As an electricity consumer you may not really know the
importance of a circuit breaker, but I want to tell you a little about its
roles and functions especially in Nigeria where electricity is not too stable.
Far back 2009 while I was still in the polytechnic studying
for my Diploma in Electrical engineering I never knew I was going to find
myself in the power industry;
I have always wanted to work in the oil and gas
sector because we all want good pay and a good life. During my schooling days, my
lecturers made so much emphasis on this topic but I never circuit breakers were
so interesting and at same time dangerous to work with.
WHAT IS A CIRCUIT BREAKER?
I am not going to give you those lengthy and bogus
definitions you find on text books; rather I am going to be very practical. What
does it mean to be practical? I am going to tell you what a circuit breaker is
ideally.
From my own experience, I can authoritatively tell you that
a circuit breaker is an electro-mechanical device that is used to make (switch
ON) or break (cut OFF) an electric circuit under normal or abnormal conditions.
I am now going to tell you what switch OFF mean in the
context of our discussion. We all in Nigeria are familiar with the way power
failure is experienced. The electricity distribution operator may have received
an order from the control office to switch off a particular feeder, he does
that by switching off the breaker feeding that feeder or the breaker may have
sensed a fault and tripped.
Switch ON simply means restoration of power supply. This is
done by the operator in charge of substation.
OPEARATING PRINCIPLES
The circuit breaker does not function with the amount of
voltage it interrupts (maybe 330kv, 132kv, 33kv or 11kv). Most of the breakers
used by the electricity distribution companies are coordinated by a tripping
unit which consists of a 110v dc source, a relay, and the trip coil. The 110v
dc actually coordinates the function of the relay.
Now under a fault condition, the relay senses the fault and
sends signal to the trip coil, the signal sent to the trip energizes the
contacts of the trip coil to move from normal open to normally close thereby
forcing the breaker to move from its closed position to open or trip on fault.
TYPES OF CIRCUIT BREAKER
In the Nigerian power sector the most common circuit breakers
in use are as follows;
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Gas operated circuit breaker
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Air blast circuit breaker
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Vacuum circuit breaker
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Oil circuit breaker
Now we are going to discuss two of the most widely used
breakers in Nigeria, The gas operated and vacuum breakers.
The gas operated circuit breaker makes use of sf6 gas. The sf6
gas is an electro-negative gas that is used as the arc quenching medium during
operation.
This is one of the most common breakers in the Nigerian power
sector.
The vacuum circuit breaker is the most common I have worked
with as a substation operator. The arc quenching medium is the absence of air
in the vacuum that houses the contacts.
CIRCUIT BREAKER MANUFACTURERS
ABB
Schneider electric
Alstom. etc
The essence of this whole write up is to tell you the
distribution companies in Nigeria are working round the clock to improve
distribution of power to its customers, but the major problem is inadequate
load allocation from the National grid as Nigeria generates less than 4000MW of
electricity.
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