Switch Gear & protection
Chapter-08
(Construction and operation of circuit
breaker)
-Asiqur Rahman Milon,EETE-DIU,EEE-IEB(Con)
#What is the circuit breaker?
A circuit breaker is an automatically operated electrical switch designed to protect an electrical
circuit from damage
caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a
fault is detected. Unlike a fuse, which operates once and then must be replaced, a circuit
breaker can be reset (either manually or automatically) to resume normal
operation.
#
What is the principle of operation and circuit breakers and it’s operation?
- Working Principle of
Circuit Breaker
Circuit breaker essentially consists of fixed
and moving contacts. These contacts are touching each other and carrying the
current under normal conditions when the circuit is closed. When the circuit
breaker is closed, the current carrying contacts, called the electrodes,
engaged each other under the pressure of a spring.
During the normal operating condition,
the arms of the circuit breaker can be opened or closed for a
switching and maintenance of the system. To open the circuit breaker,
only a pressure is required to be applied to a trigger.
Whenever a fault occurs on
any part of the system, the trip coil of the breaker gets energized and the
moving contacts are getting apart from each other by some mechanism, thus
opening the circuit.
Types of Circuit
Breaker
Circuit breakers are mainly classified on the
basis of rated voltages. Circuit breakers below rated voltage of 1000V are
known as the low voltage circuit breakers and above 1000V are called the high
voltage circuit breakers.
The most general way of the classification of
the circuit breaker is on the basis of the medium of arc extinction. Such types of circuit breakers are as
follows :-
2. Minimum Circuit Breaker
3. Air Blast Circuit Breaker
All high-voltage circuit breakers may be
classified under two main categories i.e oil circuit breakers and oil-less
circuit breaker.
Sulphur Hexafluoride (SF6) Circuit Breaker
A circuit breaker in which SF6 under
pressure gas is used to extinguish the arc is called SF6 circuit
breaker. SF6 (sulphur hexafluoride) gas
has excellent dielectric, arc quenching, chemical and other physical properties
which have proved its superiority over other arc quenching mediums such as oil
or air. The SF6 circuit breaker is
mainly divided into three types
·
Non-puffer piston circuit breaker
·
Single- puffer piston circuit breaker.
·
Double-puffer piston circuit breaker.
The circuit breaker which used air and oil as
an insulating medium, their arc extinguishing force builds up was relatively
slow after the movement of contact separation. In the case of high voltage circuit
breakers quick arc extinction properties are used which require less time for
quick recovery, voltage builds up. SF6 circuit
breakers have good properties in this regards compared to oil or air circuit
breakers. So in high voltage up to 760 kV, SF6 circuit
breakers is used.
Properties of Sulphur
hexafluoride Circuit Breaker
Sulphur hexafluoride possesses very good
insulating and arc quenching properties. These properties are
·
It is colourless, odourless, non-toxic, and non-inflammable gas.
·
SF6 gas is extremely stable and
inert, and its density is five times that of air.
·
It has high thermal conductivity better than that of air and assists in
better cooling current carrying parts.
·
SF6 gas is strongly
electronegative, which means the free electrons are easily removed from
discharge by the formation of negative ions.
·
It has a unique property of fast recombination after the source
energising spark is removed. It is 100 times more effective as compared to arc
quenching medium.
·
Its dielectric strength is 2.5 times than that of air and 30% less than
that of the dielectric oil. At high pressure the dielectric strength of the gas
increases.
·
Moisture is very harmful to SF6 circuit
breaker. Due to a combination of humidity and SF6 gas,
hydrogen fluoride is formed (when the arc is interrupted) which can attack the
parts of the circuit breakers.
Construction of SF6 Circuit Breakers
SF6 circuit
breakers mainly consist of two parts, namely (a) the interrupter unit
and (b) the gas system.
