Selectivity and Zone Selective Interlocking for Low ...

Selectivity and Zone Selective
Interlocking for Low Voltage Circuit
Breakers

LV voltage selectivity

No longer just a Time Current curve overlay… started changing in 2005 when
articles 700.27 (Coordination for Emergency Systems) and 701.18
(Coordination for Legally Mandated Standby Systems) changed…

Due to Arc Flash and Electrical Safety concerns, turning instantaneous off,
setting delays slow or pickups insensitive… no longer good enough…

Industry has responded by;

• Selectivity tables where added as a selectivity tool in addition to traditional
curve overlays.

• Tables assume “upstream” CB’s instantaneous set to maximum or off…

• Analytical methods  peak let-through analysis, often used to generate
tables

• GE now has multiple methods to achieve selectivity, while still using
instantaneous protection set at low sensitive pickups… all the way to the first
MV devices.

- Energy nesting Methods are
- WFR (Waveform Recognition) GE’s selectivity
- I-ZSI (Instantaneous Zone Selective Interlocking)
system

11/4/2013
Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

1/
GE /

Instantaneous Selectivity at every level

Transformer primary Setting table or MCC Branch
curve inspection Spectra F
I-ZSI (MV)
Multilin F35 UR (I-ZSI) Spectra E M

Others (ZSI) TECL

I-ZSI CL fuses

I-ZSI (main & feeder) Logic MCC
EntelliGuard G WFR
WavePro
AKR Energy LP branches
branch & feeders
Switchgear/swbds Energy TEYF
R+ G STEY
On typical industrial I-ZSI R+ E
projects. WFR provided WFR THQL
good AF solutions up to Swbds/PP
250A MCCB or 400A fuse FB
branches. 400A-1200A
MCCB require I-ZSI. R+ G I-ZSI (feeder only) LP
frame marginal for PB2
commercial projects
Spectra K MET

Spectra G MET* Selectivity tables

Swbds/PP/MCC

* G does not take advantage of

WFR at this time

Required WFR setting is the key, the

lower, the easier to get good AF solution

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

Optimum Protection & selectivity
simultaneously

13.8kV 52
(F35)

• Complex but flexible Medium  Large  480V I-ZI
Large MV I-ZI
• Arc flash protection & I-ZSI/ZSI 4000A
selectivity
Medium  Large 3200A
• Adjustability Electronic Proxy for Energy
(LT/ST/I/GF/ZSI/I-ZSI) I-ZI
WFR
+ 2000A WFR
Small  Medium MCCB I-ZI 600A
• Alternative (RELT)… Energy Based
but not preferred 1200A

WFR energy
600A 250A

energy
20A

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

2/
GE /

I-ZSI & WFR create a system wide solution!

I-ZSI and ST-ZSI up to GE Multilin
MV Relays = selectivity from

Higher V LVCB to MV substation feeder!

Lower V

I-ZSI allows selective
instantaneous pickups in large
mains and ties! (*1)
Same
as main

Solution for Instantaneous WFR allows
400-1200A selective instantaneous pickups
MCC CB above current limiting devices @

relatively “low” pickups!
These features are unique to GE!

(*1) I-ZSI In/Out available in all ANSI CB & EntelliGuard G ICCB. PB2 & MET Out only.

Future improvements planned Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

Three types of selectivity

Mechanical - Mechanical  Electronic - Electronic
“2” layers “1” layer “n” layers

Molded Case CBs – Molded Case CB Molded Case CB – Trip Unit Trip Unit – Trip Unit

Between the 3 selectivity technology solutions a package can
be assembled for commercial, or industrial, switchboard, MCCs,
panels or switchgear.
+ WFR works with downstream fuses (current limiting)
+ WFR & I-ZSI work separate from mechanical device… works

on WavePro or Westinghouse DS!
+ More adjustable curves (3 ST slopes) CB and fuse LT, faster ST,

more adjustability, More ZSI options

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

3/
GE /

Energy Nesting

The mechanical equivalent of how fuses are selective
• Fuses – Thermal Energy nesting
• Circuit breakers – Mechanical Energy nesting

—Energy allowed by downstream, device is less than what
upstream device needs to trip)

—Assumes upstream CB setting are, maximum for
instantaneous, per curve for everything else

Probability Let- Commit
through Energy
energy

Energy 11/4/2013
Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

Energy Nesting

•Applies to specific GE molded case Circuit Breakers.
Particularly used in commercial applications

•Record Plus G & E frame CBs were designed to be part of a
selective CB system. They have nested current limiting
characteristics and an electronic instantaneous algorithm that
“works” with the current limitation to help selectivity.

