Condition assessment of Surge Arrester S.K.Mishra A.G.M O ... 2013 Presentations/Day-2 at PMI... ·...
33
Condition assessment of Surge Arrester S.K.Mishra A.G.M O&M Consultancy Wing NTPC
Transcript of Condition assessment of Surge Arrester S.K.Mishra A.G.M O ... 2013 Presentations/Day-2 at PMI... ·...
Condition assessment of
Surge Arrester
S.K.Mishra
A.G.M O&M
Consultancy Wing NTPC
Objective
Analysis of present Monitoring technique.
Evaluation of technologies
IR Thermography
Resistive leakage current
Insulation resistance
C-tan delta
When to replace (Ageing factor)
LIGHTENING
ARRESTER
CROSS
SECTON VIEW
MO element
Sealing
gasket
Cross section of LA
Surge Arrester Cross section
Technologies
Surge counters
Online leakage current Monitoring LCM
IR Thermography
C- Tan Delta Monitoring
Insulation resistance
IDENTIFICATION OFTEHNOLOGY MATRIX
DESIGN FACTOR TECHNIQUE
TEMPERATURE THERMOGRAPHY
RESISTANCE TAN DELTA
DIELECTRIC CAPACITANCE
DIELECTRIC LOSS TAN DELTA
TOTAL LOSS RESISTIVE CURRENT
SURGE COUNTERS OPERATES :-
IMPULSE CURRENT ABOVE AMPLITUDE.
IMPULSE CURRENT DURATION
DISADVANTAGE :-
NEGLECT SHORT IMPULSE <50 ms.
NO SPECIFIC INFORMATION ABOUT THE CONDITION
OF THE ARRESTER.
HEALTHINESS OF MONITOR ?
Third harmonic current monitoring with
compensation : IEC-99-5
Principle :-Non-linear property of Metal Oxide generate
third harmonic current .
DISADVANTAGE :
Manufacturer in India do not specify design safe value.
presence of third harmonic in system.
Wide variation in Temperature .
Wide Voltage variation.
Require expertise for analysis of data.
Trend of leak current
1
10
100
1000
10000
1 2 3 4 5 6 7 8 9 10 11 12 13 14
time
leak c
urre
nt
in m
icro
am
p
Series1
Series2
Series3
Series4
Series5
LA LEAKAGE CURRENT GT -1 R phase
0
50
100
150
200
250
300
350
400
Ju
n-0
8
Ju
l-0
8
Au
g-0
8
Se
p-0
8
Oct-
08
No
v-0
8
De
c-0
8
Ja
n-0
9
Fe
b-0
9
Ma
r-0
9
Ap
r-0
9
Ma
y-0
9
Ju
n-0
9
Ju
l-0
9
Au
g-0
9
TIME
MIC
RO
A
LCM : Leakage Current monitoring
THERMAL IMAGING
INSTRUMENT USED : THERMOVISION CAMERA
METHODOLOGY:-
Thermal image of each LA taken from a close distance and
stored in computer. Delta temperature is analysed.
Max temperature span is 10 to 20 c.
Images are taken when ambient temperature is stabilised (night
time )& Calm weather with less humidity.
THERMAL IMAGE OF HEALTHY STACK
Temperature
distribution is
uniform
UNIFORM
TEMPERATURE
GRADIENT.
GRADIENT LESS THAN 6
C.
TOP STACK
COMPARATIVELY MORE
HOT
THERMAL IMAGE OF DEFECTIVE LA.
CASE STUDY :1 DADRI-MANDULA1 -Y- PH
DELTA
> 8 C
400 KV LINE LA TOP STACK
Max
78.4
Max
78.4
Max
49.6
Max
49.6
Diff. 14
Max.
28.7
BALLABHGURH -1 LINE LA -Y- PH
*>70.0°C
*<-20.0°C
-20.0
-10.0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
CAPACITANCE AND TAN DELTA
PARAMETER INDICATION
CAPACITANCE PHYSICAL
INTEGRITY.
TAN DELTA RESISTIVE LOSS,
CONTAMINATION.
DEL-TANDELTA AGEING
METHODOLOGY : BENCH MARKING
CLASSIFICATION OF EXISITING LA
TESTING OF OLD LA STACKS FOR TAN DELTA, C AND IR
VALUE.
