H0, X0, etc). A neutral terminal common to two or more windings is marked
with the combination of the appropriate winding letters followed by the subscript 0
(e.g. H0X0 as for autotransformers).
The grounded terminal of a two-terminal transformer is designated with the
subscript 2 and the undgrounded terminal is designated with the subscript 1.
2.10 Vector Diagrams
Vector diagram shows the angular displacement between phases as shown by the
transformer terminal markings and is related to its winding diagram.
The vector lines of the diagram represent induced voltages using the recognized
counter-clockwise direction of rotation for phase sequence. The vector
representing any phase voltage of a given winding is drawn parallel to the other
phase voltages of the same winding that it is associated with.
2.11 Angular displacement between voltages of windings for three-phase
transformers
The angular displacement between high-voltage and low-voltage phase voltages of
three-phase transformers with Δ–Δ or Y–Y connections is 0°.
The angular displacement between high-voltage and low-voltage phase voltages of three-phase transformers with Y–Δ or Δ–Y connections is 30°, with the low
voltage lagging the high voltage by 30° (or high voltage leads the low voltage by
30°). Refer to Figure 1.
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The angular displacement of polyphase transformers is the time angle, expressed in
degrees, between the line-to-neutral voltage terminal (H1) and the line-to-neutral
voltage of the corresponding identified low-voltage terminal (X1).
Figure 1 - Phase relation of terminal designation for three-phase
transformers.
Winding Diagram
The winding diagram shows the internal winding connections for the various tap
positions and external bushing connection. Winding diagrams are normally
incorporated into the vector diagram.
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2.12 Percent Impedance (%Z)
The percent impedance is the percent voltage required to circulate rated current
flow through one winding when another winding is short-circuited at the rated
voltage tap at rated frequency. %Z is related to the short circuit capacity of the
transformer during short circuit conditions.
For a two winding transformer with a 5% impedance, it would require 5% input
voltage applied on the high voltage winding to draw 100% rated current on the
secondary winding when the secondary winding is short-circuited. If 100% rated
voltage is applied to the high voltage winding, approximately 20X rated current
would flow in the secondary winding when the secondary winding is short-
circuited.
Table: 4 Impedance Levels
Based kVA Minimum Impedance, %0 – 150 Manufacturer’s standard
151 – 300 4
301 – 600 5
601 – 2,500 6
2,501 – 5,000 6.5
5,001 – 7,500 7.5
7,501 – 10,000 8.5
Above 10,000 9.5
Notes:a. The impedance of a two-winding transformer shall not vary from the guaranteed value
by more that ± 7.5%
b. The impedance of a transformer having three or more windings or having zig-zag windings shall not vary from the guaranteed value by more than ± 10%
c. The impedance of an auto-transformer shall not vary from the guaranteed value by more
than ± 10%d. The difference of impedances between transformers of the same design shall not exceed
10% of the guaranteed values
e. Differences of impedance between auto-transformers of the same design shall not exceed
10% of the guaranteed values
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2.13 Basic Impulse Insulation Level
The line terminals of a winding are assigned a basic lightning impulse insulation
level (BIL) to indicate the factory dielectric tests that these terminals are capable of
withstanding.
The impulse level is the crest value of the impulse voltage during a lightning strike
that the transformer is required to withstand without failure. The impulse level is a
momentary withstand rating. The BIL ratings are shown in Table 5
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Table 5: Insulation Voltage Class and Dielectric Tests for Dry-type Transformer*
Insulation Voltage
Class, kV
Nominal Voltage Applied Potential
Test, kV
BIL, full and
chopped-wave, kV
crest
Chopped-wave
minimum time to
flashover, µs
1.2 1,200 and less 4 ----- -----
2.5 2,400 10 20 1.0
5.0 4,160/2,4004,160
4,800
12 30 1.0
8.7 8,320Y/4,8007,200
8,320
19 45 1.25
15.0 12,470/7,200
13,860Y/8,000
12,470
13,860
31 60 1.5
18.0 24,940 GrdY/14,400
27,600 GrdY/16,000
34 95 1.6
25.0 35,500 GrdY/19,900
24,940Y/14,400
24,94027,600Y/16,000
27,600
40 125 2.0
34.5 34,50034,500Y/19,900
46,000 GrdY/26,600
50 150 2.25
* Higher voltage rating is available when specified Notes:
1) Applied potential test levels are for application to windings that do not have reduced neutral terminal insulation.2) Equipment having a voltage rating between listed values shall be tested at the higher values.
3) Transformer terminals that may be subjected to transient overvoltages exceeding 80% of their BIL should be protected by surgearresters.
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3. Safety Consideration
3.1 High Voltage Safety
Many of the tests involve the use of high voltage test equipment; testing should be performed by qualified personnel familiar with the test set operations and the
hazards associated with the tests.
Refer to Module 2 for Safety Working Practices and Guidelines.
Refer to IEEE Standard 510 – 1983, Recommended Practice for Safety in High
Voltage & High Power Testing.
3.2 Electrostatic Charge
After any high potential voltage is removed, an electrical charge may be retained by the insulating system. Failure to discharge the residual electrostatic charge
could result in an electrical shock. Always ground the last test point(s) before
moving the test leads.
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4.1 Insulation Resistance Test
The insulation resistance test is of value for future comparison and also for
determining if the transformer is to be subjected to the applied voltage test. The
winding insulation resistance test is a DC high voltage test used to determine the
dryness of winding insulation system. The test measures the insulation resistance
from individual windings to ground and/or between individual windings.
