Pres11 - Selective Coordination 2-02

© 2001 Cooper Bussmann, Inc.

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Selective Coordination



• For 600 Volts & less

• Easy concept to understand

• Hard to verify, if you do not know what to look for

• Misinterpretations or lack of understanding is very prevalent

• People review curves (hand drawn or computer generated) and they do not know how to interpret



Definition:

The act of isolating a faulted circuit from the remainder of the electrical system, thereby eliminating unnecessary power outages. The faulted circuit is isolated by the selective operation of only the overcurrent protective device closest to the overcurrent condition.

Without Selective Coordination With Selective Coordination

Selective Coordination: Avoids BlackoutsSelective Coordination: Avoids Blackouts

OPENS

NOT AFFECTED

UNNECESSARYPOWER LOSS

OPENS

NOT AFFECTEDFault Faul

t


Selective Coordination: NEC®

240.2 Definitions

Coordination.

The proper localization of a fault condition to restrict outages to the equipment affected, accomplished by the choice of selective fault-protective devices.


Selective Coordination: NEC®

240.12 Electrical System Coordination where orderly shutdown required to minimize hazards

620.62 Selective Coordination required where more than one elevator is supplied by single feeder.

517.17 Selective coordination between main and feeder required for health care facilities where main has GFP (feeder also required to have GFP).



Chapter 2 Video




Coordination

Circuit Breakers


Spring Loaded ContactsLatch

Bimetal

Magnetic Element

Line

Load

Trip BarCircuit Breaker

Operation



Bimetal

Line

Load

Trip Bar Thermal Overload Operation

Normal State



Line

Load

Trip Bar

Bimetal

Thermal Overload Operation

Unlatch & Open



Magnetic Element

Line

Load

Trip Bar Short Circuit Operation

Normal State


Spring Loaded ContactsUnlatch

Magnetic Element

Line

Load


Unlatching



Magnetic Element

Line

Load


Opening



Magnetic Element

Line

Load


Cleared


Coordination - Thermal-Mag Circuit BreakersCoordination - Thermal-Mag Circuit Breakers

Thermal Magnetic Molded Case Circuit Breaker Time-Current Curve Overload Region

Instantaneous RegionInterrupting TimeUnlatching Time

Interrupting RatingInterrupting Rating


Coordination - Thermal-Mag Circuit Breakers (See SPD)Coordination - Thermal-Mag Circuit Breakers (See SPD)



Current

Tim

e

A

B

C

D

4000A Fault


OPENS

NOT AFFECTED

UNNECESSARYPOWER LOSS Fault

Lacking Coordination


Selective Coordination - Insulated Case Circuit Breakers (See SPD)


2000A Insulated Case Circuit Breaker STD Is an Option - Allows breaker to delay opening Instantaneous Override built-in: may be as low as 12X the breaker rating Will often result in lack of coordination




2000A Insulated Case with STD and Instantaneous Override and 100A Molded Case Thermal Magnetic Circuit breaker - NO Coordination in Short-Circuit Region (above 21,000A)


Selective Coordination - LV Air Power Circuit Breakers (See SPD)Selective Coordination - LV Air Power Circuit Breakers (See SPD)

Short Time Delay - Allows the fault current to flow for up to 30 cycles.

Used to coordinate with downstream

Subjects equipment to high mechanical and thermal stresses, often violating 110.10

Arc Flash/ Blast Risks Much Higher

High Cost, Larger Equipment


Selective Coordination: Fuses


Time Current Curves

Selective Coordination:Fuses (See SPD)


Selectivity Ratio

Guide Based on

Thermal Principle

Based on I2t Clear Clear

Not MeltNot Melt

I2t melting > I2t Clearing 1200 A 600 A

Selective Coordination:Fuses (See SPD)


Selective Coordination (See SPD )

Selectivity Ratio Table Assures Coordination!No Plotting required!

LOW-PEAK® : LOW-PEAK®

2:1 Line:Load Ratio

Lin

e S

ide

Fu

se

Load Side Fuse


Example:

Main: KRP-C 1200 SP

Feeder: LPS-RK 200 SP

Branch: LPS-RK-30 SP

MSB

1200 A

200 A

30 A

480V, 3 phase

MCC

GFP

Selective Coordination - Fuses


Selective Coordination - Fuses

Use Selectivity Table

Main KRP-C 1200 SP

Feeder LPS-RK 200 SP

Branch LPS-RK 30 SP

What happens: Branch Circuit Isca = 5000 A or 50,000A or 300,000A ?


Lineside KRP-C 1200SP to Loadside LPS-RK 200SP

1200/200 = 6:1 Table only need 2:1 Selective Coordination

Lineside LPS-RK 200SP to Loadside LPS-RK 30SP

200/30= 6.67:1 Table only need 2:1


Selective Coordination- Fuses


Fault

NOT AFFECTED

OPENS




Simple Rules for Checking

• Circuit Breakers (instantaneous trip)

• Fuses

Can you look at this Can you look at this and assess whether and assess whether coordinated?coordinated?

You do not even You do not even need to draw curve!need to draw curve!

Simple Rule:Simple Rule:(Amp rating) x (I.T. setting) =(Amp rating) x (I.T. setting) = Isca @ which CB will unlatch:Isca @ which CB will unlatch:

CB IT ITCB IT IT Amp Amp Set Set Amp PickupAmp Pickup 100 5X100 5X 500 500 200 5X200 5X 1,000 1,000 400 10X 4,000400 10X 4,0001600 12X1600 12X 19,00019,000

See SPD See SPD

100 A100 A200 A200 A

400 A400 A

1600 A1600 A



• You already know the simple rule for fuses.

