Power Transfer Applications & Considerations John Stark – Russelectric Inc.

Power Transfer Applications & ConsiderationsPower Transfer Applications & Considerations

John Stark – Russelectric Inc.John Stark – Russelectric Inc.

Power Transfer Applications & ConsiderationsPower Transfer Applications & Considerations •Design ConsiderationsDesign Considerations

•Transfer Switch Transfer Switch ApplicationsApplications•Bypass Functions (pros & cons)Bypass Functions (pros & cons)

•TimersTimers

•Common Mistakes & Common Common Mistakes & Common Sense TipsSense Tips

•Selective Coordination and Selective Coordination and codescodes

CommercialUtility Power

UPS

UPS Batteries

Air conditioning, Lighting,Mechanical, Building Loads,etc.

Network Computer Loads

Transfer Switchgear

Generator ParallelingControl Switchgear

EmergencyGenerators

Transfer Equipment in a Common Scenario Transfer Equipment in a Common Scenario

With regard to the emergency back-With regard to the emergency back-up and transfer scheme, it is up and transfer scheme, it is incumbent upon engineers to select incumbent upon engineers to select the proper equipment for the the proper equipment for the application. There are many application. There are many considerations and they are considerations and they are becoming more with each decade.becoming more with each decade.

OverviewOverview

Recent changes to the National Electrical Code (NEC) require the selective Recent changes to the National Electrical Code (NEC) require the selective coordination of overcurrent protective devices at hospitals and other mission-coordination of overcurrent protective devices at hospitals and other mission-critical facilities. Transfer switches with 30-cycle closing and withstand critical facilities. Transfer switches with 30-cycle closing and withstand ratings dramatically simplify designing to that requirement.ratings dramatically simplify designing to that requirement.

What is Selective Coordination?What is Selective Coordination?

• Definition Definition (Article 100 – NEC)(Article 100 – NEC)

Localization of an overcurrent condition to restrict outages to the circuit or Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective equipment affected, accomplished by the choice of overcurrent protective devices and their ratings.devices and their ratings.

““For the full range of possible overcurrents, the act of isolating an overloaded or faulted circuit For the full range of possible overcurrents, the act of isolating an overloaded or faulted circuit from the remainder of the electrical system, thereby eliminating unnecessary power outages.”from the remainder of the electrical system, thereby eliminating unnecessary power outages.”

The circuit causing the overcurrent is isolated by the selective operation of only that overcurrent The circuit causing the overcurrent is isolated by the selective operation of only that overcurrent protective device which is closest upstream to the overcurrent condition.protective device which is closest upstream to the overcurrent condition.

Article 100 provides the Code definition. Here is another way to describe it:Article 100 provides the Code definition. Here is another way to describe it:

Selective coordination was first required by the NEC in 1993 for elevator circuits. Amendments to the Code in 2005 and 2008 strengthened the requirements and expanded them to include emergency and legally required standby systems, as well as critical operations power systems. Selective coordination, as defined in the 2008 NEC, is the “localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings.” It is a complicated process of coordinating the ratings and settings of overcurrent protective devices, such as circuit breakers, fuses, and ground fault protection relays, to limit overcurrent interruption (and the resultant power outages) to the affected circuit or equipment (the smallest possible section of a circuit). In other words, the only overcurrent protective device that should open is the device immediately “upstream” from the circuit/equipment experiencing an overcurrent condition.

Selective Coordination Requirements

Proper Selective Coordination is becoming more and more of an Proper Selective Coordination is becoming more and more of an engineering consideration and is being enforced more often…engineering consideration and is being enforced more often…

Refer to IAEI handout “Selective coordination restricts outages to the circuit or equipment affected, Refer to IAEI handout “Selective coordination restricts outages to the circuit or equipment affected, ensuring reliability of electrical power.”ensuring reliability of electrical power.”

NEC 2008 –Verbiage on Selective CoordinationNEC 2008 –Verbiage on Selective Coordination

• NEC(2008) 700.27 Coordination: requires “Emergency system(s) overcurrent devices shall NEC(2008) 700.27 Coordination: requires “Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices.”be selectively coordinated with all supply side overcurrent protective devices.”

• NEC(2008) 701.18 Coordination: requires “Legally required standby system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices.”

• NEC(2008) 517.26 Application of other articles: requires “The essential electrical system NEC(2008) 517.26 Application of other articles: requires “The essential electrical system shall meet the requirements of Article 700.”shall meet the requirements of Article 700.”