The measurement values are subject to wide variation in design, temperature,
dryness and cleanliness of the parts. This makes it difficult to set minimum
acceptable insulation resistance values that are realistic for wide variety of
insulation systems that are in use and performing satisfactorily. If a transformer is
known to be wet or if it has been subjected to unusually damp conditions, it should
be dried before the application of the applied voltage test. Low readings can
sometimes be brought up by cleaning or drying the apparatus.
The insulation resistance test should be performed at a transformer temperature as
close as possible or at 20 °C. Test conducted at other temperature should be
corrected 20°C with the use of temperature correcting factor.
The test equipment is calibrated to read in Megohm and commonly know as a HV
Megger. Typical maximum test set voltage values may be 1kV, 5kV or 15kV. The
30kV Megger is also available.
Duration of the test voltage shall be 1 minute.
In the absence of manufacture’s recommended values, the following readings may
be used. Refer to Table 6.
Table 6: Transformer Insulation Resistance Acceptance Testing
Winding Insulation Class, kV Insulation Resistance, MΩ*
1.2 600
2.5 1000
5.0 1500
8.7 200015 3000
* Normally dried transformers may be expected to have readings 5 to 10 times the above
minimum values.
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Note:
Table 6 was sourced from IEEE C57-94-1982 Recommended Practice for
Installation, Operation and Maintenance of Dry-type General Purpose Distribution
and Power Transformer. Table 6 differs from NETA Table 100.5 figures for
transformer Insulation Resistance Acceptance Testing values. There is no industry
consensus for satisfactory values.
Other references noted a general rule of thumb for acceptable insulation values at
1MΩ per 1kV of nameplate rating plus 1MΩ.
Note:
Under no condition should the test be made while the transformer is under vacuum.
Note:The significance of values of insulation resistance test requires some interpretation
depending on design, dryness and cleanliness of the insulation involved. It is
recommended that the insulation resistance values be measured during periodic
maintenance shutdown and trended. Large variation in the trended values should be
investigated for cause.
Note:
Insulation resistance may vary with applied voltage and any comparison should be
made with the same measurements at the same voltage and as close as possible to
the same equipment temperature and humidity as practically possible.
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4.1.1 Insulation Resistance Test Procedure:
1. Isolate the equipment, apply working grounds to all incoming and outgoing
cables and disconnect all incoming and outgoing cables from the transformer
bushing terminals connections. Disconnected cables should have sufficient
clearance from the switchgear terminals greater that the phase spacing
distance. Use nylon rope to hold cable away from incoming and outgoing
terminals as required.
2. Ensure the transformer tank and core is grounded.
3. Disconnect all lightning arresters, fan system, meter or low voltage control
systems that are connected to the transformer winding.
4. Short circuit all winding terminals of the same voltage level together.
5. Perform a 1 minute resistance measurements between each winding group to
the other windings and ground.
6. Remove all shorting leads after completion of all test.
Table 7: Insulation Resistance Test Connections for Two Winding Transformer
Test No. Single-phase transformer Three-phase transformer
1 High voltage winding to lowvoltage winding and ground High voltage winding to low voltagewinding and ground
2 High voltage winding to low
voltage winding
High voltage winding to low voltage
winding
3 High Voltage winding to
ground
High voltage winding to ground with
low voltage winding to guard
4 Low Voltage winding to high
voltage winding and ground
Low voltage winding to high voltage
winding and ground
5 Low voltage winding to
ground
Low voltage winding to ground and high
voltage winding to guard
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4.2 Applied-Voltage Test
The applied-voltage (high-potential dielectric withstand) test is a 60 Hz, AC high
voltage test used to verify the integrity of the insulation system between the
winding being tested to all other windings and to ground. The test is conducted at
the specified voltage level for 1 minute.
Field dielectric test are conducted at 75% of the factory voltage test levels of the
test values listed in Table 8. When field test are made on a periodic basis, it is
recommended that the test voltages be limited to 65% of factory test.
Note: If dc test equipment is used, the test voltage should not exceed the factory
rms test voltage. Test equipment should be of the full-wave bridge design
with ripple content should be less than 1%.4
4.2.1 Voltage Rate of RiseThe voltage should be brought up gradually to full value in not more than 15
seconds and held for 1 minute. It should then be gradually reduce in not more that
5 seconds.3 This is a stark contrast to the circuit breaker’s vacuum bottle integrity
test at which the voltage rate of rise is much lower where a fast rising voltage may
cause a vacuum dielectric breakdown.
3 IEEE Standard C57.12.91-2001
Test Code for Dry-type Distribution and Power Transformers
4 ANSI/IEEE C57.94-1982
Recommended Practice for Installation, Application, Operation and
Maintenance of Dry-type General Purpose Distribution and Power
Transformers
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4.2.2 Testing Guidelines
1. A winding-to-winding and winding-to-ground applied voltage test shall be made
in accordance with Table 8 on Δ and Y-connected windings when the neutral is
ungrounded. This suggests that ungrounded Y winding are fully insulated to the
line terminal values.
2. For internally solidly grounded-Y windings;
a) A line-terminal-to-ground test voltage shall be induced from another
winding. This test voltage shall be twice the operating line-terminal-to-
neutral voltage, with the neutral grounded;
b) A phase-to-phase test voltage shall be induced from another winding, which
will develop twice the operating phase-to-phase voltage between line
terminals.
c) Twice the rated turn-to-turn voltage shall be developed in each winding.