• Simply use amp rating ratios

• Typically 2:1 for

Low Peak Fuses to Low Peak Fuses



• Do coordination exercise using simple rules– Fusible system

– Circuit breaker system

• It’s simple!


Fault 10000 Amps

Low PeakKRP-C 1000 SP

Low PeakLPJ 200 SP

Low PeakLPJ 20 SP

Are These Selectively Coordinated?


Fault 10000 Amps


Low PeakLPJ 200 SP

Low PeakLPJ 20 SP


OPENS

NOT AFFECTED

Fault 10000 Amps


Low PeakLPJ 200 SP

Low PeakLPJ 20 SP

Selectively Coordinated



Fault 10000 Amps

1000 A. CBIT @ 10 X

200 A. CBIT @ 10 X

20 A. CBIT @ 10X



Fault 10000 Amps

1000 A. CBIT @ 10 X

200 A. CBIT @ 10 X

20 A. CBIT @ 10X

Not Coordinated

OPENS

NOT AFFECTED

Fault 10000 Amps

1000 A. CBIT @ 10 X

200 A. CBIT @ 10 X

20 A. CBIT @ 10X


UnnecessaryBlackout

The Issue:Lack of coordinationtakes out other loads

OPENSFault 10000 Amps

1000 A. CBIT @ 10 X

200 A. CBIT @ 10 X

20 A. CBIT @ 10X


Ground Fault Protection 230-95


See SPDSee SPD


GFP Health Care 517-17

Where one level of GFP is provided per 230.95 or 215.10 an additional step of GFP on feeders required.

The Ground Fault Protection for service and feeder shall be fully Selectively Coordinated

What does this mean ?


517-17 Health Care GFP

Main 1200 A CB

Feeder 200 A CB

GFP on Main & Feeder

Does this meet 517-17?


517-17 Health Care GFP

Main 1200 A Fuse

Feeder 200 A Fuse

GFP on Main & Feeder

Does this meet 517-17?


Following Excerpts from IEEE Standards


IEEE 242-1986 “BUFF BOOK”Protection and Coordination of Industrial and Commercial Power Systems

Page 263 6.4.1 Protection (Series Connection). It should be noted that selectivity will not be provided at any current level where the breaker trip characteristic curves overlap when this protection scheme is used, that is, both circuit breakers will trip.



Page 528 Coordination 14.2.2

Coordination can easily be achieved with low voltage current-limiting fuses that have fast response times. Manufacturer’s time current curves and selectivity ratio guides are used for both overload and short-circuit conditions, precluding the need for calculating time intervals.


IEEE 141-1993 “RED BOOK” Electrical Power Distribution for Industrial Plants

Page 256 5.7.2.3 Low-voltage circuit breakers. To achieve this level of selectivity, power circuit breakers utilize short-time delay trips. The equipment protected by this breaker must be designed to handle the available short-circuit current for the duration of the short-time delay.



Page 528 Coordination 14.1 A coordination study should be made when the available short-circuit current of the source to the plant is increased.



Page 528 Coordination 14.1 A coordination study or revision of a previous study may be needed for an existing plant when new loads are added to the system or when existing equipment is replaced with higher rated equipment.


IEEE 602-1996 “WHITE BOOK”Electrical Systems in Health Care Facilities

Page 57/58 3.7.1.1 Protection requirements. As total selectivity and maximum safety to personnel are critical, a total short-circuit coordination, and component protection study shall be performed.


IEEE 141-1993 “RED BOOK” Electrical Power Distribution for Industrial Plants

Page 256 5.7.2.3 Low-voltage circuit breakers. It should be recognized that providing selectivity to the load-side devices may result in equipment bus structures being underprotected. The Standards for such equipment, ANSI/UL 891-1984 [B21] for switchboards, ANSI/UL 845-1987 [B20] for motor control centers,


IEEE 1015-1997 “BLUE BOOK” Applying Low-Voltage Circuit Breakers Used in Industrial and Commercial Power Systems

Page 135 5.5.4 Short-time delay

All MCCBs and most ICCBs with a short time delay have an instantaneous override. If selective coordination is required for fault currents above the instantaneous override level, a power circuit breaker defined as an LVPCB with a short-time delay option, as shown in Figure 5-16, should be considered.



Page 252 6.3 Trip Unit The resulting combination of long-time delay and short-time delay characteristics provides delayed tripping for all levels of overcurrent below the instantaneous response. This provides time for downstream circuit breakers to operate and clear the fault. The withstand of other electrical components in the current path should be checked to be certain they can handle the additional stress associated with the longer clearing time.



Page 62 3.38 Series-connected rating. Sometimes it is erroneously thought that series combinations are at a disadvantage with regard to coordination as compared to fully rated systems. The fact is that even fully rated circuit breakers with instantaneous trips will not “coordinate” once the fault level exceeds both circuit breakers’ instantaneous trip levels.



Page 134 5.5.3 Series MCCBs

Selective coordination is limited to currents below the instantaneous pickup of the line-side circuit breaker. For any fault downstream of the load-side MCCB having a current greater than the instantaneous pickup of the line-side MCCB, both circuit breakers trip, and power is interrupted to unfaulted circuits fed by the line-side circuit breaker.

Pres11 - Selective Coordination 2-02

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