Interrupter Unit – This unit consists of moving and fixed contacts comprising a set
of current-carrying parts and an arcing probe. It is connected to the SF6gas reservoir. This unit consists slide vents in
the moving contacts which permit the high-pressure gas into the main tank.
Gas
System –
The closed circuit gas system is employed in SF6 circuit
breakers. The SF6 gas is costly,
so it is reclaimed after each operation. This unit consists low and
high-pressure chambers with a low-pressure alarm along with warning switches.
When the pressure of the gas is very low due to which the dielectric strength
of gases decrease and an arc quenching ability of the breakers is endangered,
then this system gives the warning alarm.
Working Principle of SF6 Circuit Breaker
In the normal operating conditions, the
contacts of the breaker are closed. When the fault occurs in the system, the
contacts are pulled apart, and an arc is struck between them. The displacement
of the moving contacts is synchronised with the valve which enters the
high-pressure SF6 gas in the arc
interrupting chamber at a pressure of about 16kg/cm^2.
The SF6 gas
absorbs the free electrons in the arc path and forms ions which do not act as a
charge carrier. These ions increase the dielectric strength of the gas and
hence the arc is extinguished. This process reduces the pressure of the SF6 gas up to 3kg/cm^2 thus; it is stored in
the low-pressure reservoir. This low-pressure gas is pulled back to the
high-pressure reservoir for re-use.
Now a day puffer piston pressure is used for
generating arc quenching pressure during an opening operation by mean of a
piston attached to the moving contacts.
Advantage of SF6 circuit breaker
SF6 circuit
breakers have the following advantages over conventional breaker
1.
SF6 gas has excellent insulating, arc
extinguishing and many other properties which are the greatest advantages of SF6 circuit breakers.
2.
The gas is non-inflammable and chemically stable. Their decomposition
products are non-explosive and hence there is no risk of fire or explosion.
3.
Electric clearance is very much reduced because of the high dielectric
strength of SF6.
4.
Its performance is not affected due to variations in atmospheric
condition.
5.
It gives noiseless operation, and there is no over voltage problem
because the arc is extinguished at natural current zero.
6.
There is no reduction in dielectric strength because no carbon particles
are formed during arcing.
7.
It requires less maintenance and no costly compressed air system is
required.
8.
SF6 performs various duties like
clearing short-line faults, switching, opening unloaded transmission lines, and
transformer reactor, etc. without any problem.
Disadvantages
of SF6 circuit breakers
1.
SF6 gas is suffocating to some
extent. In the case of leakage in the breaker tank, the SF6 gas being heavier than air and hence SF6 are settled in the surroundings and lead
to the suffocation of the operating personnel.
2.
The entrance of moisture in the SF6 breaker
tank is very harmful to the breaker, and it causes several failures.
3.
The internal parts need cleaning during periodic maintenance under clean
and dry environment.
4.
The special facility requires for transportation and maintenance of
quality of gas.
Vacuum Circuit Breaker
A breaker which used vacuum as an arc extinction
medium is called a vacuum circuit breaker. In this circuit breaker, the fixed and moving
contact is enclosed in a permanently sealed vacuum interrupter. The arc is
extinct as the contacts are separated in high vacuum. It is mainly used for
medium voltage ranging from 11 KV to 33 KV.
Vacuum circuit breaker has
a high insulating medium for arc extinction as compared to the other circuit breaker. The pressure inside the vacuum
interrupter is approximately 10-4 torrent and at this pressure,
very few molecules are present in the interrupter. The vacuum circuit breaker
has mainly two phenomenal properties.
1.
High insulating strength: In comparison to various other insulating
media used in circuit breaker vacuum is a superior dielectric medium. It is
better than all other media except air and SF6, which
are employed at high pressure.
2.
When an arc is opened by moving apart the contacts in a vacuum, an
interruption occurs at the first current zero. With the arc interruption, their
dielectric strength increases up to a rate of thousands time as compared to
other breakers.