Simplified table, for complete table see GE DET-760B • Main MUST be
R+E set to maximum
• See page 9 in DET 760B Mains
Branches R+ G 250 instantaneous
• # poles makes a
250 400 600 difference

R+ E 480/277 15-250A 100kA up to 14kA • Branch size, main
up to 14kA size makes a
R+ FB 480/277 15-100A 65kA 65kA 65kA up to 14kA difference

TEYL 480/277 15-125 65kA 65kA 65kA up to 10kA

TEYH 480/277 15-125 35kA 35kA 35kA up to 10kA

TEYF 480/277 15-125 14kA 14kA 14kA up to 40kA

TEY 480/277 15-125 2.5 - 14kA

THQL 240V 15-125A 2.5 - 10kA

THHQL 240V 15-125A 2.5 - 22kA

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

4/
GE /

WFR - interpreting current limiting

And Arc Flash protection! Small current limiting devices as branch circuit
protectors enhance arc flash protection… They also enhance selectivity if
the line side trips are designed to take advantage of it.

100,000 Required upstream threshold Prospective
80,000 Let-through
60,000
Prospective fault
current (Ibf)

40,000 Required upstream threshold Let-through I peak
20,000 Possible upstream threshold Let-through I2t

-

- 0.005 0.010 0.015 0.020
(20,000)

(40,000) Amperes

(60,000)

(80,000) Seconds

We are used to do all analysis based on RMS or offset peak… but its
always been peak for CL MCCB instantaneous, & now its ~ “energy”

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

Implementing Solution requires
understanding downstream branch device

SWGR-1 • GE has tested and documents settings for
GE Spectra & Record Plus MCCB/MCPs & a
Entelliguard method (in collaboration with Ferraz) to
TU determine the required setting above
Various Ferraz CL Fuses
MCC-1
• Above other devices it can be estimated but
there is no testing data to verify it

• Published data is a very simple table

Spectra Current Limiting CB (<=250A) or MCP, Ferraz fuse (<=400A), or
fuse protected CB (TECL), or Record Plus (<=600A)

Spectra G frame has capability but requires too high a threshold to
be valuable… but with MET trip it can use I-ZSI to force selectivity

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

5/
GE /

One value per branch to know

• Setting not Upstream CB dependent only downstream
device dependent

• Any CB with an Entelliguard TU trip unit above a Spectra E
or Record Plus E frame, set larger than 9,600A is selective
up to some value determined by the CB, regardless of fault
current available. @ <= 480V.

• Maximum selectivity is upstream device dependent

- Limited by Override or by frame short circuit rating
• Older ANSI CB  no override  fully selective
• PowerBreak II  peak sensing override in frame set
high  fully selective
• EntelliGuard G CB  di/dt sensing override… seems to
not have an effect but due to lack of testing we claim
selectivity ends at override

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

Documenting selectivity Line identifies threshold
for upstream setting
• Since the value is associated with 1000.00

the branch (downstream device) it

is that device that must document 100.00

required setting.

• Traditional Instantaneous clearing

times shown on TCC are very 10.00

conservative. Seconds

• This method of drawing curves 1.00
allows communication of required 0.10
setting & achieved selectivity.

• Voltage dependent… no data 0.01
available for 600V at this time 100.00

1,000.00 10,000.00 100,000.00

Amperes

Adjustable Electronic Mechanical current limiting
instantaneous tripping clearing the ETU can understand

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

6/
GE /

Add a CB with the ETU

1000.00 Seconds • Drawing the curves allows
100.00 you to set the CB exactly
10.00 where it needs to be… just
1.00 like the old fashioned way
0.10
0.01 • Overlap with sloped portion
100 of the curve does not
matter because the algorithm
filters out Current Limiting
behavior

Only system in the industry that
allows user to “see” instantaneous
selectivity on the TCC & allows
“optimized” instantaneous setting
of the upstream CB

1,000 10,000 100,000

Amperes

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

1000.00 Selectivity you can see

100.00 Current limiting portion of MCCB curve as
recognized by the trip unit
10.00
• For a fault at (A), the lower pickup
setting in the instantaneous time
range at CB1 allows for faster
clearing

