Short Circuit (WIC) Testing and Parameters.

- for -

IEEE-IAS - by -

James S. Nasby

Columbia Engineering

C.E. IEEE-IAS 2

Topics to be Covered High Current Effects Medium Current Effects Breaking the Circuit (Clearing the Fault) Effects and Construction Components Design Parameters Testing Safety (Arc Flash & PPE Requirements)

C.E. IEEE-IAS 3

Definitions Ip = Peak Current Attained (Magnetic Effects) I2t = Total "Energy" (Thermal Effects) I2 x R = P (Power in watts) & P x t = E (Energy in watt-seconds or joules), but R is a constant so I2t ~ Energy

P.F. Power Factor Higher Current Circuits Tend to be More

Inductive (Higher X:R Ratios) Hence Lower Power Factor

C.E. IEEE-IAS 4

More Definitions Current Limiting = Fuses or Breakers (or Blow Apart Isolating Switches) which Completely Clear (Interrupt Current Flow) Prior to the First Half Line Cycle

Blow Apart Design = Current Flows in a "U" Shape Path ("Self Protecting") which Creates Opposing Magnetic Force at High Currents. When said Force Exceeds Spring Force, Contacts Begin to Separate. Breaker Trip Mechanism is also triggered to complete opening of the breaker.

C.E. IEEE-IAS 5

Yet More Definitions IEC Type 1 Protection = Basically the U.L. Criteria, Namely that Equipment:

Won't Start a Fire Won't Become a Shock Hazard Will Contain the Event (Parts Stay Inside) Equipment May (and usually is) Damaged Beyond Use

or Safe Operation

IEC Type 2 Protection = Basically the U.L. Criteria, Namely that Equipment:

Meets all of Type 1 Protection -and- Equipment is Largely Undamaged E.g.: Still Functional; although some repair may be

needed.

C.E. IEEE-IAS 6

Still More Definitions First Half Cycle Offset Occurs in Inductive A.C. Circuits Maximum when Circuit is Closed at a Voltage Zero

Crossing Minimized when Circuit is Closed at a Voltage Peak This is Because Inductive Component of Current

Lags the Voltage by 90 Degrees

This also affects Motor Starting Inrush Current Max Theoretical Peak Current = 17 x FLA Max "Practical" = Approx. 13 x FLA

C.E. IEEE-IAS 7

First Half Cycle Offset Waveforms

2.83 x LRA = 6 x 2.83 x FLA = 17.0 x FLA Maximum Theoretical.

13x is "Max. Practical".

Does the Controller withstand at least 13xFLA for all three poles of the I/S and the C/B?

This curve shows starting a motor which still has BACK EMF (voltage) present.

A-T-L Starting

C.E. IEEE-IAS 8

Type of Faults (Shorts)

Fault to Ground Line to Line (Phase to Phase) Bolted (Solidly) Fault Medium Current Faults (Impedance Faults) Arcing Fault Lower Level Faults

C.E. IEEE-IAS 9

Typical Fire Pump Controller Breaker Curve

EC Series - "F" Frame Breaker Trip Curve

0.001

0.01

0.1

1

10

100

1000

10000

1 10 100 1,000 10,000

Multiples of Range Setting

Tri

p T

ime

(Sec

onds

)

Notes:

1) “F” Frame = 250 Amp Frame Rating.

(260 x 250A = ~ 65 Kamp)

2) Typically two devices are used in series (I/S + C/B) to achieve ratings up to 100 Kamp.

3) Ratings to 200 Kamp are available

4) Curve shown is different for Current Limiting Breakers

C.E. IEEE-IAS 10

Typical EFPC Ratings Nameplates

Note

C.E. IEEE-IAS 11

What’s wrong with this picture?

Note: Most Fire Pump Controllers are U.L. Listed as Suitable as Service Entrance Equipment.

Many are so Used.

Note soot on back wall & Burned Incoming Conduit

C.E. IEEE-IAS 12

Major Reason for Bolted Fault Short Circuits…

…and for Motor Junction Box Explosion.

Note that Workmanship is Vital.

C.E. IEEE-IAS 13

Cause for Overpressure

C.E. IEEE-IAS 14

Clearing the Fault(Safely Breaking the Circuit)

Single Phase Arcs are interrupted 120 times per second, although inductive loads obviate this to at least some degree. Three Phase Arcs are Continuous (No Zero Crossing). They Rotate Around the Three Poles of Whatever is Arcing.

C.E. IEEE-IAS 15

Testing UL-218 & FM-1321/23

Short Circuit Test: Parameters Criteria Dielectric Voltage - Withstand

Test Shock Hazard

C.E. IEEE-IAS 16

Testing UL-218 & FM-1321/23

Short Circuit Test - Fault Currents From 10,000* Amperes test current to

a maximum of 200,000 Amperes. Tested at 100 - 105% of rated voltage. Power factor range from 0.80 through

0.20 depending on test current.

* = Minimum Allowed for 400 Hp

C.E. IEEE-IAS 17

Testing UL-218 & FM-1321/23

Short Circuit Test. No parts discharge from the enclosure. No damage to a conductor or terminal

connector. No breakage of insulating bases which

would compromise mounting integrity. Door must remain closed only by the

intended latch mechanism, no major deformation.

Circuit breaker must remain operable.

C.E. IEEE-IAS 18

Testing UL-218 & FM-1321/23

Short Circuit Test: Closing Test (UUT Closes on Fault) Withstand Test (Voltage Applied to UUT with

current path already closed)

Must Not Blow 30 Amp Ground Fuse (or wire link) After Testing: Dielectric Voltage - Withstand Test Door Wiring Flexing Test Circuit breaker must remain operable.

C.E. IEEE-IAS 19

Testing UL-218 & FM-1321/23

Allowed to Change Components Between Tests Never Needed for More Robust Designs Should Not be needed for IEC Type "2" Commonly Needed with Most Designs Some Controllers Endure Multiple Shots

with Same Components Installed. Even at 100 Ka and 200 Ka Testing

C.E. IEEE-IAS 20

Arc Flash and PPE Requirements

NFPA 70E (Workplace Safety) requires that Equipment be marked where installed. This requires a specific Short Circuit Available (Available Fault Current) study along with the environment (Indoors, Outdoors, Room Layout, No. of Doors, etc.) The Arc Energy is then calculated which then yields the PPE level of protective clothing required.

C.E. IEEE-IAS 21

Selective Coordination NFPA-70 (NEC®) §700.27 & 400.18 require Selective Coordination. It is Important to Note that the Fire Pump is usually the Largest Load on the Emergency System, and that it can (and sometimes does) create a Bolted Fault on the system. Selective Coordination prevents the Fire Pump from taking out Other (All Other) Emergency Loads, and vice versa.

Note that the latest Edition of NFPA-99 negates NEC Requirements in 700, 701, 708, 517 & 620.

C.E. IEEE-IAS 22

http://www.cooperbussmann.com/presentations/player.html

C.E. IEEE-IAS 23

Questions ?