ABB HU Manual

Instruction
Leaflet
41
-
347.1
S
A
mi
MINI
ABB
Power
T
&
D
Company
Inc
.
Relay
Division
Coral
Springs
,
FL
33065
Type
HU
,
HU
-
1
and
HU
-
4
Transformer
Differential
Relays
Effective
:
April
1991
Supersedes
41
-
347.1
R
,
Dated
April
1987
(
|
)
Denotes
Change
Since
Last
Issue
File
No
.
E
103204
the
restraint
transformers
of
the
HU
and
HU
-
1
relays
are
connected
in
parallel
,
and
the
I
IT
pickup
of
these
relays
is
ten
times
the
relay
tap
value
.
On
the
other
hand
,
the
rectified
outputs
of
the
restraint
transform
-
ers
of
the
HU
-
4
relay
are
connected
in
series
,
and
the
IIT
-
unit
for
this
relay
is
set
at
fifteen
times
the
tap
value
.
Otherwise
,
the
three
relays
are
identical
.
Three
-
winding
banks
normally
require
the
HU
-
1
re
-
lay
,
although
the
auto
transformer
application
uses
the
HU
if
the
tertiary
is
not
loaded
.
The
HU
-
4
is
par
-
ticularly
applicable
to
protect
a
transformer
and
bus
section
combination
.
It
also
may
be
applied
to
three
-
winding
transformers
with
one
side
connected
to
two
breakers
.
CAUTION
Before
putting
relays
into
service
,
remove
all
blocking
which
may
have
been
inserted
for
the
purpose
of
securing
the
parts
during
shipment
,
make
sure
that
all
moving
parts
operate
freely
,
inspect
the
contacts
to
see
that
they
are
clean
and
close
properly
,
and
operate
the
relay
to
check
the
settings
and
electrical
connections
.
These
instructions
apply
to
the
following
types
of
relays
:
•
HU
•
HU
-
1
The
HU
,
HU
-
1
and
HU
-
4
are
available
with
a
sensi
-
tivity
of
either
30
%
or
35
%
times
tap
.
The
30
%
sen
-
sitivity
relay
satisfactorily
handles
up
to
15
%
mis
-
match
(
e
.
g
.
,
±
10
%
transformer
tap
changing
plus
5
%
ct
mismatch
)
.
The
35
%
sensitivity
relay
handles
as
much
as
20
%
mismatch
.
See
Figures
13
and
14
for
a
comparison
of
the
characteristics
of
the
two
sensitivities
.
Any
of
the
relays
may
be
recalibrated
in
the
field
to
obtain
either
characteristic
.
•
HU
-
4
1
.
APPLICATION
The
types
HU
,
HU
-
1
,
and
HU
-
4
relays
are
high
speed
relays
used
in
the
differential
protection
of
transformers
.
These
relays
can
be
applied
where
the
magnetizing
inrush
current
to
the
transformer
is
severe
.
Current
transformer
ratio
error
should
not
exceed
10
%
with
maximum
symmetrical
external
fault
cur
-
rent
flowing
and
the
maximum
symmetrical
error
cur
-
rent
which
is
flowing
in
the
differential
circuit
on
ex
-
ternal
faults
should
not
exceed
10
times
relay
tap
setting
.
The
types
HU
,
HU
-
1
,
and
HU
-
4
relays
have
two
,
three
,
or
four
restraint
transformers
,
respectively
,
and
associated
rows
of
taps
.
The
rectified
outputs
of
Ordinarily
the
30
%
sensitivity
relay
will
suffice
;
how
-
ever
,
where
ct
mismatch
is
abnormally
high
or
where
the
transformer
tap
-
changing
range
exceeds
±
10
%
,
this
calibration
may
be
too
sensitive
.
Z
CONSTRUCTION
The
types
HU
,
HU
-
1
and
HU
-
4
relays
consist
of
a
dif
-
ferential
unit
(
DU
)
,
a
harmonic
restraint
unit
(
HRU
)
,
an
indicating
instantaneous
trip
unit
(
NT
)
and
an
All
possible
contingencies
which
may
arise
during
installation
,
operation
,
or
maintenance
,
and
all
details
and
variations
of
this
equipment
do
not
purport
to
be
covered
by
these
instructions
.
If
further
information
is
desired
by
purchaser
regarding
this
particular
installation
,
operation
or
maintenance
of
this
equipment
,
the
local
Asea
Brown
Boveri
representative
should
be
contacted
.
Printed
in
USA
Courtesy of NationalSwitchgear.com

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Operating
Ckt
.
Resistor
{
DU
)
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Restraint
Transf
.
4
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Operating
Ckt
.
Resistor
(
DU
)
Hi
t
Harmonic
Restraint
Unit
(
MRU
)
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-
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Restraint
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IHRU
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Reactor
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Filter
)
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Unit
(
DU
)
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T
-
^
TAP
BLOCK
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Restraint
Transf
.
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jig
—
Restraint
Transf
.
2
3
—
Restraint
Transf
.