The overcurrent protective devices may include the following:The overcurrent protective devices may include the following:

Molded Case Circuit BreakersMolded Case Circuit BreakersFused devicesFused devicesInsulated Case Circuit BreakersInsulated Case Circuit BreakersAir Power Circuit breakersAir Power Circuit breakers

One-lineOne-line

G Utility

4000AAPCB

1600AAPCB

1600AAPCB

800AICCB

400AMCCBAn overcurrent event (overload, short

circuit, or ground fault) here should trip the 400A MCCB

ATS

MCCB's (Molded Case Circuit Breaker) typically instantaneous or Current Limiting Devices.

ICCB's (Insulated Case Circuit Breaker) are 30 cycle withstand or up to 4 Cycle Instantaneous.

APCB's (Air Power Circuit Breaker) are typically 30 cycle withstand devices.

Selective CoordinationSelective Coordination

G Utility

4000AAPCB

1600AAPCB

1600AAPCB

800AICCB

400AMCCB

Fault on load side of ATS could see up to 30 cycles of fault current -depending on the Air Power Circuit Breaker settings that is feeding it- and could travel through the ATS and the ATS contacts.

ATS

If the 400A MCCB does not trip/clear…

ATS

In the absence of other means to satisfy selective coordination, the ATS must withstand a fault or even close on potential fault to be properly coordinated.

More on Selective CoordinationMore on Selective Coordination

RequirementsRequirements

Selective coordination requirements for life safety are not Selective coordination requirements for life safety are not a new concept for the a new concept for the CodeCode. There has been a . There has been a CodeCode requirement to coordinate selectively the over-current requirement to coordinate selectively the over-current protective devices for elevator circuits since 1993. protective devices for elevator circuits since 1993.

Most engineers agree this is the simplest way to assure Most engineers agree this is the simplest way to assure coordination, however…..coordination, however…..

BreakersBreakersInstantaneous circuit breakers will not coordinate properly Instantaneous circuit breakers will not coordinate properly because typically, they aren’t adjustable.because typically, they aren’t adjustable.

Fuses

Code RequirementsCode Requirements

• Article 517 Health Care FacilitiesArticle 517 Health Care Facilities 517.26 Application of Other Articles517.26 Application of Other Articles

• Article 620 Elevators, etcArticle 620 Elevators, etc 620.62 Selective Coordination (2008)620.62 Selective Coordination (2008)

• Article 700 Emergency SystemsArticle 700 Emergency Systems 700.9 (B)(5)(b), Exception700.9 (B)(5)(b), Exception

• Article 701 Legally Required Standby SystemsArticle 701 Legally Required Standby Systems 701.18 Coordination701.18 Coordination

• Article 708 Critical Operations Power SystemsArticle 708 Critical Operations Power Systems 708.54 Selective Coordination708.54 Selective Coordination

2005 Code Adoption2005 Code Adoption

  2005 NEC   1999 NEC   2002 NEC   Local Adoption

2008 Code Adoption2008 Code Adoption

2005 NEC – 8 States

WV

WI

MT ND

SD

WA

OR

NV

ID

UT

AZNM

TX

CO

WY

NB

M I

KY

TN

MN

IA

MO

AR

LA

MS

ILIN

OH

ALGA

KS

OK

NH

ME

NY

PA

VA

DE

NJ

MA

RI

FL

NC

SC

VT

CA

Local Adoption – (10)

MD

2008 NEC – 32 States

M I

Note: Some local adoption states have earlier than 2005 adoptions in some jurisdictions

Basically 2002 NEC but some islands back

to 1993 NEC

CT

AK

Revised April 19, 2010

State Adopted Unincorporated

Areas

State Adopted

S. Carolina Code Council adopted

2009 IRC with 2008 NEC 3/22/10 with

implementation 1-1-11

Expected July 10’

Expected January 2011

Expected July 2010

Code RulingsCode Rulings

•Panel 20 Statement:Panel 20 Statement:““The overriding theme of Articles 585 (renumbered to 708) is to keep the power on for vital loads. Selective The overriding theme of Articles 585 (renumbered to 708) is to keep the power on for vital loads. Selective coordination is obviously essential for the continuity of service required in critical operations power systems. coordination is obviously essential for the continuity of service required in critical operations power systems. Selective coordination increases the reliability of the COPS system.” Selective coordination increases the reliability of the COPS system.”

In the 2008 Code Cycle there were challenges to the selective coordination requirement. Proposal 13-135 In the 2008 Code Cycle there were challenges to the selective coordination requirement. Proposal 13-135 proposed the elimination of the selective coordination requirement for 700.27.proposed the elimination of the selective coordination requirement for 700.27.

