Electricity

Hospitality and service industries require and use vast amounts of electrical energy. Electrical energy is a secondary energy source which means that we get it from the conversion of other sources of energy like coal, oil, natural gas, nuclear power and other natural sources, which are called primary sources. The energy sources we use to make electricity can be renewable or non-renewable, but electricity itself is neither renewable nor non-renewable.

We can formally define current as the free flow of electrons (negative charge) in any conductor.

Potential may be defined as the status of some entity (e.g. liquid in a tank, a metal plate at a given temperature, a terminal of an electric cell etc.) in respect of its ability to do some work. A body at a higher potential is said to have higher energy level than a body at lower energy level and if both are connected at identical situation, the energy will flow from higher energy level to lower energy level or there will be exchange of energy and potentials will become equal causing no further energy transfer, unless energy is added to maintain the potential difference. Let us have an idea of the following potentials.

Gravitational potential- A body at a higher height from the surface of the earth is at a higher potential than a body at a lower height.

Electric potential- It is the electrical potential energy per unit of charge that is associated with a static (not changing with time) electric field. It is measured in volts. The difference in electrical potential between points is known as voltage. Electric potential may be considered as ‘electric pressure’. Where this ‘pressure’ is uniform no current flows and nothing happens. Difference of electric potential causes flow of electrons in a circuit.

Temperature potential- A body at a higher temperature is at a higher thermal potential than a body at a lower temperature.

Concentration potential- A space having a higher concentration of some species (say, carbon dioxide) is at a higher carbon dioxide potential than a space having lower concentration.

Terminology

Current– It is the free flow of electrons in any conductor. Represented by I. ST unit is Ampere. Ex. 5 ampere or 5A.

Volt– Volt is force or pressure (potential difference) which causes the flow of electrons in any closed circuit. It is represented by V. Unit is volt. In practice there are two volts are in use, 220V for domestic purposes and 415V for industrial purposes.

Resistance– Electrical appliances when connected to a circuit it is a load or resistance through which current is to flow consuming electric power. Resistance may be defined as the property of a substance that opposes the flow of electricity through it. It is represented by R. Unit is Ohm (Ω).  

Ohm’s Law– The voltage drop across the load resistance of the circuit is directly proportional to the current flowing through it, provided physical parameters like length, cross-section, temperature, and material of the load resistance remain the same.

The mathematical expression is V α I.  So, V = R x I, where R is the constant of proportionality known as resistance responsible for energy waste.

One Volt– It is defined as the potential difference necessary between the ends of a conductor whose resistance is 1 ohm (Ω), to produce a current of 1 ampere (A).

Ampere– It measures the rate of flow of a current. One ampere = 1 Coulomb/sec

                                                                                                     = 1 / (1.6 x 10-9) electrons/sec

                                                                                                     = 6.25 x 108 electrons/sec

Watt– It measure power, that is, amount of electricity used by an appliance. 1000 watt = 1 Kw. Kw-hour is the unit of amount of current consumed.

Ex. 1000 watt appliance in use for 1 hour will consume 1 Kw-hour or Kwh, which is the measure of one unit of electric power or 2 nos. of 500 watt appliance in use for 1 hour, or 2 nos. of 250 watt appliance in use for two hours.

One unit (1 Kwh) produces 3412 BTU of heat.

We know, V = R x I,

So, V / R = I, if the voltage of the main supply =240 v., wire and other connections leading to a socket outlet has a resistance of 48 Ω, the socket-outlet is able to supply 5 amps.

Watts = Amp x Volt. Ex, A 5 amp socket using a current of 220 volts can supply an electrical appliance rated at 1100 watts.

Amp =Watt / Volt.  Ex, 4 nos. of 100 watt lamps using 220 volts could be safely supplied by a 2 amp plug.

 Closed Circuit: An electric circuit that provides an endless continuous path for uninterrupted supply of electric current.