1.00 • For a fault at (B), there is full
selectivity in the instantaneous time
CB1 EG TU range & the downstream MCCB
(CB2) trips

X (A) • Overlap does not indicate lack of
selectivity – selective CB pair tables
0.10 are published by GE

Seconds CB2 • Note 12ms commit time & 50ms (3

x (B) cycle) clearing. Selectivity seen on

0.01 TCC – used to identify selective

100Ampe re s 1,000 10,000 100,000 portion of algorithm

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

7/
GE /

List of CB’s Selectivity & AF Features/tool kit

GE Product RELT 15X >15X WFR Selective Multiple LT Mutliple ST M ultiple I-ZSI ST / GF / 25mS
IPU IPU with MCCB curve slopes GF shapes Slope ZSI M inimum
shapes TD Band
below

EntelliGuard G STD, ANSI YES YES NO YES YES YES YES YES  YES YES

EntelliGuard G Ext, ANSI YES YES YES YES YES YES YES YES  YES YES

EntelliGuar G UL 489 YES YES NO YES YES YES YES YES  YES YES

EntelliGuard TU in other ANSI CB YES NO NO YES YES YES YES YES  YES YES

PowerBreak II with EntelliGuard TU YES NO NO YES YES YES YES YES  YES YES

Spectra K with regular MET YES NO NO NO Limited YES YES YES  YES YES

Spectra K with Selective MET YES YES YES YES YES YES YES YES  YES YES

Spectra G with MET YES NO NO NO Limited YES YES YES  YES YES

R+ G NO NO NO NO YES NO NO NO NO No slope 40ms

R+ E NO NO NO NO YES NO NO NO NO NO No

Entellisys YES NO NO YES YES NO NO NO NO No slope YES

• Not everything is available everywhere.

• I-ZSI is only provided as an “output” function in some CB, both input & output other CBs.

• Entellisys has a host of other additional capabilities.

• 3rd party software has not caught up with GE capabilities.

• Retrofit kits, WavePro, AKR about the same as the EntelliGuard G ANSI except the
instantaneous range is lower and extended range is not available.

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

EntelliGuard G UL 489 CB

1000.00 Notice that if the upstream IPU is set at With some GE CBs ZSI improves
100.00 maximum it can only provide ~ 55kA protection & selectivity
10.00 maximum selectivity. But override i1s00a0t.00
85kA!

Downstream CB is a Selective Spectra
K with IPU at maximum

100.00

But if ZSI/I-ZSI is implemented then
the un-adjustable instantaneous
between 55 7 85kA will shift! So with I-
ZS1I0y.0o0 u get selectivity up to 85kA.

A rare instance of where ZSI helps
protection & selectivity.

1.00 1.00

Seconds Restrained position
Seconds due to blocking signal
Permanent TCC
adjustment due to
lack of ZSI

0.10 0.10

0.01 10,000 100,000 0.01 10,000 100,000
1,000 Am peres 1,000 Am pSeelercetivsity and Zone Selective Interlocking for Low Voltage Circuit Breakers

8/
GE /

ZONE SELECTIVE INTERLOCKING

M. VALDES

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

Zone Selective Interlocking

• A way to identify fault location and improve protection.
• Usually not considered a way to improve selectivity… But how GE performs

Instantaneous ZSI with UL 489 Entelliguard G CB improves both protection
and selectivity.
• Requires simple wiring between tiers of devices.
— How it is wired affects how ZSI works! Will the tie be selective or handled

like a third main depends on “wiring”! Not easy to change in the field as
it may require different number of TMI modules.
• Usually implemented within “a” piece of equipment, but can be wired longer
distances from equipment to equipment.
• In LV usually implemented using hardwired analog circuits. 0-~24V signal.
But in MV it can be implemented via IEC 61850.
— Entellisys can provide a discrete signal or via IEC 61850 GOOSE message.
• ST & GF ZSI is common in the industry… GE has unique separate
Instantaneous ZSI capability… fastest known in the industry.
• GE can also ZSI ST and GF slopes, and can allow a upper tier to be set faster
than the lower tier if required. Also may be unique in industry.

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

9/
GE /

GE Zone Selective Interlocking Language

• Blocking signal: A trip unit with 24V at ZSI input terminals is “blocked”, aka
“restrained”, aka operating at “selective” time delays…
— If the wires are cut the trip reverts to the “protective”, aka
“unrestrained”, aka “un-blocked” time delays.