Note: Voltage levels may have to be reduced such that no winding need be
tested above its specified level to meet the test requirements of another
winding.
3. The voltage should be started at one-quarter or less of the full value and be
brought up gradually in not more than 15 seconds. After being held for the
specified duration, it should be gradually reduced in not les than 5 seconds to
one-quarter of the maximum value and then turned off.
Caution:
It is important to recognize that the neutral terminal of a wye-connected
transformer that is designed for a grounded wye connection may have an insulation
level lower than that of the line terminal. The insulation level of the neutral end of
the winding may differ from the insulation level of the highest voltage neutral
terminal. In such case, the dielectric test on the neutral shall be determined by
lower insulation value of the neutral terminal or the neutral end of the winding.
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Table 8: Insulation Voltage Class and Dielectric tests for Dry-type
Transformers (Factory Test Levels)
Insulation Voltage
Class, kV
Nominal Transformer
Voltage
Applied Potential Test,
kV
1.2 1,200 and less 4
2.5 2,400 10
5.0 4,160 / 2,400
4,160
4,800
12
8.7 8,320Y / 4,800
7,200
8,320
19
15.0 12,470 / 7,200
13,860Y / 8,00012,470
13,860
31
18.0 24,940 GrdY / 14,400
27,600 GrdY / 16,000
34
25.0 35,500 GrdY / 19,900
24,940Y / 14,400
24,940
27,600Y / 16,000
27,600
40
34.5 34,500
34,500Y / 19,900
46,000 GrdY / 26,600
50
Notes:
1) A single voltage of 4160 represents a delta-connected 3-phase transformer for connection to a 3-wire system or a single-phase transformer for connection to a 2-wire
ungrounded system. A voltage such as 4160 GrdY / 2400 represents a wye-connected 3-
phase transformer having an effectively grounded neutral for connection to a 4-wiremultigrounded system. It also represents a 2400 V single-phase transformer with an
effectively grounded neutral end in the 2400 V winding. I may be connected line-to- ground or as part of a 3-phase bank on a 4160 V 4-wire multigrounded system. A voltage such as 4160Y / 2400 represents a 3-phase transformer with a fully insulated neutral for
connection to a 416 V 4-wire system.
2) Power frequency dielectric withstand test levels are for application to windings that do
not have reduced neutral terminal insulation.3) Equipment having a voltage rating between listed values shall be tested at the higher
level.
4) See “Caution” above for windings that are grounded Y.
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Figure 1: Applied Voltage Test of the HV winding to LV winding and Ground
Figure 2: Applied Voltage Test of the LV winding to HV winding and Ground
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4.2.3 Applied Potential Test Procedure
(Two winding Δ-Y transformer with 100% neutral insulation level)
1. Isolate the equipment, apply working grounds to all incoming and outgoing
cables and disconnect all incoming, outgoing cables from the transformer
bushing terminals connections. Disconnected cables should have sufficient
clearance from the switchgear terminals greater that the phase spacing
distance. Use nylon rope to hold cable away from incoming and outgoing
terminals as required.
2. Isolate the neutral bushing connection from transformer grounding bar.
3. Short-circuit all high voltage bushing terminals together.
4. Short-circuit all low voltage bushing terminals and the neutral bushingterminal together.
5. Perform a high-voltage winding to low-voltage winding and ground test, at
75% of the specified value in Table 5 for the high-voltage winding
insulation class level.
Refer to Figure 1.
6. Attain the test voltage level at a constant rate of rise, to achieve the test
voltage level at the end of 15 seconds.
7. Hold the test voltage for 1 minute. This is a go-no-go test.
8. Reduce the voltage to zero at a constant rate of decline, no faster than 5
seconds.
9. Perform a low-voltage winding to high-voltage winding and ground test, at
75% of the specified value in Table 5 for the low-voltage winding insulation
class level.
Refer to Figure 2.
10. Repeat steps 6 through 8.
11. Remove all shorting jumpers after all tests are completed. Reconnect neutral
connection.
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4.3.1 Turns Ratio Test Procedure
1. Isolate the equipment, apply working grounds to all incoming and outgoing
cables and disconnect all incoming and outgoing cables from the transformer
bushing terminals connections. Disconnected cables should have sufficient
clearance from the switchgear terminals greater that the phase spacing
distance. Use nylon rope to hold cable away from incoming and outgoing
terminals as required.
2. Connect the H designated three-phase test lead with the military style
connector at one end to the mating connection on the test set marked with an
H. Ensure that the connector’s index notch lines up properly.
3. Connect the X designated three-phase test of lead military style connector at
one end to the mating connection on the test set marked with an X. Ensurethat the connector’s index notch lines up properly.
4. Connect the H1, H2, H3 designated test lead to the corresponding H1, H2,
H3 transformer terminal / bushing. Connect the H0 test lead if H0
terminal/bushing is present.
Refer to Figure 3.
5. Connect the X1, X2, X3 designated test leads to the corresponding X1, X2,
X3 transformer terminals / bushings. Connect the X0 test lead if X0
terminal/bushing is present.
