PRESENTATION
Brussels • 8-10 April 2008
A Risk Based Approach to
Electricity Distribution System
Asset Management
Speaker:
Company:
Dag Eirik Nordgård
NTNU / SINTEF Energy Research
Co-author:
Company:
Maren K. Istad
SINTEF Energy Research
Co-author:
Company:
Kjell Sand
SINTEF Energy Research
© Euromaintenance 2008 – Belgium - www.euromaintenance.org
1
Content
Introduction
MV Electricity distribution systems
What is it
System and component characteristics
Maintenance and reinvestments in distribution systems
Risk management in distribution systems
Risk assessment in maintenance and reinvestment
decisions
Methods and approaches
Example: Risk assessment for MV overhead lines
Measuring risk and performance
Concluding remarks
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Electricity Distribution systems – What is it?
Production
Transmission
Subtransmission
420 kV
300 kV
132 kV
66 kV
G
MV Distribution
22 kV
11 kV
LV
customers
230 V
400 V
G
G
G
Import/Export
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Transmission / sub-transmission
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MV Distribution system
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LV Distribution System
MV/LV Sub-station
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Focal area for this presentation
Production
Transmission
Subtransmission
420 kV
300 kV
132 kV
66 kV
G
MV Distribution
22 kV
11 kV
LV
customers
230 V
400 V
G
G
G
Import/Export
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MV System and component characteristics
MV electricity distribution systems:
An already existing infrastructure - most of it being built during the last 50 years
Having challenges of handling an ageing infrastructure
Putting emphasis on maintenance and reinvestments
MV distribution system characteristics:
Widely geographically dispersed
Vast amounts of components
Majority of static components (e.g. overhead lines, cables and transformers)
Minority of the components have moving parts (e.g. load breakers, sectioning
switches, transformer tap-changers)
Component lifetimes are typically 30 to 60 years – with large variations in average
lifetime
In many cases there are few maintenance activities which can prevent the
degradation of the distribution system components, and if the component
condition is questioned, reinvestments (partial or total) of components are the
available option. Hence maintenance and reinvestment decisions are closely
related.
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Risk management in Distribution Systems
“What do we actually do when we manage a business? In
our view, we manage the risk – of safety and
environmental incidents, adverse publicity, loss of
efficiency and productivity, and loss of market share.”
V. Narayan - “Effective maintenance Management – Risk and reliability
Strategies for Optimizing Performance”
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Risk management concept
Risk management are coordinated activities to direct and control an
organization with regard to risk – including the tasks of risk
assessment, risk treatment, risk acceptance and risk communication
Risk assessment
Risk analysis
Source identification
Risk estimation
Risk treatment
No
OK?
Yes
Risk acceptance
Decision making
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Risk avoidance
Risk optimization
Risk transfer
Risk retention
Risk communication
Risk evaluation
Consequence categories
There are several consequence categories which are
relevant for distribution companies, including:
Economy
Safety (occupational and public)
Company reputation
Environmental impact
Quality of supply
Fulfilling of contractual obligations.
There will be interdependencies between the different
consequence categories – and unwanted events will often
have impact on more than one category at the time.
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Risk assessment
Risk assessment requires some kind of modeling of the entity
in question – choosing risk analysis methods to perform risk
analysis.
Different risk analysis methods exist with different degrees of
detail and data demand – from aggregated pragmatic
approaches to highly detailed models.
The vast number of components in the electricity distribution
system makes it is unrealistic to perform a thorough risk
assessment on every component or sub-system in the grid.
More pragmatic and generic approaches must therefore be
adapted.
Other analyses will also contribute to the overall analysis and
understanding of the problem, e.g.:
Load flow analysis
NPV-analysis of expected future cash flows
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The aim for risk assessment
The overall aim of performing risk assessment
should be:
Not to seek the “correct objective solution”,
Rather contributing to a risk-informed decision basis
for the decision maker’s evaluation of the problem at
hand
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Degree of explicit modeling
Demand for resources – Effort
Methods for risk assessment
QRA
Quantitative
risk assessment
Informal risk
assessment
”Gut feeling”
Qualitative /
semi-quantitative
risk assessment
Qualitative
Quantitative
Informal
Formal
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Example:
Establishing maintenance strategy for MV
overhead lines
Based on work performed for a group of
Norwegian electricity distribution companies
Semi-quantitative risk analysis is used for
the task
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Establishing maintenance strategies:
Identification of maintenance entities.
Dividing the actual system into a suitable grouping of
entities.
Risk analysis concerning each of the maintenance
entities.
Identifying unwanted events,
Quantifying probabilities for the events
Quantifying consequences of the events
Estimating risk.
Finding possible maintenance actions to control risk.
Evaluation and adaptation of results.
Through discussions of existing practice and the results
from the risk analysis, a maintenance strategy is
formulated.
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Identification of maintenance entities
For the analysis of MV overhead lines the
following sub-components were identified:
Poles (including traverse, insulators, ..)