• Restrained: Operating parameters associated with blocked or selective
performance.

• Unrestrained: Operating parameters associated with unblocked or
protective performance.

• Instantaneous ZSI: Ability to send very fast blocking signal due to current
in sending CB exceeding the instantaneous threshold & ability in receiving
CB to shift the timing associated with its instantaneous protection
separately from ST signal or shifting. Some CB can “only” send a I-ZSI
signal, some can send and shift.

Currently Zone Selective Interlocking technology only addresses time delays
or response time in LV CBs. It does not affect pickup thresholds in amperes.
GE has filed patent on a way to change thresholds and is implementing in
EntelliGuard TU trip unit.

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

ZSI basics GTU Curve, Legacy CBs, CB1 & CB21000.00 GTU Curve, Legacy CBs, CB1 & CB2
Receives signal & incorporate into
trip logic before committing to trip 1000.00

 alters protection timing

100.00 100.00

Trip

10.00 10.00

ZSI blocking signal. 1 Seconds ST ZSI
Seconds I ZSI
X signal used for all ZSI

(ST, GF & Inst) 1.00 1.00

Trip

0.10 0.10

X Signal sent when
threshold 1st exceeded
0.01 0.01

(ST/GF/Inst) 1,000 10,000 100,000 1,000 10,000 100,000

0.00 0.00
Amperes Amperes

Fault in feeder’s zone of
protection.

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

10 /
GE /

Instantaneous ZSI = complete selectivity

1000.00 Main Fault 1000.00 Feeder Fault 1000.00 Tie Fault

This is AF protection

100.00 100.00 M 100.00 M

M

X
10.00 10.00 T 10.00 T

TX
FF

FX
Seconds
Seconds
Seconds

1.00 1.00 1.00

Ability of lower

CB to issue a

suitable blocking

signal has not 0.10
0.10 relat0io.10nship to

lower curves

shape. Only to its

pick up threshold

0.01 100,000 0.01 100,000 0.01 100,000
1,000 Amperes 10,000 1,000 Amperes 10,000 1,000 Amperes 10,000

User does not adjust Instantaneous ZSI restrained timing
factory set at 58 or 67ms depending on CB type

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

I-ZSI + ST Slope ZSI, selectivity & flexibility

This is AF protection Feeder Fault Tie fault

1000.00 1000.00 1000.00 ZSI can change

slopes, allow feeder to
M M M be set slower than

100.00 X 100.00 100.00 upper tier trips,

combination of both +
T T T Instantaneous

10.00 10.00 10.00 X
F
F F
X

1.00
Seconds
Seconds
Seconds
&
Main1.00 1.00

Fault

0.10 0.10 0.10

0.01 100,000 0.01 100,000 0.01 100,000
1,000 Amperes 10,000 1,000 Amperes 10,000 1,000 Amperes 10,000

Ability of lower CB to issue a suitable blocking signal has no

relationship to lower curves shape. Only to its pickup threshold. So

lower curve can be slower or have completely different shape. Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

11 /
GE /

ZSI in Entellisys

•Zone selective interlocking in Entellisys is done differently
•CBs in an Entellisys system are assigned tiers (aka levels).
•Then each tier is assigned a ZSI delay, usually 100ms but could

be 200 or 300ms as well.
•When system identifies a fault in a tier, the tier above is

incremented by the assigned delay, the tier above is
incremented by an additional delay if so programed, etc.
•No CB is delayed beyond 500ms clearing
•Timing bands after ZSI delayed are normal bands plus 100 or
200ms. EZP does not currently model these delays, but could if
desired.
•In an Entellisys system different system topology
configurations can be assigned different ZSI tiers and delays,
as well as different setting combinations

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

EZP EXAMPLE & LVMV INTERLOCKING

BY JOHN MCQUILKIN AND M. VALDES

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

12 /
GE /

250A Spectra load .5 .6 .8 1 CURRENT IN AMPERES X 100 AT 480 VOLTS
1000
900 2 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 100 2 3 4 5 6 7 8 9 1000 2 3 4 5 6 7 8 9 10000
1000
F-US2 900
800 T-US2 EAST-#4-US2 [6A] - 50/51 ZSI S&C 800
FLA 700
700