6. Perform turns ratio measurements for all tap positions.
7. Confirm that the measured ratios is within .5% of the calculated ratios.
Note:
Transformers that have wye connections but do not have the neutral of the wye
brought out shall be tested for ratio with three-phase power supply. Any inequality
in the magnetizing characteristics of the three phases will then result in a shift of the neutral and thereby cause unequal phase voltages. When such inequality is
found, the connection should be changed, either to a delta or to a wye connection,
and the line voltages measured. When these are found to be equal to each other and
the proper values (1.732 times the phase voltages when connected in wye), the
ratio is correct.
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4.3 Polarizing Index Test
The Polarizing Index (PI) test is an extension of the winding insulation resistance
test. Two insulation resistance measurements are taken, one reading at 1 minute
and the second reading at 10 minute.
Polarisation Index = R 10 / R 1
Where:
R 10 = megohms insulation resistance
at 10 minutes
R 1 = megohms insulation resistanceat 1 minute
The 10 minute resistance is divided by the 1 minute resistance to give the PI value.
The PI indicates the relative dryness and level of moisture ingress into theinsulation.
A PI of winding to winding and winding to ground should be determined. A PI
below 2 calls for further investigation.
Readings at every minute intervals are recorded for graphing purposes. A falling
off of the insulation value near the testing time could indicate insulation problems.
Figure 4: Example of Time Dependent Insulation Readings for Normal and
Poor Insulation.
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4.3.1 Polarizing Index Test Procedure
Note: The polarizing index tests should be combined with the insulation resistance
test by extending the required test time to 10 minutes. This will minimize
testing time when both tests are combine versus performing two separate
tests.
1. Isolate the equipment, apply working grounds to all incoming and
outgoing cables and disconnect all incoming and outgoing cables from the
transformer bushing terminals connections. Disconnected cables should have
sufficient clearance from the switchgear terminals greater that the phase
spacing distance. Use nylon rope to hold cable away from incoming and
outgoing terminals as required.
2. Ensure the transformer tank and core is grounded.
3. Disconnect all lightning arresters, fan system, meter or low voltage
control systems that are connected to the transformer winding.
4. Short circuit all winding terminals of the same voltage level together.
5. Perform a 10 minute resistance measurements between each winding
group to the other windings and ground. Record all data points required at
the various intervals;
Every 15 seconds for the first minute,
Every 30 seconds up to 4 minutes,
Every 1 minute up to 10 minutes test time.
6. Remove all shorting jumpers after all tests are completed.
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4.4 Winding Resistance Test
The winding resistance test is a low voltage constant DC current test used to
measure the ohmic values of the individual transformer windings. The ohmic
values can be used for:
- Calculations of the I2R component of conductor losses.
- Calculation of winding temperature at the end of a temperature test cycle.
- As a base for assessing possible damage in the field.
Regardless of the configuration either wye or delta, the winding resistance
measurements are made phase-to-phase and comparisons are made to determine if
the readings are comparable.
If all readings are within 1% of each other then they are acceptable.
The purpose of the test is to test for gross differences between the windings and for
checking if there are open circuits in the connections. Measuring the resistance of
the windings assures that the connections are correct and the resistance
measurement indicates that there are no severe mismatches or open.
Operating Principles
A DC current is passed through the transformer winding and an internal standard
current shunt in the test set. After both DC voltage drops are measured they are
ratioed and the display is read as resistance on the front panel meter.
Measurement of the voltage drop across the winding uses the standard formula for
a voltage drop across an inductor, where:
VL = IL x R + (L di/dt) = voltage across the transformer winding
IL = DC current through transformer winding
R = resistance of the transformer winding
L = inductance of the transformer
With zero ripple voltage, then di/dt is zero and the term L di/dt becomes zero.
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Caution:
When a DC current is flowing in an inductive element, opening the circuit will
be generate high voltages during kickback from the collapsing magnetic field in
the coil. DO NOT open the circuit during testing
When terminating the test, wait until the “charged” indicator on the test set goes
off before removing any leads. If it takes 30 second for the winding to charged, it
will take a longer time for the winding to discharge.
When transferring leads from one winding to another, the same relative polarity
should be maintained with regard to the measuring leads and the transformer
terminals.
Limitations
The transformer resistance test has several limitations which should be recognizedwhen performing the test and interpreting test data:
The information obtained from winding resistance measurements on delta
connected windings is somewhat limited. Measuring from the corners of a closed
delta the circuit is two windings in series and in parallel with the third winding.
The resistance of the transformer's winding can limit the effectiveness of the test in
detecting problems. The lower the resistance of a winding the more sensitive the
test is with respect to detecting high resistance problems. Windings with high DC
resistance will mask problems.
The detection of shorted turns is not possible in all situations. Often shorted turns
at rated AC voltage cannot be detected with the DC test. If the fault is a carbon
path through the turn to turn insulation it is a dead short at operating potentials.
However, at test potential, 30 V DC, the carbon path may be a high resistance
parallel path and have no influence on the measured resistance.
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4.4.1 Winding Resistance Test Procedure
1. Isolate the equipment, apply working grounds to all incoming and outgoing
cables and disconnect all incoming and outgoing cables from the transformer
bushing terminals connections. Disconnected cables should have sufficient
clearance from the switchgear terminals greater that the phase spacing
distance. Use nylon rope to hold cable away from incoming and outgoing
terminals as required.
2. Select the correct winding metal type (aluminum or copper) on the test set if
provided. Resistivity of copper and aluminum is different.
