By

Mat

t Hor

vath

, P.E

.

Nov

embe

r 6, 2

018

Intr

oduc

tion

to B

us P

rote

ctio

n

Pre

sent

atio

n O

utlin

e1.

Phy

sica

l Bus

Typ

es2.

Typi

cal B

us C

onfig

urat

ions

3.B

us P

rote

ctio

n M

etho

ds &

Sch

emes

4.H

igh

Z B

us D

iffer

entia

l Pro

tect

ion

Afte

r thi

s pr

esen

tatio

n yo

u w

ill b

e ab

le to

:•

Iden

tify

com

mon

bus

arr

ange

men

ts•

Iden

tify

and

unde

rsta

nd th

e op

erat

ion

of c

omm

on b

us

prot

ectio

n sc

hem

es•

Und

erst

and

high

impe

danc

e bu

s di

ffere

ntia

l ope

ratin

g pr

inci

ples

(SE

L-58

7Z)P

urpo

se &

Lea

rnin

g O

bjec

tives

Ele

ctric

al B

uses

PhysicalandElectricalJunctio

n

“Abu

sisa

criticalelemen

tofa

power

system

,asitisthe

pointo

fconvergenceof

manycircuits.”

From

IEEE

Std.C3

7.97

AGu

idefor

ProtectiveRelayAp

plica

tions

toPower

System

Buses

•M

ain

Com

pone

nts

–C

oppe

r or a

lum

inum

con

duct

or–

Sup

porti

ng s

truct

ures

–P

ost I

nsul

ator

s–

Sol

id a

nd/o

r fle

xibl

e co

nnec

tors

•A

dvan

tage

s–

Rel

ativ

ely

Eco

nom

ical

–S

impl

e–

Eas

y to

trou

ble

shoo

t–

Sho

rt re

pair

time

–Lo

nger

Fre

e S

pans

Ope

n A

ir R

igid

Bus

•D

isad

vant

ages

•E

xpos

ure

•La

rger

foot

prin

t req

uire

d

•M

ain

Com

pone

nts

–Fl

exib

le C

ondu

ctor

s–

Sup

porti

ng S

truct

ures

–S

train

insu

lato

rs

•A

dvan

tage

s–

Sm

all f

ootp

rint

–S

impl

icity

–Ve

ry E

cono

mic

al–

Sho

rt re

pair

time

Stra

in B

us

•D

isad

vant

ages

•Lo

wer

relia

bilit

y•

Exp

osur

e•

Con

duct

or s

paci

ng a

nd c

apac

ity

•M

ain

com

pone

nts:

–R

idge

d ce

nter

con

duct

or–

Sup

porti

ng in

sula

tors

–A

ir di

elec

tric

–B

ushi

ngs

at te

rmin

atio

n po

ints

–E

xter

nal s

uppo

rting

stru

ctur

es

•A

dvan

tage

s–

Hig

her r

elia

bilit

y–

Pro

tect

ed–

Sm

alle

r con

duct

or s

paci

ng–

Forc

ed a

ir co

olin

g po

ssib

le

Isol

ated

-Pha

se B

us

•D

isad

vant

ages

•H

igh

cost

•Lo

ngre

pair

time

•E

xpen

sive

•M

ain

com

pone

nts:

–R

idge

d ce

nter

con

duct

or–

Sup

porti

ng in

sula

tors

–In

sula

ting

gas

–B

ushi

ngs

at te

rmin

atio

n po

ints

–E

xter

nal s

uppo

rting

stru

ctur

es

•A

dvan

tage

s–

Hig

her r

elia

bilit

y–

Pro

tect

ed–

Very

sm

all c

orrid

or

Gas

Insu

late

d B

us

•D

isad

vant

ages

•H

igh

cost

•D

iffic

ult t

roub

lesh

ootin

g•

Long

repa

ir tim

e

•M

ain

Com

pone

nts

–A

lum

inum

or c

oppe

r con

duct

or–

Sol

id C

onne

ctor

s–

Sup

porti

ng In

sula

tors

•A

dvan

tage

s–

Vers

atile

–S

mal

l foo

tprin

t–

Pro

tect

ed•

Dis

adva

ntag

es–

Con

fined

spa

ce

Indo

or S

witc

hgea

r Bus

Bus

Fau

lt C

hara

cter

istic

s

•N

ot v

ery

com

mon

Whe

n th

ey d

o oc

cur:

