Distribution system for buildings
Protection equipment
Fuses
Circuit Breakers
Protective Relays
Ground Fault indicators
Switching equipment
Safety switch
Various Boards
Switch board
Distribution Panel board
Switch Gear
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Protection Control Devices For Wiring Design-Energy, Power Grid, Distribution and Utilization-Lecture Slides, Slides of Power Distribution and Utilization
Main paints of this course are Distribution system (its components, design and protection), Utilization system (illumination, machines, heating, etc and design of electrical systems at customer level). Main points for this lecture are: Protection, Control, Devices, Wiring, Design, Fuses, Circuit, Breaker, Relays, Safety, Switch, Gear, Panel, Frequency
Typology: Slides
2011/2012
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Distribution system for buildings ^ Protection equipment^ ^ Fuses^ ^ Circuit Breakers^ ^ Protective Relays^ ^ Ground Fault indicators ^ Switching equipment^ ^ Safety switch ^ Various Boards^ ^ Switch board^ ^ Distribution Panel board^ ^ Switch Gear
Distribution system for buildings Protection equipment ^ There are many devices that are used to
protect
electrical power systems
from damage due to
abnormal conditions. For example: Switches, fuses, circuit breakers, lightning arresters, and^ protective relays
are all used for this purpose.
^ Mechanism of Protection system
^ Some devices
automatically disconnect
the equipment from
power lines
before any damage can occur
.
^ Other devices
sense variations from the normal operation of the system and
make the changes necessary to compensate
for abnormal circuit conditions
Fuses (Protection Equipment) The simplest type of protective device is a
fuse
^ Advantage: Fuses are^ ^ low-cost items and^ ^ have a fast operating speed ^ Disadvantages:,^ ^ In three-phase systems, since each hot line must befused, two lines are still operative if only one fuseburns out.^ ^
Three-phase motors will continue to run with one phaseremoved which will cause: ^ Motor torque greatly reduced, and overheating. Replacements
are required.
Protection equipment (Fuse) ^ Working Mechanism:^ ^ All metals have resistance, so when current flowsthrough metal, heat energy is produced.^ ^ As the current increases, more heat is produced,causing the temperature of the metal to increase^ ^ When the
melting point
of the fuse metal is
reached, the fuse will open, causing the circuit towhich it is connected to open The current rating of fuses depends ^ upon the melting temperature of the fuse metal, as wellas its shape, size, and the type of enclosure used.
Fuses (Protection Equipment) Types of Fuses: ^ Plug
Fuses
are used in safety switches and power distribution panels for voltages below 125V (10A:5:35A) Cartridge fuses
are commonly used in power distribution systems for voltages up to 600V (60:1000A) Time Delay Fuses
is modification of above.
^ The fuse element melts only when an excessive current issustained over the time-lag period^ ^ To Delay the circuit-interrupting action for momentary high currentsexist periodically.^ ^ To limit current on systems including electricmotors, which drawhigher currents during their start cycle than during normaloperation.
Circuit Breaker
(Protection Equipment)
^ Circuit breakers
are somewhat more sophisticated
overload devices than are fuses. Although their function is the same as that offuses, circuit breakers are much more
versatile
^ In three-phase systems, circuit breakers
can open all
three hot lines
when an
overload
occurs.
^ They may also be activated by remote-control relays. ^ They are designed so that they will automatically openwhen a current occurs that exceeds the rating of thebreaker. Ordinarily Manual reset is required ^ Most circuit breakers employ either a
thermal tripping
element or a
magnetic trip
element
Protective Relay
(Protection Equipment)
^ Provide an accurate and sensitive method ofprotecting electrical equipment^ ^ from short circuits and other abnormal conditions^ ^ Overcurrent relays are used to cause the rapid openingof electrical power lines when the current exceeds apredetermined value^ ^ The
response time
of the relays
is very important in
protecting the equipment from damage. Some common types of faults that relays protect againstare^ line-to ground short circuits
,^ line-to-line short
circuits
,^ double line-to-ground short circuits
, and
three-phase line short circuits
Motor Fault Current Protection(Protection Equipment) Motor fault currents ^ are excessive currents that occur in motors as the resultof some
unnatural malfunction
^ Since motor fault currents cannot be withstood for anyduration of time, some type of protection must beprovided to disconnect the motor from the powerdistribution system when a fault condition occurs ^ Such protection may be provided by
motor starters,
circuit breakers,
or^ fuses.
^ The type of protection used is dependent upon severalcharacteristics of the power distribution system and themotor.
Switch board ^ The role of a switchboard is^ ^ to divide the main current
provided to the
switchboard into smaller currents for furtherdistribution to provide
switching, current protection, and metering
for these various currents
^ Elements that make up a switchboard are:^ ^ a^
frame, buses, overcurrent protectivedevices, service metering, and outer covers
Low-voltage Switchgear Metal-enclosed
low-voltage switchgear
is used in
many industrial and commercial buildings as adistribution control center ^ to house the
circuit breakers
,^ bus bars
, and^ terminal
connections
that are part of the power distribution system a combination of switchgear and distributiontransformers is placed in adjacent metal
enclosures.
^ This combination is referred to as a
load-center unit
substation,
since it is the central control for several loads.