Megger DELTA 4000, Reference Manual

Page: 19 / 48

ZM-AH02E DELTA 4000 19
3 TESTING POWER SYSTEM COMPONENTS
to verify the existence of a shield or a concentric-winding
arrangement.
Three-winding transformer test connections are described
in Table 3.2.
Table 3.2
Three-winding transformer test connections
Te
st
N
o
.
In
su
la
ti
o
n
te
ste
d
Low voltage lead
configuration
Test lead
connec-
tions to
windings
R
em
ark
s
Te
st
m
o
d
e
M
ea
sur
e
G
ro
un
d
G
uar
d
H
ig
h
v
o
lt
ag
e
Re
d
B
lu
e
1
CHG+
CHL
GSTg-B Red Blue H L T
L Grounded
T Guarded
2 CHG
GSTg-
RB
Red &
Blue
H L T
L & T
Guarded
3 CHL UST-R Red Blue H L T T Grounded
4 CHL – Test 1 minus Test 2 – – –
Calculated
intercheck
5
CLG +
CLT
GSTg-
BR
Blue Red L H T
T Grounded
H Guarded
6 CLG
GSTg-
RB
Red &
Blue
L H T
T & H
Guarded
7 CLT UST-RB Blue Red L H T H Grounded
8 CLT – Test 5 minus Test 6 – – –
Calculated
intercheck
9
CTG +
CHT
GSTg-B Red Blue T H L
H Grounded
L Guarded
10 CTG
GSTg-
RB
Red &
Blue
T H L
H & L
Guarded
11 CHT UST-R Red Blue T H L L Grounded
12 CHT – Test 9 minus Test 10 – – –
Calculated
intercheck
Equivalent Circuit Note: Short each winding on
itself.
Measurement Interchecks (Cal-
culated)
Capacitance Watts
C
4
= C
1
- C
2
W
4
= W
1
- W
2
C
8
= C
5
- C
6
W
8
= W
5
- W
6
C
12
= C
9
- C
10
W
12
= W
9
- W
10
Note: Subscripts are test num-
bers
H High-voltage winding
L Low-voltage winding
T Tertiary winding
G Ground
Autotransformers
In the design of an autotransformer, the secondary winding
is actually part of the primary winding. For a given power
output, an autotransformer is smaller and cheaper than a
conventional transformer. This is particularly true if the
ratio of the incoming line voltage to outgoing line voltage
lies between 0.5 and 2.
Autotransformers may have a tertiary winding. If so, both
primary and secondary bushings are shorted together and
the tertiary bushings are shorted to each other. The auto-
transformer is then tested as a two winding transformer.
Individual tests should be performed on each bushing if
they are equipped with a test tap.
If the autotransformer does not have a tertiary winding,
short the high voltage bushings and the low voltage bush-
ings together and perform a GST test. Test voltage should
be suitable for the rating of the low voltage winding
Transformer excitation current tests
Transformer excitation current tests are helpful in deter-
mining possible winding or core problems in transformers,
even when ratio and winding resistance tests appear normal.
Excitation tests should be conducted routinely along with
power factor testing.
Test connections
Test connection described in table 3.3.