•U

sual

ly b

olte

d fa

ults

•H

ighe

r fau

lt m

agni

tude

s

Bus

Fau

lt Im

pact

:•

All

bus

circ

uits

mus

t be

inte

rrup

ted

•C

an re

sult

in s

ever

e sy

stem

di

stur

banc

es

Impo

rtanc

e of

Bus

P

rote

ctio

n•

Ded

icat

ed p

rote

ctio

n•

Hig

h sp

eed

oper

atio

n fo

r in

tern

al fa

ults

•Tw

o-ou

t-of-t

wo

trip

crite

ria•

Opt

iona

l red

unda

nt p

rote

ctio

n sc

hem

e•

Rem

ote

back

up p

rote

ctio

n•

Tim

e ov

ercu

rrent

pro

tect

ion

•

Sec

urity

for o

ut-o

f-zon

e fa

ults

•S

ensi

tivity

for m

inim

um in

tern

al

faul

ts

Bus

Pro

tect

ion

Phi

loso

phy

Prin

cipl

e an

d O

pera

tion

•Tr

ips

and

lock

outs

the

bus

brea

kers

•M

any

outp

ut c

onta

cts

•O

pera

tion

isol

ates

its

trip

coil

•Ve

ry fa

st o

pera

tion

•H

ardw

ired

to b

reak

er tr

ip

circ

uits

•C

an b

e us

ed to

pro

tect

re

lay

cont

acts

Bus

Loc

kout

Rel

ays

•Im

prov

es s

yste

m re

liabi

lity

•M

inim

izes

Impa

ct o

f Out

ages

•U

tiliz

es V

ario

us A

rrang

emen

ts–

Com

bine

d A

rrang

emen

ts–

Ope

ratin

g Fl

exib

ility

–S

elec

tivity

–B

us p

rote

ctio

n m

ust a

dapt

Bus

Sec

tiona

lizin

g

Diagram

1

Diagram

2

One

of t

he m

ost b

asic

and

ec

onom

ical

des

igns

No

oper

atin

g fle

xibi

lity

No

sele

ctiv

ity

Zone

of P

rote

ctio

n•

Enc

ompa

sses

the

who

le b

us

Bus

faul

t will

inte

rrupt

all

asso

ciat

ed s

ervi

ces

Sin

gle

Bus

–S

ingl

e B

reak

er•

Zone

of P

rote

ctio

n:

–B

us a

nd T

rans

form

er p

rote

ctio

n is

co

mbi

ned

•U

sual

ly u

sed

in d

istri

butio

n su

bsta

tions

•N

o se

lect

ivity

•N

o fle

xibi

lity

•Fa

ult l

ocat

ion

diffi

culty

•Ve

ry e

cono

mic

al

Bus

& T

rans

form

er –

Sin

gle

Bre

aker

Dou

ble

Bus

w/B

us T

ie

–S

ingl

e B

reak

er

•Zo

ne o

f Pro

tect

ion:

•

Bus

A a

nd B

us B

ha

ve in

depe

nden

t an

d de

dica

ted

prot

ectio

n

•Li

ttle

Flex

ibili

ty

•S

ome

Sel

ectiv

ity

Mai

n &

Tra

nsfe

r Bus

–

Sin

gle

Bre

aker

Breakersub

stitu

tion

Zone

ofProtectio

nEncompasses

mainbu

son

ly

Transfer

busp

rotection

provided

bytransfer

breaker

Noselectivity

Flexibilityincreases

Ofte

nCo

mbine

d

Dou

ble

Bus

–S

ingl

e B

reak

er•

Zone

of P

rote

ctio

n:

•B

us 1

and

Bus

2 h

ave

inde

pend

ent

prot

ectio

n as

sign

ed b

ased

on

switc

hing

co

nditi

on

•Lo

ts o

f ope

ratin

g fle

xibi

lity

•S

ome

sele

ctiv

ity

•C

ompl

ex s

witc

hing

•C

T w

indi

ng a

ssig

nmen

ts c

hang

e

•N

ot c

omm

only

use

d in

the

U.S

.