3
(
HU
-
1
Only
)
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Restraint
Transf
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Restraint
Transf
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Transf
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Transf
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Restraint
Transformers
{
DU
)
Indicating
Contactor
Switch
(
ICS
)
Restraint
Transformer
(
DU
)
i
w
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t
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*
Indicating
Instantaneous
Trip
(
IIT
)
Indicating
Contactor
Switch
(
ICS
)
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:
>
!
|
«
M
Indicating
Instantaneous
Trip
(
IIT
)
To
Restraint
Transf
.
3
(
HU
-
1
Only
)
To
Restraint
Transf
.
2
To
Restraint
Transf
.
1
To
Restraint
Transf
.
3
To
Restraint
Transf
.
2
To
Restraint
Transf
.
1
Figure
1
.
Type
HU
,
HU
-
1
Relays
(
Front
View
)
Figure
2
.
Type
HU
-
4
Relay
(
Front
View
)
Courtesy of NationalSwitchgear.com

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Restraint
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Filter
-
Reactor
(
MRU
Restraint
)
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Parallel
Fiiter
-
Reaotor
(
Operate
MRU
)
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;
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-
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Parallel
Filter
-
Reactor
(
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Restraint
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Filter
-
Reactor
(
Restraint
HRU
)
&
4
7
:
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Parallel
Filter
-
Reactor
(
HRU
Restraint
)
t
.
Operating
Transf
.
(
HRU
)
-
-
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Operating
Transf
.
(
HRU
)
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Operating
Transf
.
(
DU
)
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Transf
.
(
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)
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Operating
Circuit
Filter
Capacitor
(
HRU
)
(
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MFD
)
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Operating
Circuit
Filter
Capacitor
(
HRU
)
(
4
MFD
)
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:
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Capacitor
--
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MFD
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Restraint
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Restraint
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it
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Figure
4
.
Type
HU
-
4
Relays
(
Rear
View
)
Figure
3
.
Type
HU
,
HUH
Relays
(
Rear
View
)
Courtesy of NationalSwitchgear.com

I
.
L
41
-
347.1
S
indicating
contactor
switch
(
ICS
)
.
The
principal
parts
of
the
relays
and
their
locations
are
shown
in
Figures
1
to
7
.
rear
with
two
brass
spacers
and
silver
solder
.
These
non
-
magnetic
joints
represent
air
gaps
,
which
are
bridged
by
two
adjustable
magnetic
shunts
.
The
windings
are
wound
around
a
magnetic
core
.
The
ar
-
mature
is
fastened
to
this
core
and
is
free
to
move
in
the
front
air
gap
.
The
moving
contact
is
connected
to
the
free
end
of
a
leaf
spring
,
which
,
in
turn
,
is
fas
-
tened
to
the
armature
.
2.1
Differential
Unit
(
DU
)
The
differential
unit
of
these
relays
consists
of
re
-
straint
circuits
,
full
wave
rectifiers
,
saturating
operat
-
ing
transformer
,
and
a
dc
polar
unit
.
The
basic
differences
in
the
differential
unit
of
the
three
relays
is
in
the
restraint
circuit
.
The
restraint
circuit
of
the
HU
-
4
relay
consists
of
four
air
-
gap
restraint
transformers
and
four
full
wave
rec
-
tifiers
whose
outputs
are
connected
in
series
.
The
restraint
circuit
of
the
HU
-
1
relay
consists
of
three
air
-
gap
restraint
transformers
and
three
full
wave
rectifiers
whose
outputs
are
connected
in
parallel
.
The
restraint
circuit
of
the
HU
relay
consists
of
two
air
-
gap
restraint
transformers
and
two
full
wave
rec
-
tifiers
whose
outputs
are
connected
in
parallel
.
Each
of
the
restraint
transformers
and
the
operating
transformer
are
provided
with
taps
to
compensate
for
mismatch
of
line
current
transformers
.
These
taps
are
incorporated
in
the
relay
in
such
a
manner
that
changing
a
tap
on
a
restraint
transformer
auto
-
matically
changes
the
same
tap
on
the
operating
transformer
.
2.4
Indicating
Contactor
Switch
Unit
(
ICS
)
The
dc
indicating
contactor
switch
is
a
small
clapper
-
type
device
.
A
magnetic
armature
,
to
which
leaf
-
spring
mounted
contacts
are
attached
,
is
attracted
to
the
magnetic
core
upon
energization
of
the
switch
.
When
the
switch
closes
,
the
moving
contacts
bridge
two
stationary
contacts
,
completing
the
trip
circuit
.
Also
,
during
this
operation
,
two
fingers
on
the
arma
-
ture
deflect
a
spring
located
on
the
front
of
the
switch
,
which
allows
the
operation
indicator
target
to
drop
.
The
front
spring
,
in
addition
to
holding
the
target
,
provides
restraint
for
the
armature
and
thus
controls
the
pick
-
up
value
of
the
switch
.
2.5
Indicating
Instantaneous
Trip
Unit
(
NT
)
The
instantaneous
trip
unit
is
a
small
ac
operated
clapper
type
device
.
A
magnetic
armature
,
to
which
leaf
-
spring
mounted
contacts
are
attached
,
is
at
-
tracted
to
the
magnetic
core
upon
energization
of
the
switch
.
When
the
switch
closes
,
the
moving
contacts
bridge
two
stationary
contacts
completing
the
trip
cir
-
cuit
.
