BBMB has transitioned from using silicon carbide (SiC) surge arresters to metal-oxide (MO) surge arresters for monitoring conditions. The continuous leakage current flow through gapless MO arresters allows for condition monitoring, unlike gapped SiC arresters. BBMB guidelines specify testing MO arresters every 2 years if the third harmonic resistive leakage current is below 200 microamperes, or every 6 months if above. Currents over 1000 microamperes require replacement, while those from 200-1000 on transformers require relocation. Periodic monitoring has helped prevent outages, though the technique has shortcomings and guidelines may need revision based on manufacturer and batch.

1. BBMB EXPERIENCE IN CONDITIONBBMB EXPERIENCE IN CONDITION
MONITORING OF HV SURGEMONITORING OF HV SURGE
ARRESTERSARRESTERS

2. WHAT IS A SURGE ARRESTERWHAT IS A SURGE ARRESTER
 Inexpensive device which allows passage of very small
leakage current through it under normal conditions, but
diverts away high voltages inimical to insulation of
equipment it is supposed to protect by giving them a
path through itself, thereby prevents outage of costly
equipment due to insulation failure
 Reasons of High voltages – Switching, lightening
 Indispensable device in Insulation-coordination
 BIL for 400kV Sys. Around 1425kV.As per IEC highest
allowed is 1239kV
 The smartness of SA lies in limiting the voltage rise well
below 1239kV when a lightning impulse current of
10kA/20kA is impressed.

3. WHAT IS A SURGE ARRESTERWHAT IS A SURGE ARRESTER

4. WHAT IS A SURGE ARRESTERWHAT IS A SURGE ARRESTER

5. - -
-
Rg

6. WHAT IS A SURGE ARRESTERWHAT IS A SURGE ARRESTER

7. DEVELOPMENT HISTORY OFDEVELOPMENT HISTORY OF
SURGE ARRESTERSSURGE ARRESTERS
 Extremely nonlinear characteristic of MO type SAs thereby doing
away with need of disconnection from mains through serial spark-
gaps as in case of SiC type
 Continuous flow of leakage current through gapless MO type SAs
render them suitable for condition monitoring, which was earlier not
possible in case of gapped SiC type SAs. This continuous flow of
leakage current gives picture of inside of MOSA
 Condition monitoring of SA required to pre-access performance of
SA during system over voltages when it is supposed to intervene
in addition to prevent consequential damages it may cause due to
its own bursting

8. COMPARISON OF VI CHARACTERISTICSCOMPARISON OF VI CHARACTERISTICS
OF MOSA AND SiCOF MOSA AND SiC

9. Introduction of MOSA typeIntroduction of MOSA type
Arresters in BBMBArresters in BBMB
• Being one of the oldest among power utilities was having
vast population of conventional valve type SAs with SiC
discs
• Self realization of disadvantages of SiC type arresters
• Feedbacks from other utilities
• Decision to replace convention type with MOSA in
phased manner taken in 1990s.
• First priority Generating Stations
• Rest in phased manner

10. Techniques for monitoring ofTechniques for monitoring of
MOSA type ArrestersMOSA type Arresters
• Realization developed that technique is insufficient
and periodic recording of “Third harmonic resistive
leakage current” is must for checking condition of
MOSAs
• TransiNor make LCM-II procured in year 2002-03.
• Centralized team formed to measure the above
parameter so as to collect sufficient data for
developing some internal standards

11. Guidelines adopted in BBMB forGuidelines adopted in BBMB for
condition monitoring of MOSAcondition monitoring of MOSA
type Arresterstype Arresters
Periodicity of testing
1.For third harmonic resistive leakage current less
than 200 micro Ampere - After 2 years
2.For third harmonic resistive leakage current
more than 200 micro Ampere - After 6 months

12. Guidelines adopted in BBMB forGuidelines adopted in BBMB for
condition monitoring of MOSA typecondition monitoring of MOSA type
ArrestersArresters
• For third harmonic resistive leakage current
more than 1000 micro Ampere—Surge arrester
is to be replaced
• For third harmonic resistive leakage current
more than 200 micro Ampere—Surge arrester
on transformer is to be shifted to transmission
line and surge arrester having less than 100
micro Ampere of resistive leakage current

13. Over all experience of BBMBOver all experience of BBMB
• The adoption of MOSAs having better Volt-amp.
characteristics as compared to valve type SAs helped in
saving costly equipments
• There have been instances where surge arresters
having current of more than 800 micro ampere have got
damaged.
• On the other hand surge arresters having current of
range 300-400 micro ampere have also got damaged.
• Periodical condition monitoring of MOSAs also helped in
preventing unpredictable outages and consequential
damages resulting from a Surge arrester bursting

14. Shortcoming of THRM techniqueShortcoming of THRM technique
• LCM for condition monitoring of MOSA quite popular but
the technique still suffers from certain drawbacks
• Influence of weather conditions and poor repeatability of
readings either due to lack in training of LCM operating
personals or uncontrolled electrical interference
prevalent in HV substations.
• The methodology adopted to extract third harmonic
resistive current is based on considerable assumptions.
• The actual temperature inside the MOSA is not known .
• Absolute values of third harmonic resistive current can
not be used as criteria, only comparative analysis on
time scale can be used.

15. Revision of guidelinesRevision of guidelines
• The main basis of review is that condition of ZnO blocks
is dependent on their manufacturing process including
sintering temperature.
• It has therefore been proposed that analysis of third
harmonic resistive leakage current should be made in
reference to population of surge arrester of individual
manufacturer and if possible, from single batch and
comparison be made on time scale for assessing the
healthiness of surge arrester.
• Another techniques like thermovision scanning of surge
arrester be proactively be used to assess the condition
of surge arrester.

16. Problems faced for procuring LeakageProblems faced for procuring Leakage
current monitoring kitcurrent monitoring kit
• During specification preparation for procurement of new
LCM, problem of selecting range of resistive leakage
current
• One manufacturer says upto 900µA sufficient where as
other stresses nothing less than 9mA will be suffice
• Convoluted explanations of manufacturers obligated us
to refer the issue to CPRI
• Based on inputs from CPRI and references from IEC
60099-5, specification freezed