600 EAST-#4-US2 [6A] - 50/51 SM 600
SM-20 500
50/51 500
400 175E 400

300 300

3800A LV main  200 EAST-#4-US2 [6A] - 50/51 200
3800A LV tie  GE F35
1200A LV feeder  100 SUB 2 MAIN [5B] 51/50 IEEE 100
250A spectra F CB in MCC Extremely Inverse 90
90 GE Entelliguard TU CT Ratio = 600/5 80
All selective! 80 Tap = 0.5 (300A) 70
70 Sensor = 4000 Time Multiplier = 0.68 60
60 Instantaneous Pickup = 4.2 (2520A) 50
50 Plug = 4000 40
T-US2 30
40 Cur Set = 0.95 (3800A) 2500 / 3220 kVA
LT Curve = Thermal (I^2T) 5.65% 20
30 LT Band = C-7

20 STPU = 2 (7600A)
ST Delay = 1

ST Delay I²t = Out EAST-#4-US2 [6A] - 50/51 ZSI

10 Inst = 5 (20000A) GE F35 10
9 51/50 IEEE 9
8 Extremely Inverse 8
7 7

6 6
TIME IN SECONDS
TIME IN SECONDS
5 SUB 2-1 TIE [3D] CT Ratio = 4000/5 5
4 GE Entelliguard TU
Tap = 2.2 (8800A) 4

3 Sensor = 4000 Time Multiplier = 0.7 3

Plug = 4000 Instantaneous Pickup = 2.7
2 Cur Set = 0.95 (3800A)
(10800A) 2

LT Curve = Thermal (I^2T) Instantaneous Delay = 0.02 sec

1 LT Band = C-3 1
.9 .9
.8 STPU = 1.5 (5700A) MCC-G-LRGST BKR .8
.7 GE Spectra RMS .7
ST Delay = 1 Frame = 250 .6
Plug = 250 .5
.6 ST Delay I²t = Out Cur Set = 1 (250A) .4
.5 LT Band = Fixed
.4 Inst = 4 (16000A) STPU = Max (1250A) .3
ST Delay = Fixed
.3 ST Delay I²t = In .2
Inst = Max (2500A)
.2 FDR 3-MCC-G [4A] .1
.09
GE Entelliguard TU T-US2 .08
2500 / 3220 kVA .07
Sensor = 1200 INRUSH .06
.05
.1 Plug = 1200 .04
.09
.08 Cur Set = 0.95 (1140A) .03

.07 LT Curve = Thermal (I^2T)
.06

.05 LT Band = C-4

.04 STPU = 3.5 (3990A)

.03 ST Delay = 1

ST Delay I²t = Out

.02 Inst = 9.5 (11400A) .02
EAST-#4-US2 [6A]
Override = 69550A 9288A

.01 2 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 100 2 3 4 5 6 7 8 9 1000 .01
.5 .6 .8 1 2 3 4 5 6 7 8 9 10000

CURRENTSeINlecAtMivPityEaRnEdSZXon1e00SeAleTc4ti8v0e VInOteLrTloScking for Low Voltage Circuit Breakers

Selective MV CB  MCCB at MCC, + low Ei

119.7" AFB - #1 122.9" AFB - #1 Incident Energy exposure for previous
3.9 cal / cm² @ 36" 4.0 cal / cm² @ 36" system a maximum of 5.6 calories at
210-US2 PRI 200-MAINBUS-EAST switchgear, 3 calories at MCC

9.4" AFB - #0 GE VB-13.8-750 1) WFR
0.3 cal / cm² @ 36" 1200A 2) I-ZSI
3) I-ZSI – 50 element in relay
T-US2

2500 / 3220 kVA 600/5 50
51
13.8 - 0.48 kV

4000/5 5.65%
51.5" AFB - #2*

5.6 cal / cm² @ 18"

215-US2 SEC

225-SUB 2 51" AFB - #2*
5.6 cal / cm² @ 18"

GE GA40B 40.6" AFB - #1 All selective !
4000/3800 4.0 cal / cm² @ 18" Lets take it one step at a time

31.3" AFB - #1

3.0 cal / cm² @ 18"
230-MCC-G

18.5" AFB - #1
1.3 cal / cm² @ 18"

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

13 /
GE /

WFR

Spectra F250A frame CB in MCC
or panel
• Exact trip does not matter
EntelliGuard G, 1200A Sensor
feeding MCC
• WavePro, Westinghouse DS,

