Marine Electrical System

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Operational Consideration in

Electrical Power Plant

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Objectives

•• State common parameters of AC electrical

State common parameters of AC electrical

supply onboard

•• Describe how the power is distributed to

Describe how the power is distributed to

consumers using line diagram (incorporate

shore supply and emergency source of power)

•• Describe the insulated neutral system and why

Describe the insulated neutral system and why

it is preferred

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Introduction

•• Auxiliary services ranging from ER pumps and fans,Auxiliary services ranging from ER pumps and fans, deck winches & windlasses to general lighting,

deck winches & windlasses to general lighting, catering & AC

catering & AC

•• Electrical power – used to drive most of theseElectrical power – used to drive most of these auxiliaries

auxiliaries

•• Electrical power system - designed to provide securedElectrical power system - designed to provide secured supplies with adequate built-in protection for both

supplies with adequate built-in protection for both equipment & operating personnel

equipment & operating personnel

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Switchboard

•• To distribute generated electricity to where it isTo distribute generated electricity to where it is needed

needed

•• Can be classified as one of following:-Can be classified as one of

following:- –

– Main switchboardsMain switchboards –

– Emergency switchboardsEmergency switchboards –

– Section boards - supplied directly/via transformers etcSection boards - supplied directly/via transformers etc –

– Distribution boardsDistribution boards

•• Metal-clad, dead front switchboards are Metal-clad, dead front switchboards are mandatorymandatory for AC systems

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Distribution system

•• Main board - built in 2 sections which can operateMain board - built in 2 sections which can operate independently in case one

independently in case one section damagedsection damaged

•• One side carries port & One side carries port & fwd motors (group motor fwd motors (group motor starter) while other section carried s

starter) while other section carried stbd & aft motorstbd & aft motors •• Central section used for control the main generatorsCentral section used for control the main generators •• Switchgear cubicles on generator panel sides used for Switchgear cubicles on generator panel sides used for

essential services, flanked by group motor starter essential services, flanked by group motor starter boards

boards

•• Separate section will controls 3-phase 220V &Separate section will controls 3-phase 220V & lighting services

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Distribution system (cont/…)

•• 440V/220V lighting transformers may mounted inside main440V/220V lighting transformers may mounted inside main swbd cubicle, or free-standing behind it

swbd cubicle, or free-standing behind it

•• Main generator supply cables connected directly to their Main generator supply cables connected directly to their CBCB •• Short copper bars, then connected to three bus bars Short copper bars, then connected to three bus bars whichwhich

run through

run through switchboard lengthswitchboard length

•• Busbars - may seen if Busbars - may seen if rear door are opened, in rear door are opened, in specialspecial enclosed bus-bar duct

enclosed bus-bar duct

•• Swbd contain frequency Swbd contain frequency meters, synchroscopes, wattmetersmeters, synchroscopes, wattmeters,, voltage and current

voltage and current transformers, ammetetransformers, ammeter switches, voltager switches, voltage regulations & means for adjusting prime movers speed

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Shore supply

•• Required during deadship - dry-docking for major overhaulRequired during deadship - dry-docking for major overhaul •• Log of supply kWh meter taken for costing purposesLog of supply kWh meter taken for costing purposes

•• Suitable connection box to accept shore supply cable -Suitable connection box to accept shore supply cable -accommodation entrance or emergency generator room accommodation entrance or emergency generator room •• Connection box - suitable terminals including earthingConnection box - suitable terminals including earthing

terminal, dedicated CB, switch & fuses - protect cable linking terminal, dedicated CB, switch & fuses - protect cable linking to main switchboard

to main switchboard

•• Plate giving details of ship’s electrical system (voltage andPlate giving details of ship’s electrical system (voltage and frequency) & method for connecting must provided

frequency) & method for connecting must provided

•• For AC supply, phase sequence indicator is fitted - indicateFor AC supply, phase sequence indicator is fitted - indicate correct supply phase sequence - usually lamp

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Shore supply

(cont/…)

•• It is not norIt is not normal practice to parallel shore supply withmal practice to parallel shore supply with ship’s generators

ship’s generators

•• Therefore, ship’s generators must disTherefore, ship’s generators must disconnectedconnected

before shore supply resume connection – interlocked before shore supply resume connection – interlocked provided

provided

•• Shore supply may also connected directly toShore supply may also connected directly to

emergency board - ‘back feeds’ to main switchboard emergency board - ‘back feeds’ to main switchboard •• When phase sequence indicator indicate reverseWhen phase sequence indicator indicate reverse

sequence, simply interchanging any two leads to sequence, simply interchanging any two leads to remedy this fault

remedy this fault

•• Incorrect phase sequence cause motors to run Incorrect phase sequence cause motors to run inin reverse direction

