7
High Voltage Instrument Transformers | CA/UT/KA
User Manual
Type Code Test Observations
Physical inspection
A1 Packaging Look for signs of rough handling
A2 Insulator Check that is not damaged and is clean. Check that it is not loose, bent or broken
A3
Primary
Terminals
Check that they are not loose, bent or broken
A4
Secondary
Terminal
Box
Check that it is not damaged and is securely fastened to the tank or transformer holder
A5
Check that no rain water enters the terminal box
Check that the ventilation openings are not blocked
A6 Metal parts Check for dents, scratches or signs of corrosion
A7 Unusual behavior Check for unusual noises, vibrations or odors
B1
Primary
connections
Check that there is good contact, that there are no signs of corrosion and that all nuts and bolts
are properly tightened. The use of conductive grease is recommended to improve contact, such as
Penetrox A13
B2
Connections
for changing
primary ratio
(if applicable)
In addition to the above, make sure that the connection matches the real primary current
B3
Secondary
circuits
Check that all screws are properly tightened, and that there are no signs of corrosion.
In the case of secondary windings with intermediate taps, check that the connection matches the real
transformer ratio
Check that unused current secondaries are short-circuited
Check that unused voltage secondaries are open-circuited
B4 Grounding
Check that the grounding terminal is correctly connected to the substation grounding network, that the
screws are correctly tightened and that there are no signs of corrosion
B5
Connection
DDF (tgδ)
(if applicable)
If the unit is provided with this tap, when the transformer is energized the outlet must be properly
grounded. Open this tap only for measuring and when the transformer is not energized
Leaving it open when the transformer is energized will cause overvoltages and damage to the
transformer
B6
Voltage
transformer
neutral
connection
(if applicable)
Only UTx and KA. Check that the neutral terminal (N) of the primary winding is grounded.
Leaving it open when the transformer is energized will cause overvoltages and damage to the
transformer
B7 Readings Check that the reading values of the secondary match the values expected
C1
Oil level
indicator
Check that it remains within the red areas at all times
C2
Oil stains
or leaks
Check the following areas for visible oil traces:
› Insulator fl anges
› Junctures between parts of the metal enclosure
› Junctures between the secondary terminal box and the tank or base
› Primary terminals’ surrounding area
Dielectric tests
D1 PF/DDF/tgδ
The limit values of this parameter depend on the transformer’s voltage level. The recommended values
are given with the order. It is also important to control this parameter’s change over time. A change
in the value of this parameter indicates a change in the properties of insulation, but it is not defi nitive
proof of faulty insulation. For this reason, if the value of the delta tangent is above the recommended
value or has increased, a careful investigation should be carried out and further testing may be required.
In this case, contact Arteche for assistance.
For details on the test procedure, follow Annex III
D2
Measurement of
the Insulation
resistance
For fi eld tests, the use of the megohmmeter (Megger) is very common, and the tests that are usually done are:
› Primary vs. secondary + Ground for current
› N/P2 against secondary and ground for voltage
› Each secondary against ground
› Among the secondaries
In the case of new equipment, the value obtained does not provide any information, unless a short circuit is
detected. Generally, values above 200 MΩ should be expected. However, the comparison of long-term values,
as in the case of tanδ, or power factor, can help determine whether a device is still in good working order.
Do not test at voltages above 3 kV AC or 1 kV DC.
Do not test for more than one minute. It is not recommended to repeat this test often as the
internal insulation could be damaged.
For details on the test procedure, follow Annex III
D3 Ratio test
The Portable Transformer Ratio Meter is commonly used to measure the ratio, excitation current and
polarity of windings. The values obtained are a sign that the transformer is in good condition and can
be energized.
They should not be compared with the results of factory tests carried out in the manufacturing plant
laboratory. Due to the high precision required for this measurement, the actual uncertainty of the test
must be taken into account when testing on site.
For details on the test procedure, follow Annex III
Oil tests
E1 Visual aspect The oil’s visual aspect may be an indication of contamination
E2 Water content
This value will provide information about the contamination of the oil. Reference values according
to IEC 60599
E3
PF/DDF/tgδ
(at 90ºC)
This value will provide information about the contamination of the oil. Reference values according to
IEC 60599
E4 DGA
The are several gases which may be dissolved in the transformer oil. The contents of each gas can be
related to di erent aspects. Reference values according to IEC 60599
Tes ts
thermo-
graphic
F1
Thermographic
analysis
Using thermographic cameras, hot spots can be detected in the operation of transformers. In most cases, hot
spots on instrument transformers occur at the primary terminals’ connection point to the line. If present, check
the integrity of the connectors, as well as their correct position and whether they are correctly tightened
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