ELECTRICAL SERVICES Power Point Slides by TH FOO

ELECTRICAL SERVICES Power. Point® Slides by TH FOO NADZIRAH ZAINORDIN

MALAYSIAN PRACTICES

INTRODUCTION • • Electricity is a manufactured product Electric power is manufactured from a rotating machine –electrical generator After it is generated or manufactured, it is when delivered through copper wires to where it is utilized For large commercial buildings, the pattern of layout and use of electronic equipment need to consider: i. very large open spaces with cable access to every point and substantial air-conditioning ii. the sizes of space an the heat generated by equipment and lighting

Provisions for electrical installation in all buildings: - • The sizes of cables and control equipment are modest compare with most other services • The need for access to all parts of the building • The requirement for installation are very important • Influence on planning and space requirements for cable distribution

HOW IS POWER GENERATED? • An electric generator is a device for converting mechanical energy into electrical energy Mechanical energy Electrical energy • The process is based on the relationship between magnetism and power • When a wire or any other electrically conductive material moves across a magnetic field, an electric current occurs in the wire • The large generators used by the electric utility industry have a stationary conductor

POWER TRANSMISSION PROCESS • Power travels form the power plant through distribution grid • The main components of power transmission are: • The Power Plant i. Single Phase Power ii. Three Phase Power • Transmission Substation

• • • Electrical power starts at the power plant Generally the power plant consist of a spinning electrical generator need to spin This spinning electrical generator might be: a. b. • • • A water wheel in a hydroelectric dam, a large diesel engine and gas turbine Steam turbine might be created by burning coil, oil or natural gas or nuclear reactor Commercial electrical generators of any size generate 3 -Phase Alternating Circuit (AC) power The 3 -phase power leaves the generator and enters a transmission substation at the power plant This substation uses large transformers to convert the generator’s voltage up to extremely high voltages for long distances transmission grid

• • A substation is required for the conversion transformation and control of electric power When a building requires more power than the local low or medium voltage (240 V or 415 V) distribution can provide a substation must be built on the customer’s premises This is fed by high voltage cable from the Electricity Board’s nearest switching station Factors influencing the numbers of substation are depending on: a. b. • • Number & Size of transformer Number & Size of switches A transformer consist 2 electric winding magnetically inter-linked by an iron core An alternating electro-motive force applied to one of the winding produces by electromagnetic induction, a corresponding electro motive force in the other winding

• Typical voltage for long distance transmission are in the range of 155, 000 V to 765, 000 V in order to reduce line losses • A typical maximum transmission distance is about 300 miles or 483 km • High-V transmission lines are normally looks like a huge steel towers • All power towers are normally have 3 wires for 3 phase • Many powers have extra wires running along the tops of the towers • These are ground wires and functioned primarily in an attempt to attract lightning

Electrical Distribution Schematic

DOMESTIC ELECTRICAL INSTALLATION

ELECTRICITY BOARD INTAKE • The supply or intake cable may enter the building through an underground duct or via an overhead supply • An underground supply is preferred since all of the electrical service is hidden • The supply cable is terminated in the area board’s fused sealing chamber which should be sited in a dry accessible position • From the sealing chamber, the supply passes through the meter, which records the electricity consumed in units of kilowatt/hours, to the consumer unit which has a switch controlling the supply to the circuit breakers or circuit fuses.

• These fuses are a protection againts excess current or overload of the circuit since when overloading occurs the fuses or circuit breaker will isolate the circuit from the source of the problem • The consumer unit should be fitted close to the point of service entry and from here the service is divided into a number of sub-circuit • It is normal in a domestic installation to separate power circuit and lighting circuits so that if a fault occurs then not all socket outlets or lights are isolated • Sometimes an external cabinet is used for easy meter reading

Electrical Distribution

COMPONENTS OF POWER SYSTEM 1. 2. 3. 4. 5. SUPPLY CONTROL METERING MAIN SWITCH (SERVICE DISCONNECT) SUB-MAIN CABLES DISTRIBUTION UNIT

1. SUPPLY CONTROL • • The service cables usually terminates inside the building in a main cut-out fitted as near as possible to the service cable entry A meter is fitted after the main cut-out and everything up to and including the meter are property and responsibility of TNB A switch or circuit breaker is fitted after meter and a distribution board (DB) follow the switch From the switch to furthest outlet point is the responsibility of the building owner

2. METERING • A meter is normally provided at the service entrance to measure how much electricity a consumer uses • TNB may install a single meter for an entire facility or multiple meter for different types of services and tenancy

3. MAIN SWITCH • • • A switch is a device to bridge or break the flow of electricity The main switch is disconnect of an entire building from the electrical services Main switch is located near the point of service entry to the building

4. SUB-MAIN CABLES • • Sub-main cables which connect between the main switched board and distribution boards may consist of pvc cables in steel ducts any other form These size cable will be determined by the total connected load which they have to carry

