FMJL Current Transformer Failures - Energy Networks Association

MANAGEMENT OF SAFETY RISKS FROM EQUIPMENT
RETAINED IN SERVICE WITH AN ABNORMAL CONDITION
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Gary Thornton, Asset Strategy & Engineering Manager
10:30 – 10:50

What are the Consequences of Equipment Failure?
Willesden QB Failure 2008
Cardiff East FMJL Failure 2009
Connahs Quay FMJL
Failure 2011
Deeside FMJL Failure 2009
Indian Queens FMJL Failure 2010
3

FMJL Current Transformer Failures
FMJL
Type - Bar
Primary
Primary goes through CT on a
straight bar
CT rings arranged around the primary
Secondary leads go to the bottom of
the CT
The CT rings are covered by a copper
tape
Secondary wires go through a metal
pole
Both connected together and earthed at
bottom
Primary Current 2000A down to
Secondary Current of 1A. Used for
Protection (measures up to 63,000A
fault current) and Metering
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FMJL / FMVG Failures by 2009
2009 - Deeside 400kV FMJL
2009 - Upper Boat 33kV FMVG
2009 - Cardiff East 275kV FMJL
1997 - Oldbury 400kV FMJL – Not established /
breather manufacturing defect
1992 - Littlebrook 132kV FMJL – Not established /
possible insulation design
5 failures (2 pre 2000) & 6 removed from service
following poor oil results
Significant number of failures world wide – 22
5

FMJL Failures
Understanding the Failure Modes
Major insulation failure of toroid or stem insulation due to:-
Materials / Manufacturing Defect (normally ‘burn in’ issue)
Degradation by partial discharge
Degradation due to thermal or moisture or poor quality of oil
High Temperature Operation
HV internal bonding lead connection failure
Loss of Insulation oil
Breather blockage
Open Circuit CT / CT Test Tap
CT on open circuit develops an infinite voltage leading to rapid
insulation breakdown and disruptive failure
6

Progression Mechanism for a Dielectric Failure of the
Insulation in an Oil Impregnated Instrument Transformer
DGA
FREE GAS
FORMATION
AUDIBLE NOISE
THERMOVISION AND LARGE AMOUNTS OF RFI
FAILURE
CHANGES IN OIL INDICATORS OR PRESSURE GAUGES
RISING
ACETYLENE
DETECTABLE CHANGE IN CAPACITANCE
DETECTABLE RFI
DETECTABLE CHANGE IN TAN DELTA
Gas level rising
LONG TERM
MEDIUM TERM
SHORT TERM
V SHORT
TERM
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FMJL Failures
How we managed the risk Since 2009
Quantified Risk Assessment based on ALARP principles using historic
failures, number of units, length in service, equipment condition data,
ballistic data, diagnostic data, exposure, and vulnerability
Risk cannot be justified
except in extraordinary
circumstances
Control measures
introduced for the risks in
this region to drive the
residual risk toward the
broadly acceptable region
Level of residual risk
regarded as insignificant
and further effort to
reduce risk is not likely to
be required
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FMJL Failures
How we managed the risk Since 2009
Unacceptable risk under normal site operating conditions putting public
and staff at risk
2009 - 142 sites affecting 40% of the network
Risk mitigation considerations ERICPD –
Switch Out (remove the hazard)
Risk Management hazard zones (75m)
Physical Barriers (ballistic screening)
Development of PD Trailer and Alarm Pod
2009, 94 Site Specific Risk Assessments undertaken in one week where
RMHZ extended onto public land
Issued ENA, Dangerous Incident Notice (DIN) and Suspension of
Operating Practice (SOP) notice and set up ENA working group to provide
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an industry response

Overlapping RMHZs – Restricting Access,
Impact of Overdue Maintenance and
Mitigation Measures
All SGTs have RMHZs
applied to FMJLs on the HV
In order to replace SGT2
FMJLs and outage is
required on SGT1, 2 and
potentially 3 to allow access
to the work area for cranes.
This is not always possible
Steel containers are good
for perimeter protection
but due to phase & earth
clearances can not always
be applied within the
substation
Ballistic Screening takes up a large
footprint requires outages to erect
and cannot always be applied
between circuit bays
Failure to maintain
CB due to FMJL
RMHZ may incur an
additional 50m
RMHZ until complete
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Development of PD Trailer and
Alarm Pod
Mobile PD monitoring trailer can be deployed and set up in any position in
the substations using wireless communication and gives:
Directional coverage to indicate location and specific area of PD, i.e.
detection of the first signs of electrical breakdown prior to a fault
Time of flight measurement calculated to give range and direction onto a
2D layout drawing hosted onto a web server for remote access
Alarm pod built with audible (sounding alarm) and visible warning (flashing
lights):
Sends a text alert when activated to selected staff and our Networks
Operations Centre
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FMJL Failures
Result of Intensive Forensic Analysis
2011 - Connah’s Quay 400kV FMJL – Materials /
manufacturing defect
2010 - Indian Queens 132kV FMJL – Moisture ingress
2009 - Deeside 400kV FMJL – Test tap circuit failure
2009 - Cardiff East 275kV FMJL – Moisture ingress
1997 - Oldbury 400kV FMJL – Not established /
breather manufacturing defect
1992 - Littlebrook 132kV FMJL – Not established /
possible insulation design
2009 – Upper Boat 33kV FMVG – Moisture ingress /
manufacturing defect
Overall Conclusion – Remove from the System
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FMJL/VG – Replacement Programme as
at end March 2012
Original population – 467 circuits, 199 circuits removed to date
43% of population
54 circuits removed prior to 11/12
145 circuits removed in 11/12
Aiming to have all FMJL and FMVG removed by end 2013/14
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Summary
Safety of our staff, contractors and the public is our number
“1” priority
Significant number of FMJL/VG failures UK and world wide
Forensic Analysis confirms removal of these units the right
course of action
When dealing with assets in an abnormal condition:
Understand potential failure modes and determine cause of
actual failures
Quantify the risks using a quantified risk assessment using
ALARP principles
Use ERICPD Principles to mitigate the risks
Understand and deal with your secondary risks
14

Thank you
Mark Osborne, System Strategy, National Grid