south african standard sans 10142 - the wiring of premises

Technology Training that Works

South African Standard SANS 10142 – The Wiring of Premises

Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare

Objectives

• 3-phase AC electrical system

• Generation,Transmission and Distribution

• Transformer

• Switching

• Circuit Breaker LV and HV

• Danger of Electricity

• Need of Safety in operation


3-Phase electrical system

• Three separate coils in the generator stator are physically offset by an angle of 120° to each other

• Load of a three-phase system balanced equally among the phases

No current flows through the neutral point

• Unbalanced (linear) load Neutral current < Highest phase currents

• IN a three-phase systemThree circuit conductors carry three alternating currents (same frequency) which reach their instantaneous peak values at different times


Produce a rotating magnetic field in an electric motor

Three-phase power transformer

3-Phase electrical systemContinued

• Method of electric power transmission :

Mainly used to power motors

Less conductor material to transmit electric power

Constant power transfer over each cycle of the current

• Delay between "phases“:


Methods of Power Generation

• Conventional methods:

Hydraulic

Stem

Diesel

• Non-Conventional methods :

Solar power

Wind power

Atomic energy


Different forms of power generation

• Steam turbine

Stem goes through a turbine, which spins

Turning copper wire (armature) inside the generator generate an electric current

• Hydro turbine

Water pushes against turbine blades, causing the rotor to spin

• Gas turbineHot gases go through a turbine, which spins

• Wind turbineWind pushes against the turbine blades, causing the rotor to spin

• Nuclear power plants

Nuclear reactions create heat, which turns into steam goes through a turbine which spins


Generation of Electricity

Produces electricity

Rotor - Revolving section

Stator – A series of wire coils which form a cylinder around the rotor

An electro-magnet, revolves at high speed to generate electricity (alternating current) in the stator

• Generator


Electric power transmission (“grid”)

• Power transmission :

Takes place at high voltage (110 kV or above)

Transmitted over long distance through overhead power transmission lines

Underground power transmission - Only in densely populated areas

No energy to the load• Currents flow in components

of transmission line

• Reactive current flow Extra losses in the transmission circuit

• Power factorRatio of real power (transmitted to the load) to apparent power Electrical power

Power loss Resistance1

voltage2

Transmission between the power plant and a substation near a populated area


Distribution of Electricity


Transformer

• A transformer :

Device that transforms voltage from one level to another

Possible to transmit power at an economical transmission voltage and to utilize power at an economically effective voltage

Reduces current before transmitting electrical energy over long distances through wires

Transmits electricity more efficiently

Reduces the energy lost, enabling the economic transmission of power over long distances


Values for current and Voltages

Connection Line Voltage Line Current

Phase Voltage Phase Current

(a) Delta-Delta

Primary Delta v I V I/1.732

Secondary Delta V/a Ia V/a Ia/1.732

(b) Delta-Star

Primary Delta V I V I/17.32

Secondary Star 1.732V/a Ia/1.732 V/a Ia/1.732

(c) Star-Star

Primary Star V I V / 1.732 I

Secondary Star V/a Ia V / 1.732 a Ia

(d) Star-Delta

Primary Star V I V / 1.732 I

Secondary Delta V/ 1.732 a 1.732 Ia V / 1.732 a Ia


Types of Transformer

Oil filled self cooled

Oil filled water cooled

Air blast type

Core type

Shell type

Power transformer

Potential transformer

Current transformer

Isolation transformer

• According to Cooling type:

• According to construction:

• According to application:


Important Points of Transformer

• Used to transfer energy from one AC circuit to another

• Frequency remains the same in both the circuits

• No ideal transformer exists

• Used in metering applications (current transformer i.e. CT, potential transformers)

• Used for isolation of two different circuits (isolation transformers)

• Transformer power is expressed in VA (Volt amperes)

• Transformer polarity is indicated by using dots.


Circuit Breaker

• Function

• Isolation

• Control

Functional

Emergency switching

Switching-off for mechanical maintenance

• Protection

Overload

Short-circuit

Insulation fault (With differential-current relay)

Under Voltage (With undervoltage -trip coil)

• Basic unit of switchgear for any electrical installation


Types of Circuit Breakers

• H-V AC circuit breakers :

• Vacuum circuit breaker

Current up to 3000 A

Voltages up to about 35,000V

Longer life than air circuit breakers

• Air circuit breakerCurrent up to 10,000 A

Used for main power distribution in large industrial plant

• Classified by the medium used to extinguish the arc :

• Oil-filled (dead tank and live tank) • Oil-filled, minimum oil volume • Air blast • Sulfur hexafluoride


Performance curves of a typical LV current-limiting circuit-breaker

L.V.Circuit Breaker

• L V CB < 1000 V :MCB (Miniature Circuit Breaker) — < 100 A

MCCB (Moulded Case Circuit Breaker) — < 1000 A


30°C - Domestic-type CBs

40°C - Industrial-type CBs

Selection of CB

• Criteria for selection :

Electrical characteristics of the installation

Eventual environment - Ambient temperature, etc.