3. For delta or wye connected windings, connect +ve DC current source lead to
the H1 (or X1) terminal and the –ve DC current source lead to the H2 (or
X2) terminal.
4. Connect the +ve DC voltage sensing lead to the H1 (or X1) terminal closer
toward the winding and the –ve DC voltage sensing lead to the H2 (or X2)
terminal closer toward the winding.
5. Perform winding measurement for the H1-H2 ( or X1-X2) winding.
6. Repeat step 3 and 4 for H2-H3 (or X2-X3) and H3-H1 (or X3-X1) while
maintaining the relative polarity of the test leads.
7. For Wye connected windings, connect +ve DC current source lead to the H1
(or X1) terminal and the –ve DC current source lead to the H0 (or X0)
terminal.
8. Connect the +ve DC voltage sensing lead to the H1 (or X1) terminal closer
toward the winding and the –ve DC voltage sensing lead to the H0 (or X0)
terminal closer toward the winding.
9. Perform winding measurement for the H1-H0 ( or X1-X0) winding.
10. Repeat step 7 and for H2-H0 (or X2-X0) and H3-H0 (or X3-X0) while
maintaining the relative polarity of the test leads.
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4.6 Power Factor Test
The power factor test is a maintenance test used to determine the insulation system
dielectric power loss by measuring the power angle between an applied AC voltage
and the resultant current. Power factor is defined as the ratio of the power
dissipated divided by the input volt-ampere multiplied by 100%. This test may be
required to be performed during the acceptance testing stage to establish a baseline
reading for future test comparison.
Figure 5: Insulation System Equivalent Circuit and Power Factor Vector
Diagram
Dielectric losses in and power factor can be calculated by:
Watts = E x IT x Cosine Ө
Power factor = Cosine Ө = Watts / (E x IT)
PF test is performed for detecting insulation deterioration or degradation usually
caused by moisture, carbonization or other forms of contaminants of the winding
and bushing. Winding distortions results in a change in winding capacitance and
short-circuited and partially short-circuited turns result in abnormally high
excitation current.
Types of transformers that are normally subjected to the power factor test are:- Two winding transformers
- Three winding transformer
- Auto-transformers
- Instrument transformers
Other test names synonymous with the PF test are Dielectric loss angle, dissipation
factor test, tan delta or Doble test.
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General conditions required for testing transformers are:
1. The unit must be de-energized and isolated from the power system including
the neutral connection from ground.
2. Transformer enclosure must be properly grounded and applicable to when
testing spare units.
3. All terminal of each winding are short-circuited together including the
neutral terminals. This will minimize the effect of winding inductance
during testing.
4. LTC should be set of neutral if it has arrester-type elements that are not
effectively short circuited in the neutral position.
The power factor test typically applies a test voltage less than the stress working
levels of the equipment. Refer to Table 6.
Table 6 Recommended Power factor Test Voltage for Dry-type Power
Transformer connected in delta and ungrounded-wye
Winding Rating
Line-to-line, kV
Test Voltage
Line-to-ground, kV
Above 14.4 2 and 10
12 to 14.4 2, 10 and at operating line-to-ground
voltage
5.04 to8.72 2 and 5
2.4 to 4.8 2Below 2.4 1 Note: Transformer windings provided with neutral insulation rating which is less than the line
insulation rating should be tested below the neutral insulation rating level.
The required tests are noted in Table 7 and its connection is shown in Figure 6 and
Figure 7. The difference between the high-voltage winding tests and the low-
voltage winding tests are the placement of the test leads and the test voltage levels.
Test 3 and test 8 of Table 7 should generate the same value as they both measure
the same capacitance between the windings.
Table 7 Power Factor test connection for two winding dry-type
transformer
Test
Number
Test
Mode
Energized
Winding
Ground Guard UST Measure
1 GST High Low ----- ----- CH+CHL
2 GST High ----- Low ----- CH
3 UST High ----- ----- Low CHL
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4 Calculate Test 1 minus Test 2 CHL
5 GST Low High CL+CHL
6 GST Low High CL
7 UST Low High CHL
8 Calculate Test 5 minus Test 6 CHL
Figure 6: Power Factor High Voltage Winding Test Connection
Figure 7: Power Factor Low Voltage Winding Test Connection
Caution: Always ground to the previously energized terminal with a grounding
stick before making any connection changes to bleed off any electrical
charge that may be present. Leave the grounding connected until
connection changes is completed and before the start of the next test.
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4.6.1 Power Factor Test Procedure
(Two winding dry-type transformer)
1. Isolate the equipment, apply working grounds to all incoming and outgoing
cables and disconnect all incoming and outgoing cables from the transformer
bushing terminals. Disconnected cables should have sufficient clearance
from the switchgear terminals greater that the phase spacing distance. Use
nylon rope to hold cable away from incoming and outgoing terminals as
required.
2. Isolate the neutral bushing connection if applicable from the transformer
grounding bar.
3. Short-circuit all high voltage bushing terminals together.
4. Short-circuit all low voltage bushing terminals and the neutral bushing
terminal together.
5. Connect the power factor test set.
Refer to Table 7 for the test measuring mode and associated test number.
6. Apply the specified test voltage levels as noted in Table 2.
7. Record PF and watts loss values.
8. Repeat step 5 to 7 until all tests are completed
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4.7 Capacitance and Dissipation Factor Test
The capacitance and dissipation factor test is an AC low voltage maintenance test
and is very similar to the power factor test. The test as it is termed, measures the
capacitance and dissipation factor (or loss factor) of the transformer insulation
system. This test may be required to be performed during the acceptance testing
stage to establish a baseline reading for future test comparison.
