UNIT -VI ELECTRICAL INSTALLATIONS AND SAFTEY PROCEDURES
Syllabus • Components of LT Switchgear: Switch Fuse Unit (SFU), MCB, ELCB, MCCB, • Types of Wires and Cables • Earthing , Electrical Shock and its Typical effects - first aid, • Elementary calculations for energy consumption - simple case study, • types of batteries-important characteristics of batteries, battery backup.
Components of LT switch gear The apparatus used for switching, controlling and protecting the electrical circuits and equipment is known as switchgear. The ‘switchgear’ term is a generic term encompassing a wide range of products like circuit breakers, switches, switch fuse units, off- load isolators, HRC fuses, contactors, earth leakage circuit breakers (ELCBs), etc...
FUSE A fuse is a short piece of wire or thin strip which melts when excessive current flows through sufficient time. whenever the current flowing through fuse element increases beyond its rated capacity then short circuit or overload occurs. This raises the temperature and the fuse element melts, disconnecting the circuit is protected by it.
SWITCH FUSE UNIT (SFU) It is Switched Fuse Unit. It has one switch unit and one fuse unit. When we operate the breaker, the contacts will get close through switch and then the supply will passes through the fuse unit to the output.
MCB MCB is an electromechanical device which guards an electrical circuit which automatically switches off electrical circuit during abnormal condition of the network means in over load condition as well as faulty condition. The normal current rating is ranges from 0.5-63 A with a symmetrical short circuit breaking capacity of 3-10 KA, at a voltage level of 230 or 440V. Characteristics of MCB The characteristics of an MCB mainly include the following • Rated current is not more than 100 amperes • Normally, trip characteristics are not adjustable • Thermal magnetic operation
ELCB Early earth leakage circuit breakers are voltage detecting devices, which are now switched by current sensing devices (RCD/RCCB). An ECLB is one kind of safety device used for installing an electrical device with high earth impedance to avoid shock . There are two types of Earth Leakage Circuit Breaker (ELCB) Voltage Operated ELCB Current Operated ELCB Characteristics of ELCB This circuit breaker connects the phase, earth wire and neutral The working of this circuit breaker depends on current leakage
MCCB Molded case circuit breakers are a type of electrical protection device that is commonly used when load currents exceed the capabilities of miniature circuit breakers. They are also used in applications of any current rating that require adjustable trip settings, which are not available in plug-in circuit breakers and MCBs. The main distinctions between molded-case and miniature circuit breaker are that the MCCB can have current ratings of up to 2,500 amperes, and its trip settings are normally adjustable.
Types of wires and cables: Wire is a single electrical conductor, whereas a cable is a group of wires swathed in sheathing.
CABLES • The main requirements of the insulting materials used for cable are: 1. High insulation resistance. 2. High dielectric strength. 3. Good mechanical properties i.e. tenacity and elasticity. 4. It should not be affected by chemicals around it. 5. It should be non-hygroscopic because the dielectric strength of any material goes very much down with moisture connect
TPES OF CABLES RUBBER: used for house wiring, buildings, factories and low power work. PVC(Polyvinyl chloride): It is a thermo plastic insulating material. These are used up to 1.1kv voltages especially in concealed wiring system . TRS(Tough rubber sheathed) or Cab type sheathed(CTS): These are used 250/ 500v circuits.
Electrical Earthing The process of transferring the immediate discharge of the electrical energy directly to the earth by the help of the low resistance wire is known as the electrical earthing. Mostly galvanised iron is used for earthing.Earthing provides simple path to the leakage current. Earthing is an important component of electrical systems because of the following reasons: • It keeps people safe by preventing electric shocks • It prevents damage to electrical appliances and devices by preventing excessive current from running through the circuit • It prevents the risk of fire that could otherwise be caused by current leakage
Types of Electrical Earthing: • Neutral Earthing: In neutral earthing, the neutral of the system is directly connected to earth by the help of the GI wire. The neutral earthing is also called the system earthing. Ex. Generator, T/F, Motor etc., • Equipment Earthing: Such type of earthing is provided to the electrical equipment. The non- current carrying part of the equipment like their metallic frame is connected to the earth by the help of the conducting wire.
