Webinar_ProtectiveDevCoord1

7/27/2019 Webinar_ProtectiveDevCoord1

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Arc Flash with EasyPower


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Topics:

EasyPower, LLC

Molded-case Circuit Breaker vsLow Voltage Power Circuit

Breakers Coordination of MCCBs

Transformer Damage Curves

Transformer Protection TCC Clipping & Tick Marks

I2T Settings What and Why?

Questions2


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Molded Case Circuit Breakers vs LowVoltage Power Circuit Breakers

Designed, Built and Tested to MeetDifferent Standards:

MCCBs & ICCBs UL489

LVPCBs UL1066 (ANSI C37)

In general:

MCCBs Switchboards

LVPCBs Switchgear (Drawout)

EasyPower, LLC 3


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Comparison

Characteristic MCCB LVPCB

Maintenance No user-serviceableparts

Can be inspected andmaintained, including

contacts, arc-chutes,etc.

Short-Time Duty Cycle Not Required (But canbe tested)

Carry Fault Current fortwo 30-cycle periods

Short Circuit Testpower factor

15 to 20% (> 20kA) 15% max

Instantaneous Trip Required Not Required

Normal Use Switchboards (UL891) Switchgear (ANSIC37.20.1)

Cont Current Rating 80% (unless 100%

rated)

Always 100%

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Look at Short Circuit Example

EasyPower, LLC 5

3 PHASE Fault Total Fault Currents Equipment DutiesBus Name Bus kV Sym Amps X/R Ratio Mult Factor Asym Amps Equip Type Duty Amps

SUB 8A 0.480 39609.5 6.89 1.35 53629.1 LVPCBMCCB 10-20 kAMCCB > 20 kA

39890.246332.142129.4

Calculated SC

Current= pf of 14.4%

Adjusted Duty de-rated

So, 42 kA LVPCB OK, 42 kA MCCB NOT OK


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Impact on Coordination: Short-time withstand rating allows

LVPCB to stay closed, allowing

downstream equipment to clear fault.

Lack of short-time rating means thatMCCB must have instantaneous trip to

trip breaker at the short circuitwithstand rating

Newer MCCBs may be tested for short-

time withstand. EasyPower, LLC 6


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Coordinating MCCBs and LVPCBs

In general, MCCBs in series will often not coordinatewith each other due to instantaneous trip elements.

Coordination is much more reliable with LVPCBs IFthe proper trip units and settings are used.

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Short-time Withstand

Improves Coordination Specify LVPCBs with no instantaneous or switchable

Will coordinate with downstream MCCBs

Use Short-time delay to coordinate between mainand feeder breakers

Can also use Zone Selective Interlocking withLVPCBs.

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MCCBs in Series General case do not coordinate

May coordinate below certain levels offault current.

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Easypower, LLC 10

Typical MCCBCoordination

Overlapindicatescoordinationproblem


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Easypower, LLC 11

TypicalLVPCB

Coordination


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Selective Coordination of

MCCBs In 2005 NEC required selective

coordination of emergency power

systems This spurred MCCB manufacturers to

improve testing and documentation ofMCCB coordination

Fuses, if applied per manufacturersinstructions (2:1) have been shown tocoordinate by test

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Two techniques to coordinate

MCCBs Use upstream breaker with high short-

circuit withstand rating and set

instantaneous above actual maximumfault current available

Use MCCBs that are tested combination

and shown to coordinate up to certainfault current

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Series Coordination of MCCBsValid only by test

Test data shows MCCBs will coordinateeven though curves overlap on TCC

Limited to same manufacturer

Tracked in EasyPower Library Data

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Set Option in PDC Options

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EasyPower, LLC 17

SeriesCoordinationTest Data in

EasyPower


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Coordination Time Intervals

Low Voltage Breakers and Trip Units TCCs include all breaker operating time

and tolerances as long as they do nottouch, they should coordinate

Relay curves show only nominal relay

operate time need to allow additionaltime separation

Traditionally we have used 0.3 to 0.4

seconds EasyPower, LLC 18


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CTI Limits Number of Relays

in Series Since we must allow this CTI between

each pair of relays, clearing times get

very slow when we have more than twoor three relays in series.

