A . Visual and mechanical inspection :
1- Inspect exposed sections of cables for physical damage and
evidences of
overheating and
corona.
2- Inspect terminations and splices for evidences of overheating
and corona.
3- Inspect all bolted electrical connections for high resistance
using one of the following methods:
i - Use of low –
resistance ohmmeter.
ii - Verify tightness of accessible bolted electrical
connections by calibrated torque-wrench method in accordance with
manufacturer's published data.
iii- Perform thermo graphic survey .
4- Inspect comparison – applied connections for correct cable
match and identification.
5- Inspect for shield grounding , cable support , and
termination.
6- Verify that visible cable bends meet or exceed ICEA and/or
manufacturer's minimum allowable bending radius.
7- Inspect fireproofing in common cable areas , if specified.
8- If cables are terminated through window –type current
transformers, make an inspection to verify that neutral and ground conductors
are correctly placed and that shields
are correctly terminated for operation of protective devices.
B .Electrical Tests:
1- Perform a shield – continuity test on each power cable by
ohmmeter method.
2- Perform an insulation – resistance test utilizing
a megohmmter with a voltage output of at
least 2500 volts.Individually test each conductor with all other
conductors and shields grounded . Test duration shall be one minute.
3- Perform resistance measurements through all bolted connections
with a low resistance ohmmeter, if applicable .
4- Perform a dc high – potential test on all cables .
adhere to all precautions and limits as specified in
the applicable NEMA/ICEA standard for specific cable. Perform tests
in accordance with ANSI/IEEE standard 400.test procedure shall be as
follows , and the results for each cable test shall be recorded as specified
herein .test voltages shall not exceed 60 percent of cable manufacturer's
factory test value or Maximum test voltage in the table.
Note:
1- Insure that the input voltage to the test regulated
2- Current – sensing circuits in test equipment shall measure
only the leakage current associated with the cable under test and shall
not include internal leakage of equipment .
3- Record wet – and dry-bulb
temperatures or relative humidity and temperature.
4- Test each section of cable
individually.
5- Individually test each
conductor with all other conductors grounded. ground all shields
6- Terminations shall be
adequately corona – suppressed by guard ring , field reduction sphere , or other suitable methods as necessary.
7- Insure that the maximum test
voltage does not exceed the limits for
terminators
specified in NSI/IEEE Standards 48 or manufacturer's specifications.
8- Apply a dc high – potential
test in at least five equal increments until maximum test voltage is reached . no increment shall exceed the the
voltage
rating of the cable .Record dc leakage
current at each step after a constant stabilization
time consistent with system charging current.
9- Raise the conductor to the
specified maximum test voltage and hold for five minutes, Record readings
of leakage current at 30 seconds and one minute intervals thereafter.
10- Reduce the conductor test
potential to zero and measure residual voltage at discrete intervals
11- Apply grounds for a time
period adequate to drain all insulation stored charge.
C .Test Values:
1- Compare bolted
connection resistances to values of similar connections.
2- Bolt – torque
levels shall be in accordance with manufacturer specification.
3- Microhm or
millivolt drop values shall not exceed the high levels of the
normal ranges as indicated in the
manufacturer's published data .if
manufacturer's data is not available ,
investigate any values which deviate
from similar connections by more than 25
percent of the lowest value.
4- Shielding must
exhibit continuity . investigate resistance values in excess of
ten ohms per 1000 feet of cable.
5- Graphic plots may
be made of leakage current versus step voltage at each
increment and leakage current versus time
at final test voltages.
6- The step voltage
slope should be reasonably linear.
7- Capacitive and
absorption current should decrease continually until steady
state leakage is approached.
8- Compare test
results to previously obtained results.
INSULATION-RESISTANCE
TEST VOLTAGES FOR ELECTRICAL APPARATUS
Maximum Maintenance Test Voltages
(KV,dc)