The above two properties make the breakers
more efficient, less bulky and cheaper in cost. Their service life is also much
greater than any other circuit breaker, and almost no maintenance are required.
Construction of Vacuum
Circuit Breaker
It is very simple in construction as compared
to any other circuit breaker. Their construction is mainly divided into
three parts, i.e., fixed contacts, moving contact and arc shield which is
placed inside the arc interrupting chamber.
The outer envelope of vacuum circuit breaker is made up of glass because the glass
envelope help in the examination of the breaker from outside after the
operation. If the glass becomes milky from its original finish of silvery
mirror, then it indicates that the breaker is losing vacuum.
The fixed and moving contacts of the breaker
are placed inside the arc shield. The pressure in a vacuum interrupter at the
time of sealing off is kept at about 10-6 torr. The moving
contacts of the circuit breaker are
move through a distance of 5 to 10 mm depending upon the operating voltage.
The metallic bellows made of stainless steel
is used to move the moving contacts. The design of the metallic bellows is very
important because the life of the vacuum circuit breaker depends on the ability of the component
to perform repeated operations satisfactorily.
Working Vacuum Circuit
Breaker
When the fault occurs in the system, the
contacts of the breaker are moved apart and hence the arc is developed between
them. When the current carrying contacts are pulled apart, the temperature of
their connecting parts is very high due to which ionization occurs. Due to the
ionization, the contact space is filled with vapour of positive ions which is
discharged from the contact material.
The density of vapour depends on the current
in the arcing. Due to the decreasing mode of current wave their rate of release
of vapour fall and after the current zero, the medium regains its dielectric
strength provided vapour density around the contacts reduced. Hence, the arc
does not restrike again because the metal vapour is quickly removed from the
contact zone.
Current Chopping in
Vacuum Circuit Breaker
Current chopping in vacuum circuit breaker depends on the vapour pressure and the
electron emission properties of the contact material. The chopping level is
also influenced by the thermal conductivity–lower the thermal conductivity,
lower is the chopping level.
It is possible to reduce the current level at
which chopping occurs by selecting a contact material which gives out
sufficient metal vapour to allow the current to come to a very low value or
zero value, but this is rarely done as it affects the dielectric strength
adversely.
Vacuum Arc recovery of
Vacuum Circuit Breaker
High vacuum possesses extremely high
dielectric strength. At zero current the arc is extinguished very quickly, and
the dielectric strength is established very quickly. This return of dielectric
strength is because of the vaporized metal which is localized between the
contacts diffuses rapidly due to the absence of gas molecules. After arc
interruption, the recovery strength during the first few microseconds is 1
kV/µs second for an arc current of 100A.
Because of the above-mentioned attribute of
vacuum circuit breaker, it is capable of handling the
severe recovery transients associated with short-line faults without any
difficulty.
Property of contact
material
The contact material of the vacuum circuit breaker should have the following property.
·
The material should have high electrical conductivity so as to pass normal load
currents without overheating.
·
The contact material should have low resistance and high density.
·
The material should possess high thermal conductivity so as to dissipate
rapidly the large heat generated during arcing.
·
The material should have a high arc withstand ability and low current
chopping level.
Advantages of Vacuum
Circuit Breaker
·
Vacuum circuit breaker does
not require any additional filling of oil or gas. They do not need periodic
refilling.
·
Rapid recovery of high dielectric strength on current interruptions that
only a half cycle or less arcing occurs after proper contact separation.
·
Breaker unit is compact and self-contained. It can be installed in any
required orientation.
·
Because of the above reasons together with the economic advantage
offered, vacuum circuit breaker has high acceptance.
Disadvantage of Vaccum
Circuit Breaker
·
Requirements of high technology for production of vacuum interrupters.
·
It needs additional surge suppressors for the interruption of low
magnetizing currents in a certain range.
·
Loss of vacuum due to transit damage or failure makes the entire
interrupter useless, and it cannot be repaired on site.