But Code Panel 13 rejected this proposal by a vote of 9-4. To follow is their statement:But Code Panel 13 rejected this proposal by a vote of 9-4. To follow is their statement:

•Panel 13 Statement:Panel 13 Statement:“This proposal removes the selective coordination requirement from the mandatory text and This proposal removes the selective coordination requirement from the mandatory text and places it in a non-mandatory FPN (fine print note). places it in a non-mandatory FPN (fine print note). The requirement for selective The requirement for selective coordination for emergency system over-current devices should remain in the mandatory text. coordination for emergency system over-current devices should remain in the mandatory text. Selective coordination increases the reliability of the emergency system. The current working Selective coordination increases the reliability of the emergency system. The current working of the NEC is adequate.of the NEC is adequate. The instantaneous portion of the time-current curve is no less The instantaneous portion of the time-current curve is no less important than the long time portion. Selective coordination is achievable with the equipment important than the long time portion. Selective coordination is achievable with the equipment available now”.available now”.

Code Panel 20, which was responsible for the new Article 708, summed up the need for selective coordination in their Code Panel 20, which was responsible for the new Article 708, summed up the need for selective coordination in their statement to Comment (20-13), which was another proposal for the deletion of the selective coordination requirement. statement to Comment (20-13), which was another proposal for the deletion of the selective coordination requirement.

This comment was rejected 16-0. The actual panel statement to Comment 20-13:This comment was rejected 16-0. The actual panel statement to Comment 20-13:

Exceptions to Code RulingsExceptions to Code RulingsRefer to IEEE handout “Selective Coordination versus Arc Flash…” page 12Refer to IEEE handout “Selective Coordination versus Arc Flash…” page 12

There are numerous proposals being adopted by States and/or City or local governmental bodies which There are numerous proposals being adopted by States and/or City or local governmental bodies which modify the selective coordination requirements. modify the selective coordination requirements.

The most commonly heard proposals fall into two categories:The most commonly heard proposals fall into two categories:

1. Allow the degree of selective coordination needed to be the responsibility of the qualified person 1. Allow the degree of selective coordination needed to be the responsibility of the qualified person responsible for the project. responsible for the project.

Exception No. 2: Where the system design is under the control of a licensed professional engineer engaged in the Exception No. 2: Where the system design is under the control of a licensed professional engineer engaged in the design or maintenance of electrical installations, the selection of overcurrent protective devices shall be permitted to design or maintenance of electrical installations, the selection of overcurrent protective devices shall be permitted to coordinate to the extent practicable. The design shall be documented, stamped by the professional engineer, and coordinate to the extent practicable. The design shall be documented, stamped by the professional engineer, and made available for review by the authority having jurisdiction.made available for review by the authority having jurisdiction.

(The Commonwealth of Massachusetts was the first State to adopt such a proposal as an exception to (The Commonwealth of Massachusetts was the first State to adopt such a proposal as an exception to the Articles in 700.27, 701.18 and 708.54, which require selective coordination as follows:the Articles in 700.27, 701.18 and 708.54, which require selective coordination as follows:

Arc Flash ConsiderationsArc Flash ConsiderationsRefer to IEEE handout “Selective Coordination versus Arc Flash…” page 10Refer to IEEE handout “Selective Coordination versus Arc Flash…” page 10

This is the other side of the argument regarding the subject of Selective Coordination VS Arc Flash This is the other side of the argument regarding the subject of Selective Coordination VS Arc Flash Considerations.Considerations.

The presenter will not delve into this side of the argument, as he is in the business of providing emergency powerThe presenter will not delve into this side of the argument, as he is in the business of providing emergency powerto critical facilities and therefore is in the camp of having a non-sensitive, robust type system, selectively coordinated, to critical facilities and therefore is in the camp of having a non-sensitive, robust type system, selectively coordinated, that facility managers want to perform well when called upon. In cases of catastrophic outages, Arc flashthat facility managers want to perform well when called upon. In cases of catastrophic outages, Arc flashconsiderations might take a back seat to keeping as much of the facility up and running as possible and only considerations might take a back seat to keeping as much of the facility up and running as possible and only Tripping CB’s closest to the fault.Tripping CB’s closest to the fault.

For more details on the ARC Flash concerns, and that whole side of the argument, please refer to your handout.For more details on the ARC Flash concerns, and that whole side of the argument, please refer to your handout.

