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3.3 Protection
Protection
Protection means providing care to electrical
instruments from any hazard due to more current,
leakage current, the circuit smart, lightning and so on.
There are three types of coverage needed;
(i) the isolator or protection to control the installation
(ii) overcurrent protection (fuses, circuit breakers,
relays)
(iii) Protection against electric shock (earthing and
insulation)
Isolator
• Isolator is a device that can determine the distribution of
supplies to consumers by disconnecting life and neutral.
• For single phase supply, it uses two pole switch to a
three-phase cluster and three-pole switch cluster.
Isolator is installed at the beginning of separate circuits
for the circuit to protect consumers during wiring work or
repair the damage.
• Isolator must be capable of carrying full load current to
the load and the ability to decide or continue supply
when needed.
Over-current protection
• This tool works on its own decided upon the circuit overcurrent allowed.
• It is installed on the live wire in series with the supply.
• Its main duty is to avoid damage to electrical equipment
when current equipment is more than the maximum
potential while protecting the cable from damage.
• 3 types of over-current protection, namely;
(i) fuse
(ii) circuit breaker
(iii) relay
Fuse
• Is basically a conductor wire that will melt when the
current flows exceed its capacity.
Car fuses with plastic body (plug-in type)
Cartridge fuse used inside
equipment and 1 inch 13 A ceramic
High Capacity fuse.
80 kA breaking capacity
PPTC resettable fuses are designed
When overcurrent conditions occur, the Polymeric PTC
material heats up and its resistance increase sharply.
Such a sharp resistance increase cuts off the current in
the circuit. Upon fault current being removed, the
resettable fuse cools and its resistance drops to the
original extremely low value. The resettable fuse is
reset and allows the current through the circuit again
Circuit Breaker
• Operate automatically, can be adjusted to
current value and the time required, need
not interchangeable and can be switched
on again.
Pemutus litar- cara terma
• Component consists of a bimetallic layer attached to a
contact as a point of connection to the switch.
• If the current sign does not exceed the limit, bimetallic
unchanged physically and contacts still make the
connection.
• When the current exceeds the limit, will be hot and
warped bimetallic (where different rates of heating and
expansion).
• The track will open by spring attract.
Adjusting screw can be adjusted to determine the
opening rate of the circuit with a fast or slow protection
needs.
Magnetic circuit breaker
• The hot wire in the circuit connects to the two ends of the
switch. When the switch is flipped to the on position,
electricity can flow from the bottom terminal, through the
electromagnet, up to the moving contact, across to the
stationary contact and out to the upper terminal.
• The electricity magnetizes the electromagnet.
Increasing current boosts the electromagnet's magnetic
force, and decreasing current lowers the magnetism.
• When the current jumps to unsafe levels, the
electromagnet is strong enough to pull down a metal
lever connected to the switch linkage. The entire linkage
shifts, tilting the moving contact away from the stationary
contact to break the circuit. The electricity shuts off.
Circuit Breaker-way
electromagnetic
• Contacts operated by electromagnetic coils.
Rate adjustment made ​at the adjustment screw
cover or increase the number of windings in the
coil to get a quick change.
• When the current does not exceed the rating of
circuit breakers, magnetic coils do not have
enough energy to attract the contact and still
strong due to the adjustment screw adjustment.
• As soon as the current limit, the coil will pull the
contacts and the circuit will open.
Relay
• When the push button is pressed life, the current entry
and then complete the circuit. Then the coil will hold all
the contacts s1, s2 and s3 in the contact position.
• This allows current to flow to the load and if the current
does not exceed the full load, it has no effect on the
heating P.
• If the current entry is greater due to increasing load, the
large current flow and heating P and then switch
overload and open net.
Therefore, the contact s1, s2 and s3 will open.
Protection from Electric Shock.
• Tools, equipment and installations must be
protected from leakage current or touched by
humans or animals.
• Contact causing electric shock which depends
on the body resistance, voltage and supply
current.
• Earthing and insulation important to overcome
the problem of electric shock.
Thus, the conductor must be insulated through
the process, such as rubber and plastic
insulation.
Earthing
• Earthing is the connection made ​between the metal in
the electrical installation to the mass of the earth.
• The basic reason for grounding on the installation and
electrical devices are for the safety of electric shock and
fire in the event of leakage current.
• Connected to earth good installation system;
A. The entire system is tied to its general mass of earth.
B. All metals that have been inserted, a path is provided
for earth leakage current.
Major drawback is the cost to obtain a complete
grounding system.
The matters that need to be grounded
• All structural metal in the wiring system as
metal liner conduit, ducts, mains and
others.
• All structures that are exposed to all the
tools that are not associated with
electricity as water pipes, frames and
other home.
Earthing terminology
• 0- Dawai pengikat sama upaya tambahan
• 1- Bumi, sambungan berkesan ke bumi
• 2- Elektrod bumi
Batang rod logam, plat logam dan sebarang benda berpengalir
bagi memperolehi sambungan bumi berkesan.
jenis –jenis elektrod yang biasa digunakan ialah paip galvani,
batang rod kuprum, jalur kuprum dan struktur keluli bangunan.
• 3- Pengalir pelindung litar
- adalah pengalir yang menghubungkan semua bahagian
pengalir (logam) dalam pemasangan ke terminal utama.
• 4- Dawai pembumi
• 5- Dawai pengikat sama upaya
• 10- Punca bumi pengguna