Applications of
Vacuum Circuit Breaker
·
Because of the short gap and excellent recovery of vacuum circuit breaker, they are very useful as very high speed
making switches in many industrial applications.
·
When the voltage is high and current to be interrupted is low these
breakers have definite superiority over the other breakers.
·
For low fault interrupting capacities the cost is low in comparison to
other interrupting devices.
·
Because of the least requirements of maintenance, these breakers are
very suitable for the system which requires voltage from 11 to 33 kV
Bulk Oil and Minimum Oil Circuit Breaker
Bulk Oil Circuit Breaker: A breaker which uses a large quantity of
oil for arc extinction is called a bulk oil circuit breaker. Such type of circuit breaker is also known as dead tank-type circuit breaker because their tank is held at
ground potential. The quantity of oil requires in bulk oil circuit breaker depends on the system voltage. If the
output rating of the voltage is 110 KV, then it requires 8 to 10 thousand kg of
oil, and if their output rating is 220 KV, then breakers need 50 thousand Kg of
oil.
In bulk oil circuit breaker,
oil performs mainly two functions. Firstly, it acts as an arc extinguishing
medium and secondly, it insulates the live parts of the breaker from earth. The
quantity of oil requires for arc extinction is only about one-tenth of the
total and the rest being used for the insulation.
These large quantities of oil are subject to
the carbonisation, sludging, etc., which occurs due to arc interruption
and other causes reducing the insulating properties and requires regular
maintenance.
Bulk oil circuit breaker needs a large tank which increases
expenses and also increases the weight of the circuit breaker. Because of the following disadvantage the low
oil circuit breaker is developed which use minimum oil for arc extinction.
Minimum Oil Circuit Breaker
In this type of circuit breaker minimum oil is used as an arc
quenching medium and it is mounted on a porcelain insulator to insulate it from
the earth. The arc chamber of such type of circuit breaker is enclosed in a bakelised paper.
The lower portion of this breaker is supported by the porcelain and the upper
porcelain enclosed the contacts.
This circuit breaker is of the single breaker type in
which a moving contact tube moves in a vertical line to make or break contact
with the upper fixed contacts mounted within the arc control devices.
A lower ring of fixed contacts is in
permanent contact with the moving arm to provide the other terminal of the
phase unit. Within the moving contact, the tube is a fixed piston. When the
moving contact moves downwards, it forces the insulating oil to enter into the
arc control devices . Thus, the arc gets extinguished.
Minimum oil circuit breaker requires less space as compared
to bulk oil circuit breaker which is an important feature in large
installations. But it is less suitable in places where the frequent operation
is required because the degree of carbonisation produced in the small volume of
oil is far more dangerous than in the conventional bulk oil circuit breakers and this also decreases the
dielectric strength of the material.
The low oil circuit breakers have the advantages of a requirement
of the lesser quantity of oil, smaller space requirement, smaller tank size,
smaller weight, low cost, reduced risk of fire and reduced maintenance
problems. Minimum oil circuit breaker suffers
from the following drawbacks when compared with the bulk oil circuit breakers
·
Increased degree of carbonisation due to a smaller quantity of oil.
·
The dielectric strength of oil decreases due to a high degree of
carbonisation.
·
Difficulty in removal of gases from the contact space-time
#What is arc?
- During
opening of current carrying contacts in a circuit breaker the medium in between
opening contacts become highly ionized through which the interrupting current
gets low resistive path and continues to flow through this path even the
contacts are physically separated. During the flowing of current from one
contact to other the path becomes so heated that it glows. This is called arc.
Arc in Circuit
Breaker
Whenever,
on load current contacts of circuit breaker open there is an arc in circuit breaker, established
between the separating contacts.
#What
is the reason for arcing?
- Arc produce Cause
When a fault occurs a heavy current flows
through the contact of circuit breaker. When the contacts begin to separate,
the contacts area decreases rapidly which causes high increases in fault
current density and hence rise in temperature.