Electric shock An electric shock happens when an electric current passes through your body. This can burn both internal and external tissue and cause organ damage.
First Aid : If you receive an electric shock • Let go of the electric source as soon as you can. • If you can, call 911 or local emergency services. If you can’t, ask for someone else around you to call. • If the shock feels minor ,See a doctor as soon as you can, even if you don’t have any noticeable symptoms. Remember, some internal injuries are hard to detect at first. In the meantime, cover any burns with sterile gauze( శూభరమన గిజూగూడడ ) . Don’t use adhesive bandages or anything else that might stick to the burn. If someone else has been shocked • Don’t touch someone who has been shocked if they’re still in contact with the source of electricity. • Turn off the flow of electricity if possible. • Stay at least 20 feet away if they’ve been shocked by high -voltage power lines that are still on.
Elementary calculations for energy consumption STEP I : Calculate Watts Per Day In this step, simply multiply your device’s wattage by the number of hours you use it in a day. This will give you the number of watt-hours consumed each day. For example , say you use a 125-watt television for three hours per day. By multiplying the watts (125) by the hours used (3), we find that the television is consuming 375 watt-hours per day. 125 watts X 3 hours = 375 watt-hours per day
Cont., STEP II : Convert Watt-Hours to Kilowatts Electricity is measured in kilowatt-hours on your bill, not watt-hours. One kilowatt is equal to 1,000 watts. so to calculate how many kWh a device uses, divide the watt-hours from the previous step by 1,000. Using our previous example, this means you would divide 375 watt-hours by 1,000, resulting in 0.375 kWh. 375 watt-hours per day / 1000 = 0.375 kWh per day
Cont., STEP III : Find Your Usage Over a Month Now that you know the kWh used per day, multiply that by 30 to find your approximate usage for the month. So, if your daily usage is 0.375 kWh, your monthly usage would be 11.25 kWh. 375 watt-hours per day X 30 days = 11.25 kWh per month
Cont., STEP IV : Figure Out the Cost For the final step, refer to your last electric bill to see how much you pay per kWh, i.e. Tariff. Let’s say, according to your bill, your electric rate is 3 rupees per kWh. Multiply your electric rate (₹3) by your monthly usage (33.75) to find out how much your TV is costing you in a month (₹33.75). 11.25 kWh per month X ₹5 per kWh = ₹33.75 per month
What about devices that use more electricity? • For refrigerator, for instance, runs 24 hours a day. Most refrigerators consume anywhere between 300 to 780 watts of electricity. Let’s say your model only uses 300 watts. 300 watts X 24 hours = 7,200 watt-hours per day 7,200 watt-hours per day / 1000 = 7.2 kWh per day 7.2 kWh per day X 30 days = 216 kWh per month 216 kWh per month x ₹3 per kWh = 648 per month
Cells and Batteries • A device which is used as a source of e.m.f. and which works on the principle of conversion of chemical energy into electrical energy is called a cell. • But practically the voltage of a single cell is not sufficient to use in any practical application. • Hence various cells are connected in series or parallel to obtain the required voltage level. • The combination of various cells, to obtain the desired voltage level is called a battery.
Types of Cells • There are two types of cells, Primary Cells: • The chemical action in these cells is not reversible and hence the entire cell is required to be replaced by a new one if the cell is down. • The primary cells can produce only a limited amount of energy. • Mostly the non electrolytes are used for the primary cells. • The various examples of primary cells are i. Dry Cell (zinc-carbon) ii. Mercury cell iii. Zinc chloride cell iv. Lithium cell v. alkaline cells
Dry Cell (zinc-carbon) • The zinc container is lined with paper to avoid direct reaction of zinc with carbon. • The container is sealed with an insulator called pitch. • The tin plates are used at top and bottom which are positive and negative terminals of the cell. • Applications are Used in torch lights, Electronic apparatus and toys, wall clocks etc.
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