Especially true in industrial applications

EasyPower, LLC


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Coordination Time Interval

(CTI) Accounts For: Breaker Operating Time (2 to 8 cycles)

Relay Overtravel (Electro-mechanical)

Relay Error

CT Error

Lockout Relay Operate Time

EasyPower, LLC


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What has changed? Newer Digital Relays have no overtravel

and are extremely accurate can we

reduce the CTI?Yes we can, but keep in mind:

Still have breaker operate time and CT

error CT Saturation must still be considered as

well

EasyPower, LLC


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EasyPower, LLC 22

UPSTREAM DEVICE DOWNSTREAM DEVICE(TIMEINSECONDS)

Electro-Mech. Relay Digital Relay Direct-Acting Trip Fuse

Electro-Mech.Relay 0.30 0.25 0.20 0.20

Digital Relay 0.25 0.20 0.15 0.20Direct-Acting Trip 0.20 .20 Separation Separation

Fuse 0.30 .25 0.10 0.10

TYPICAL COORDINATION TIMEINTERVALS


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Protecting Transformers Overloads

Internal Faults

Through Faults

Transformer Damage Curves only dealwith through faults not internal faults,not overloads

If you have an internal fault thetransformer is already damaged

EasyPower, LLC

f


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Transformer Protection ANSIDamage Curve Damage Curve for

Through-Faults

ANSI C57.109

Oil Frequent vs

Infrequent faults

Mechanical

Damage =Frequent Fault

Mechanical

Thermal


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ANSI C57.109Category Single-Phase

(kVA)Three-Phase

(kVA)Frequent

Fault

I 5 to 500 15 to 500 n/a

II 501 to 1667 501 to 5000 10

III 1668 to 10,000 5001 to 30,000 5

IV Above 10,000 Above 30,000 5

EasyPower, LLC

Damage Curve Shape Varies Based onCategory, Transformer Impedance


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EasyPower LLC 26

Protecting Delta-Wye

Transformers Per-Unit Current Seen by Primary

Protection Not the Same as Seen by

Secondary Winding. Winding Damage on Through-Faults a

function of current through any one

winding. We must adjust damage curve or

primary protection curve to compensate


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EasyPower LLC 27

Protecting Delta-Wye Xfmr

1 pu

1 pu

1 pu

1 pu

.58 pu

1 pu

1 pu

Currents at Full Load -Normal


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EasyPower LLC 28

Protecting Delta-Wye Xfmr Ignoring Load

Current, PrimaryRelay or Fuse willsee only 58% of

the per unit currentin the secondarywinding for groundfault on secondaryside.

1 pu

.58 pu

.58 pu

Currents For SLG Fault on Wye Side


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We Must Adjust Damage Curve

Adjusted ForGround FaultSeen FromPrimary

Applies Only for GroundFaults on Secondary onDelta-Wye Transformers

Applies Only forPrimary Protection


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EasyPower LLC 30

NEC Requirements for

Transformer ProtectionNEC Table 450-3(A)Primary > 600V

Primary Secondary

Over 600V Over 600V 6% 400% 300% 250% 225% 125%

Supervised Any 300% 250% N.R. N.R. N.R.

6% 600% 300% 300% 250% 250%

>6% 400% 300% 250% 225% 250%


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Transformer Inrush

Transformer PrimaryProtection Must Ride

through Inrush Inrush hard to

calculate, high inharmonics

Assume 8 to 10 x FLCfor 0.1 sec

Based on Self-CooledRating


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TCC Clipping and Tick Marks Intended to aid in understanding of

impact of short circuit current on

coordination Well look at why we want to use these

features and how they behave in

EasyPower

EasyPower, LLC


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TCC Clipping and Tick Marks Consider TCC using manufacturers TCC

and no tick marks

Curve may extend to maximum faultcurrent grid line on TCC

If we do not know what the maximum

fault current through each device is, itis difficult to determine selectivity

EasyPower, LLC


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TCC Tick Marks Tick Marks Can be Added to Indicate

Maximum Fault Current Possible For

Each Device Selected under Short Circuit tab for

each protective device

Can select cycle, 5 cycle, or 30 cycle

EasyPower, LLC


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TCC Curve Clipping In addition to Tick Marks, we can stop

(clip) TCC at the maximum fault

current it can see.Also selected under Short Circuit tab

for each protective device

Can select cycle, 5 cycle, or 30 cycle

EasyPower, LLC


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TCC Defaults EasyPower Defaults as delivered:

TCC curves clipped cycle

Tick Marks for each device cycle

When TCC is opened or created, EasyPower faults every busand uses maximum current through each device to determineclipping and tick marks.

But if a single bus is faulted tick marks and clipping canchange.

EasyPower, LLC


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Last and Least I2

t Function 480 V Trip Units Generally Have I2t

function on Short-time and (sometimes)

Ground FunctionCuts off the corner of Short-Time

curve

In = ON, Out = OFF Intent is to improve coordination with

downstream fuses

EasyPower, LLC


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Last and Least I2

t Function In many situations, use of I2t function

will increase arc-flash incident energy.

Generally not necessary for coordinationwith other trip units or MCCBs.

Not widely used.

EasyPower, LLC


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