5. DISTRIBUTION UNIT • • Distribution unit is standard factory made cubicle switchboard The manufactured cubicles switchboard have the following advantages: a. b. c. d. • Quicker to install Neater in appearance Usually take up less space in the wall A locked door prevent a break through Some large building such as factory/ hospital require higher supply

METHOD OF DISTRIBUTION 1. Radial Distribution 2. Ring Distribution 3. Rising main Distribution *find the detail by yourself

POWER CIRCUIT

• When deciding on the number of circuits for a house, a useful rule is one power ring circuit for every 100 mm 2 of floor area • In large house this means that 2 circuit can be used for power socket outlets in a 2 storey house this would be one circuit for upstairs and one for downstairs • In all domestic installation a separate power circuit is required for the cooker since the electrical demands is likely to be high

RING CIRCUIT

• Ring circuits are used as a safe and economic method of distribution of electricity to socket outlets • Many consumer unit manufacturer produce 8 ways and 12 ways unit • Steel or plastic conduit is used in the walls to protect cables from mechanical damage • The conduit is buried in wall behind the plaster • This means that wall will be tracked to accommodate the circular or oval 20 mm diameter conduit

NATIONAL GRID SYSTEM

• Electricity for supply to buildings and industry is generated in power station site conveniently for fuel supplies and distributed by means of the national grid which supply to whole country • Therefore, the distribution is important and this can be achieved by having a small power station located near the consumer using the transmission system which is the grid system to connect the main distribution points

SINGLE PHASE SUPPLY

• Single phase system has one phase conductor and the neutral and 2 phase has 2 conductor and one neutral • 2 @ 3 units of single phase system can be used to configured the supply of 30 phase system services • The voltage across a pair of these conductors or between a single conductor and a neutral conductor is single phase • Single phase distribution is used when loads are mostly lighting and heating with few large electric motors • Domestic area normally used single phase electrical supply

3 - PHASE SUPPLY

OTHER COUNTRY PRACTICES

Conventional Power Generation Fuel Boiler Steam turbine Power Exhaust Condenser Heat

Power Heat

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Gas-Fired Engines are commonly used as prime movers for building CHP applications Different prime movers will have different heat to power ratios

From CIBSE knowledge Series “Energy Efficient Heating” Heat to Power Ratio = 50/30 = 1. 7: 1

An ideal CHP installation is one in which the characteristics of the load match the heat to power ratio of the prime mover through all seasons Buildings are more complicated than that

CHP Sizing Strategy To meet base heat load To meet base electrical load To contribute to the heat and electrical loads

Installation of a gas engine CHP unit at the Radisson Hotel Liverpool. Note the acoustic enclosure

Battersea Power Station District Heating Scheme After the end of the Second World War the London Power Company took the opportunity to introduce a new innovation - a district heating scheme (CHP). Some 11, 000 people benefitted from the scheme which provided hot water and central heating to the newly redeveloped areas within Pimlico.

BAXI CHP Electricity 5. 5 k. W Heat 12. 5 k. W

Domestic Combined Heat and Power (Micro-CHP)

A cabling system consists of • conductor • Insulation • Physical damage protection Identify each of these components in the following images

Industrial Commercial Wiring

Steel Conduit

Risk of physical damage from • Environment • Temperature • Fire • Vermin • Vandalism

TNC-S

Ring Main Circuit

Radial Circuit

One way lighting Circuit

Commonly used Protective Devices HBC fuse links BS 88 -6 and BS EN 60269 -2 Mainly commercial and industrial use Give excellent short-circuit current protection.

HBC fuse links BS 1361 House service and consumer unit fuses. Not popular for use in consumer units; however, gives good short-circuit current protection

MCBs and CBs (miniature circuit breakers) BS 3871, now superseded by BS EN 60898 CBs Domestic consumer units and cmmercial/industrial distribution boards Very popular due to ease of operation.

The use of RCDs are recognised as a means of providing additional protection in the event of failure of the provision for Basic Protection, as an additional means of Fault Protection, and to protect against carelessness by users.

The purpose of protective earthing is to ensure that, in the event of a fault, sufficient current flows to operate the protective devices in the required time. Every exposed conductive part shall be connected by a protective conductor to the main earthing terminal

RCD’s are required_ • Where the earth loop impedance is too high • For socket outlet circuits in domestic and similar situations • For circuits of locations containing a bath or a shower • For circuits supplying mobile equipment not exceeding 32 A for use outdooors • For cables without earthed metallic covering installed in walls or partitions at depths of less than 50 mm and not protected by earthed steel conduit or similar • For cables without earthed metallic or partitions covering installed in walls with metal parts and not protected by earthed steel conduit or the like

Residual Current device

Sub-main cables (single phase) Supply mains cable ( 3 phase)

Discrimination If a lighting circuit fed from a 6 Amp circuit breaker on this DB has a fault, it is important that the 6 A operates and not a main DB fuse Main Distribution Board

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