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Metering and Extended Protective Relaying
Parameter
Description
kW
Demand
Kilowatt
Demand Using
Fixed or Sliding
Window
Approach
Range:
!7,2O0
Accuracy: !2%
ol
Reading Provided
power
factor
is greater than
50%
and current and
voltage
signals
are within
their
sPeci-
fied accuracy
ranges.
BDU DisPlaY:
kWD =
XXXX
Power Flow Sign
Conventions
Static
Trip
lllCP/CPX model
trip devices
are
capable
of mea-
suring real
(kW)
and
reactive (kVAR) power
flows
in
both
directions. The
circuit
breaker
and
trip
unit symbols
below
showthe example where
the top
terminals
of
the
circuit breaker
are
connected
to
the normal power source, and
the
trip
unlt
is
configured
with
"V
SOURCE'
set
to
"TOP". The
term "forward"
power
flow
means
that
kilowatts
(or
kiloVARS)
are
being
consumed by
the
'LOAD";
"reverse"
flow
means
power
is
being
supplied
by
the
"LOAD
.
The sign conventions used for
kW
kVAR
and
PF
are
shown
in
the
four quadrants
of
the power
diagram
below.
Extended
Protective
Relay
Functions
Extended protective
relaying
functions are provided
with the
trip
unit
when
the
"X"
model
type
is ordered.
There
are
7
relaying functions,
described
below,
Each
function
is
capable
of
tripping
the
circuit
breaker when
the proper conditions
are
met. To
activate
a
function,
f
irst set a
pickup
value and
a
delay
value; then enable (turn
on)the
function, When the measured
conditions
relating
to the
appropriate {unction
exceed
the
pickup value,
a pickup flag will be
set and the value of
the
measured conditions
will
be
logged
into
the
trip
unit's
event
log.
lf
the pickup
stays on for the delay value time, the
circuit
breaker
will
be
tripped.
ln
addition, the measured conditions
at
the time of the
trip, the
relaying
function which caused
the
trip, the breaker status, and
the
time
of the
trip will be entered
into
a
trip
1og.
The
data
in
the event log and
trip
log
can
be
viewed from
a
master device
using the
R5-485
bus. The
trip
log
can also be
read from
the
BDU
accessory, but
without time-
stamp
information.
Note:
All
relaying functions,
except
current unbalance,
are
prevented
f
rom
operating
unless the
circuit
breaker position
is
sensed
as
closed.
This
feature prohibits repetitive pickups and
trip signals from being generated
on an
open breaker, Repeti-
tive pickups would
result
in
multiple writes
to
the
event
logs
and
trip
logs; repetitive
trip
signals would result in multiple
drive
signals being sent
to the
actuator. For example:
The
undervoltage
relay
on
an
open
feeder
breaker
is
enabled with
a pickup of
440
volts and a delay
of
1
second, An
upstream
circuit
breaker
is
opened.
Without
the
above
feature,
the
undervoltage
relay
on the
feeder
breaker
would pickup,
time-
out,
and
attempt to
trip.
This process
would
repeat every
1
second
until
manually stopped. Therefore
for
proper operation
of
the
relaying
functions, the
breaker position
switch
must be
functioning
properly.
Current
Unbalance
-
Current
Unbalance
is
a
protective
relay
function
that
protects against
an
unbalance
in the
phase
currents. Each phase current, (la,
lb
and lc)
is
compared
to
the
arithmetic average of the three phase currents,
l*.
Tripping
occurs
when
any
phase current exceeds
the
programmed
unbalance pickup
for a
period
of time equal to the delay time
setting.
The
pickup
must
remain
active
for the
entire delay time
for
a
trip
to
occur.
lf
the current
unbalance
condition
subsides
in less
time than the delay time, the
pickup
will go inactive and
the
current unbalance protective
relaying
function
will
be
reset. When
tripping occurs,
the
actual
condition that caused
the
trip
is
recorded
in
the
trip unit's
nonvolatile
trip
log.
Programmable settings:
Trip:
Yes, No or Clr
Pickup:
5%
lo
50% in increments
of
I %
Delay:
1
to
l5
seconds
in increments
of
1
second
Average current
is
defined
as
Ila + lb +
lc]/3
=
l*
Pickup
occurs
if
the absolute value of
1
-
(lallX)
or
(lb/l*)
or
(lc/l>K) X 100%
is
equal to or greater than
the pickup
setting
Current
unbalance
is
disabled
for
any phase current
less
than
15%
of
sensor rating.
Data
recorded
in
the
event
log:
Pickup
Active:
Time
at
which pickup
went active
and
la,
lb,
lc at
PickuP,
Pickup
lnactive:
Time
at
which pickup went
inactive.
,V
SOUBCE"
Forward
Power
(kwkvAR
consumed by
the
"LOAD')
Circuit Breaker/Trip Unit symbols showlng power tlows
kVAR
(react ve power)
+kW (forward
+kVAR
(forwa
+PF
(lagging)
kW (real
kVAR
(fon
)F
(leadinr
vard)
t\t
II
kW (revers
kVAR
(reve
-PF
(laggir
III
e)
\
rrSe)
s)
IV
<W
(forwar
VAB (rever
F
(leading
power)
+k\
PF
rrward)
(forward)
)rward)
reverse)
Power Diagram with Sign Conventions
in
each quadrant
22
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