When the contacts are separate, a protential difference is created between
them. If the voltage between contacts is more than dielectric strength of
medium between contacts (usually the medium is air or oil), it may sufficient
to ionise the medium between contacts.
The ionised air or vapour act as a conducting path and hence the arc is
structed between contacts.
The
voltage that appears across the contact of circuit breaker during arcing
periods is called Arc voltage.
The arc between contacts act as conductor and
persist a resistance value known as arc resistance. Current flowing between the
contacts depend on the earth resistance.
– Greater the arc resistance, smaller the current that flows between contacts.
Arc resistance depend upon flowing factors
1. Degree of ionisation: As the ionised particle between contacts is decreases, the arc resistance increases.
2. Length of arc: As the separation between contact increases, the length of arc also increases which results in increase in arc resistance.
3. Cross section area of arc: The earth resistance increases with the decrease in area of cross section of the arc.
– Greater the arc resistance, smaller the current that flows between contacts.
Arc resistance depend upon flowing factors
1. Degree of ionisation: As the ionised particle between contacts is decreases, the arc resistance increases.
2. Length of arc: As the separation between contact increases, the length of arc also increases which results in increase in arc resistance.
3. Cross section area of arc: The earth resistance increases with the decrease in area of cross section of the arc.
What is recovery voltage?
- Define Recovery Voltage
It
is the normal frequency (50 Hz) r.m.s. voltage that appears across the contacts
of the circuit breaker after final arc extinction. It is approximately equal to
the system voltage.
When
contacts of circuit breaker are opened, current drops to zero after every half
cycle. At some current zero, the contacts are separated sufficiently apart and
dielectric strength of the medium between the contacts attains a high value due
to the removal of ionised particles. At such an instant, the medium between the
contacts is strong enough to prevent the breakdown by the restriking voltage.
Consequently,
the final arc extinction takes place and circuit current is interrupted.
Immediately after final current interruption, the voltage that appears across
the contacts has a transient part. However, these transient oscillations
subside rapidly due to the damping effect of system resistance and normal
circuit voltage appears across the contacts. The voltage across the contacts is
of normal frequency and is known as recovery voltage.
#Why use auto recloser in circuit
beaker?
-Reason
The instant
tripping condition in the
circuit breakers clears the fault in the system. ... Auto-reclose
circuit is used on the transmission
line to carry out the duty of
supplying quality electrical power to customers. In this project, an automatic reclose circuit breaker for low
voltage usage is designed.
Why is Testing Circuit Breaker Important?
A circuit breaker might stay idle years, but
if a malfunction occurs it has to detach fault currents of huge kiloamps
gradually within a few milliseconds. Major errors that happen on circuit
breakers are incorrect behavior, short circuits in the coils, damage/wear to
the mechanical connections or the insulation material. Therefore, circuit
breakers need to be regularly and carefully tested. Circuit breakers perform a
vital role in protecting expensive equipment from
damage through faults i.e. connecting and disconnecting
the electrical power in a reliable way; this requires proving their reliability
with on field tests during installation and with regular maintenance tests
during its lifetime to prevent costly failures and problems that could even
compromising the safety of the substation. Testing the performance of your
circuit breakers regularly is therefore an essential and cost-effective part of
any maintenance strategy. Circuit breaker testing particularly concentrates on
obtaining motion and time values on the units. However, our testing solutions
have revolutionized circuit breaker testing. Performing the tests without use
of the station battery greatly increases safety throughout the testing process.
What are the Steps in Circuit Breaker
Testing?
Type Tests of circuit breaker
Type tests are organised with the aim of
proving the abilities and making sure the rated characteristic of the circuit
breaker are exact. Such tests are conducted in the specially built testing
laboratory.
1. Mechanical Test– It is mechanical ability
type test involving the repeated opening and closing of the breaker. A
circuit breaker must close and open at proper speed and do its allocated job
and function without any failure.