4000A PowerBreak2, or
Spectra K frame with MET
would be with the same
method.
Per the table in DET 760
EntelliGuard TU must be set
larger or equal 11,210A. Line in
TCC drawn at 10,182A.
• 11,200/1.1 = 10,191… a few
extra A added for margin.
• CB IPU set at 11400A
• 11400/1.1 = 10,364A left
tolerance  > 10,182A

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

Published TCC selectivity insert-Spectra F frame

All current production GE current limiting molded case circuit breakers have
an insert, or have the instantaneous foot drawn to show the 480V selectivity
line. Same information as is in the DET-760B selectivity publication.
EZP, ETAP, SKM should show these lines for Spectra E, F & G, as well as Record
Plus FB, FE and FG. If they do not, they are wrong. This is valid for 480V and
below @ 60Hz. NOT for 600V. At 600V, as off today the traditional flat curve
applies.

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

14 /
GE /

I-ZSI – Protective position

Protective position, unrestrained
position, fast position…
• Nest pickups as required
• Overlap TDs and Instantaneous
• Force selectivity with second

setting and ZSI/I-ZSI blocking
• Low feeder set up system for

success… lowest possible feeder
setting is KEY to low AF incident
energy

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

Restrained position 1.00

Only shows ST effect 0.10
• EZP has no way to show
Seconds
instantaneous in the restrained
position 0.01 100,000
• Tie and May be adjusted with the 1,000 Amperes 10,000
main slower than the tie, or not.
• The restrained position for the EZP does not model
instantaneous is NOT a user Instantaneous shift
adjusted delay.  all restrained
instantaneous move the same.
— To 0.058 Sec for EntelliGuard G

+ 55ms clear
— To 0.067 Sec for all other CB +

60ms clear
• Inset is Excel model showing

Instantaneous offset for legacy
CB

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

15 /
GE /

UR F35/F60/T60
for LV protection

Zone interlocked with LV main
Use Excel model to determine proper
setting for UR IOC (50).
Red line shows “approximate” relay
output time
Relay IOC shape is not definite time…
its inverse
• Relay has a defined inverse time to

process analog current data
• A small additional window to

receive blocking signal
• Additional time to issue output if

not blocked
• Plus CB clearing time

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

CB trip ZSI output 1.00
CB
Determining optimum relay settings
with Excel model 0.10
• Trip unit has an output signal with
Seconds ST ZSI timing
its own characteristic response 0.01
time to fault current based on the
ST and I thresholds set for the CB Inst. ZSI timing
• Red line represents ZSI output Position lines up with maximum LV trip
signal timing
Once the output signal timing is
known… simply a mater of lining up
the input signal requirements of the
receiving device

0.00 10,000 100,000
1,000 Am peres

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

16 /
GE /

UR IOC timing 1,000.00 Primary
requirements Output contact
Secondary
• Bottom line = IOC analog current data 100.00 Instantaneous only
requirement. IOC Clearing
I commit t
• 2nd line additional time window to receive Ia
digital input to process in internal logic. 10.00 Ibf
ZSI output line must be faster than this! Blocking Window
ZSI Input signals
Entellisys ZSI output signal

• 3rd line output signal from relay. This is 1.00
the one plotted by EZP. Aux relay timing
added in EZP model here.

• 4th line is the CB clearing time, line 3 plus 0.10
CB operation time and any aux relays
added to the circuit.

• But EZP cannot draw sloped (inverse time) 0.01
shape… can only draw a flat response.

• Overlap of the two curves allows optimal 0.00 10000 100000 1000000
adjustment 1000

• Multilin GET-8400B Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

Seconds1000.00 Determining optimum settings
100.00
10.00 EZP cannot model this… but settings can be
determined this way and then transferred to EZP
1.00 or other modeling software.
0.10
0.01 Need to define a “flat” line to approximate
0.00 this line… CB clearing minus CB operating
time plus any auxiliary relays that may be
1,000 Amperes @ LV 10,000 in trip circuit

As long as red line is below the 2nd blue line
the red signal can change the operating
logic of the relay fast enough to “alter” or
“block” the relay’s IOC from operating

100,000 Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

17 /
GE /

EZP modeling

Must approximate inverse CB clearing time
with definite time function
20ms, + 50ms for 3 cycle CB
= 70ms

1.00

Seconds 0.10 70ms 70ms ~> than
probable
clearing time for
arcing or bolted
fault

0.01

0.00 10,000 100,000
1,000 Am peres

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

UR IOC EZP model

• 50/51 ZSI element defined
• Connected to LV CT
• Instantaneous timing must

be defined to approximate
real CB clearing time
• Note UR IOC additional
delays may be added in
10ms increments if required