Short-circuit current breaking and making requirements

Operational specifications

Installation regulations - Protection of persons, etc.

Load characteristics - Motors, fluorescent lighting, LV/LV transformers

Rated current of a circuit-breaker defined for operation at a given ambient temperature:


• A 1200 A 3-pole 115,000 V breaker at a generating station

High Voltage Circuit Breaker


Electrical Hazards

• From electrical equipments :

Primary Hazard:Electric shock and associated effects

Fire Hazard

Secondary Hazards :

Burns on skin at point of contact

Injuries by electric shock combined with fall

Temperature hazards due to high temperature during operation

Arc flash causing external burns and injuries by explosive expansion of air due to the arc


Hazardous Condition

Contact with current carrying parts

• Direct contact with exposed current carrying parts

• Maintenance process - Need to open up enclosure

• Defective/damaged enclosure or insulation materials

• Unsafe design

• Maintenance people more at risk

• Contact with energized conductive parts

• Indirect Contact

Electric/Ground faults

Leaking out of electricity


Equipment HazardsType of equipment Hazards

Generation equipment Electric shock, arc flash, mechanical hazards

Transformers Electric shock, arc flash, fire hazard

Overhead Transmission/distribution lines Electric shock, arc flash, fall from heights

Cables Electric shock, arc flash, fire hazard

Bus ducts Electric shock, arc flash, thermal hazard

Distribution equipment Electric shock, arc flash, thermal hazard, fire hazard

Motive equipment Electric shock, arc flash, thermal hazard, mechanical hazards

Heating equipment Electric shock, arc flash, thermal hazard

Lighting equipment Electric shock, arc flash, thermal hazard, fall from heights

Uninterrupted power supplies with battery Electric shock, arc flash, hazards from corrosive liquids and explosive gases


Need for Safety in Operation

• Periodic inspection & maintenanceDetermine whether an installation is in a satisfactory condition for continued service

• Checks:

Safety of persons/livestock against electrical hazards

Protection against damage that can arise from a defect in the installation

Confirmation that the installation has no defects that impair safety

Identification of any defects/non-compliance with Regulations

Ensure protection of property from fire and heat


Electrical Safety

• Safety measures:

• Isolating live equipment before starting any work • Eliminate faults to improve safety• Proved knowledge level• Safe design of equipment• Clear warning sign• Safe operation and maintenance practice• Periodic inspection • Prompt repairs• Use of personal safety equipments• Documenting the procedures • Creating an organizational safety


Need for periodic Inspection

• Test and inspection:

• Insurance• Mortgage• Licensing reasons• Change of use• Change of ownership• After additions and alterations• After damage• Change of loading• To assess compliance with current

regulations

• General areas of inspection

• Safety• Wear and tear• Corrosion• Damage• Over loading


Switching• Switching: An operation intended to switch on or off or vary the supply of electrical

energy to all or part of an installation for normal operating purposes• Example: A contactor

Provision Purpose For

Switching OFF for mechanical maintenance

To enable non-electrical work to be carried out on switched circuit with safety

Non-electrically skilled persons

Emergency Switching To cut off rapidly electrical energy to remove any unexpected hazards

Anyone

Functional Switching To enable proper functioning and control of current using equipment

Installation user


Switching Equipment

Symbol for a load-break switch

Symbol for a disconnector (or isolator)

• Elementary switching devices :

• Disconnector (or isolator):

Manually-operated, lockable, two-position device (open/closed) which provides safe isolation of a circuit when locked in open position

No standards

Should withstand short-circuit currents

• Load-breaking switch :

Operated manually, a non-automatic two-position device (open/closed)

Used to close and open loaded circuits

Does not provide any protection


Summary• 3-phase electrical system: Why it is used for transmission

• Generation, Distribution and transmission of electricity: Methods of generation, Distribution and transmission of electricity.

• Transformer: Different types, Advantages.

• Circuit breaker: Function, different types

• Dangers of electricity: Electrical Hazards, How to avoid it

• Need for safety: Different methods of safe operation and maintenance


DO YOU WANT TO KNOW MORE?

If you are interested in further training or information, please visit:

http://idc-online.com/slideshare