UL 1008 Withstand TestUL 1008 Withstand Test

34.1 When tested under the conditions described in 34.2 – 34.15, 34.1 When tested under the conditions described in 34.2 – 34.15, a transfer switch shall a transfer switch shall withstand the designated levels of current until the over-current protective devices withstand the designated levels of current until the over-current protective devices open or for a timeopen or for a time as designated in 34.3. At the conclusion of the test: as designated in 34.3. At the conclusion of the test:a)a) The switch shall be capable of being operated by its intended means;The switch shall be capable of being operated by its intended means;b)b) The fuseThe fuse mentioned in 34.14 mentioned in 34.14 shall not openshall not open,,c)c) There shall be no breakage of the switch base to the extent that the integrity of the mounting There shall be no breakage of the switch base to the extent that the integrity of the mounting

of live parts is impairedof live parts is impaired,,d)d) The door shall be prevented by its latch, without bolt or lock installed therein, from being The door shall be prevented by its latch, without bolt or lock installed therein, from being

blown open, and deformation of the door alone is not determined to be unacceptable;blown open, and deformation of the door alone is not determined to be unacceptable;e)e) No conductor shall have pulled out of a terminalNo conductor shall have pulled out of a terminal connector and there is connector and there is no damage to the no damage to the

conductor insulation or the conductorconductor insulation or the conductor (see 41.56); and (see 41.56); andf)f) For a plug in or draw out unit, For a plug in or draw out unit, the point of contact is to be the same both mechanically and the point of contact is to be the same both mechanically and

electrically as before the test.electrically as before the test.

UL 1008 Closing TestUL 1008 Closing Test

36.1 When tested in accordance with 36.2, a transfer switch shall comply with the 36.1 When tested in accordance with 36.2, a transfer switch shall comply with the requirements in 34.1(a) –(f).requirements in 34.1(a) –(f).

36.1 Revised September 18, 199636.1 Revised September 18, 1996

36.2 The sample for this test is to be that used for the withstand test. Test 36.2 The sample for this test is to be that used for the withstand test. Test procedures and conditions for the closing test are to be as described in 34.3 – procedures and conditions for the closing test are to be as described in 34.3 – 34.19. 34.19. The switch is to be closed on the circuit.The switch is to be closed on the circuit.

36.3. The 36.3. The test test (for close on)(for close on) current shall be the same as current shall be the same as that used in the that used in the withstand withstand test.test.

UL 1008 Short Circuit Test HistoryUL 1008 Short Circuit Test History

• Around 1989 UL introduced an optional 3 cycle test for any over- current protection device.

Prior to this, manufactures could test with any over-current device.

If a manufacturer didn’t test to 3 cycles, they would be required provide a label that lists all breakers that the switch was “coordinated with”.

This requirement did not take into consideration air power circuit breakers APCB’s. Some of these breakers were 4-5 cycle devices (GE AKR and Westinghouse DS)

• January 9th, 2002 UL introduced an optional short time current rating test.

A withstand and a close and withstand test is required to get a UL short time rating.

UL 1008 Temperature TestUL 1008 Temperature Test

29.1 Transfer switches when tested under the conditions described in 29.2 – 29.12 shall not attain a temperature at any point high enough to constitute a risk of fire or to damage any materials employed in the device, and shall not show temperature rises at specific points greater than those indicated in Table 29.1

29.2 For the temperature test the transfer switch is to be operated under intended use conditions and is to carry its test current continuously at the test potential specified in Table 24.1.

29.3 The test current shall be 100 percent of the rated current.

Overcurrent Protective DevicesOvercurrent Protective Devices

• Molded Case Circuit Breakers –MCCB (UL489)Molded Case Circuit Breakers –MCCB (UL489) May be Current Limiting to 200KAMay be Current Limiting to 200KA Long Time OvercurrentLong Time Overcurrent Instantaneous Interruption is less than 3 cyclesInstantaneous Interruption is less than 3 cycles

• Fuses and Fused DevicesFuses and Fused Devices Current LimitingCurrent Limiting Mostly used on 200KA circuitsMostly used on 200KA circuits

• Insulated Case Circuit Breakers -ICCB (UL489)Insulated Case Circuit Breakers -ICCB (UL489) May be Current Limiting to 200KAMay be Current Limiting to 200KA Instantaneous Interruption is typically less than 4 cycles Instantaneous Interruption is typically less than 4 cycles Short Time delay available (30 cycles) with Instantaneous over-rideShort Time delay available (30 cycles) with Instantaneous over-ride

• Low Voltage Air Power Circuit Breakers -APCB (UL1066)Low Voltage Air Power Circuit Breakers -APCB (UL1066) May be Current Limiting to 200KAMay be Current Limiting to 200KA Instantaneous Interruption is typically less than 4 cycles?Instantaneous Interruption is typically less than 4 cycles? Short Time delay available (30 cycles) without Instantaneous ?Short Time delay available (30 cycles) without Instantaneous ?

Selective Coordination - GoodSelective Coordination - Good

No overlapping fault current of individual devices.

This is coordinated properly.

In a perfect world this is great.

Selective Coordination - BADSelective Coordination - BAD

In this case, since it takes 8 cycles for the upstream breaker to clear the fault, a 3 cycle rated transfer switch is inadequate.

ATS Feeder Breaker

8 cycles to clear