While the transformer preparation is identical to the power factor test procedure,
there is no requiremnts to make connection changes once the initial test set
connections are made. High-voltage winding and low-voltage winding test set
connection changes are made through a selector switch provided on the test set
which effect the test set connections akin to Table 7.
Winding capacitance and dissipation factor test values are obtained by balancing a
null meter for each variable at every the measured variable selector switch positions.
Figure 8: Capacitance and Dissipation Factor Test connection diagram
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4.7.1 Capacitance and Dissipation Factor Test Procedure
(Two winding dry-type transformer)
1. Isolate the equipment, apply working grounds to all incoming and outgoing
cables and disconnect all incoming and outgoing cables from the transformer
bushing terminals. Disconnected cables should have sufficient clearance
from the switchgear terminals greater that the phase spacing distance. Use
nylon rope to hold cable away from incoming and outgoing terminals as
required.
2. Isolate the neutral bushing connection if applicable from the transformer
grounding bar.
3. Short-circuit all high voltage bushing terminals together.
4. Short-circuit all low voltage bushing terminals and the neutral bushing
terminal together.
5. Connect the capacitance and dissipation factor test set.
Refer to Figure 8.
6. Record the capacitance and dissipation factor values once the null meter is
balance for both phasing position. Record values for the five test-variable
selector switch position.
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4.8 Phasing Test
The vector diagram of any three phase transformer which identifies the angular
displacement and phase sequence can be verified by connecting the H1 and X1
leads together and then exciting the high-voltage windings at a suitably low
voltage with a know phase sequence from the three phase source. Voltage
measurements are taken between various pairs of lead and comparing them for
their relative magnitude with the aid of the corresponding vector diagrams.
This section is limited to the two-winding transformer having a phase displacement
of 0 and 30 degrees. Six-phase unit are excluded from this discussion but can be
referenced in IEEE C57.12.91 – 2001 Standard Test Code for Dry-type
Distribution and Power Transformer.
Refer to Table 8.
4.8.1 Phasing Test Procedure
1. Isolate the equipment, apply working grounds to all incoming and outgoing
cables and disconnect all incoming and outgoing cables from the transformer
bushing terminals. Disconnected cables should have sufficient clearance
from the switchgear terminals greater that the phase spacing distance. Use
nylon rope to hold cable away from incoming and outgoing terminals as
required.
2. Isolate the neutral bushing connection if applicable from the transformer
grounding bar.
3. Connect H1 and X1 terminals.
4. Apply a low voltage having A-B-C phase sequence to H1, H2 and H3
terminals respectively. Select an applied voltage to effect proper
measurement.
5. Measure the voltages between the various terminals as shown in Table 8 for
the respective winding group.
6. Ensure the voltage check measurements conforms to the conditions as
shown in Table 8.
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Table 8 Three-phase Transformer Vector Diagram and Terminal Markings
Group 1 having 0 degree angular displacement
Angular Displacements Measurement Connection Measurement Checks
Connect:
Measure:
Check:
H1 to X1
H1-H2,H2-X2,H2,X3,
H3-X2,
H3-X3
H2-H3 = H3-X2,
H2-X2 < H1-H2,H2-X2 < H2-X3,
H2-X2 = H1-X3
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Table 8 Three-phase Transformer Vector Diagram and Terminal Markings
Group 2 having 30 degree angular displacement
Angular Displacements Measurement Connection Measurement Checks
Connect:
Measure:
Check:
H1 to X1
H1-H3,H2-X2,
H2-X3,
H3-X2,H3-X3
H3-X2 = H3-X3
H3-X2 < H1-H3H2-X2 < H2-X3
H2-X2 < H1-H3
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5. NETA Large Dry-type, Air Cooled Transformer Acceptance Testing
Procedure
Note: The NETA transformer acceptance testing procedures applicable to the MV
large dry-type class has been recompiled with minor revisions.
Refer to ANSI/NETA ATS-2009, Standard for Acceptance Testing
Specifications for Electrical Power Equipment and Systems.
Note: Many of the listed tests in the NETA standard are optional while optionally
indicate tests may be required to be performed; as such, those notes have
been excluded in this document. Any personnel responsible for performing
acceptance testing should determine which specific tests are required for
each specific projects.
5.1 Visual and Mechanical Inspection1. Compare equipment nameplate data with drawings and specifications.
2. Inspect physical and mechanical condition.
3. Inspect anchorage, alignment, and grounding.
4. Verify that resilient mounts are free and that any shipping brackets / bolts have
been removed.
5. Verify the unit is clean.
6. Verify that control and alarm settings on temperature indicators are as specified.
7. Verify that cooling fans operate and that fan motors have correct overcurrent
protection.
8. Inspect bolted electrical connections for high resistance using one or more
of the following methods:
a. Use of a low-resistance ohmmeter.
b. Verify tightness of accessible bolted electrical connections by calibrated
torque-wrench method in accordance with manufacturer’s published data or Table 2 of module 2 or Table 100.12 of NETA ATS-2009.
c. Perform thermographic.
9. Perform specific inspections and mechanical tests as recommended by the
manufacturer.
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10.Verify that as-left tap connections are as specified.
11.Verify the presence of surge arresters.