Open Circuit: An incomplete electric circuit in which the normal path of current is interrupted.

Short Circuit: It is a closed circuit in which a direct connection is made with no appreciable resistance between the terminals of the source of EMF (Electromotive Force).

Series and Parallel Circuits: A Series Circuit is one in which the devices or elements of the circuit are arranged in such a way that the entire current passes through each element without division or branching into parallel circuits. When two or more resistances are in series in a circuit, the total resistance may be calculated by adding the values of such resistances, like R= r1+r2+r3……

A Parallel Circuit has more than one path for current flow. The same voltage is applied across each branch. If the load resistance is the same in each branch, the current flow in each branch will be the same. But if the load resistance is different in each branch, the current flow in each branch will be different. If one branch is broken, the current flow will continue through other branches, like

 Rtotal = 1 / (1/R1 + 1/R2 + 1/R3…….)

A Series Parallel Circuit has some components in series and some in parallel. The power source and control or protection devices are usually in series, the loads are usually in parallel. The same current flows in the series portion, but different current flows in parallel portion. If the series portion is broken, current stops flowing in the entire circuit. If a parallel portion is broken, current continues flowing in the series and the remaining branches.  

There are two systems of electric generation and supply like Direct Current (DC) and Alternating Current (AC).

DC is the kind of electric current that may or may not change the magnitude but the direction of the current (the sign of polarity of the voltage source terminals) will never change.

AC is the kind of electric current which change not only its magnitude but also its sign as time passes, in a definite manner.

 Conductor- It is a substance through which electricity flows freely without much resistance. Ex, copper, aluminium, water or wiring system of a building.

Silver is the best as conductor among all metals, but not used due to cost and deterioration due to atmospheric oxidation. Copper is the best as conductor, though costly but having better current carrying capacity and flexibility. Brass is used as contact elements in fittings and appliances.

      Material                        Resistivity (-m) at 20oC             (in descending order of conductivity)

       Silver                             0.165 x 10-7

       Copper                           0.17 x 10-7

       Aluminium                     0.266 x 10-7

       Brass                               0.5 to 0.9 x 10-7

       Iron                                 0.91 x 10-7

       Tin                                   1.15 x 10-7

Insulator- These are substances which offer maximum resistance so that they allow practically no electricity to flow through them. Example, rubber, asbestos, bakelite, mica, ebonite etc. Ceramics are used in utility poles.

                                                           

   Material                        Resistivity at 0oC    (ohm-m)

   Bakelite                                     1

   Distilled Water                         105

   Glass                               5 x 109  to  1013

   Mica                                1011    to    1015

   Porcelain                         1012    to     1013

 

Wires- These are used for carrying current from one point to another. Cable and wire are same, but cable is used for all heavy section insulated conductors, a wire means a thin section insulated / bare conductor. Wires are expressed in number of strands twisted together. Example, 3/22, 3/20 etc. A 3/22 wire means a cable has three smaller wires of 22 standard wire guage (SWG) stranded together.

Types of Conductors / Cables

Vulcanized Indian Rubber (VIR)- Copper wire covered with a rubber insulation with a protective cotton braid over it. It is now obsolete, used in irons where maximum flexibility is required.

Lead Alloy Sheathed Wires- VIR is unsuitable in damp conditions – a thin lead covering is made on VIR to make this type. These are expensive.

Cab Type Sheathed / Tough Rubber Sheathed (CTS / TRS) – These are moisture proof. These are cheaper than lead sheathed cables. These are also obsolete now.

Poly Vinyl Chloride (PVC) – Bare conductors are insulated with PVC insulation. These are used in domestic wiring system.

Flexible cable- These are made with two or three PVC wires in stranded position. These are used for temporary lines.

FUSE

Fuses are special devices that are inserted in the circuit and consist of wires of low melting point. A fuse is a device that cuts off the circuits when more than the predetermined value of current flows in a circuit. It is the weakest point of the circuit, which breaks when more than normal current flows in the circuit. 