Dou

ble

Bus

–D

oubl

e B

reak

er•

Zone

of P

rote

ctio

n:•

Bus

1 a

nd B

us 2

hav

e in

depe

nden

t pro

tect

ion

•Fu

ll op

erat

ing

flexi

bilit

y

•Im

prov

ed S

elec

tivity

•In

crea

sed

cost

•Ve

ry c

omm

on

Rin

g B

us

•N

o de

dica

ted

bus

prot

ectio

n

•Fu

ll op

erat

ing

flexi

bilit

y

•G

ood

sele

ctiv

ity

•S

hare

d br

eake

rs

•E

cono

mic

al

Bre

aker

-And

-A-H

alf

Bus

•Fu

llop

erat

ing

flexi

bilit

y

•E

xcel

lent

sel

ectiv

ity

•W

idel

y us

ed

•Zo

ne o

f Pro

tect

ion:

•

Bus

A a

nd B

us B

hav

e in

depe

nden

t an

d de

dica

ted

prot

ectio

n zo

nes.

•Li

ne p

ositi

on p

rote

ctio

n pr

ovid

ed b

y br

anch

circ

uits

•E

cono

mic

al

Diff

eren

tial O

verc

urre

nt

•C

T se

cond

ary

lead

s su

mm

ed o

ut s

ide

the

rela

y

•Id

entic

al T

ap ra

tios

•C

T m

atch

ing

•D

iffer

ence

Cur

rent

usi

ng

51/5

0 el

emen

ts

•Ti

me

dela

yed

•Av

oid

mis

oper

atio

ndu

e to

tra

nsie

nt s

atur

atio

n

Adv

anta

ges

•E

cono

mic

al

Dis

adva

ntag

es•

Sec

urity

•S

trong

sou

rces

•Ti

me-

dela

yed

clea

ring

•D

iffic

ult t

o se

t pro

perly

•N

ot s

uita

ble

in a

reas

of s

yste

m

with

hig

h X

/R ra

tio

Diff

eren

tial O

verc

urre

nt

(con

tinue

d)

Par

tial B

us D

iffer

entia

l

Ope

ratin

g P

rinci

ples

:

•S

ourc

e C

T le

ads

sum

med

ou

tsid

e re

lay

•Ti

e br

eake

r CTs

incl

uded

•O

verc

urre

nt e

lem

ent

•P

icku

p se

t abo

ve lo

ad

•S

elec

tivity

requ

ired

•O

ptio

nal:

Dis

tanc

e el

emen

ts

Par

tial B

us D

iffer

entia

l (C

ontin

ued)

Par

tial B

us D

iffer

entia

l (C

ontin

ued)

Adv

anta

ges:

•

Very

eco

nom

ical

Dis

adva

ntag

es:

•Fa

ult C

urre

nt/F

LA•

Req

uire

d se

lect

ivity

•R

educ

ed s

ensi

tivity

•U

sed

with

radi

al

circ

uits

Zone

Inte

rlock

Sch

eme

(Fas

t Bus

Trip

ping

)O

pera

ting

Prin

cipl

e: (A

nim

atio

n)•

Sou

rce

circ

uit(s

) •

Tim

e de

laye

d •

Rec

eive

s/S

ends

Blo

ck

Sig

nal

•D

irect

iona

lity

•R

adia

l circ

uit(s

)•

Inst

anta

neou

s el

emen

t se

nds

bloc

k si

gnal

•C

omm

unic

atio

n

Zone

Inte

rlock

Sch

eme

(Con

tinue

d)

Adv

anta

ges:

•Fa

st c

ompa

red

to in

vers

e-tim

e O

C e

lem

ents

•R

elat

ivel

y ec

onom

ical

Dis

adva

ntag

es:

•R

equi

res

Com

mun

icat

ion

Sch

eme

•S

ecur

ity a

gain

st C

T S

atur

atio

n•

Slo

wer

than

hig

h-Z

or p

erce

ntag

e-re

stra

int

sche

mes

Dire

ctio

nal C

ompa

rison

Ope

ratin

g P

rinci

ple:

•D

ista

nce

Ele

men

ts

Adv

anta

ges

•R

elat

ivel

y E

cono

mic

al•

Few

CT

cons

train

ts

Dis

adva

ntag

es•

Volta

ge R

efer

ence

•M

ultip

le F

ailu

re P

oint

s

Hig

h C

urre

nt

Inte

rrup

tion

& L

imiti

ngFu

ses

& S

hort

Circ

uit L

imite

rs•

Hig

h In

terr

upt r

atin

g•

IS li

mite

r ope

rate

s in

less

th

an 1

ms

Adv

anta

ges

•E

xtre

mel

y H

igh

Spe

ed

Dis

adva

ntag

es•

Rep

lace

men

ts n

eede

d w

ith fu

sibl

e in

terr

upte

rs

Arc

Fla

sh P

rote

ctio

n

Opt

ical

Sen

sors

•Fi

ber o

ptic

sen

sors

or l

oops

•In

door

Sw

itchg

ear

Adv

anta

ges

•R

elat

ivel

y E

cono

mic

al•

Ext

rem

ely

Hig

h S

peed

Dis

adva

ntag

es•

Sup

ervi

sion

with

opt

ical

Per

cent

age

Res

train

ed

Diff

eren

tial

Ope

ratin

g P

rinci

ple:

(Ani

mat

ion)

•R

elay

mea

sure

s di

ffere

nce

and

rest

rain

t qua

ntiti

es•

Trip

if d

iffer

ence

cur

rent

exc

eeds

a s

et p

erce

ntag

e of

the

rest

rain

ing

quan

tity

TieBK

RN.O.

I01C

FI02C

FI01

I02

BKR2

N.C.

BKR1

N.C.

Per

cent

age

Res

train

ed

Diff

eren

tial (

Con

tinue

d)

•O

pera

te v

s. R

estra

int R

elat

ions

hip

•S

lope

Set

ting

•C

ontro

lling

Fac

tors

•C

T P

erfo

rman

ce•

X/R

Rat

io•

Faul

t Mag

nitu

de

•D

uel S

lop

Cha

ract

eris

tic

Per

cent

age

Res

train

ed

Diff

eren

tial (

Con

tinue

d)

Per

cent

age

Res

train

ed

Diff

eren

tial (

Con

tinue

d)P

erce

ntag

e R

estra

ined

D

iffer

entia

l (C

ontin

ued)

CT4Cu

rren

ts:

Per

cent

age

Res

train

ed

Diff

eren

tial (

Con

tinue

d)

•Re

layconstantlymon

itors

changesinop

erateand

restraintcurrents

•Increase

inrestraint

with

outa

nincrease

inop

eratecurren

tind

icates

externalfault

•Re

layentershigh

securitymod

e

•Onlyrequ

iress

hortpe

riod

(~24m

s)of

unsaturated

operation

Per

cent

age

Res

train

ed

Diff

eren

tial (

Con

tinue

d)

Settings

Considerations

•Minim

umpickup

mustb

egreaterthanerrord

ifferen

cecurrent,

butlessthanminim

umavailablefaultcurrent

•Typically

setto1p

uof

busc

ontin

uous

ratin

gon

solid

grou

nded

system

s•

Lower

pickup

susedon

impe

dancegrou

nded

system

s

•Slop

esettings

•With

standmeasuremen

terrorsa

tlow

curren

ts•

With

standsaturatio

nindu

cederrorsat

high

curren

ts

•Mod

ernrelays

with

adaptivean

slope

characteristic

provide

enhanced

securityandsensitivity

Per

cent

age

Res

train

ed

Diff

eren

tial (

Con

tinue

d)

Adv

anta

ges:

•Fa

st O

pera

tion

•G

ood

secu

rity

Dis

adva

ntag

es:

•C

T cr

iteria

and

pe

rform

ance

crit

ical

•M

ay re

quire

man

y re

lay

curr

ent i

nput

s

•S

ensi

tivity

—H

igh

Z G

roun

ded

Sys

tem

s

IOP=|I1+I2|

IRST

=|I1|

+|I2|

Hig

h Im

peda

nce

Bus

(V

olta

ge) D

iffer

entia

l In

trodu

ctio

n an

d B

asic

Con

cept

(Ani

mat

ion)

