Curcuit Breaker Abstract Essay, Research Paper
Abstract
A circuit breaker was examined to determine how it works.
Basically, it is designed to disconnect the current if the current passing
through the breaker is higher than the allowable current. Its main parts
consist of a switch, connecting pads, and the disconnect device. Since
the breaker consists of many individual parts, the only improvement found
was to combine some of the parts into a single part.
Introduction
Our group dissected a thirty-amp household Circuit-breaker. Its purpose is
to protect electrical appliances from being damaged though excessive
currents. A circuit breaker limits the amount of current that may safely
enter a household electrical system via a predetermined amperage rating.
It is placed in series between your house and the provided electricity.
Any current in excess of the rated current amount will trip the circuit
breaker in to a non-conducting or open path condition. The closed path is
maintained until either magnetism or thermal expansion causes the circuit
to trip.
Device Description
The circuit breaker has several features that are worth noting in the
design discussion. First is its ability to detect various types of loading
situations. The breaker can not only open a circuit in response to a
current spike, but can also react to a sustained moderate current draw,
just above its rated current. The circuit breaker also has an easily
resetable 3-position switch, and various internal safety features such as
spark arrestors and cavity vents.
Operation of the circuit breaker is simple, but utilizes complex
mechanisms. Essentially there are to main internal mechanisms; the trigger
and the switch. The trigger is the device that senses the abnormal current
load. A sharp spike in current will cause a magnetic field to form in the
trigger, releasing the switch. A slightly elevated, but more constant
current draw through the breaker will cause the bi-metal composition of
the trigger mechanism to deflect in an arc like manner, which is also
capable of releasing the switch. This reaction may take a longer amount of
time to open the circuit, but is designed to provide the user with a short
time of extended current draw through the circuit before the breaker
opens.
The switch, which is activated internally by the trigger or externally
by the user, simply opens or closes a set of contacts which complete the
circuit. The switch can be set to open or closed from the outside of the
breaker’s case, but can only be set to the “tripped” position internally,
as a results of the trigger mechanism. Once the breaker has been tripped
internally, it must be reset externally by switching it off, and then back
on.
The features enable the breaker to do several jobs at once, eliminating
the need for multiple elements in the circuit. For example, it provides
the user with an easily assessable on/off switch, fault protection against
current spike, and fault protection against heavy current draw. The design
of the trigger mechanism allows one internal part to the job of two, as
does the switch, which by design can be shut off either internally or
externally.
Some problems that come to light with these features include a limited
service life and expensive manufacturing. Limited service life is a
function of build quality. Many internal parts move without precise
surface preparation or lubrication, indicating that repetitive motion
could wear out the assemblies. Several internal springs may also wear out
over time. And, because there are may small parts that fit integrally with
each other, manufacturing costs may be inflated.
Discussion
It has been discussed that the circuit breaker has many good design
points, such as double fault protection, a manually switchable mode, and
built in safety features to prevent spark ignition and meltdown. And it
seems that there aren’t many undesirable features of the unit, possibly
with the exception of cost. Because of the complexity of the inner
workings, manufacturability is more difficult, thus raising costs.
A small inspection was done to determine if any parts could be eliminated
or combined to reduce the build cost, but no immediate solutions were
identified. It appears that all attempts to improve or simplify the device
have been implemented and maximized, leaving the only avenue for
complexity reduction to be a change in application for the part.
Conclusion
A common household thirty amp circuit breaker was dissected in lab this
week. It consisted of hard plastic, moving metal parts, and two springs
(Figure 1). The circuit is placed in series between an electrical power
source such as Georgia Power and the fuse box or beginning of a home’s
electrical system. The circuit breaker operates via two mechanisms. The
circuit is tripped or opened when either a high peak current exceeds the
rated value of the circuit as when under constant thermal expansion the
circuit experiences small spikes in the current that exceeds the amperage
rating. The mechanism for tripping the circuit during a high peak value
is magnetism. A metal sleeve when subjected to high peak voltages acts
much as a solenoid, which magnetically attracts the triggering device
allowing the tension in the spring to disconnect the contact, points and
hence open the circuit. Similarly for the tripping mechanism under
constant thermal expansion the expansion of the top of the bimetallic
strip causes the trigger to be pulled down which has the same effect. The
circuit breaker’s best point is that the device is effective and compact.
On the other had it is not 100% effective and must also be manually reset
which can be problematic if it is dark and no lights are available with
which to see the fuse box. Another bad point is that the circuit breaker
has many moving parts, which complicates construction. Simpler or fewer
parts might drive cost down and make manufacturing more efficient.