2. Thermal Test– Thermal tests are
carried out to check the thermal behavior of the circuit breakers. Due to the
streaming of rated current through its pole in a rated condition, the breaker
under test undergoes steady-state temperature rises. The temperature rise for
rated current should not exceed 40° for current less than 800A normal current
and 50° for normal value of current 800A and above.
3. Dielectric Test– These tests are
performed to check power frequency and impulse voltage withstand
capacity. Power frequency tests are kept on a new circuit breaker; the test
voltage changes with a circuit breaker rated voltage. In impulse tests, impulse
voltage of particular value is employed to the breaker. For outdoor circuit dry
and wet tests are conducted.
4. Short -Circuit Test– Circuit breakers are
subjected to sudden short-circuits in short-circuit test laboratories, and
oscillograms are taken to know the behaviour of the circuit breakers at the
time of switching in, during contact breaking and after the arc extinction. The
oscillograms are studied with particular reference to the making and breaking
currents, both symmetrical and asymmetrical restriking voltages, and switchgear
is sometimes tested at rated conditions.
Routine Tests of a Circuit Breaker
Routine tests are done as per references of
standards of Indian Engineering Service and Indian Standards. These tests are
performed on the manufacturers’ premises. Routine tests confirm the proper
functioning of the circuit breaker. The routine tests confirm the proper
functioning of the circuit breaker. Routine testing doesn’t necessarily include
complex gear in order to ensure that a circuit breaker is functional.
Some guidelines and recommendations for these tests include routine maintenance
and verifying that that circuit breaker performance is in line with manufacture’s
calibration curves. It is crucial that these tests are performed under
stable conditions at suitable temperature so that there are no variations in
the data. Some of the tests are listed below.
Preventative Maintenance of Circuit Breaker, Inspection, and Testing
Preventative maintenance depend operating
conditions for circuit breakers. Primary inspections of CB (circuit
breakers) will look at particulate matter that’s contaminating the inner
workings of the CB. Accumulation of particulates can generally be
disposed of by flipping the lathe on the breaker “Off” and “On” switch to clear
away the accumulated dust
Circuit Breaker Trip Test
By analysing the current consumed by the trip
coil during the circuit breaker’s operation, it is possible to determine
whether there are mechanical or electrical issues present. In many cases, such
issues can be localised to aid in finding the root cause. Optionally,
monitoring the tripping supply’s voltage during the operation can detect issues
arising with tripping batteries.
Insulation Resistance Test
For individual breaker resistance testing,
load and line conductors should be preferably disconnected. If not detached the
test values will also involve the characteristics of the connected
circuit. Resistance testing is crucial for verifying that the insulating
material which makes up the molded cases breakers are performing
correctly. In order to test for insulation resistance, an instrument
known as a megger is used. A megger instrument applies a known DC voltage to a
given wire for a given period of time in order to test the resistance within
the insulation on that particular wire or winding. It is vital that
voltage is employed as the resistance checked with an ohmmeter may differ when
there are no report of potential differences. It should also be noted
that if you apply a voltage that is too high for that insulation to withstand,
then you could potentially damage the insulation.
Connection Tests
Connection testing is important to make sure
that an appropriate electrical connection is available and to recognise traces
of overheating denoted by colour difference. It is important that
electrical connections are properly installed to the CB to prevent and reduce
overheating.
Contact Resistance Test
Normal wear and tear of contacts within the
CB emerges after extended usage. An easy method to identify traces of
weakening within the circuit breaker is to quantify the resistance across every
pole of the breaker. Indications of abnormal conditions within the CB such as
erosion and contamination of contacts are evident if there are excessive
millivolt drops across the breaker. The contact resistance test is important
in finding out if or not a circuit breaker is still apt for functioning.
Overload Tripping Test
Overload tripping components of CBs can be
tested by inputting 300% of the breaker rating into each pole of the circuit
breaker to determine that it will open automatically. The motive of this
is to make sure that the circuit breaker will operate or not. Refer to
NETA standards for trip times that are acceptable for the overload tripping
test. When trying to find out tripping characteristics, it is advisable
to consult with manufacturer’s manuals.