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5.2 Electrical Tests
1. Perform insulation-resistance tests winding-to-winding and each winding-
to-ground. Apply voltage in accordance with manufacturer’s published data.
In the absence of manufacturer’s published data apply 2500 Vdc for
winding rating up to 5000 Vac and apply 5000 Vdc for winding rating over
5001 Vac.
2. Perform power-factor or dissipation-factor tests on all windings in
accordance with the test equipment manufacturer’s published data.
3. Perform a power-factor or dissipation-factor tip-up test on windings greater
than 2.5 kV.
4. Perform turns-ratio tests at all tap positions.
5. Perform an excitation-current test on each phase.
6. Measure the winding resistance at each tap connection.
7. Measure core insulation resistance at 500 Vdc to determnine if the core is
insulated.
8. Perform an applied voltage test on all high and low-voltage windings-to-
ground. See ANSI/IEEE C57.12.91 sections 10.2 and 10.9.
9. Verify correct secondary voltage, phase-to-phase and phase-to-neutral, after
energization and prior to loading.
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5.3 Test Values
5.3.1 Test Values – Visual and Mechanical
1. Control and alarm settings on temperature indicators shall operate within
manufacturer’s recommendations for specified settings.
2. Cooling fans should be operational.
3. Compare bolted connection resistance values to values of similar connections.
Investigate values which deviate from those of similar bolted connections by
more than 50 percent of the lowest value.
4. Bolt-torque levels shall be in accordance with manufacturer’s published data.
In the absence of manufacturer’s published data or table 2 of module 2 or Table
100.12 of NETA ATS-2009
5. Results of the thermographic survey shall be in accordance with Section 9.
6. Tap connections shall be left as found unless otherwise specified.
5.3.2 Test Values – Electrical
1. Compare bolted connection resistance values to values of similar connections.
Investigate values which deviate from those of similar bolted connections by
more than 50 percent of the lowest value.
2. Minimum insulation-resistance values of transformer insulation shall be in
accordance with manufacturer’s published data. In the absence of
manufacturer’s published data, use Table 100.5 or refer to section 4.1, Table
6.
Values of insulation resistance less than this table or manufacturer’s
recommendations should be investigated. The polarization index shall not
be less than 1.0.
3. CH and CL power-factor or dissipation-factor values will vary due to supportinsulators and bus work utilized on dry transformers. The following shall beexpected on CHL power factors:
Power transformers: 2.0 percent or less
Distribution transformers: 5.0 percent or less
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Consult transformer manufacturer’s or test equipment manufacturer’s
data for additional information.
4. Power-factor or dissipation-factor tip-up exceeding 1.0 percent shall be
investigated.
5. Turns-ratio test results shall not deviate more than one-half percent from
either the adjacent coils or the calculated ratio.
6. The typical excitation current test data pattern for a three-legged core
transformer is two similar current readings and one lower current reading.
7. Temperature-corrected winding-resistance values shall compare within
one percent of previously-obtained results.
8. Core insulation-resistance values shall not be less than one megohm at 500
volts dc.
9. AC dielectric withstand test voltage shall not exceed 75 percent of factory test
voltage for one minute duration. If no evidence of distress or insulation failure
is observed by the end of the total time of voltage application during the
dielectric withstand test, the test specimen is considered to have passed the test.
10.Phase-to-phase and phase-to-neutral secondary voltages shall be in agreement
with nameplate data.
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6. Test Set Operational Manual
Three-phase Transformer Turns Ration Test Set
Digital Low Resistance Ohmmeter
Power Factor Test Set
Capacitance and Dissipation Factor Test Set
10 kV Insulation Resistance Test Set
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SUBSTATION COMMISSIONING COURSE
7. Test Forms
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SUBSTATION COMMISSIONING COURSE
CUSTOMER DATA
Name: EITCA Date (mm/dd/yy):
Address: 4234 – 93 STREET City, Province: EDMONTON ALTA
Location: INDOOR Address: 4234 – 93 STREET
Substation: TRAINING LAB Postal code: T6E 5P5
Panel ID: Phone: 780-462-5729
Equipment ID: Contact person: MR. R. MATTHEWSTested by:
EQUIPMENT NAMEPLATE DATA
Make: HV Winding rating: kV
Type: LV Winding rating: kV
Load Rating: kVA BIL Rating; HV / LV / kV
Impedance: %