Also
,
during
the
operation
,
two
fingers
on
the
ar
-
mature
deflect
a
spring
located
on
the
front
of
the
switch
which
allows
the
operation
indicator
target
to
drop
.
A
core
screw
accessible
from
the
top
of
the
switch
provides
the
adjustable
pickup
range
.
3
.
OPERATION
The
types
HU
and
HU
-
1
relays
are
connected
to
the
protected
transformer
as
shown
in
Figures
10
and
11
.
The
HU
-
4
is
connected
to
the
protected
trans
-
former
as
shown
in
Figure
12
.
In
such
a
connection
the
relays
operate
to
protect
the
transformer
for
faults
internal
to
the
differential
zone
of
the
trans
-
former
,
but
not
for
faults
external
to
the
zone
.
Neither
do
the
relays
operate
on
magnetizing
inrush
currents
2.2
Harmonic
-
Restraint
Unit
(
HRU
)
The
harmonic
-
restraint
unit
of
the
HU
relays
consists
of
an
air
gap
operating
transformer
,
a
second
har
-
monic
block
filter
,
a
fundamental
block
second
har
-
monic
pass
filter
,
two
full
-
wave
rectifiers
,
indicating
instantaneous
trip
unit
,
varistor
,
and
a
dc
polar
unit
.
Taps
are
also
incorporated
in
this
unit
to
compen
-
sate
for
mismatch
of
the
line
current
transformers
.
Changing
a
tap
on
the
restraint
transformer
of
the
differential
unit
also
changes
the
tap
of
this
unit
.
2.3
Polar
Unit
The
polar
unit
consists
of
a
rectangular
shaped
mag
-
netic
frame
,
an
electromagnet
,
a
permanent
magnet
,
and
an
armature
.
The
poles
of
the
crescent
shaped
permanent
magnet
bridge
the
magnet
frame
.
The
magnetic
frame
consists
of
three
pieces
joined
in
the
4
Courtesy of NationalSwitchgear.com

I
.
L
41
-
347.1
S
associated
with
energization
of
the
transformer
even
though
these
currents
may
appear
as
an
internal
fault
.
To
avoid these
false
operations
,
each
unit
of
the
relay
performs
a
separate
function
.
The
differen
-
tial unit
(
DU
)
prevents
operation
on
an
external
fault
,
while
the
harmonic
-
restraint unit
(
HRU
)
prevent
op
-
erations
on
magnetizing
inrush
currents
.
Hence
,
the
operation
of
the
relay
can
best be described under
the
headings
of
external
fault
current
,
internal
fault
currents
,
and
magnetizing
inrush
currents
.
and HU
-
1
relays
and
to
the
sum
of
the restraint
cur
-
rent
flowing
in
the HU
-
4
relay
.
The
sum
of
the
re
-
straint
current
flows
into
the
operating
transformer
and
produces
an
excess
of
operating
torque
,
and the
differential
unit
operates
.
In
the
case
of
an
internal
fault fed from
one source
only
,
the
fault
current
flows
in
one
restraint
trans
-
former
and
the
operating
transformer
.
An
excess
of
operating
torque
is
produced
on
the
differential
unit
and
it
operates
.
Faults
normally
appear
as an
offset
sine
wave
with
a
decaying
dc
component
,
and
contain
very
few
har
-
monics
.
As
a
result
,
the
harmonic
-
restraint unit
will
operate
during
internal
faults
to
permit
tripping
of
the
relay
.
For
heavy
internal
faults
,
the
indicating
instanta
-
neous
trip
unit
(
NT
)
will
operate
.
Since
this unit is
connected
to
an
air
gap
transformer
,
essentially only
the sine
wave
component
of
an
internal
fault
is
ap
-
plied
to
the
NT
unit
.
The
dc
component
of
the
fault
is
bypassed
by
the
transformer
primary
.
The varistor
connected
across
the
dc
side
of
the
re
-
straint
rectifier of
the harmonic
restraint unit
prevents
excessive
voltage
peaks
from
appearing
across
the
rectifiers
.
These
peaks
arise
through
transformer
ac
-
tion
of
the
harmonic
-
restraint
polar
-
unit coils
during
heavy
internal
faults
.
The
varistor
has
a
large
value
of
resistance
for
low
voltages
,
while
presenting
a
low
value
of
resistance
for
high
voltages
.
This
character
-
istics
effectively
reduces
the
voltage
spikes
on
heavy
internal
faults
while
not
hampering
perfor
-
mance
during
inrush
,
where
the
voltage
is
consider
-
ably
lower
.
3.1
External Fault
Currents
The
HU
family
of
relays
have
a
variable
percentage
characteristic
.
This
means
that the
operating
current
required
to
close the
contact
of
the
differential
unit
expressed
in
percent
of
restraint
varies
with
the
magnitude
of
the
larger
restraint
current
in
the HU
and HU
-
1
current
relays
and
with
the
sum
of
the
re
-
straint
current
in
the HU
-
4
relays
.
Figures
13
and
14
illustrate
these
characteristics
.
To
use
these
curves
,
divide each restraint
current
by
the
appropriate
tap
and
enter
the horizontal axis
using
the
larger
or
larg
-
est
restraint
multiple
.