Phase conductor
Line trace
Pole-mounted switches
Cable terminations
Pole-mounted MV/LV sub-stations
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Phase conductor
Poles (including traverse,
insulators, ..)
MV / LV substation
Switches
Cable termination
Line trace
Risk consequence categories
For each of the maintenance entities risk
estimation was performed with regards to the
following consequence categories:
Safety
Environmental impact
Reputational impact
Economy
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Risk analysis – component Poles
Though brainstorming and discussions among a group of
company experts the following unwanted events were
identified:
Event #
1
2
3
4
5
6
7
Description
Pole breakage
Pole askew
Pole damaged by fire
Event #
8
9
10
Insulator flashover
Conductor falls on traverse / burnt
traverse
Broken traverse
Flashover / discharge of insulator
chain
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11
Description
Displaced traverse
(Partially) defect discharger
Fall down from (and / or with) pole
Person climbing in pole and touching
live MV parts
12
Poor earthing connections
13
Insulators destroyed by vandalism
Creosote impregnation run-off to
water and/or soil
14
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x
x
x
x
x
x
Reputation
x
Environment
Safety
1 - Pole breakage
2 - Pole askew
3 - Pole damaged by fire
4 - Insulator flashover
5 – Conductor falls on traverse / burnt traverse
6 - Broken traverse
7 - Flashover / discharge of insulator chain
8 - Displaced traverse
9 - (Partially) defect discharger
10 - Fall down from (and / or with) pole
11 - Person climbing in pole and touching live MV parts
12 - Poor earthing connections
13 - Insulators destroyed by vandalism
14 - Creosote impregnation run-off to water and/or soil
Economy
Grouping of risk impact
x
x
x
x
x
x
x
x
x
x
x
x
x
(x)
x
x
x
x
Location in risk matrix for Safety
Consequence
Probability
C1
Negligible
C2
Small
C3
Medium
C4
Serious
C5
Catastrophic
P5 : Highly probable
P4 : Very probable
P3 : Probable
P2 : Less probable
P1 : Improbable
8
3
1
6
10
11
Some of the 14 initial events are not relevant with regards
to the consequence category safety, and are hence not
included in the matrix.
Events 10 and 11 have been identified as being the most
critical with regards to safety in our risk mapping.
# 10 - Fall down from (and / or with) pole
# 11 Person climbing in pole and touching live MV parts
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Risk evaluation and adaptation of results
Based on the risk analysis for safety – the maintenance
strategy gives emphasis on the following maintenance
activities:
Control of occurrence of rot in poles, and
Vegetation management near overhead lines
The intervals for the maintenance activities are
established based on existing practice and the experience
and knowledge of the company experts.
An important result from the process is the documentation
of what risks are considered and what measures have
been chosen to meet the risk challenges.
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Measuring performance and risk
Important to measure critical parameters of the
distribution system asset management process.
Both looking backwards (on performance achieved) and
forwards (on parameters affecting future possible
outcomes)
Risk
indicators
Possible
outcome(s)
Improvements?
Distribution system
asset management
Actual
outcome
Performance
indicators
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Concluding remarks I
Electricity distribution companies in Norway are now in the process of
adapting the principles of risk management as guidance for their asset
management.
There are of course some challenges included in this process.
Three key challenges are:
Changes in mentality.
Challenge the existing way of thinking
Establishing a culture for risk management
Tools and methods.
Development of methods to support distribution system decisions
An important part of this will be documentation of risk evaluations performed
Input data for analyses.
Finding / choosing numerical values to be used in computations is a challenging task.
Experience shows that one often will find little help in statistical data due to lack of
representative data. One has to choose an approach where the (possible) input from
statistical values is used in combination with expert judgment.
Improving the registration of maintenance data for to aid statistical analysis.
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Concluding remarks II
Important:
The results from the risk analyses will not provide
“objective correct results”
It will rather contribute to problem overview, understanding and
solution
The search for the “objective answer” is a path that leads to little
but frustration (since the ‘one and only’ objective answer does not
exist..).
The aim of risk assessment should therefore be to
contribute to a risk informed decision for the decision
maker
The responsibility of asset management decision making
can and should not be replaced by the calculations in a
risk analysis model, but the results from the analyses
should instead contribute to the basis for making good
decisions.
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Brussels • 8-10 April 2008
Contact
Speaker
Name :
Function :
Department :
Phone :
Mobile :
Fax :
E-mail :
Dag Eirik Nordgård
PhD-candidate / Research Scientist
Department of Electrical Power Engineering
+47 73 59 76 63
+47 93 22 16 79
+47 73 59 72 50
[email protected]
Company
Name :
Main activity :
Address :
Zip code :
City :
Country :
Web site :
NTNU – Norwegian University of Technology and Science
University
Sem Sælandsv. 11
N-7491
Trondheim
Norway
www.energy.sintef.no/prosjekt/RISKDSAM
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