•P

opul

ar B

us P

rote

ctio

n S

chem

e•

Arc

Fla

sh M

itiga

tion

Vsmall

Vbig

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

•CTsc

onne

cted

inparallelw

ithhigh

impe

dancerelayinpu

t

•Re

layop

erates

onvolta

geacross

high

impe

danceinpu

ts

•Ca

naccommod

atealarge

numbe

rofterminals

•Excellent

sensitivity

and

speed

•Simpleelem

enttoconfigure

Characteristicsa

ndTypicalA

pplicationLayout

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

ExternalFault(or

typicalloa

ding)C

ase:

•Cu

rren

tcirculates

betw

eenCTs

•Negligiblecurren

tflowthroughhigh

impe

dancerelayinpu

t(high

resistance/bu

rden

path)

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

Worst

Case

ExternalFault:

•CT

2completelysaturates(do

esno

tsup

plyanyrepresentativesecond

arycurren

twaveform)

•High

impe

danceinpu

tseesv

oltage

develope

dby

second

arycurren

tflowingthrough

CTwinding

resistanceandlead

resistance

•Elem

entp

ickupmustb

esetg

reater

than

thisvolta

ge(typicallyby

afactor

of1.5to

2)forsecurity

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

InternalFaultC

ase:

•Cu

rren

tflowsthrou

ghstabilizin

gresistora

ndprod

uces

high

second

aryvolta

ges

•Vo

ltage

magnitude

limite

dby

MOV

•LO

R‘a’con

tactsreq

uiredacrosshigh

impe

danceinpu

t

•CTsp

rodu

cecurren

tand

second

aryvolta

geun

tilthey

saturate

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

•S

tabi

lizin

g re

sist

or

•M

OV

pro

tect

s el

emen

t

•B

us L

OR

requ

ired

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

•S

EL

587Z

Rel

ay•

Use

s a

2000

resi

stor

•M

OV

siz

e op

tions

•S

EL

Rec

omm

ende

d S

ettin

gs (P

er A

N20

08-0

1)•

Vs

setti

ng o

f 200

V•

Opt

iona

l Tim

e D

elay

ed S

ettin

g

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

Man

ufac

ture

r Int

erna

l Fau

lt Te

stin

g•

Test

cur

rent

s of

20

kA, 4

0 kA

and

60

kA a

pplie

d.•

Hea

vy C

T sa

tura

tion

obse

rved

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

Wav

efor

ms

obta

ined

from

man

ufac

ture

r tes

ting

•D

iffer

entia

l cur

rent

and

vol

tage

wav

efor

ms

•N

ote

the

volta

ge is

lim

ited

to 1

500V

by

the

inte

rnal

MO

V•

C20

0 12

00:5

CTs

, 60

kA in

tern

al fa

ult

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

60 k

A In

tern

al F

ault

Test

1. C

T Vo

ltage

(Gre

en)

2. T

otal

Cur

rent

(Blu

e)3.

Exc

itatio

n C

urre

nt (R

ed)

•R

esis

tor v

s. M

agne

tizin

g C

urre

nt

•Th

e vo

lt-tim

e ar

ea

C40

0

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

C10

0

Volttim

earea

prop

ortio

naltoCratin

g

Dictated

bylowestratedCT

indiffe

rentialcircuit

SELrecommen

dsat

leasta

C200

CT

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

Vo

lttim

earea

issim

ilarfor

CTsw

itheq

uivalent

Cratin

g,even

ifratio

sare

diffe

rent

Maxim

umvolta

gelim

itedby

MOV

Man

ufac

ture

r Ext

erna

l Fau

lt Te

stin

g R

esul

ts

•Fa

ult c

urre

nts

of 2

0 kA

, 40

kA a

nd 6

0 kA

.

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

MO

V S

izin

g fo

r SE

L-58

7Z•

MO

V re

quire

men

ts b

ased

on

ene

rgy

diss

ipat

ion

limits

for

4-cy

cle

dura

tion

•Re

quire

s86“a”

contactswire

dacross

relayinpu

ts!