Number of taps: Temperature rise: / ºC
Manufactured Date: Cooling Class:
HV Winding material Total weight:
LV Winding material Winding configuration: /
VISUAL / MECHANICAL INSPECTION
Physical condition: Primary winding connection: Bushing Integrity:
Cleanliness: Sec. winding connection: Winding condition:
Anchorage: Core temperature sensors: Fan /fan motor condition:
Ground bus connections: Core grounding strap: Temp. controller integrity:
Comments:
INSULATION RESISTANCE TEST
H WINDINGS L WINDINGS
H to L & Gnd MΩ L to H & Gnd MΩ
H to Gnd MΩ L to Gnd MΩH to LV MΩ ----- ----- -----
Test Voltage kV Test Voltage kV
Test Duration sec Test Duration sec
Temperature: °C Humidity: %
Test Equipment: Calibration Date:
Serial Number: Test Equipment ID:
Comments:
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SUBSTATION COMMISSIONING COURSE
WINDING RATIO TEST
T
AP
HV
WINDINGRATING
CALCRATIO
H1-H3 / X1-X0 H2-H1 / X2-X0 H3-H2 / X3-X0
MEASRATIO
DIFF EXCIT RATIO DIFF EXCIT RATIO DIFF EXCIT
% mA % mA % mA
1 V
2 V
3 V4 V
5 V
As found tap conn / rating: As left tap conn. / rating:
Test Equipment: Calibration Date:
Serial number: Test Equipment ID:
Comments:
APPLIED VOLTAGE TEST
H WINDINGS L WINDINGS
H to L & Gnd MΩ L to H & Gnd MΩ
Test Voltage kV Test Voltage kV
Test Duration sec Test Duration sec
Comments:
WINDING RESISTANCE TEST
T
AP
HIGH VOLTAGE WINDING LOW VOLTAGE WINDING
H1-H2 H2-H3 H2-H1 X1-X0 X2-X0 X3-X0mΩ mΩ mΩ mΩ mΩ mΩ
1 ---------- ---------- ----------
2 LOW VOLTAGE WINDING
3 X1-X2 X2-X3 X3-X1
4 mΩ mΩ mΩ
5 ---------- ---------- ----------
As found tap conn / rating: As left tap conn. / rating:
Test Equipment: Calibration Date:
Serial Number: Test Equipment ID:
Comments:
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SUBSTATION COMMISSIONING COURSE
POLARIZING INDEX TEST / INSULATION RESISTANCE TEST
H to L & Gnd L to H & Gnd
TIME RESITANCE TIME RESITANCE
15 sec GΩ 15 sec GΩ
30 sec GΩ 30 sec GΩ
45 sec GΩ 45 sec GΩ
1 min GΩ 1 min GΩ1.5 min GΩ 1.5 min GΩ
2 min GΩ 2 min GΩ
2.5 min GΩ 2.5 min GΩ
3 min GΩ 3 min GΩ
3.5 min GΩ 3.5 min GΩ
4 min GΩ 4 min GΩ
5 min GΩ 5 min GΩ
6 min GΩ 6 min GΩ
7 min GΩ 7 min GΩ
8 min GΩ 8 min GΩ
9 min GΩ 9 min GΩ10 min GΩ 10 min GΩ
Test Voltage: Vdc Test Voltage: Vdc
P.I. Ratio P.I. Ratio:
Temperature: °C Humidity: % %
Test Equipment: Calibration Date:
Serial Number: Test Equipment ID:
Comments:
CORE INSULATION RESISTANCE TEST
Test Voltage: 500 Vdc Core Ground Resistance: MΩ
Comments:
CAPACITANCE / DISIPATION TEST
TEST
CAPACITANCE DISSIPATIONMULTI
pFDIAL
READING
VALUE RANGE DIAL
READING
VALUE 20 ºC
CORR pF %
CHL + CHG
CHG
CHL
CLG
CLH + CLGTest Equipment: Calibration Date:
Serial Number: Test Equipment ID:
Comments:
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SUBSTATION COMMISSIONING COURSE
VECTOR DIAGRAM
PHASING TEST (H1 CONNECTED TO X1)
Measured voltage Voltage Relationship Voltage Checks -----
H1-H3: V H3-X2 = H3-X3 -----
H2-X2: V H3-X2 < H1-H3 -----H2-X3: V H2-X2 < H2-X3 -----
H3-X2: V H2-X2 < H1-H3 -----
H3-X3: V ----- ----- -----
Applied Voltage: V Phase Sequence ----- -----
Comments:
TSTING NOTES and OBSERVATIONS
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SUBSTATION COMMISSIONING COURSE
8. Transformer Test Form References and Suggested Reading
1. CSA Standard C9-02
Dry-Type Transformers
© 2002 by the Canadian Standard Association
5060 Spectrum Way, Suite 100
Missisauga, Ontario, L4W-5N6, CANADA
ISBN 1-55397-063-2
2. IEEE Standard C57.12.01-2005
General Requirements for Dry-type Distribution and Power Transformer,
Including Those with Solid-Cast and/or Resin Encapsulated Windings
© 2006 by the Institute of Elelctrical and Electronics Engineers, Inc.
3 Park Avenue, New York, NY 10016-5997, USAPrint: ISBN 0-7381-4880-6
PDF: ISBN 0-7381-4881-4
3. IEEE Standard C57.12.91-2001
Test Code for Dry-type Distribution and Power Transformers
© 2001 by the Institute of Elelctrical and Electronics Engineers, Inc.
3 Park Avenue, New York, NY 10016-5997, USA
Print: ISBN 0-7381-2734-5
PDF: ISBN 0-7381-2735-3
4. ANSI/IEEE C57.94-1982
Recommended Practice for Installation, Application, Operation and
Maintenance of Dry-type General Purpose Distribution and Power
Transformers
© 1982 by the Institute of Elelctrical and Electronics Engineers, Inc.
345 East 47th Street, New York, NY 10017-2394, USA
5. ANSI/NETA ATS 2009
American National StandardStandard for Acceptance Testing Specifications for Electrical Power Equipment
and Systems
Copyright © 2009 by International Electrical testing Association
3050 Old Centre Avenue, Suite 102, Portage, MI 49024, USA
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SUBSTATION COMMISSIONING COURSE
References and Suggested Reading
6. Doble Test Procedures
Copyright © 2000 by Doble Engineering Company
85 Walnut Street, Watertown, Massachusetts, 02472-4037, USA
PN 500-0397