2014 Fort Collins Utilities L&P Equipment Failure Review
4.9.15
Kraig Bader, Standards Engineering Manager
Overview of Major Equipment Categories
Cable
Elbows & Multi-position Junctions
Transformers
Total Number of Equipment Failures
70
60
50
49
40
30
Switches
20
10
0
1995
2000
2005
2010
2015
Equipment Failures by Customer Hours
Typical Submersible Transformer Installation
Typical Padmounted Transformer Installations
Medium Voltage Underground Cable Anatomy
Jacket
Concentric Neutral
Conductor Shield
Conductor
Insulation
insulation Shield
Medium Voltage cable designs incorporate two semi-conductive shield layers
as well as an overall concentric neutral. Semi-conductive layers are
designed to control voltage stress in the bulk of the insulation.
Cable Failures
Most end-of-life cable failures occur
as a result of dielectric (insulation)
failure
Insulation failure mechanisms
called “water treeing” and “electrical
treeing” are the usual failure
morphology
Cables are often hit by excavators
and directional drilling operations
as well
Cable Dielectric Failure Mechanisms
Water Trees converting to electrical trees in the cable insulation system are the
primary mechanism by which most end-of life cable failures occur.
Conditions for possible development of water trees
• Electrical field
• Water
• Electric field disturbances (voltage transients from switching or lightning)
• Time in service
2
0
2
15
2014
2013
20
2012
2011
2010
2009
4
2008
6
2007
10
2006
2
2005
5
2004
2003
3
2002
2001
5
2000
1999
3
1998
5
1997
3
1996
2
1995
1
1994
5
1993
2
1992
1
1991
1990
2
1989
2
1988
1
1987
1986
1985
1984
Yearly Failures
Fort Collins Utilities Total Cable Failures
25
20
20
14
10
11
9
7
8
5
6
3
4
2
Cable Failures Comparison by Cable Size
20
18
16
14
14
12
10
8
6
4
2
1/0 Failures
750 failures
2014
2012
2010
2008
2006
2004
2002
2000
1998
1996
1994
1992
1990
1988
1986
1984
0
Fort Collins Cable Failures by Month As of 31 Dec 2014
Total Fort Collins Cable Failures by Month since 1984
30
24
25
22
20
20
14
15
12
10
10
12
14
12
11
10
9
5
December
November
October
September
August
July
June
May
April
March
February
January
0
Load-break Elbow Failures
End-of-life medium voltage
loadbreak elbow failures are
usually the result of dielectric
failure.
• Dielectric failures occur
when the insulation can no
longer hold up against the
electric field stress that the
elbow is under
Load-break Elbow Failures
Loadbreak elbow failures also occur as a
result of damage during installation
• Morphology:
- Unintended knife cut leaves
metallic particles in the
insulated portion of the elbow.
- Micro-arcs that don’t actually
reach ground potential occur
within the elbow (this
phenomenon is known as
partial discharge, or PD)
- Partial discharge at metallic
particles begins carbonizing a
leakage current path in the
insulation
– Some leakage current
might follow the metallic
particle path
- PD eventually eats away the
insulation, resulting in
dielectric failure mode
Load-break Elbow Failures
Loadbreak elbow failures also occur as a
result of loose or cross-threaded electrical
connections
• Morphology:
- Loose or cross-threaded
connection creates heat
- Thermal degradation of the
elbow and cable insulation
reduce dielectric strength and
may create carbonized
leakage current path
- Often look very similar to endof-life failures, but dissection
reveals evidence of long-term
localized heating
200 Amp Load-break Elbow Failures
25
21
20
20
# of Elbow Failures
18
18
15
15
14
13
13
11
10
10
10 10
10
10
9
9
8
7
9
9
8
8
7
6
5
11
10
6
5
5
4
4
0
2014
2012
2010
2008
2006
2004
2002
2000
1998
1996
1994
1992
1990
1988
1986
1984
12
December
10
November
October
12
September
20
August
30
July
June
May
April
50
March
12
February
January
# Elbow Failures
Elbow Failures by Month as of 31 Dec 2014
70
63
60
54
46
40
33
30
20
17
12
7
0
Bushing & Junction Failures
Load-break bushings are used on
junctions, transformers, switches and
insulating stand-off modules.