Standard sizes of fuses are given below:-

  1. 2 amps (for lamp) – consuming not more than 480 watts at 240 volt
  2. 5 amps – consuming not more than 1200 watt at 240 volt
  3. 10 amps – consuming not more than 2400 watt at 240 volt
  4. 13 amps – consuming not more than 3120 watts at 240 volt

The material of the fuse is generally Copper-tin or Lead-tin alloy. In Lead-tin alloy there is 37% lead and 67% tin. The minimum length of a fuse is generally 65 mm to 100 mm.

Types of fuse holders are:-

  1. Semi-enclosed or re-wire able ( or Kit Kat)
  2. Totally enclosed or Cartridge type
  3. High Rupturing Capacity fuse (HRC)
  4. Miniature Circuit Breaker (MCB)

 WIRING

Type of wiring:    

  1. Cleat- Porcelain or wooden cleats are fixed on walls at a distance of 4 to 5 m apart. VIR or PVC wires are normally used in this type of wiring. Suitable for temporary wiring purposes (marriage halls, indoor fairs etc.), dismantled very quickly and materials can be reused.
  2. Wooden Batten- Wires are carried on wooden battens with clips. TRS or PVC wires are used. Installation is easy and less costly.
  3. Casing and Capping- Common type in indoor and domestic installations. VIR wires are used in PVC casing and finally covered by PVC capping. Wires are not visible from outside. This is costlier but more reliable and nice looking.
  4. Lead Sheathed- Lead sheathed wires are fixed by metal clips on wooden batten. The lead covering protects the wire from mechanical damage. As these wires are costly, these are not in use nowadays.
  5. Conduit- For workshops and public buildings these are best and desirable. VIR or PVC wires are carried through steel or iron pipes. Maybe over the walls or concealed.

Precautions to be taken in working or handling electrical equipment

  1. To be careful and not to be unmindful while working with electrical equipment.
  2. Immediately after the repair one should not energize the conductor without ensuring the safety clearance.
  3. The plug should not be disconnected by pulling cable.
  4. Before doing any work, the main switch should be kept ‘off’.
  5. Safety demands good earthing. So, earth connection should be good.
  6. While moving electrical appliances like table fan, iron, heaters etc. these are to be disconnected from supply, simply switching off is not enough- there might be leakage.
  7. Live wire should always be connected through switch.
  8. In case of electrical fire, water should not be used. Only CO2 extinguishers are to be used.
  9. Tools should not be used without handle. Pliers should not be used as hammer. Tester as screw driver.
  10. Any work to be done above ground, proper precaution must be taken while using ladders and to be done by qualified electrician.
  11. Hands should not be wet while handling electrical equipments. Electrical poles should not be used for hanging cloths etc.
  12. Rubber sole footwear has to be put on foot while handling electrical appliances.
  13. Every electrical appliance to be connected with a proper socket on the wall. For example, one 15A or 10A plug has to be inserted to the compatible socket only.
  14. Too many appliances are not to be connected to one socket outlet by any means to avoid overloading which may cause catching of fire.
  15. All connections should be periodically checked for tightness to avoid accidents.
  16. All single pole switches should always be placed in live wire only and not in the neutral wire.
  17. Correct size of fuse wires to be used. Use of oversize or undersize may give trouble unnecessarily.
  18. For replacing a blown fuse, main switch should first be switched off.

 Testing tools

Tester– It completes the circuit through our body, but we remain safe because the amount of current flowing through body is very less due to high resistance of the tester wire itself.

Megger– It is the instrument by which the insulation resistance of a conductor can be measured.