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

18 /
GE /

Entellisys version 1,000.00 Primary
Output contact
Just a little slower… but direct IEC 61850 Secondary
output is possible. Instantaneous only
IOC Clearing
• With everything else the same the relay’s 100.00 I commit t
IOC would need 20ms delay for a 90ms Ia
CB clearing time Ibf
Blocking Window
• But Relay IOC is set very low… one can ZSI Input signals
adjust pickup up & TD up… Entellisys ZSI output signal

10.00

• If PU can be adjusted to 16kA then only 1.00
10ms additional delay is needed…
selective ~ up to full Ibf

~ 90 ms clear

~ 80 ms clear

0.10
0.10

0.01 0.01 Entellisys output
timing

0.00 10000 100000 1000000 Trip unit output
1000 timing

0.00
1000 Selectivity and Z1o0n0e0S0elective Interlocki1ng00fo0r0L0ow Voltage Circu1it0B0r0e0a0ke0rs

Relay/CT connection

• Use one relay two sets of CTs

52 50/51 50/51 • Use two relays, two CTs, transfer trip… may add CB
(1) (2) clearing time as well

• Use one relay, 1 CT, alternate settings and add
timing logic to get around transformer inrush if

ZSI required. 2nd harmonic filtering?

signal

• LV 50/51 better set with two 50 delays and ZSI
signal used to toggle between the two

• ZSI signal could come for LV Main

• ZSI signal could come from LV Main and LV feeders,
or just the feeders (requires different wiring)
87T 50/51
52
(1) (2) • ZSI signal could come from feeders if there is no
main (retrofit of old subs without LV mains)

• 87T can be included for transformer protection, CTs
ZSI at transformer terminals, 50/51 protection below
signal CTs.

•…

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

19 /
GE /

Example with 400A Spectra G with I-ZSI

• LV Main set same as before
• Tie set same as before
• 400A Spectra branch set with

instantaneous at maximum, ST at 6X
• Notice lumped motor inrush on bus

with 400A MCCB bus feeder ST
must be set out of the way! Ex: A CB
in the middle of the ZSI scheme that
cannot ever use the lowest ST TD!
1) Fdr. ST out of the way of mtr.
inrush, but can be interlocked with
ST and Inst. of 400A MCCB
2) Fdr’s ST & Inst. interlocked with
time & main above… they do not
need to change…
• Not sure if this can be done with
anybody else’s CB ZSI!

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

600A Record plus

• Common panelboard main,
or power panel feeder

• Instantaneous must be set at
maximum for “it” to be
selective

• It requires upstream trip to
be set >20kA

• Arc Flash protection from LV
Main and Tie worsens
because Instantaneous
thresholds and even short
time are too high….

New feature to be provided in
EntelliGuard TU trip units will
help with this!

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

20 /
GE /

And you need to Seconds 1.00
0.10
• MV relay and main ST 0.01
pickup too high! Too close
to arcing current

• Need to reduce all these
pickups for good AF
protection, large 600A
branch drives upstream
pickups too high

0.00 100,000
1,000 Amperes @ LV 10,000

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

NEW Threshold ZSI

Short time & Instantaneous
pickups can overlap
In this case
• Overlapped Tie & Main ST
• Feeder, Tie & Main

Instantaneous PU
• Allows F35 IOC to be moved

from 20kA to 16kA pickup
• Systems remains fully

selective

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

21 /
GE /

Protection improved with I-ZSI & Threshold ZSI
capability
Pickups below 85% Ia

Pickups too high to protect properly Better than 8 calorie protection

Sec
Sec

8 calorie line 0.10

0.10

85% & 100% Ia 0.01

0.01

Improved curve on right: LV Main ST
PU & MV relay PU < 85% Ia

0.00 100,000 0.00 100,000
1,000 Amperes @ LV 10,000 1,000 Amperes @ LV 10,000

If MV relay could implement Threshold ZSI protection would be more robust.
For main bus protection interlocking MV relay with LV main is optional

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

Selectivity and Zone Selective Interlocking for
Low Voltage Circuit Breakers

Thank you!
Any questions?

Selectivity and Zone Selective Interlocking for Low Voltage Circuit Breakers

22 /
GE /