Megger DELTA 4000, Справочное руководство

Страница: 36 / 48

36 DELTA 4000 ZM-AH02E
3 TESTING POWER SYSTEM COMPONENTS
arrester stacks. When testing in the field, disconnect the
related high-voltage bus from the arrester. Surge arresters
are often rated on the basis of watts loss.
Test connections
Table 3.11
Surge arrester test connections
Te
st
N
o
.
Su
rg
e a
rr
est
er
s
ym
b
ol
In
su
la
ti
o
n
te
ste
d
Low voltage lead
configuration
Test con-
nections
to surge
arrester
R
em
ark
s
Te
st
m
o
d
e
M
ea
sur
es
G
ro
un
d
G
uar
d
H
ig
h
v
o
lt
ag
e
Re
d
B
lu
e
1 SA -A UST-B Blue Red 2 3 1
Terminal 3
Grounded
2 SA - B UST-R Red Blue 2 3 1
Terminal 1
Grounded
3 SA - C UST-R Red Blue 4 3 –
4 SA - D GST Red 4 3 –
Terminal 3
Guarded
Note: All tests normally made at 10 kV.
Typical multi-unit arrester stack
It is recommended that tests be made on individual arrester
units rather than on a complete multi-unit arrester stack. A
single arrester unit can be tested by the normal ungrounded
specimen test (UST) in the shop; however, it can only be
tested by the grounded specimen test (GST) when mounted
on a support structure in the field.
▪
When testing in the field, disconnect the related high-
voltage bus from the arrester.
▪
Connect a ground wire from the test set to the steel
support structure of the arrester stack,
▪
When connecting the high voltage lead, ensure that the
cable extends out away from the arrester and does not
rest on the porcelain.
Test procedure
Always observe safety rules when conducting tests. Power
factor testing is extremely sensitive to weather conditions.
Tests should be conducted in favorable conditions whenever
possible. Measurements on surge arresters should always be
performed at the same or recommended test voltage since
voltage dependent (non-linear) may be built into an arrester.
Except for the specific purpose of investigation surface leak -
age, the exposed insulation surface of an arrester should be
clean and dry to prevent leakage from influencing the mea -
surements. Follow the test sequence as in the table. The test
mode and the number of tests performed will be depending
on the number of arresters in the stack.
Test results
For all power factor testing, the more information recorded
at the time of testing will ensure the best comparison of re-
sults at the next routine test. Test data should be compared to
factory or nameplate data if available. If no data is available,
compare the test results to prior tests on the same arrester
and results of similar tests on similar arresters. The following
additional information should be recorded on the test form.
▪
Record all the nameplate information of the arrester.
▪
Identify each set of readings with the arrester serial
number.
▪
Note any special or unusual test connections or
conditions.
▪
Record actual test voltage, current, watts, power factor
and capacitance. Correct the current and watts to a
standard test voltage 10kV.
▪
Record ambient temperature and relative humidity and
a general indication of weather conditions at the time of
the test
Surge arresters are often rated on the basis of watts loss
(10 kV equivalent). On multi-unit arrester stacks the UST
loss readings may be less that the arresters tested in the
GST mode because stray currents do not affect the UST
test results.
An increase in watts loss values compared with a previous
test or tests on identical arresters under the same conditions
may indicate:
▪
Contamination by moisture
▪
Contamination by salt deposits
▪
Cracked porcelain housing
▪
Corroded gaps.
A decrease in watts loss values may indicate:
▪
Open shunt resistors
▪
Defective pre-ionizing elements.