Conversion of AC to DC supply

For engineering and economic reasons, almost all supply systems in India are in AC system. But many electrical equipment and machines used in household and industrial purposes require DC supply for technical reasons, like DC motors are better for traction purposes such as tram cars,

electric locomotives etc. DC supply is also used in electrical arc welding for improved quality of welding. So, there is a need to convert AC supply to DC supply in hotel premises for particular machines. The process of converting AC to DC is known as rectification. This can be done by one of the following:-

  1. Generator set Rotary converter 3. Solid state rectifier 4. Mercury arc rectifier

Electric Tariff and energy bill

There are various systems of electric tariffs for charging consumers for electricity like one-part, two-part and three-part system. The word ’tariff’ means the schedule of rates framed by electric supply companies for their consumers. There are various factors to decide the tariff scheme. But mainly depend on type of consumers like domestic, commercial or industrial. BOT is the electrical commercial unit of energy and expressed in kWh, which is equal to 36,000 Joule.

1 BOT unit = 1 kWh = 1000 Wh = 36,000 Watt-second = 36,000 Joule

Calculation of electrical expenses based on wattage of loads and their running hours only from the following example:-

Problem: – Find out the bill for the month of September 2012 for the following loads in a domestic apartment.

  1. 06 nos. 100 watt bulbs working for 10 hours a day
  2. 05 nos. 60 watt ceiling fans working for 15 hours a day
  3. 01 no. 2 kW heater working for 5 hours a day
  4. 01 no. 3 kW oven working for 10 hours a day
  5. 01 no. 2 hp motor working for water pump running for 2 hours a day

There are two nos. electrical energy meters (one for motor and one for other loads) in the apartment. Electricity charges for 1 kWh (1 BOT unit) energy used is Rs.5.00 Meter rent for the month is Rs. 20.00 per meter.

Solution: – The month September has 30 days (be particular about this in case of leap year). Convert 2 hp motor to its kW equivalent. 1 hp = 746 Watt = 0.746 kW. So, 2 hp = 2 x 0.746 kW = 1.492 kW.

Now, find the energy consumed by each type of load in kWh = (power in watt x number of units for the particular type of load x hours run in a day x number of days of the month) / 1000.

If power is given in kW, division by 1000 is not needed.

Following this, we get as follows: –

  1. Energy consumed by 100 watt lamps = (100 x 6 x 10 x 30) / 1000 = 180 kWh
  2. Energy consumed by 60 watt fans = (60 x 5 x 15 x 30) / 1000 = 135 kWh
  3. Energy consumed by 2 kW heater = (2 x 1 x 5 x 30)  =  300 kWh
  4. Energy consumed by 3 kW oven = (3 x 1 x 10 x 30)  =  900 kWh
  5. Energy consumed by 2 hp (1.492 kW) motor = (1.492 x 1 x 2 x 30) = 89.52 kWh

                Total energy consumed by all loads during the month = 1604.52 kWh

  So, total electrical units consumed are 1605 BOT units (rounded off). Rate per unit = Rs. 5.00

 Amount of electricity charge = 1605 x 5 = Rs. 8025

Meter rent for 2 meters = Rs. 20 x 2 = Rs. 40.00

Therefore, total amount of bill = electricity charge + meter rent for the month

                                                  = Rs. 8025 + Rs. 40 = Rs. 8065

Earthing: The risk of shock can arise from damage to insulation, the presence of water, or a loose connection. Electricity always takes the path of least resistance to the earth. Protection against shock can therefore be given by ensuring that every circuit has an energy path to earth (known as earth-continuity circuit), which will conduct away harmlessly any leaking electricity.

There are two types of earthing, like metal conduit and metal-sheathed. When earthing is there the circuit protects the whole wiring and fixed appliances together with portable appliances if a three-pin plug is used.

Electric Lighting

One of the primary uses of electric energy is for artificial lighting. In most buildings lighting represents the second highest energy use, following electric motor requirements. Light, its reflection, and object visibility all are interrelated. A light source radiates energy that we cannot see. Air does not absorb or reflect that energy passing through it. As light energy strikes a surface, it may be absorbed and converted to heat, which lowers lighting efficiency. The surface may transmit some of the energy or light may be reflected. Then only we can see the reflected light.

