Preface
This article is the first in a series of articles that will help
to bring light to the maintenance practices presently applied to
power circuit breakers.
A list of the most popular tests used; with reference to the
international standards compliance, is included at the end. Each
test provides a bit of information that is complementary to the
others, providing a general overview of the circuit breakers
testing practices.
A circuit breaker is an important equipment to power electric
networks. Its importance is due to the protection role it is
playing. Hence, it is imperative to assure its proper operation.
This is only possible by applying suitable maintenance.
The main purpose is to help us understand, accurately, the real
condition of the breaker being tested thus helping targeting the
corrective actions. This targeting helps minimize maintenance
spending and increase network reliability, hence leading to
efficient network management.
Introduction
A power circuit breaker is equipment intended to switch on and
off electric currents on power transmission and distribution
networks for routine operations and protection of other
equipment.
Electric transmission system breakups and equipment destruction
can occur if a circuit breaker fails to operate because of a
lack of preventive maintenance.
Description
Its name, circuit breaker, indicates clearly its role. It breaks
electric circuits. To achieve this purpose, it separates
mechanically two points in the circuit to a certain distance
large enough to break the flow of electric currents.
Circuit breakers come in a great variety and use different
technologies:
Despite the big difference all types share common principals,
they all have to provide two main functionalities highly
related:
- Electrical functionality (Interrupter).
- Mechanical functionality (Mechanism).
Electrical functionality
Circuit breakers are designed to satisfy predetermined breaking
conditions and have electrical properties that can be resumed by
the following:
- Current carrying property;
- Insulating property;
- Current breaking property.
Mechanical functionality
The requested electrical properties imposes mechanical
properties that can be more or less demanding depending on the
used technology:
Current carrying property imposes:
• Contact material that is highly conductive;
• High quality of contact make;
• Low contact reaction to ambient atmosphere and temperature.
Insulating property, depending on the voltage level imposes:
• The contacts parting distance in open position;
• Line to ground distance;
• Characteristics of the insulating medium and reaction over
time
Current breaking & making properties, imposes:
• The speed of the opening or closing contacts;
• Arc blowing techniques;
• Resistant to arc material;
• Energy required to carry on the breaking or making of large
short circuit currents;
• Characteristics of the insulating medium and reaction over
time and frequency of current interruption.
Frequency of operation property, influences greatly all the
above-mentioned parameters.
Preventive maintenance
The need for maintenance of circuit breakers is often not
obvious, as circuit breakers may remain idle, either open or
closed, for long periods of time. The need to predict the proper
function of circuit breakers grew over the years as transmission
networks expanded and carried increasing energy to longer
distances.
The technology advance over the years brought low maintenance
breakers but it did not bring more reassurance to network
management as to the reliability of operation.
The circuit breaker is, in fact, a black box. The only way to be
sure of its condition is to open it for physical inspection.
Unfortunately, this way is costly and must be reduced to minimum
to prevent unnecessarily maintenance.
Predictive maintenance
Maintenance people created what is now widely known as the
predictive maintenance. The purpose is to predict accurately the
condition of the breaker, without having to open it for
inspection.
Required open inspection would then be limited to corrective or
preventive intervention, thus reducing dramatically the cost of
maintenance and increasing to the same level its efficiency.
The prediction can take three ways complementary to each other:
TESTING: a wide range of tests where invented to verify the
conformity of each of the electrical and mechanical properties
to meet the design criteria. Some of these tests are
acknowledged and documented by international standards (IEC,
ASTM, etc.). Some are still under development and promise great
expectations.
MONITORING: continuous surveillance of the breaker by the means
of multitude transducers controlled by a computer. Alarms or
actions are triggered when settings are reached thus permitting
just in time intervention. This way is still under development
and is very promising.
STATISTIC STUDY: continuous measurements, samplings and
maintenance interventions, are noted over the years on each
breaker. This information assembled in databases, helps conduct
statistic studies aiming to target the faulty components or
helps a probabilistic modeling of aging in Circuit Breakers for
Maintenance.
A practice widely spreading by network administrators, is to
require for each type of new breaker a statistic study from the
supplier on the reliability of the new equipment components,
based on their own experience. This will help to focus the
maintenance actions on the most vulnerable parts.
