electrical machines
DESCRIPTION
Electrical Machines. LSEGG216A 9080V. Parallel Operation & Auxiliary equipment. Introduction. Identify. Parallel Operation. Why not get a bigger one?. Can carry many of the same size so maintenance is easier & cheaper If one fails can still supply some load - PowerPoint PPT PresentationTRANSCRIPT
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Electrical Machines
LSEGG216A9080V
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Parallel OperationParallel Operation&&
Auxiliary equipmentAuxiliary equipment
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IntroductionIntroduction• Identify
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Parallel Parallel OperationOperationWhy not get a bigger one?
• Can carry many of the same size so maintenance is easier & cheaper
• If one fails can still supply some load• Can turn one off if load reduces
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Parallel Parallel OperationOperationBoth transformers must have:
• Same voltage• Frequency• Roughly the same VA rating• Same polarity
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Parallel Parallel OperationOperationSingle Phase
Incorrect Polarity
High circulation currents will flow
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Parallel Parallel OperationOperationSingle Phase Correct Polarity
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Parallel Parallel OperationOperationTesting for Polarity
Place a voltmeter across the transformer terminal
and the supply line
Correct polarity =Incorrect polarity =
0 VoltsTransformer voltage or higher
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3 Phase 3 Phase TransformersTransformers
TypesStar
PRIMARY SECONDARY
No Phase Shift
Star
Reference
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3 Phase 3 Phase TransformersTransformers
TypesDelta
PRIMARY SECONDARY
No Phase Shift
Delta
Reference
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3 Phase 3 Phase TransformersTransformers
TypesDelta
PRIMARY SECONDARY
V2 Leads V1 by 30
Star
30Reference
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3 Phase 3 Phase TransformersTransformers
TypesDelta
PRIMARY SECONDARY
V2 Lags V1 by 30
Star
30
Reference
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Paralleling 3 Phase Paralleling 3 Phase TransformersTransformers
Must be from the same vector groupMust have the same effect on voltage:
-Δ paralleled with -Δ
Δ- paralleled with Δ-
Δ- paralleled with -Δ Provided that the line voltages are equal
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Paralleling 3 Phase Paralleling 3 Phase TransformersTransformers
Must be from the same vector groupMust have the same effect on voltage:
-Δ paralleled with -Δ
Δ- paralleled with Δ-
Δ- paralleled with -Δ
Δ- -30 & -Δ +30
The voltage phase difference would be 60
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Auxiliary Auxiliary EquipmentEquipment• Protection
• Voltage adjustment
• Over temperature• Over pressure• Low oil level• Oil quality• Reduction of water
• Tap changers
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Transformer Transformer ConstructionConstruction
• Most large transformers are oil filled
• The oil level must be high enough to cover the transformer
• Oil must be kept dry and clean
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Transformer Transformer ConstructionConstruction
Sealed Tank
Conserver Tank
Tank always stays full
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Transformer Transformer ConstructionConstruction
Pressure relief valve allows over pressure oil to escape
Over temperature thermostat trips circuit breaker if
transformer gets too hot
Buchholz relay monitors oil between transformer and
conserver tank
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Buchholz Buchholz relayrelay
• Presence of air bubbles due to faulty initial filling or faulty seal of gaskets
• Formation of gas due to burning of oil or solid insulation
• Lowering of oil level due to leak of the tank
• Oil flow from tank to conservator due to explosion or short circuit
Monitors
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Buchholz Buchholz relayrelay
On a slow accumulation of gas, due to slight overload accumulates in the top of the relay and forces the oil level down. A float operated switch in the relay is used to initiate an alarm signal
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Buchholz Buchholz relayrelay rapid gas accumulation, flow of oil
operates a switch attached to a vane
Test port to allow the accumulated gas to be withdrawn for testing
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Buchholz Buchholz relayrelay
Oil & Gass from Tx Oil to conserver
Oil for testing
Gas testingDry air test
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Tap ChangersTap ChangersTwo types:• Off Load• On Load
Can be located on the primary or secondary of the transformer
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Off LoadOff Load• Basically a multi-position switch
• Open circuits output between positions
• Contacts not rated to open circuit under load
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Transformer Open circuited
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On LoadOn Load• Manual• Automatic
Transformer windings
Common terminal
Sliding switch
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On LoadOn LoadInductors carry
current when contact is between taps
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On LoadOn LoadContact moves to new tap