Proper design of lighting is one of the key factors for successful functioning of the hotel industry.

The objectives of proper lighting are:-

  1. To provide good working conditions to prevent strain and fatigue to the personnel.
  2. To create proper ambience.
  3. To help people know the directions etc. by use of proper lighting signs.
  4. To maintain safety standards.
  5. To enhance security.
  6. To attract people.

Lamp is a source of light. A lamp is inserted into a lighting fixture. The combined lamp and lighting fixture is called a luminaire. Lamplight output is given in lumens. A lumen is a quantity of light. The lumen is the amount of light energy that strikes an area at a specific distance from a standard candle. If 1 lumen falls on a 1 square foot area of distance of 1 foot from a standard candle, it is called 1 foot-candle of light intensity, or if 1 lumen strikes 1 square metre of surface of a distance of 1 metre from a standard candle, it is called 1 lux.  Foot-candles or lux refer to the intensity of light.

Lighting design depends on the foot candle (lux) intensity required at the work surface. Proper intensity of light can increase the productivity of working personnel. The level of natural light on a bright sunny day is about 50,000 lux, on a cloudy day it is only 5,000 lux and moonlight produces only 0.2 lux.

Types of Lighting

Different types of common light sources such as common electric bulbs, fluorescent tube lights, mercury vapour lights, neon signs, sodium vapour lamps etc. are all familiar terms. All these light sources can be broadly classified into two basic types depending on the physical principles like- i) Resistance-type Lamp and ii) Electric Discharge Lamp. For example, incandescent lamps or general lighting service (GLS) lamps, tungsten-halogen (TH) lamps are resistance-type lamps, whereas fluorescent lamp, metal halide lamp, sodium vapour lamp, mercury vapour lamp etc. are electric-discharge type lamps.

Another type of lighting is Light-emitting Diode (LED) which is an electronic light source based on the semiconductor diode. When the diode is switched on, electrons are able to recombine with holes and energy is released in the form of light. This effect is called electroluminescence and the colour of the light is determined by the energy gap of the semiconductor. The LED is usually small in area with integrated optical components to shape its radiation pattern and assist in reflection. These are powered by low-voltage DC supply. These are very efficient, durable, low cost, reliable with dimming feature, environment friendly etc. Many hotels are fast replacing fluorescent and incandescent lamps with these bulbs. They may even replace CFLs in near future as they produce more light per watt.

Lighting System

Depending on effects of lighting, several lighting systems are available. They are direct, semi direct, diffuse, semi indirect and indirect.

The most efficient lighting system is Direct lighting system. Here all the light is directed to the activity area. This is found in institutional buildings due to low installation and operating costs. Approximately 90% light goes downwards and 10% of light goes upward.

Semi direct lighting system diverts a portion of the light towards the ceiling (usually less than 40%) and a larger percentage is directed towards into the activity area. Most of the board, conference, and meeting rooms use this type of lighting. Though it is not as efficient as direct lighting system but most of the food service managers prefer it over direct lighting system.

Diffuse lighting system directs approximately equal amounts of light downward into the activity area and upward to the ceiling. It is mostly used in public areas, dinning rooms and conference rooms. Cost of installation and operating is almost double than direct or semi direct lighting.

Semi indirect lighting system directs between 10% to 40% of the light output directly to the activity area. These are costly to install and operate for high foot-candle (lux) intensities.

Indirect lighting system reflects 90% or more of the emitted light from the luminaire to the ceiling and upper walls of the room, and redirected from these surfaces down towards the activity area.

Generally, only direct, semi direct and diffuse lighting are recommended for large areas and rooms. The indirect and semi indirect systems are recommended only for small rooms where special effects are to be created, or where we want a relaxed environment such as cocktail lounge or in guest house.     

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