Then
enter
the vertical axis
,
us
-
ing
the
difference of
the
restraint
multiples
.
With
the
relay
connected
as
shown
in
the schematic
diagram
of
Figure
15
a
,
an
external
fault
causes
cur
-
rent to
flow
in
the air
-
gap
restraint
transformers
of
the
differential
unit
.
If
the line
current
transformers
do
not saturate
and the
correct
ratio
matching
taps
ap
-
plied
,
no
effective
current
flows
in
the
operating
transformer
of
the
relay
.
Hence
,
only
contact
-
open
-
ing
torque
is
produced
on
the
differential
unit
.
On
heavy
external
faults
where
a
main
current
trans
-
former
saturates
,
current
flows
in
the
operating
cir
-
cuit
of
the
relay
.
With
such
a
condition
,
the harmonic
-
restraint
unit
may
or
may
not
close its
contacts
,
de
-
pending
upon
the harmonics
present
in
the
false
op
-
erating
current
.
However
,
operation
of
the
relay
is
prevented
by
the
variable
percentage
characteristic
of
the
differential
unit
,
since
a
large
differential
cur
-
rent
is
required
to
close its
contacts
during
heavy
ex
-
ternal
faults
.
3.3
Magnetizing
Inrush
Currents
Magnetizing
inrush
current
waves
have
various
wave
shapes
.
A
typical
wave
appears
as a
rectified
half
wave
with
decaying
peaks
.
In
any
case
,
the
var
-
ious
wave
shapes
are
rich
in
harmonics
with
the
sec
-
ond harmonic
predominant
.
Since
the second
har
-
monic is
always
present
in
inrush
waves
and
not
in
internal
fault
waves
,
this harmonic is used
to
restrain
the
harmonic
-
restraint unit
during
inrushes
.
The
dif
-
ferential
unit
may
or
may
not
close its
contacts
,
de
-
pending
on
the
magnitude
of
the inrush
.
3.2
Internal
Faults
In
the
case
of
an
internal
fault
as
shown
in
Figure
15
b
,
the restraint
of
the
differential
unit is
proportion
-
al
to
the
largest
restraint
current
flowing
in
the HU
5
Courtesy of NationalSwitchgear.com

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L
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S
When
a
magnetizing
inrush
wave
is
applied
to
the
re
-
lay
,
the
dc
component
of
the
wave
is
bypassed
by
the
air
-
gap
operating
transformer
.
The
other
compo
-
nents
are
fed
into
the
filter
circuits
.
The
impedance
characteristics
of
these
filters
are
such
that
the
sec
-
ond
harmonic
component
flows
into
the
restraint
coil
of
the
polar
unit
,
while
the
other
harmonics
flow
into
the
operating
coil
.
The
polar
unit
will
not
close
its
contacts
unless
the
second
harmonic
content
is
less
than
15
percent
of
the
fundamental
component
.
be
approximately
1.0
volt
.
Use
Figure
17
if
the
pick
-
up
is
0.35
times
tap
.
Pickup
of
the
harmonic
-
restraint
unit
and
the
differ
-
ential
unit
is
either
30
or
35
%
of
tap
value
current
.
Pick
up
of
the
indicating
instantaneous
trip
unit
is
10
times
tap
value
current
for
the
HU
and
the
HU
-
1
re
-
lay
and
15
times
tap
value
current
for
the
HU
-
4
.
Components
of
the
harmonic
-
restraint
unit
are
se
-
lected
such
that
15
%
second
harmonic
will
prevent
operation
of
the
unit
.
This
factor
is
adequate
to
pre
-
vent
false
operation
on
inrushes
.
The
frequency
response
of
the
HU
and
HU
-
1
60
Hz
relays
is
shown
in
Figure
19
and
,
for
the
HU
and
HU
-
1
50
Hz
relays
is
shown
in
Figure
28
.
The
indicating
instantaneous
trip
unit
(
NT
)
will
not
op
-
erate
on
inrush
.
The
air
-
gap
transformer
will
bypass
Ihe
dc
component
of
the
inrush
thereby
reducing
the
magnitude
of
the
wave
applied
to
the
IIT
unit
.
If
the
inrush
has
an
initial
peak
of
16
times
tap
-
value
cur
-
rent
,
the
air
-
gap
transformer
will
reduce
this
peak
to
approximately
8
times
tap
value
on
the
secondary
of
the
transformer
.
4.1
Trip
Circuit
The
main
contacts
will
safely
close
30
amperes
at
250
volts
dc
,
and
the
seal
-
in
contacts
of
the
indicat
-
ing
contactor
switch
will
safely
carry
this
current
long
enough
to
trip
a
circuit
breaker
.
The
indicating
contactor
switch
has
two
taps
that
provide
a
pick
-
up
setting
of
0.2
or
2
amperes
.
To
change
taps
requires
connecting
the
lead
located
in
front
of
the
tap
block
to
the
desired
setting
by
means
of
a
screw
connection
3.4
Breaker
Maintenance
Before
some
of
the
ct
’
s
are
bypassed
for
breaker
maintenance
the
trip
circuit
should
be
opened
,
as
shown
in
Figures
9
through
12
.