Safety Practices
Maintenance procedures have to respect the safety practices and
the following points require special attention:
a) Be sure the circuit breaker and its mechanism are
disconnected from all electric power, both high voltage and
control voltage, before it is inspected or repaired.
b) Exhaust the pressure from air receiver of any compressed air
circuit breaker before it is inspected or repaired.
c) After the circuit breaker has been disconnected from the
electrical power, attach the grounding leads properly before
touching any of the circuit breaker parts.
d) Do no lay tools down on the equipment while working on it as
they may be forgotten when the equipment is placed back in
service.
Breaker testing
Maintenance tests enable personnel to determine if breakers are
able to perform their basic circuit protective functions.
The tests mentioned in the following table of tests, may be
performed during routine maintenance and are aimed at assuring
that the breakers are functionally operable. These tests are to
be made only on breakers and equipment that are deenergized.
The Table of Tests lists the tests and their purposes, regrouped
by the purpose category (Mechanical, Electrical, Chemical).
In general, to conduct a successful test, the following
conditions has to be observed:
• Application procedure (provided by the test equipment
provider);
• Design specifications with defined tolerances (provided by the
breaker designer);
• The breaker instruction book and related outline, basic and
elementary drawings (provided by the breaker designer);
• The international standards definitions and specifications if
required by the test.
• Good sense of analysis
Maintenance Program
The same need to predict the proper function of circuit breakers
that created the predictive maintenance, and since it is not
feasible to test indefinitely the circuit breakers, it was
obvious to structure the maintenance acts in a maintenance
program that defines the maintenance actions and frequency.
Most of breaker manufacturers recommend maintenance programs
that suit better their equipment. They generally define three
levels:
1- Routine inspection: includes:
• Visual inspection of the outer shape of the equipment.
• Checking the operation counters.
• Checking the pressure gauges.
• Detecting visual or audible leaks.
• Measuring temperature.
• Etc.
This is done with the breaker in service.
Frequency: generally 6 months to 1 year
2- Minor maintenance: Includes, in addition to the routine
inspection:
• Thorough inspection of the state and function of
subassemblies,
• Breaker testing
• Minor interventions to replace easy access ware parts,
• Changing filters, oil or gas etc.
This needs to isolate the breaker from the network.
Frequency: generally 6 to 8 years
3- Major maintenance: Includes, in addition to the minor
maintenance, opening the major assemblies to access internal
parts:
• Interrupter;
• Mechanism;
• Tank receiver.
This needs to isolate the breaker from the network.
Frequency: depends on breakers technology (12 years for air
blast, 20 years for SF6, etc.)
Bibliography
MAINTENANCE OF POWER CIRCUIT BREAKERS; HYDROELECTRIC RESEARCH
AND TECHNICAL SERVICES GROUP; FACILITIES INSTRUCTIONS, STANDARDS
AND TECHNIQUES VOLUME 3-16; UNITED STATES DEPARTMENT OF THE
INTERIOR BUREAU OF RECLAMATION DENVER, COLORADO.
About the Authors
Dr. Fouad Brikci is the president of Zensol Automation Inc. He
was the first to introduce the concept of truly-computerized
test equipment in the field of circuit breaker analyzers. As a
former university teacher in Ecole Polytechnique — Algiers and
CNRS LAAS researcher in France, Dr. Brikci has developed
experience in the fields of electronics, automation, and
computer science. Most activities were focused on the industrial
application of computers. Among his achievements are the
development of fully computerized measuring systems for quality
control in circuit breaker manufacturing, laboratories, and
maintenance services of electric utilities. Dr. Brikci holds a
PhD in Electronics and a Master in Sciences in EEA
(electronics, electrotechnics, and automation) from the
University of Bordeaux, France.
http://www.zensol.com,
email : zensol@zensol.com
Emile Nasrallah is an electrical engineer specialized in Power
circuit breakers maintenance. Since graduation in 1984 he worked
as a field engineer. In1990 he joined the worldwide circuit
breaker manufacturer GEC ALSTHOM as a specialized field
engineer. In 1997 he became the manager of MV & HV circuit
breaker SF6 division of ALSTOM, responsible of technical
support, maintenance and training for SF6 circuit breakers. In
2001 he became manager of Air blast circuit breaker division for
AREVA. He was in charge of the Air blast (PK and PKV)
refurbishing program in partnership with hydro-Quebec and
introduced a unique administration system for the program
(average of 35, 735 kV PK air blast circuit breaker per year).
In 2005 he joined General Electric Company of Canada as a senior
circuit breaker specialist and is in charge of the circuit
breaker division of the Montreal service centre, responsible of
the remanufacturing program for Oil circuit breakers