Instantaneous Magnetic Tripping
In routine tests, it is relevant to find out
that the magnetic feature is functional and will trip the circuit breaker
instead of finding the precise value at which the instantaneous magnetic
feature functions.
How Testing of Circuit Breaker is Performed?
Different circuit breaker test equipment are
used to check the operation and condition of circuit breakers on the power
systems. How to test a circuit breaker involves many different test techniques
and type of testers. This will define how to test a circuit breaker through
different testing tools to be applied to check the equipment under a range of
conditions or operation types. Discover how to test a circuit breaker with the
different test sets that you can need.
Testing with Different Equipment:
To consider how to test a circuit breaker, it
is required a deep knowledge of the breaker itself:
·
How it works
·
Its tolerances,
·
Reference values of previous tests,
·
Initial values with which to compare the actual results, sometimes
defined by a rated timing graph,
·
Established settings or initial features given by manufacturer
In this sense, how to test a circuit breaker
becomes a trending analysis since test results are not always definitive but
have meaning just when compared to previous data or results.
Testing with
Circuit Breaker Analyzer
The timing tests of the different open and
close operations of the breaker is an efficient way of how to test a circuit
breaker, analyzing not only the trip times but also the essential synchronism
of the poles in the different operations. This define how to test a circuit
breaker through different simulations of its operation, which can be directly
commanded from the circuit breaker analyzer, or initiated by an external
signal, checking the opening or closing time of each pole, in single or
combined operations, and checking the possible difference between poles or
mismatch time which may lead to a dangerous lack of synchronism. How to test a
circuit breaker with a circuit breaker analyzer depends also on the type of
possible problems to be confirmed, which leads to check other features such as
the possible bouncing, the proper performance of the pre-insertion resistances,
the coils condition, and the mechanical analysis through contact travel speed
and acceleration data with the use of the appropriate transducers.
Testing with a
Micro-ohmmeter
Circuit breakers generally bear a huge value
of current. Greater contact resistance cause greater losses, low current
carrying capability and threatening hot spots in the breaker, so that the
resistance testing with micro-ohmmeters are other way of how to test a circuit
breaker for identifying and avoiding upcoming issues. How to test a circuit
breaker with a micro-ohmmeter requires also reliable measurements and a wide
injection range with high power that enables for longer test leads, less
connections problems, and more accurate measurements.
Testing with a
High Current Primary Injection Tester
The analysis of the tripping time
characteristics of LV circuit breakers and molded-case circuit breakers is
performed using high current injection, as the way to check the entire
functionality. How to test a circuit breaker of this type depends on its
maximum rated current, the trip protection settings and the inverse curve types
which will define the overload and short-circuit trip pickup levels and time
delays; all these features must be checked with the appropriate primary
injection test set with the capacity to simulate the corresponding high current
faults required and capture the answer of the breaker. A system which be easily
upgraded in power capacity enables how to test a circuit breaker in the
different possible situations and range of breakers; how to test a circuit
breaker of this kind also needs a bendable design of the test set to fruitfully
attain the certain large current job, and a design that create possible to
position it nearer to the breaker, and so decreasing the power needed with
smaller test leads; this is the case of the Raptor System, a modular and
flexible primary injection system which easily and quickly adapts its power
capacity to the several high currents ratings of the different circuit
breakers.
Benefits of Circuit Breaker Testing
·
Quick and easy to perform on site
·
Circuits can be tested on or off load
·
Tests performance of whole tripping cycle
·
Tests overall timing of tripping system
·
Identifies need for maintenance
·
Part of a comprehensive diagnostic maintenance program
·
Find early indications of possible problems
·
Avoid issues other than pick up pieces
·
Build up a test record database for trending
·
Pick out the bad actors
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