7.0 Transmission

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8/13/2019 7.0 Transmission

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Lecture Outline• Switchgear and cabling• Circuit protection• Tariffs and power factor• Extra-low voltage and intrinsic safety

Power Lines

Types of Power Lines

Substations

Switchgear and cablingWhat is switchgear?

Within a power system, an electricity supply is essential.However, it is necessary to protect machinery such as motorsor generators from dangerous fault conditions which canoccur.

• This is achieved by allowing the power supply to be switchedon or off under no load, load conditions, or fault condition.

• Switchgear is a term used to describe the various pieces ofequipment used for switching and protecting purposes in apower system.

• A switchgear cable is a flexible electrical cable,which is used in a switchgear system designedto isolate electrical equipment

Circuit protection

Circuit protection• Circuit protection devices are used to protect

wires and connectors from being damaged byexcess current flow caused by over current orshort-circuit.

• Excess current cause excess heat which causes

circuit protection to be open circuit• Circuit protection device are such as fuses,

fuse elements, fusible links, circuit breakers.

Tariffs and power factor

Tariffs and power factorWhat is Power Factor• Power Factor is an index used to compute the

efficiency level of electricity usage. The index ismeasured from 0 to 1.

• A higher index shows efficient usage of electricity

and vice versa.• Low power factor shortens the lifespan of

electrical appliances and causes power system

losses to electric distribution company (e.g TNB).

• Power Factor is the ratio of Working Power toApparent Power.

• For efficient usage of electricity, power factormust approach 1.0. Power factor that is lessthan 0.85 shows inefficient use of electricity.

• Calculation for Power Factor = KW √(KW2 + KVAR2)

Extra-low voltageand intrinsic safety

Extra-low voltage• In electricity supply, using extra-low voltage (ELV)

is one of several means to protect

against electrical shock.• The International Electrotechnical

Commission (IEC) and its member organizationsdefine an ELV circuit as one in which the electricalpotential of any conductor against earth (ground)is not more than 50 V for alternating current andnot more than 120 V for direct current

Intrinsic safety

• “Intrinsically Safe” (IS) is a protectioncertification for safe operation with electronicequipment in explosive atmospheres.

• The concept was developed for safe operationof process control instrumentation inhazardous areas, particularly around petro-chemicals.

• A device termed “intrinsically safe” is designedand certified to eliminate or encapsulate anycomponents that produce sparks or which could

generate enough heat to cause an ignition inareas with flammable gasses, dusts or fuels.

• Electrical apparatus for use in hazardous areas

needs to be designed and constructed in such away that it will not provide a source of ignition.

7.0 Transmission

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