Otherwise
the
false
-
unbalanced
current
will
cause
the
relay
to
trip
.
It
is
not
necessary
to
short
-
circuit
the
relay
operating
cir
-
cuit
since
it
has
an
adequate
continuous
-
current
rat
-
ing
.
(
See
“
Energy
Requirements
”
)
.
4
.
CHARACTERISTICS
Taps
are
incorporated
in
the
HU
family
of
relays
to
compensate
for
main
current
transformer
mismatch
.
These
taps
are
as
follows
:
2.9
,
3.2
,
3.5
,
3.8
,
4.2
,
4.6
,
5.0
,
8.7
.
To
measure
the
effective
unbalance
,
a
sensitive
low
-
reading
voltmeter
(
5000
ohms
per
volts
)
can
tempo
-
rarily
be
connected
across
the
operating
coil
resistor
(
at
top
of
case
)
.
With
a
perfect
balance
,
the
voltmeter
reading
will
be
zero
.
The
reading
should
not
exceed
the
values
indicated
by
the
15
%
mismatch
curve
at
Figure
16
when
the
relay
pickup
is
0.30
times
tap
.
If
the
amount
of
mismatch
is
measured
or
calculated
,
the
measured
voltage
can
be
checked
against
the
in
-
terpolated
value
from
the
curve
.
For
example
,
as
-
sume
that
the
larger
restraint
current
is
measured
as
1.5
tap
multiple
and
the
calculated
mismatch
is
7
%
.
Then
,
from
Figure
16
the
measured
voltage
should
5
.
SETTING
CAUTION
Since
the
tap
block
screw
carries
operating
cur
-
rent
,
be
sure
that
the
screws
are
turned
tight
.
In
order
to
avoid
opening
current
transformer
circuits
when
changing
taps
under
load
,
the
re
-
lay
must
be
first
removed
from
the
case
.
Chassis
operating
shorting
switches
on
the
case
will
short
the
secondary
of
the
current
transformer
.
The
taps
should
then
be
changed
with
the
relay
outside
of
the
case
and
then
reinserted
into
the
case
.
To
set
the
relay
,
calculations
must
be
performed
as
shown
under
“
Setting
Calculations
”
.
After
the
correct
tap
is
determined
,
connections
can
be
made
to
the
relay
transformers
by
placing
the
connector
screws
in
the
various
terminal
-
plate
holes
in
front
of
the
re
-
lay
.
Only
one
tap
screw
should
be
inserted
in
any
horizontal
row
of
taps
.
6
Courtesy of NationalSwitchgear.com

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L
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S
5.1
Indicating
Contactor
Switch
(
ICS
)
No
setting
is
required
on
the
ICS
unit
except
the
se
-
lection
of
the
0.2
or
2.0
ampere
tap
setting
.
This
se
-
lection
is
made
by
connecting
the lead located
in
front
of
the
tap
block
to
the
desired
setting by
means
of
the
connecting
screw
.
When the
relay energizes
a
125
-
or
250
-
volt dc
type
WL
relay
switch
,
or
equiva
-
lent
,
use
the
0.2
ampere
tap
;
for
48
volt
dc
applica
-
tions
set
relay
in
2
tap
and
use
Type
WL
Relay
coil
S
#
304
C
209
G
01
or
equivalent
.
Trip
Circuit Constants
Indicating
Contactor
Switch
(
ICS
)
6.2
Definitions
of
Terms
Ip
=
Primary
current at
(
KVA
)
M
IR
=
Relay
input
current at
(
KVA
)
M
IRH
,
IRL
.
IRI
ate
same
as
IR
except
for
high
,
low and intermediate
voltage
sides
respec
-
tively
.
Is
=
ct
secondary
current
at
(
KVA
)
M
T
=
relay
tap
setting
.
TH
,
TL
,
Tl
=
are same
as
T
except
for
high
,
low and intermediate
voltage
windings
,
re
-
spectively
.
N
=
Number
of
current
transformer
turns
that
are
in
use
.
Np
=
N
/
NT
(
Proportion
of
total
turns
in
use
)
Nj
=
Current
transformer
ratio
,
full
tap
VCL
=
“
C
”
accuracy
class
voltage
ZA
=
Burden
impedance
of
any
devices
other than
the HU
,
HU
-
1
,
or
HU
-
4
relays
,
with
maximum
external
fault
current
flowing
.
•
ext
=
max
symmetrical
external
fault
current
in
sec
-
ondary
RMS
amperes
.
Zj
=
Total
secondary
burden
in
ohms
(
excluding
current
transformer
winding
resistance
.
)
0.2
ampere
tap
-
6.5
ohms
dc resistance
2.0
ampere
tap
-
0.15
ohm
dc resistance
5.2
Indicating
Instantaneous
Trip
(
IIT
)
No
setting
is
required
on
the
indicating
instanta
-
neous
trip
unit
.
This
unit is
set
at
the
factory
to
pickup
as
follows
:
•
HU
/
HU
-
1
Relays
10
times
tap
value
current
•
HU
-
4
Relay
15
times
tap
value
current
6
.
SETTING CALCULATIONS
Select
the ratio
matching
taps
.
There
are
no
other
settings
.
In
order
to
calculate the
required
tap
set
-
tings
and check
current
transformer
performance
the
following
information
is
required
.
