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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 k. A 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 s 1, s 2 and s 3 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 s 1, s 2 and s 3 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