Use of Reliability Data from High Voltage Equipment CIGRE Survey

 

Introduction

 

When undertaking a survey into the reliability of electrical equipment it is important to consider how utilities/manufacturers/universities apply and benefit from the calculated availability, failure rates and other parameters in the survey. A summary is given of the views of the working group, together with information from CIGRE brochure No. 211 “General overview on experience feedback methods in the field of electrical equipment” and other CIGRE surveys for high voltage equipment.

 

General

 

The use of the reliability data from the survey can generally be split into two main areas, either to look at the overall network performance or to look at individual asset (equipment) performance.

 

A number of electrical networks worldwide have an increasingly aged population of electrical equipment. This survey should be able to help understand the impact both on network performance and help mitigate the effects through proper operation, effective maintenance, monitoring, asset refurbishment and asset replacement.

 

Additionally the survey will aid in adopting a more statistical approach to asset management including maintenance and replacement.

 

Network Performance

 

Network reliability can be modelled by splitting the network into a number of components (for example transformers, circuit breakers, overhead lines, etc) and then the reliability of each component can be used to predict the overall network performance.

 

Typically such studies are of interest to network operators, owners, universities, regulators and suppliers of transmission systems.

 

Studies can be made into structures of transmission/distribution networks. Typical studies could be:

• Analysis of existing network and substations to find and improve weak area
• Predict future network and substation performance due to aging of equipment
• Design optimum network and substation layouts

 

These studies would examine the following:

• Network resilience and complexity – to look at the reliability of a network including the ability to take outages for repairs and construction work
• Substation design and layout – examining different substation layouts and the need for redundancy

 

It should be noted that some data needed for such a study, such as the potential outcome of the failure (trip of circuit, unscheduled maintenance outage, failed item remaining undiscovered in service, etc) and length of outage are not collected although these can be inferred from the data collected if correctly presented.

 

Asset (Equipment) Performance

 

The performance of an asset can be split into the asset lifecycle. At each stage reliability data can be used to monitor and improve the process by equipment users, manufacturers, regulators or by interested third parties such as universities.

 

A summary of the uses of reliability data is given in Table 1. The survey collects data to enable calculation of failure rates and also estimates how failure rates change with the age of equipment. Additionally data about causes, modes of failures, location of equipment, components that fail and different technologies employed is gathered and failure rates can be compared within the survey in each of these categories. Users of the survey may calculate failure rates of their own equipment and may compare their failure rates to those in the survey, either for individual equipment or for the user’s overall performance. Additionally the survey collects information on maintenance.

 

Specification, Design, Manufacture and Installation

 

The survey will compare failure rates to identify failure causes, modes and components that cause the most problems. This can be used for:

• Research and development to address the technical issues and failure mechanisms highlighted in the survey.
• Specifications and standards can optimise the testing requirements of the equipment focusing on the most likely causes of failures.
• Designs can be optimised so that the design addresses failure mechanisms identified in the survey.
• Improved application
• Manufacturing and installation methods can be reviewed to minimise identified failure mechanisms.

 

As part of the survey, different technical solutions will be compared. Specifications can make requirements on particular technology solutions that have a higher reliability or designers can design systems that use technical solutions that have a higher reported reliability.

 

The reliability of equipment in different locations can be compared and may lead to direct recommendations on improved application of equipment. The information may be used in combination with technology information to lead to improvements in design.

 

 

 

 

Building

Operating

Replacing

R&D

Specification and standards

Design optimisation

Improved application

Manufacturing and factory testing

Installation and site testing

Life Cycle Costing

Operation

Maintenance

Monitoring

Insurance requirement

Identification of asset  replacement / refurbishment

Asset refurbishment content

Asset replacement strategy

Absolute failure rates

x

x

x

x

x

Failure rate with age

x

x

x

x

x

Comparative failure rate (causes, modes, components)

x

x

x

x

x

x

x

x

x

x

x

Comparative failure rate (location)

x

x

x

x

Comparative failure rate (technological solution)

x

x

x

x

x

Maintenance information in survey

x

x

User compares own design / equipment with survey

x

x

x

x

x

x

x

x

x

x

x

User compares overall failure rates with survey

x

x

x

x

Table 1: Summary of Asset (Equipment) Performance Improvements That Typically Can Use Reliability Data