• Bushing failure morphology:
- Loose connection from
improperly seated elbow,
loose or cross-threaded
elbow, or elbow that has
been backed off by other
fault events creates
thermal degradation
condition
- Thermal degradation either
results in
– 1. Mechanical
breakdown of plastic
components
– 2. Dielectric failure of
EPDM rubber
components
Multi-position Junction Failures as of 31 Dec 2014
Total Yearly Junction Failures
12
10
10
8
8
7
6
6
6
6
7
6
6
6
7
6
6
5
4
4
4
4
4
3
3
2
2
3
3
2
2
2
1
2013
2011
2009
2007
2005
2003
2001
1999
1997
1995
1993
1991
1989
0
1987
# of Junction Failures
10
Multi-position Junction Failures by Month as of 31 Dec 2014
Junction Failures by Month of Occurrence
30
26
21
22
19
20
18
15
11
9
5
4
4
February
10
January
5
5
3
December
November
October
September
August
July
June
May
April
0
March
# of Junction Failures
25
Junction Failures & Elbow Failure Comparison by
Month of Failure as of 31 Dec 2014
Elbow Failures by Month of Occurrence
•Both show a tendency to fail as the
weather warms up in springtime,
though junction failures tend occur
later in the season
63
54
46
30
7
12
Decem…
17
Novem…
Septe…
August
July
June
May
April
12
March
12
February
20
12
October
33
January
# Elbow Failures
70
60
50
40
30
20
10
0
Junction Failures by Month of Occurrence
26
25
15
22
11
9
5
3
Novem…
August
July
June
May
April
March
0
5
October
4
Septem…
4
February
10
5
318
–Total Junction Failures as of 12/31/14: 149
18
Decem…
20
–Total Elbow Failures as of 12/31/14:
21
19
January
# of Junction Failures
30
•Elbow failures have occurred at a
rate of roughly 2-3 times that of
junctions
•The elbow population is roughly 3 to
4 times that of the junction population,
so the relative failure rate makes
sense.
Statistical Measures of Availability & Reliability
ASAI – Average System Availability Index
•
Percentage time the system is available to customers
SAIFI – System Average Interruption Frequency Index (sustained Interruptions)
•
Number of interruptions the average customer experienced
MAIFI – Momentary Average Interruption Frequency Index (momentary
interruptions)
•
Number of momentary interruptions the average customer experienced
SAIDI – System Average Interruption Duration Index
•
Average amount of time each customer would have been out had they all experienced an
outage
CAIDI – Customer Average Interruption Index
•
Average length of the outage time for time each customer who experienced an outage
Average System Availability Index (ASAI)
Goal: 99.9886% or Higher
ASAI (Average System Availability Index)
The Reliability of the System is:
Desired Result:
100.0000%
Goal
99.9980%
99.9956%
99.9960%
99.9951%
99.9940%
99.9920%
99.9900%
99.9880%
99.9860%
99.9840%
99.9820%
99.9800%
2014
2013
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
System Average Interruption Frequency Index (SAIFI)
Goal: .66 or fewer outages per customer
SAIFI (Sustained Average Interruption Frequency Index)
The Average Customer Had the Following Number of Sustained Outages:
Desired Result:
1.40
Goal
1.20
1.00
0.80
0.66
0.60
0.37
0.40
0.20
0.00
2013
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
Customer Average Interruption Index (CAIDI)
Goal: 30.00 Minutes or Less
SAIDI (System Average Interruption Duration Index)
If All Customers Had Been out of Power, they Would Have Been Out For:
Desired Result:
80.00
Goal
70.00
60.00
Minutes
50.00
40.00
30.00
30.00
25.54
20.00
10.00
0.00
2014
2013
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
Comparison of Reliability Statistics
Fort Collins (0.37, 25.54)
THANK YOU!
Kraig Bader
[email protected]