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Effect of higher voltage

•• Contribute to sparking condition

Contribute to sparking condition

•• Current drawn proportional to terminal voltage

Current drawn proportional to terminal voltage

•• Cause excessive starting current

Cause excessive starting current

•• Motor overheat due to high current

Motor overheat due to high current

•• Motor accelerates fast and may overload the

Motor accelerates fast and may overload the

drive

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Effect of lower voltage

•• Motor draw more current to keep sMotor draw more current to keep same power outputame power output •• Starting Starting torque torque V², V², thus thus to to 72.5%72.5%

•• Take longer period to build up Take longer period to build up speedspeed •• High reactance motor will stalledHigh reactance motor will stalled

•• Overheating will occur Overheating will occur

•• Motor may stall & burn due to Motor may stall & burn due to overheating – 49x fulloverheating – 49x full load heating

load heating

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Effect of higher frequency

•• Motor run 20% faster, increase overall speed

Motor run 20% faster, increase overall speed

•• Overload, overheated & overstress driven

Overload, overheated & overstress driven

loads

•• Power

Power produced

produced

(speed)³

•• Supply will reduce stator flux

Supply will reduce stator flux

•• Affect starting torque

Affect starting torque

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Effect of lower frequency

•• Stator flux increases

Stator flux increases

•• Magnetising current will increase

Magnetising current will increase

•• Motor runs slower & hot

Motor runs slower & hot

•• Speed reduced to 17%

Speed reduced to 17%

•• Overheating will take place

Overheating will take place

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Emergency power supply

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Emergency power supply

•• Provided, in event of emergency (blackout etc), supply still available for Provided, in event of emergency (blackout etc), supply still available for emergency lighting, alarms, communications, watertight doors & other emergency lighting, alarms, communications, watertight doors & other essential services - to maintain safety & safe

essential services - to maintain safety & safe evacuationevacuation •• Source - generator, batteries or bothSource - generator, batteries or both

•• Self-contained & independent from other ER power supplySelf-contained & independent from other ER power supply

•• Emergency generator must have ICE as prime mover with own FOEmergency generator must have ICE as prime mover with own FO supply tank, starting equipment & switchboard

supply tank, starting equipment & switchboard

•• Must initiated following a total electrical power failureMust initiated following a total electrical power failure

•• Emergency batteries - ‘switch in’ immediately after power failureEmergency batteries - ‘switch in’ immediately after power failure

•• Emergency generators - hand cranked, but automatically started by air /Emergency generators - hand cranked, but automatically started by air / battery possible - ensure

battery possible - ensure immediimmediate run-upate run-up •• Power rating - determined by size & ship rolePower rating - determined by size & ship role

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•• Larger & complicated vessels - may require hundreds of kW for Larger & complicated vessels - may require hundreds of kW for emergency lighting, chronological restarting & fire fighting supply emergency lighting, chronological restarting & fire fighting supply •• Connected to own emergency swbd - located in compartment aboveConnected to own emergency swbd - located in compartment above

water line water line

•• Normal operation - emergency board supplied from main board via Normal operation - emergency board supplied from main board via ‘bus-tie’

‘bus-tie’

•• Impossible to synchronise with main generators due to interlocks – Impossible to synchronise with main generators due to interlocks – newer design permit short period of synchronising

newer design permit short period of synchronising

•• Starting automatically - initiated by relay which monitors normal mainStarting automatically - initiated by relay which monitors normal main supply

supply

•• Falling mains frequency / voltage causes ‘start-up’ relay to operateFalling mains frequency / voltage causes ‘start-up’ relay to operate generator starting equipment

generator starting equipment

•• Arrangement for starting – electrical, pneumatic, hydraulicArrangement for starting – electrical, pneumatic, hydraulic

•• Regular tests - power loss simulation will triggers start sequenceRegular tests - power loss simulation will triggers start sequence

•• Detailed regulations - 1972 SOLAS Convention, IEE Regulations for Detailed regulations - 1972 SOLAS Convention, IEE Regulations for Electrical and Electronic Equipment of Ships, regulations from

Electrical and Electronic Equipment of Ships, regulations from Classification Societies (LR, ABS, DNV etc) and etc