6.3
Calculation
Procedure
a
.
Select
current
transformer
taps
,
where
multi
-
ra
-
tion
types
are
used
.
Select
a
tap
to
give
approximately
5
amperes
at
maximum
load
.
This
will
provide
good sensitivity
and
will
produce
no
thermal
problem
to
the
ct
.
,
the leads
,
or
the
relay
.
Better
sensitivity
can
be
achieved
by
selecting
a
tap
to
give
more
than
5
amperes
if
a
careful
check
is made
of
the
ct
,
the leads
,
and the
relay
capabil
-
ity
.
For
determining
the
required
continuous
rating
of
the
relay
,
use
the
expected
two
hour
maximum
load
,
since the
relay
reaches
final
temperature
in
this time
.
b
.
Calculate
the
relay
currents
,
IR
.
All
relay
currents
for
relay
tap
selection
should be based
on
the
same
KVA
capacity
.
c
.
Calculate
the
relay
current
ratio
(
s
)
using
the low
-
est current
as
reference
.
6.1
Required
Information
a
.
Maximum
transformer
power
rating
(
KVA
)
M
b
.
Maximum external
fault
currents
c
.
Line
-
to
-
Line
voltage ratings
of
power
transformer
(
VH
.
VI
.
VJ
d
.
Current
transformer
ratios
,
full
tap
(
Nj
)
e
.
Current
transformer
“
C
”
accuracy
class
voltage
(
or
excitation
or
ratio
correction
factor
curve
)
f
.
One
way
current
transformer
lead
resistance
at
25
°
C
(
RL
)
.
When
using
excitation
curve
,
include
ct
winding
resistance
.
g
.
Current
transformer
connections
(
wye
or
delta
)
ct
secondary winding
resistance
,
Rs
-
7
Courtesy of NationalSwitchgear.com

I
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L
41
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347.1
S
d
.
Select
the
tap
ratio
as
close
as
possible
to
relay
current
ratio
from
Table
1
.
Choose
the
first
relay
tap
ratio
using
the
largest
current
ratio
from
step
3
.
The
other
tap
ratios
should
be
determined
us
-
ing
the
lower
tap
from
the
first
tap
ratio
as
reference
.
IR
should
not
exceed
relay
continuous
rating
as
defined
in
Energy
Requirement
Table
.
e
.
Check
IIT
operation
.
The
IIT
pickup
is
ten
times
the
relay
tap
value
for
the
HU
and
HU
-
1
,
or
15
times
tap
value
for
the
HU
-
4
.
Therefore
,
the
max
-
imum
symmetrical
error
current
which
is
flowing
in
the
differential
circuit
on
external
fault
current
due
to
dissimilar
ct
saturation
should
not
exceed
10
or
15
times
relay
tap
.
f
.
Determine
Mismatch
For
2
winding
banks
:
relay
ing
accuracy
classif
ication
.
If
the
“
C
”
accura
-
cy
is
used
,
performance
will
be
adequate
if
:
[
NpVci
-
(
lext
-
100
)
Rs
]
/
lext
is
greater
than
Zj
(
2
)
NOTE
:
Let
lext
=
100
where
maximum
external
fault
current
is
less
than
100
A
.
For
wye
-
connected
ct
:
Zj
=
lead
resistance
+
relay
burden
+
2
A
=
1.13
(
Rl
+
+
ZA
)
ohms
(
3
)
(
R
|
_
multiplier
,
1.13
,
is
used
to
account
for
0.15
temperature
rise
during
faults
.
proximation
.
Use
2
way
lead
resistance
for
single
phase
to
ground
fault
.
For
delta
-
connected
ct
:
an
ap
-
T
/
*
RL
_
\
\
VI
V
RH
0
)
%
mismatch
=
100
S
0.15
+
ZA
)
ohms
^
ZT
=
3
(
1.13
RL
+
where
S
is
the
smaller
of
the
two
terms
,
T
0.45
W
or
(
4
)
=
3.4
(
RL
+
T
+
3
Za
)
h
.
Examples
:
Refer
to
Tables
6
and
7
and
Figure
20
for
setting
ex
-
amples
.
For
3
winding
banks
:
Repeat
calculation
of
equation
(
1
)
and
apply
sim
-
ilar
equations
to
calculate
mismatch
from
the
intermediate
to
high
and
from
and
from
the
inter
-
mediate
to
low
voltage
windings
.
Where
tap
changing
under
the
load
is
performed
the
relays
should
be
set
on
the
basis
of
the
middle
or
neutral
tap
position
.
The
total
mismatch
,
includ
-
ing
the
automatic
tap
change
should
not
exceed
15
%
with
a
30
%
sensitivity
relay
,
and
20
%
with
a
35
%
sensitivity
relay
.
Note
from
Figures
13
and
14
that
an
ample
safety
margin
exists
at
these
lev
-
els
of
mismatch
.
g
.
Check
current
transformer
performance
.
Ratio
er
-
ror
should
not
exceed
10
%
with
maximum
symmetrical
external
fault
current
flowing
.
An
ac
-
curate
method
of
determining
ratio
error
is
to
use
ratio
-
correction
-
factor
curves
(
RCF
)
.
