ABB Circuit Shield 87B User Manual

High
-
Impedance
Differential
Relays
IB
7.6
.
1.7
-
7
Page
9
These
conservative
calculations
can
be
refined
to
produce
lower
settings
if
the
following
or
other
practical
conditions
are
considered
:
Maximum
fault
current
is
usually
lower
than
interrupting
ratings
.
Faulted
circuit
CT
'
s
of
standard
design
never
saturate
completely
.
Source
CT
'
s
may
enter
saturation
region
.
Phase
-
to
-
ground
external
fault
currents
in
resistance
grounded
systems
are
relatively
low
,
hence
3
-
phase
fault
currents
and
one
-
way
lead
resistance
become
the
controlling
factors
.
Junction
points
of
leads
may
not
be
equidistant
but
closer
to
CT
'
s
of
feeders
which
are
subject
to
external
faults
.
Withstand
-
Internal
Faults
The
thermal
withstand
of
the
relay
is
controlled
by
internal
dissipation
limits
.
Energy
depends
on
the
speed
of
the
differential
and
lockout
relay
operation
,
maximum
available
fault
current
,
and
CT
saturation
characteristics
.
In
general
,
the
wattsecond
rating
of
high
impedance
relays
of
any
type
should
be
checked
against
expected
energy
.
For
convenience
,
one
could
use
a
simplified
method
as
reflected
in
Table
2
that
is
based
on
limits
of
CT
saturation
voltages
with
respect
to
relay
currents
and
a
conservative
total
operating
time
of
40
milliseconds
(
from
inception
of
the
fault
to
closing
instant
of
the
lockout
relay
contacts
)
.
Table
2
Typical
Input
Current
and
Energy
Limits
Current
Transformers
Max
Current
Transformers
Max
system
fault
current
(
Symm
RMS
)
Max
.
relay
Current
(
Symm
RMS
)
Max
.
system
fault
current
(
Symm
RMS
)
Max
relay
Current
(
Symm
RMS
)
Current
Transformers
Max
system
fault
current
Symm
RMS
)
relay
Current
(
Symm
RMS
)
Minimum
Ratio
Max
Max
.
Satur
.
Voltage
Minimum
Ratio
Minimum
Ratio
Max
Satur
.
Voltage
Satur
.
.
Voltage
170
A
240
V
1500
:
5
1200
:
5
800
:
5
50
KA
37.5
KA
25
KA
100
A
2500
:
5
2000
:
5
1500
:
5
50
KA
37.5
KA
25
KA
350
V
300
A
170
V
1000
:
5
800
:
5
500
:
5
50
KA
37.5
KA
25
KA
150
A
260
V
50
KA
37.5
KA
25
KA
90
A
2000
:
5
1500
:
5
1000
:
5
360
V
3000
:
5
2500
:
5
1500
:
5
50
KA
37.5
KA
25
KA
250
A
200
V
1000
:
5
800
:
5
500
:
5
135
A
50
KA
37.5
KA
25
KA
280
V
2000
:
5
1500
:
5
1000
:
5
50
KA
37
.
5
KA
25
KA
75
A
4000
:
5
2500
:
5
2000
:
5
400
V
50
KA
37.5
KA
25
KA
220
A
210
V
1200
:
5
1000
:
5
600
:
5
50
KA
37.5
KA
25
KA
125
A
290
V
2000
:
5
1500
:
5
1000
:
5
50
KA
37.5
KA
25
KA
62
A
440
V
4000
:
5
3000
:
5
2000
:
5
50
KA
37.5
KA
25
KA
200
A
220
V
1500
:
5
1000
:
5
800
:
5
50
KA
37.5
KA
25
KA
310
V
110
A
2500
:
5
2000
:
5
1200
:
5
50
KA
37.5
KA
25
KA
40
A
600
V
(
*
)
50
KA
37.5
KA
25
KA
(
*
)
4000
:
5
(
*
)
CT
'
s
in
this
range
are
not
widely
available
due
to
limited
window
area
.
Consult
factory
.
If
the
maximum
fault
current
(
in
symmetrical
RMS
amperes
)
and
the
ratio
are
known
,
the
selected
saturation
voltage
of
any
CT
should
not
be
higher
than
indicated
on
the
corresponding
line
.
Conversely
,
the
CT
ratio
should
not
be
lower
than
one
shown
for
corresponding
values
of
the
system
fault
current
and
CT
saturation
voltage
.
Intermediate
values
can
be
obtained
by
interpolation
.
Alternatively
,
the
energy
can
be
accurately
calculated
from
the
instantaneous
product
of
secondary
'
current
and
voltage
pulses
.
One
should
bear
in
mind
,
however
,
that
the
total
circuit
is
not
linear
during
faults
.
Courtesy of NationalSwitchgear.com

ABB Circuit Shield 87B Specifications

General

Brand	ABB
Model	Circuit Shield 87B
Category	Relays
Language	English