•E

nerg

y ra

ting

is a

func

tion

of k

nee-

poin

t vol

tage

and

m

axim

um s

econ

dary

cu

rren

t

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

H

igh

Impe

danc

e B

us

Diff

eren

tial (

Con

tinue

d)

Man

ufac

ture

r Tes

ting

Res

ults

for S

EL-

587Z

Rec

omm

ende

d H

igh-

Valu

e S

ettin

g:•

200V

with

no

time

dela

y•

Sen

sitiv

e an

d S

ecur

e

Opt

iona

l Rec

omm

enda

tions

For

Low

-Val

ue S

ettin

g:•

Onl

y ne

eded

in s

ome

appl

icat

ions

(e.g

. HR

G/L

RG

)•

Min

imum

sen

sitiv

ity c

alcu

latio

ns•

Impl

emen

t a ti

me

dela

y (m

in 1

cyc

le).

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

Sec

ure

Volta

ge S

ettin

g C

alcu

latio

n

•S

ensi

tivity

impa

cted

by

wiri

ng d

esig

n

•W

orst

-cas

e ou

t-of-z

one

faul

t con

ditio

n

•R

elay

pic

kup

set t

o a

mul

tiple

of V

r

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

ontin

ued)

Min

imum

Sen

sitiv

ity C

alcu

latio

n•

Verif

y fo

r Int

erna

l Fau

lt•

Igno

re M

OV

leak

age

curr

ent

•U

se C

T E

xcita

tion

Cha

ract

eris

tic•

Whe

n V

s <

knee

poi

nt v

olta

ge:

•W

hen

Vs

> kn

ee p

oint

vol

tage

:

Hig

h Im

peda

nce

Bus

D

iffer

entia

l (C

oncl

usio

n)

Advantages:

•Very

fastop

eration

•High

security

•Incorporates

largenu

mbe

rof

term

inals

Disadvantages:

•Sensitivity

decreasesa

snum

bero

fCTsa

nd/orleadlengthsincreases

•Mustu

seCTsw

ithC2

00ratin

gor

greater

•Co

mplexities

associated

with

mixed

ratio

CTs

•B

us p

rote

ctio

n is

crit

ical

•B

us S

ectio

naliz

ing

–O

pera

ting

flexi

bilit

y–

Sel

ectiv

ity

•B

us P

rote

ctio

n S

chem

es–

Wid

e va

riety

of s

chem

es

avai

labl

e ba

sed

on a

pplic

atio

n•

Crit

ical

ity•

Avai

labl

e fa

ult c

urre

nt &

X/R

ratio

•S

ensi

tivity

/Spe

ed R

equi

rem

ents

•C

T av

aila

bilit

y

Sum

mar

y

•IE

EE

Std

. C37

.97,

Gui

de fo

r Pro

tect

ive

Rel

ay A

pplic

atio

ns to

Pow

er B

uses

•B

lack

burn

, J. L

ewis

, Pro

tect

ive

Rel

ayin

g, P

rinci

ples

and

App

licat

ions

, Thi

rd

Edi

tion,

New

Yor

k: M

arce

l Dek

ker,

1998

•B

asle

r Ele

ctric

Com

pany

, Bus

Pro

tect

ive

Rel

ayin

g, M

etho

ds a

nd

App

licat

ion,

Rev

isio

n D

ate:

6-8

-200

5

•G

ener

al E

lect

ric C

ompa

ny, B

us D

iffer

entia

l Pro

tect

ion,

WP

RC

199

5, G

ER

-39

61

•Zo

chol

l, E

. Sta

nley

and

Cos

tello

, Dav

id, S

chw

eitz

er E

ngin

eerin

g La

bora

torie

s, In

c., A

pplic

atio

n G

uide

lines

for M

icro

proc

esso

r-Bas

ed, H

igh-

Impe

danc

e B

us D

iffer

entia

l Rel

ays

•C

oste

llo, D

avid

and

Moo

ney,

Joe

, App

lyin

g th

e S

EL-

587Z

in S

witc

hgea

r, S

EL

App

licat

ion

Not

e A

N20

08-0

1

Ref

eren

ces

Than

k yo

u fo

r you

r tim

e!Th

is c

oncl

udes

the

educ

atio

nal c

onte

nt o

f thi

s ac

tivity

.

Mat

t Hor

vath

, P.E

.

Elec

tric

al E

ngin

eer

(509

) 780

-004

2

mat

t.Hor

vath

@po

wer

ing.

com