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Insulated neutral system

Insulated system - totally electrically

insulated from earth (ship’s hull)

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Earthed neutral system

Earthed system has one pole or Earthed system has one pole or neutral point connected to earth neutral point connected to earth

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General

•• Shipboard systems - insulated from earth (ship's Shipboard systems - insulated from earth (ship's hull)hull) •• Shore system - earthed to the groundShore system - earthed to the ground

•• HV systems (>1000V) - earthed to HV systems (>1000V) - earthed to ship's hull viaship's hull via neutral earthing resistor (NER) or

neutral earthing resistor (NER) or high impedancehigh impedance transformer to limit earth fault current

transformer to limit earth fault current

•• Priority for shipboard - Priority for shipboard - maintain electrical supply tomaintain electrical supply to essential equipment in event of single earth fault

essential equipment in event of single earth fault •• Priority ashore - Priority ashore - immediatimmediate isolation earth-faultede isolation earth-faulted

equipment equipment

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3 basic circuit faults

An open-circuit fault is due An open-circuit fault is due to a break in the conductor, to a break in the conductor, as at A, so that current

as at A, so that current cannot flow

cannot flow

An earth fault is due to a break An earth fault is due to a break in the insulation, as at B,

in the insulation, as at B,

allowing the conductor to touch allowing the conductor to touch the hull or an earthed metal

the hull or an earthed metal enclosure

enclosure

A short-circuit fault is due A short-circuit fault is due to a double break in the to a double break in the insulation

insulation, as , as at C,at C,

allowing both conductors allowing both conductors to be connected so that a to be connected so that a very large current very large current

by-passes or "short-circuits" passes or "short-circuits" the load.

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The preferred system??

•• If earth fault occurs on insulated pole of ‘EARTHEDIf earth fault occurs on insulated pole of ‘EARTHED DISTRIBUTION SYSTEM’ - equivalent to ‘short DISTRIBUTION SYSTEM’ - equivalent to ‘short circuit’ fault

circuit’ fault

•• Large earth fault current Large earth fault current would immediately ‘blow’would immediately ‘blow’ the fuse in line conductor

the fuse in line conductor

•• Faulted electrical equipment immediately isolatedFaulted electrical equipment immediately isolated from supply & rendered SAFE, but loss of

from supply & rendered SAFE, but loss of equipmentequipment •• Could create hazardous situation iCould create hazardous situation if equipment wasf equipment was

classed ESSENTIAL classed ESSENTIAL

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The preferred system??

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•• If earth fault ‘A’ occurs on one line of ‘INSULATEDIf earth fault ‘A’ occurs on one line of ‘INSULATED

DISTRIBUTOIN SYSTEM’ - not trip any protective gear & DISTRIBUTOIN SYSTEM’ - not trip any protective gear & system resume function normally

system resume function normally •• Thus, equipment still operatesThus, equipment still operates

•• If earth fault ‘B’ developed on another line, 2 earth faultsIf earth fault ‘B’ developed on another line, 2 earth faults

would equivalent to a short-circuit fault & initated protective would equivalent to a short-circuit fault & initated protective gear

gear

•• An insulated distribution system requires TWO earth faults onAn insulated distribution system requires TWO earth faults on TWO different lines to cause an earth fault current.

TWO different lines to cause an earth fault current.

•• An earthed distribution system requires only ONE earth faultAn earthed distribution system requires only ONE earth fault on the LINE conductor to create an earth fault current.

on the LINE conductor to create an earth fault current. •• Therefore an insulated system is more effective than anTherefore an insulated system is more effective than an

earthed system - maintain supply continuity to equipment, thus earthed system - maintain supply continuity to equipment, thus being adopted for most marine electrical systems

being adopted for most marine electrical systems

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High voltage system

•• Shipboard HV systems - ‘earthed’ via resistor Shipboard HV systems - ‘earthed’ via resistor connecting generator neutrals to earth

connecting generator neutrals to earth

•• Earthing resistor with ohmic value - chosen Earthing resistor with ohmic value - chosen to limitto limit maximum earth fault current < generator full

maximum earth fault current < generator full loadload current

current

•• Neutral Earthing Resistor (NER) - Neutral Earthing Resistor (NER) - assembled withassembled with metallic plates in air – due to single earth

metallic plates in air – due to single earth fault willfault will cause circuit disconnected by its protection device cause circuit disconnected by its protection device

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