A
less
accu
-
rate
,
but
satisfactory
method
is
to
utilize
the
ANSI
t
The
factor
of
3
accounts
for
conditions
existing
during
a
phase
fault
.
Table
1
HU
Relay
Tap
Ratios
TAP
8.7
2.9
5.0
3.2
3.5
3.8
4.2
4.6
3.000
2.9
1.000
1.103
1.586
1.724
1.207
1.310
1.448
3.2
1.563
2.719
1.000
1.094
1.188
1.313
1.438
2.486
3.5
1.000
1.086
1.200
1.314
1.429
2.289
3.8
1.316
1.000
1.105
1.211
2.071
1.190
4.2
1.000
1.095
1.087
1.890
4.6
1.000
1.740
5.0
1.000
1.000
8.7
8
Courtesy of NationalSwitchgear.com

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S
than the
lower
polar
unit
.
However
,
if
the
pickup
val
-
ue
is
considered
to
be
too
low
,
it should be checked
after
applying
a
polarizing
current
magnitude
of
20
times
tap
value
to
relay
terminals
3
and
7
.
This
will
cause
the
upper
polar
unit
to
pickup
at
a
current
of
approximately
1.65
amperes
.
7
.
INSTALLATION
The
relays
should
be
mounted
on
switchboard
pan
-
els
or
their
equivalent
in
a
location
free
from
dirt
moisture
,
excessive vibration and heat
.
Mount the
relay vertically
by
means
of
the
four
mounting
holes
on
the
flange
for
semi
-
flush
mounting
,
or
by
means
of
the
rear
mounting
stud
or
studs
for
projection
mounting
.
Either
a
mounting
stud
or
the
mounting
screws
may
be
utilized
for
grounding
the
relay
.
The
electrical
connections
may
be
made
directly
to
the
terminals
by
means
of
screws
for
steel
-
panel
mount
-
ing
or
to
the
terminal
studs
furnished
with
the
relay
for
thick
panel
mounting
.
The terminal
studs
may
be
easily
removed
or
inserted
by
locking
two nuts
on
the
stud and then
turning
the
proper
nut
with
a
wrench
.
For detailed
FT
case
information
,
refer
to
I
.
L
.
41
-
076
.
8.1
.
2
Indicating
Instantaneous
Trip Pickup
.
With
switch
open
and
relay
set
on
the number
5
tap
,
apply
current
specified
in
following
table
to
relay
.
In
-
stantaneous
trip
should
pickup
and its
target
should
drop
freely
:
HU
/
HU
-
1
HU
-
4
50
amperes
75
amperes
The
contact
gap
should
be
approximately
0.094
inches between
the
bridging
moving
contact
and the
adjustable
stationary
contacts
.
The
bridging
moving
contact
should
touch both
stationary
contacts
simul
-
taneously
.
8
.
ADJUSTMENTS
AND
MAINTENANCE
The
proper
adjustments
for
correct
operation
of
this
relay
have
been made
at
the
factory
and should
not
be
disturbed
after
receipt
by
the
customer
.
8.1
.
3
Indicating
Contactor
Switch
(
ICS
)
Block
contacts
of
the
polar
units
closed
.
Pass
suffi
-
cient direct
current
through
the
trip
circuit
to
close the
contacts
of
the
ICS
.
This
value
of
current
should be
not
greater
than the
particular
tap
setting
being
used
.
The
operation
-
indicator
target
should
drop
freely
.
8.1
Performance
Check
The
following
check
is
recommended
to
verify
that
the
relay
is
in
proper
working
order
.
All
checks
can
best
be
performed
by
connecting
HU
and
HU
-
1
re
-
lays
per
test
circuit
of
Figure
21
and the HU
-
4
relay
per
test
circuit
of
Figure
22
.
Relays
must
be
tested
in
the
case
.
8.1
.
4
Differential
Characteristic
a
.
Close
switch
to
position
1
.
Set
lac
to
zero
and
ISR
to
either
28
amperes
for
HU
/
HU
-
1
relays
or
38
amperes
for
HU
-
4
relay
.
Adjust
lac
to
20
amperes
.
Check
the
operating
point
for
the
relay by
gradu
-
ally adjusting
ISR
.
Operation
should
occur
between
the
following
limits
:
8.1
.
1
Minimum
Trip
Circuit
.
NOTE
:
The
moving
contact
of
the
upper
polar
unit
(
HRU
)
closes
to
the
left
-
hand
(
front
view
)
stationary
contact
.
The
moving
contact
of
the lower
polar
unit
(
DU
)
clos
-
es
to
the
right
hand
(
front
view
)
station
-
ary
contact
.
Relay
Type
ILR
lac
With
SPDT
switch
open
and
relay
set
on
5
-
ampere
tap
,
apply
1.35
to
1.65
amperes
for
the
30
%
sensitiv
-
ity relay
and
1.6
to
1.9
amperes
for
the
35
%
sensitiv
-
ity
relay
.
The
upper
polar
unit
(
HRU
)
should
operate
.
The
upper
polar
unit
may
operate
for
lower
currents
,
but
not
below
1.0
ampere
.
