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UNIT-VI
ELECTRICAL INSTALLATIONS AND SAFETY PROCEDURES
COMPONENTS OF SWITCH GEAR:
The apparatus used for switching, controlling and protecting the electrical circuits and equipment is known as switchgear.
The term ‘switchgear’ is a term related with a wide range of products like circuit breakers, switches, switch fuse units, earth leakage circuit breakers (ELCBs), etc...
A switchgear essentially consists of switching and protecting devices such as switches, fuses, isolators, circuit breakers, relays, control panels, lightning arrestors, current transformers, potential transformers, and various associated equipments.
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.
Whereas in Fuse Switch Unit there is no separate switch and fuse unit. There is only fuse unit which act itself as a switch.
MCB(miniature circuit breaker):
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. Nowadays we use an MCB in low voltage electrical network instead of fuse. The fuse may not sense it but the miniature circuit breaker does it in a more reliable way. MCB is much more sensitive to over current than fuse.
Handling a MCB is electrically safer than a fuse. Quick restoration of supply is possible in case of fuse as because fuses must be re- wireable or replaced for restoring the supply. Restoration is easily possible by just switching it ON.
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
Earth Leakage Circuit Breaker (ELCB)
Early earth leakage circuit breakers are voltage detecting devices, which are now switched by current sensing devices (RCD/RCCB). Generally, the current sensing devices termed as RCCB and voltage detecting devices named as Earth Leakage Circuit Breaker (ELCB). An ECLB is one kind of safety device used with high earth impedance to avoid shock. These devices identify small voltages of the electrical device on the metal enclosures and isolate the circuit if a dangerous voltage is identified. The main purpose of Earth leakage circuit breaker (ECLB) is to stop damage to humans & animals due to electric shock. If ample voltage seems across the ELCB’s sense coil, it will turn off the power, and remain off until manually rearrange. A voltage sensing ELCB doesn’t detect fault currents from human or animal to the earth.
Types of Earth Leakage Circuit Breaker (ELCB) 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):
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 electrical properties expected of rubber insulation are high break-down strength and high insulation resistance. In fact the insulation strength of the vulcanized rubber is so good that for lower voltages the radial thickness is limited due to mechanical consideration.
The physical properties expected of rubber insulation are that the cable should withstand normal hazards of installation and it should give trouble-free service.
Vulcanized rubber insulated cables are used for wiringof houses, building and factories for low power work.
PVC (Polyvinyl chloride) cables.
These are thermoplastic insulating materials and not used for high temperature as it gets softened and flows down to heat. These are therefore, not used for heating appliances. PVC is harder than rubber, hence a thin layer of PVC insulation is good enough. In fact, its thickness is decided by mechanical reasons rather than electrical. The PVC insulated cables are lesser in diameter as compared to TRS and more number of wires can be placed in conduit as compared to TRS wires. These are used upto 1.1 kV voltages especially in concealed wiring system.
Tough Rubber Sheathed (TRS) or Cab Type Sheathed (CTS) Cables.
This cable is used where humidity is high and it does not deteriorate even during long duration of exposure to moisture. As the name suggests these cables are provided with outer protective covering of tough rubber over normal insulation. These are available as single, twin and three cores with an earth continuity conductor. These are used on 250/500 volt circuits.
Earthing
Definition: 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. The electrical earthing is done by connecting the non-current carrying part of the equipment or neutral of supply system to the ground. Mostly, the galvanised iron is used for the earthing. The earthing provides the simple path to the leakage current. The shortcircuit current of the equipment passes to the earth which has zero potential. Thus, protects the system and equipment from damage. In almost every electrical installation made, earthing is used. The earthing system, also known as the grounding system.
Importance of Earthing or advantages of earthing: The earthing is essential because of the following reasons
The earthing protects the personnel from the shortcircuit current.
The earthing provides the easiest path to the flow of shortcircuit current even after the failure of the insulation. The earthing protects the apparatus and personnel from the high voltage surges and lightning discharge.
Types of Electrical Earthing The electrical equipment mainly consists of two non-current carrying parts. These parts are neutral of the system or frame of the electrical equipment. From the earthing of these two non- current carrying parts of the electrical system earthing can be classified into two types.
Neutral Earthing Equipment 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. Such type of earthing is mostly provided to the system which has star winding. For example, the neutral earthing is provided in the generator, transformer, 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. If any fault occurs in the apparatus, the short-circuit current to pass the earth by the help of wire. Thus, protect the system from damage.
type of current (an alternating current is often more harmful than a direct current because it
causes muscle spasms that make it harder to drop the source of electricity) symptoms of an electric shock The symptoms of an electric shock depend on how severe it is. Potential symptoms of an electric shock include:
loss of consciousness
muscle spasms(muscle contraction)
numbness (timmiri)
breathing problems
headache
problems with vision or hearing
burns
irregular heartbeat
First Aid: If you receive an electric shock, it might be difficult for you to do anything. But try to start with the following if you think you’ve been severely shocked:
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(శుభ్రమైన గాజుగుడ్డ ). Don’t use adhesive bandages or anything else that might stick to the burn.
If someone else has been shocked
If someone else receives a shock, keep several things in mind to both help them and keep yourself safe:
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. If you can’t, move the source of electricity away
from the person using a non-conducting object. Wood and rubber are both good options. Just make sure you don’t use anything that’s wet or metal based.
Stay at least 20 feet away if they’ve been shocked by high-voltage power lines that are still
on.
Call 911 or local emergency services if the person was struck by lightning or if they came into
contact with high-voltage electricity, such as power lines or if the person has trouble breathing, loses consciousness, has seizures, has muscle pain or numbness, or is feeling symptoms of a heart issue, including a fast heartbeat.
Check the person’s breathing and pulse. If the person is showing signs of shock, such as
vomiting or becoming faint or very pale, elevate their legs and feet slightly, unless this causes too much pain.
Cover burns with sterile gauze if you can. Don’t use Band-Aids or anything else that might
stick to the burn.
Keep the person warm.
Treatment for electric shock Even if the injuries seem minor, it’s crucial to see a doctor after an electric shock to check for internal injuries. Depending on the injuries, potential electric shock treatments include:
burn treatment, including the application of antibiotic ointment and sterile dressings
pain medication
For severe shocks, a doctor may recommend staying in the hospital for a day or two so they can monitor you for any heart issues or severe injuries.
Primary cells
(1) Dry Zinc-Carbon Cell
(2)Mercury Cell
Characteristics:
(2)Alkaline Cells
(i)Nickel-iron cell
(ii)Nickel – cadmium cell
Battery backup
A battery backup device is an electronic device that supplies secondary power in the absence of main power, such as during a power outage. The battery backup will supply power when it detects an outage.
Battery backup devices can also protect electronic hardware from power spikes, dirty electricity and power outages.
They make battery backup devices in all sizes and power capacities, and depending on what devices you are looking to protect, this will affect the size and capacities you will require.
unit 6
Elementary calculations of Energy consumption calculations
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
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
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. kWh, your monthly usage would be 11.25 kWh.
375 watt-hours per day X 30 days =
11.25 kWh per month
