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TEPCO

GULF TEPCO

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Short circuit currentsand Circuit breakersselection

TEPCO

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Short Circuit Currents and Circuit BreakerSelection

Part One: Short circuit and power system design

Part Two: Short circuit study (calculation)

Part Three: Selection of circuit breakers

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Part One: Short circuit andpower system designGoals of power system design

Ensure safety by Managing electrical hazards (electrocution, fire ,)

Network protection against up normal condition(over load, short circuit, arcing faults,)

Optimum selection of system components

Reduce cost by Reducing system down time

TEPCO

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Part One: Short circuit andpower system design

Wrong operation or connection

Short Circuit Definition

Cause of Short Circuit Insulation failure (mechanical stress, heat, fire ,)

TEPCO

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Part One: Short circuit andpower system design

Short circuit level affects Prevention of electric shock hazards Amount of damage to cable insulation

Circuit interruption success

TEPCO

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Part One: Short circuit andpower system design

Prevention of electric shock hazards

110V

~L

o a d

CB

Line

Neutral

PE

220V

TEPCO

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Part One: Short circuit andpower system design

Circuit interruption success

Never exceed circuit breaker interrupting capacity

TEPCO

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Part Two: Short circuit study

Short circuit

Main Studies in Power System Load flow (Connected, demand loads, sizing cables and CB)

Performing short circuit study

Short circuit limitation, development and types

IEC Standards for short circuit calculation

TEPCO

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Part Two: Short circuit study

Short circuit limitation Short circuit current is limited by supply and circuitimpedance only

circuitsupply

supply

Z Z

V I

sc

Short circuit development

50kA

93kA

TEPCO

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Part Two: Short circuit study

Short circuit types 3-phase to ground fault Phase to phase fault

Single line to ground fault Double line to ground fault

abcn

bcn

a

abcn

abcn

TEPCO

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Part Two: Short circuit study

IEC60865 Calculation of its effects

IEC Standards for short circuit calculation IEC Organization

Regional Committees (SASO in Saudi Arabia)

Technical Committees (Transformers, Cables, )

IEC technical committee 73 publications IEC60909 Calculation of short circuit currents.

TEPCO

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Part Two: Short circuit study

Performing short circuit study to IEC60909 Network elements

Impact of induction motors on short circuit

Input/Output of the study

Software calculation (NetPlan)

TEPCO

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Performing short circuit studyNetwork elements

Transformers

MV network grid Impedance given in MVA

For 13.8kV network impedance (available short circuit) 500MVA

Impedance given in per unit system (p.u.) 1p.u. 100% For 500KVA trafo , 0.04p.u. 4% For 1600KVA & 1000KVA trafo , 0.06p.u. 6% For 2000KVA trafo , 0.08p.u. 8%

kA KVA

Isc 3906.0/4003

1600

kAkV

MVA Isc 21

8.133

500

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Performing short circuit studyNetwork elements

Cables & Busways

Effect of supply voltage

Impedance given in milliohm

Max short circuit at min temperature

Min short circuit at max temperature

A

A

V Isc

)/(

Voltage regulation affect short circuit level

Max short circuit occur at max supply voltage (1.05Ur)

Min short circuit occur at min supply voltage (0.95Ur)

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Performing short circuit study

Software calculation (Moeller NetPlan)

Input/Output of Study Input: Network elements & connection between them

Output: Max/Min short circuit at each busbar& through each cable

Easy to use and learn Short circuit calculation according to IEC60909

Editable network elements master database

TEPCO

Network element dimensioning according to IEC60364

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Performing short circuit study

Short Circuit on main busbar Max Short Circuit on each bus

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Performing short circuit study

Short Circuit on main busbar Max Short Circuit on each bus

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Part Three: Determination of breakersinterrupting capacity

TEPCO

IEC Standards for circuit breakers

Circuit interruption Arcs

Circuit breaker operation

Effect of short circuit current Circuit breaker types

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Circuit interruption Arcs

TEPCO

How much voltage appear on an Arc ? Arc voltage depend on two main factors

1) Arc length (20V/cm)2) No. of segments in the arc (40V each)

10cm

V(arc)=40+20x10=240V

V(arc)=2x40+20x10=280V

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Circuit interruption

Circuit breaker types

TEPCO

Effect of short circuit current Repulsion force between contacts

Very rapid temperature rise

MCB MCCB

NZM & PMC 1, 2, 3, 4I r = 20 ... 1600 A

ACB (ICCB)

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IEC Standards for circuit breakersCircuit breaker for industrial areasIEC60947-3

TEPCO

Rated voltage

Definition of breaking capacity

Dramatic effect for current limiting circuit breaker

Non current limiting breakers also suffer from increasedarc dissipation

Rated voltage is the phase to phase voltage

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Conclusions

TEPCO

Never exceed breaker interrupting capacity As a quick rule for interrupting capacity

For 1000KVA select at least 36kA CB

For 1600KVA select at least 50kA CB Due toMotors

Interrupting capacity depend on systemvoltage and earthing

The EndThanks for listening