This low
pickup
will
not
impair
its
operation
on
magnetizing
inrush
currents
and should
not
be
disturbed
if
it is
found
to
be
less
45
to
50
amps
.
HU
/
HU
-
1
20
amps
53
to
56
amps
.
HU
-
4
20
amps
.
b
.
For
30
%
Sensitivity
Relays
:
Close
switch
posi
-
tion
1
.
Set
lac
to
zero
and
adjust
ISR
to
either
10
amperes
for
HU
/
HU
-
1
relays
or
6
amperes
for
9
Courtesy of NationalSwitchgear.com

I
.
L
.
41
-
347.1
S
HU
-
4
relays
.
Increase
lac
to
2.8
amperes
.
If
the
lower
polar
unit
does
not
operate
,
lower
IgR
.
The
relay
should
operate
between
the
following
limits
:
9
.
IN
SERVICE
TEST
Refer
to
the
Tables
2
combinations
.
3
,
or
4
for
different
tap
All
relays
should
be
checked
at
least
once
every
year
or
at
such
other
time
intervals
as
may
be
dictat
-
ed
by
experience
to
be
suitable
to
the
particular
application
.
All
contacts
should
be
periodically
cleaned
.
A
con
-
tact
burnisher
style
#
182
A
836
H
01
is
recommended
for
this
purpose
.
The
use
of
abrasive
material
for
cleaning
contacts
is
not
recommended
,
because
of
the
_
danger
of
embedding
small
particles
in
the
face
of
the
soft
silver
and
thus
impairing
the
contact
.
All
checks
can
be
performed
by
connecting
the
relay
per
the
test
circuit
of
Figures
21
or
22
.
Relays
to
be
tested
in
their
case
.
Relay
Type
lac
*
LR
HU
/
HU
-
1
2.8
to
2.95
amps
11.8
to
12.8
amps
HU
-
4
2.8
to
2.95
amps
8.0
to
9.1
amps
c
.
Reverse
leads
to
restraint
transformers
and
re
-
peat
differential
test
outlined
in
paragraphs
a
and
b
.
Results
should
be
approximately
the
same
as
obtained
under
these
paragraphs
.
d
.
For
35
%
Sensitivity
Relays
:
Close
switch
to
po
-
sition
1
.
Set
lac
to
zero
and
adjust
ISR
to
either
9
amperes
for
HU
/
HU
-
1
relays
or
5
amperes
for
HU
-
4
relays
.
Increase
lac
to
2.8
amperes
.
If
the
lower
polar
unit
does
not
operate
lower
ISR
.
The
lower
polar
unit
should
operate
between
the
fol
-
lowing
limits
.
In
the
HU
relay
,
terminal
5
supplies
the
upper
tap
block
and
Terminal
7
supplies
the
lower
tap
block
.
In
the
HU
-
1
,
Terminal
5
supplies
the
first
(
upper
)
tap
block
,
Terminal
7
supplies
the
second
tap
block
and
Terminal
9
supplies
the
lower
tap
block
.
In
the
HU
-
4
,
Terminal
13
supplies
the
first
(
upper
)
tap
block
,
Ter
-
minal
5
supplies
the
second
tap
block
,
Terminal
7
supplies
the
third
tap
block
and
Terminal
9
supplies
the
lower
tap
block
.
ISR
should
be
connected
to
the
Terminal
with
the
lowest
tap
setting
.
Relay
Type
ac
ILR
HU
/
HU
-
1
2.8
to
2.95
amps
10.8
to
11.8
amps
HU
-
4
2.8
to
2.95
amps
7.0
to
7.8
amps
9.1
Minimum
Trip
9.1
.
1
Lower
Unit
(
Differential
)
With
S
.
P
.
D
.
T
.
switch
open
,
the
lower
polar
unit
in
a
30
%
relay
should
operate
with
lac
between
30
%
and
31
%
of
the
setting
of
the
tap
block
corresponding
to
the
terminal
conducting
ILR
.
For
35
%
relays
,
opera
-
tion
should
occur
between
34
%
and
36
%
of
tap
setting
.
e
.
Reverse
leads
to
restraint
transformers
and
re
-
peat
differential
test
outlined
in
paragraphs
a
and
d
.
Results
should
be
approximately
the
same
as
obtained
under
these
paragraphs
.
8.1
.
5
Harmonic
Restraint
Characteristic
Close
switch
to
position
2
.
Short
out
ILR
ammeter
.
Set
ldc
t
°
4
amperes
and
adjust
!
ac
until
upper
polar
unit
operates
.
Iac
should
read
between
6.5
and
9
amperes
.
Upper
Unit
(
Harmonic
Restraint
)
With
S
.
P
.
D
.
T
.
switch
open
,
the
upper
polar
unit
should
operate
with
lac
between
27
%
and
33
%
of
the
setting
of
the
tap
block
corresponding
to
the
terminal
conducting
ILR
.
The
application
of
a
polarizing
cur
-
rent
of
20
times
ILR
tap
value
current
between
Ter
-
minal
3
and
the
terminal
conducting
ILR
,
will
make
9.1
.
2
As
shown
in
Figure
23
,
these
values
of
alternating
current
correspond
to
17
percent
and
14
percent
second
harmonic
.
10
Courtesy of NationalSwitchgear.com