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Victor Sokolov & Zalya Berler, ZTZ Service International Joe Watson, FPL Danny Bates, Alabama Power
Victor Sokolov & Zalya Berler,
ZTZ Service International
Joe Watson, FPL
Danny Bates, Alabama Power C1
R
V
ref
V
measured
Ø
V
C1
V
R
V
measured
V
ref
C1 Power Factor = cos(Ø)
V
ref
applied by Test Set
Ø and C1 measured by Test Set
Breakdown of the bushings insulation
shows as an increase in R and Ø Ú
f
+j




2




1




1




2




1
PF of reference bush




2
PF of specimen bush
Í
1
Í
2




=




2
-




1 Sensor for the connection to the capacitor tap Circuit of the Bushing Sensor TBS-2
Connection to the
bushing test tap
Varistor
Coax. cable Capacitance tap terminals are connected to the
connection box and test terminals. Terminals are
grounded except during testing. Connectors are
protected from overvoltages during testing by
MOVs. The connection box is mounted on the transformer.
The tests can be measured from the connection box
terminals or in the control house if the terminals
are brought to the control house. The Shunting
ground switch is on except during testing. Schematics of the Terminal Box
M4000 Output - 100/15 mA
Vector Output - 100/100 mA
CTs accuracy = 0.1%
CT
R
CT
S
Reference
Input
Test
Specimen
Input
M4000
Output
Vector
Output Comparison testing with Doble M4000
External Reference option
Reference
C1
PF1
Test
Specimen
C2
PF2
M4000
R1
R2
R1




R2
R1 = 7 Ohm
R2 = 0.36 Ohm
I
R1





15 mA Comparison testing with Vector2.0/1.2
Reference
C1
PF1
Test
Specimen
C2
PF2
Vector
R1
R2
R1 = R2 = 1.0 Ohm
TX-1268
CAP. pF
C1 POWER
FACTOR % CAP. pF
C1 POWER
FACTOR %
(DIFFERENTIAL) CAP. pF
C1 POWER
FACTOR %
H1
435
0.42
435
0.45
0.000%
7.143%
H2
430
0.35
429
0.4
-0.233%
14.286%
H3
436
0.45
433
0.52
-0.688%
15.556%
TX-1374
H1
375
0.23
373
0.3
-0.533%
30.435%
H2
377
0.24
377
0.25
0.000%
4.167%
H3
375
0.24
375
0.31
0.000%
29.167%
FOR EXAMPLE: TX-1268 H1 C1 PF MEASURED AT 0.22%.
DIFFERENTIAL = 0.22% + 0.23% = 0.45%
STANDARD
DOBLE TEST
ON-LINE
DOBLE TEST
PERCENT
DIFFERENCE
RESULTS COMPARATIVE PF TESTS
AT RATED VOLTAGE ON 750 KV CT Mnf. PF
%
Off
Line
PF,
%
On Line




PF,
%
.
C,
pF
Off Line
C,
pF
On Line




C,
%
1 1082
0.219
0.201
-0.018
488.7
489.1
0.10
963
0.243
0.261
0.018
501.0
501.1
0.02
2 1082
0.219
0.210
-0.009
488.7
489.2
0.12
963
0.243
0.252
0.009
501.0
501.3
0.06
3 1082
0.219
0.200
-0.019
488.7
489.0
0.08
963
0.243
0.262
0.019
501.0
501.0
0.00
4 1082
0.219
0.177
-0.042
488.7
488.9
0.06
963
0.243
0.285
0.042
501.0
501.1
0.02
5 1082
0.219
0.202
-0.017
488.7
489.0
0.08 In-Service Reference Test Power Factors
on 750 kV CTs
at the Zaporozhskaya NPP in 1998
61
0
62
1
60
9
57
9
58
0
61
9
62
7
57
7
70
2
93
8
62
8
14
35
98
2
92
0
10
82
94
0
13
91
12
54
12
78
98
9
91
5
10
77
12
79
PF%Off Line
0,000
0,100
0,200
0,300
0,400
0,500
0,600
0,700
0,800
0,900
PF%Off Line
PF,%On Line No need to de-energize equipment
No Clearance required
No switching required
Results measured under operating conditions
Job that takes 2-3 men a full day off-line can
be done by one man in about one hour on line On-line and off-line data are consistent and
bushing and CT power factor and
capacitance can be tested without taking
equipment out of service.