TESTING OF NEW LA FOR TAN DELTA ,C AND IR VALUE.
TESTING OF INSTALLED LA PERIODICALLY AND
TRENDING .
BENCH MARKING C,TANDELTA, IR VALUE FOR
DIFFERENT TYPE .
TEST RESULTS : TAN DELTA VALUE 220 KV -
Make OLD AND NEW
NEW OLD
DEFECTIVE
NEW
DEFECTIVE
GT-3-Y- PH BOTTOM
STACK
CAPACITANCE VALUE OF 220 KV -
Make LA OLD AND NEW
NEW
OLD
DEFECTIVE NEW
DEFECTIVE GT-3-Y-PH BOTTOM
STACK
IR VALUE OF 220 KV Make LA OLD AND
NEW
OLD
NEW
DEFECTIVE
DEFECTIVE
NEW
400 KV make : TAN DELTA OLD AND NEW.
CASE STUDY -2-
OLD
NEW
400 KV : IR VALUE OLD AND NEW
CASE
NEW
OLD
ANALYSIS OF TEST RESULT
LA WITH TEMPERATURE GRADIENT OF MORE
THAN 8 C ARE ABNORMAL.
STACK WITH HIGH TEMP SHOWS VERY HIGH TAN
DELTA VALUE AND HIGH CAPACITANCE VALUE .
STACKS WITH HIGH “C” AND “TAN DELTA” HAVE
SHOWN LOW IR.
TEST RESULTS COMPLIMENTING EACH OTHER
C0-Relation Max temp and resistive
Leakage Current
37
38
39
40
41
42
43
1 3 5 7 9 111315171921
0
200
400
600
800
1000
Max
Temperature
leakage
current
INTERNAL INSPECTION
Dismantled LA 400
kv WSI
Internal Parts
ELPRO 220 KV LA GT3 -Y- PH BOTTOM STACK
ELPRO -GT-3 -Y- PHASE BOTTOM
STACK WATER MARK
ELPRO MAKE 220 KV GT-3- -Y- PHASE
BOTTOM STACK
SURFACE
DISCHARGE
MARK ON
ELEMENTS
IDENTICAL TO
PARTIAL
DISCHARGE
WSI 400 KV MANDULA -Y-
PHASE TOP STACK
HEALTHY LA DEFECTIVE LA
WSI MAKE 400 KV MANDULA -Y- PH
TOP STACK
HEALTHY
ELEMENT DEFECTIVE
ELEMENT
BENCHMARKING OF TEST RESULT
: Make-1 220 KV CLASS
TAN DELTA : 3 TO 5 %
CAPACITANCE MAX 115 PF
IR VALUE > 20000 M OHM (CLEAN )
THERMAL IMAGING DELTA t =<6C
Make-2 400 KV CLASS
TAN DELTA 10 TO 15%
CAPACITANCE 130 PF
IR VALUE >20000 M OHM
THERMAL IMAGING DELTA t=<8 C
Replacement Criteria
Online Monitoring
Decision Tree Off Line TechnologyThermography Schedule 2 year
Not OK
OK
Online Leakage Current( 3 month)
(R-1 month )
>120 H
>500 HH
Thermography (4
month)
T max
Delta T max
>3 c H
>5 c HH
Capacitance
Tan Delta
Insulation resistance
Caunter Red Zone after
cleaning
C>120 pf
TanDelta>10%
IR<20000
Arrester OK
Not Ok
Replace
Revise Schedule
Under
Observation
OK
Master Schedule
not
ok
ok
•Resistive leakage current and IR thermography
are complimenting technology .
•Insulation Resistance or C-Tan delta test can be
used for replacement decision.
•Contamination of middle stack may not give
sufficient indication related to degradation in
either technology.
•Sudden rise in resistive leakage current indicate
water contamination.
• Arresters should be periodically tested for
IR or C-Tandelta value off line.
•A single threshold value of 500 micro amp
will not fit all arresters.
•There is no normal aging of arresters.
Hence time based replacement criteria is
not relevant.
Conclusion
•Most of the failures are due to water ingress into
stacks hence there is risk of sudden death. This can be
eliminated by proper timing of measurement.
•For arresters close to Power Transformers where
failure tolerance is zero thresholds limit should be
fixed based on analysis of the population. A 3 sigma
upper value of 200 micro amp for Indian Make is
more appropriate
Conclusion
