213
March 1996
F
Power Circuit Breakers Type DSII and
Electronic Trip Units
Protective function settings are described
below. See Figure 1.
Long Delay (L)
1.
Long Delay Pickup
Determines the continuous ampere
rating of the breaker.
2.
Long Delay Time
Determines the amount of time the
breaker will carry a low level overload
before tripping.
2A. I
2
t Response
I
2
t in: For coordination with other circuit
breakers with electronic trip devices and
for coordination with thermal magnetic
circuit breakers.
2B. I
4
t Response
I
4
t in: For coordination with fuses and up-
stream transformer damage curves.
Short Delay (S)
3.
Short Delay Pickup
Determine or set the level of fault current
at which the short time trip delay count-
down is actuated.
4.
Short Delay Time
Sets the amount of time the breaker will
carry both low level and high level fault
currents before tripping.
4A. Flat Response
I
2
t out: For coordination with other circuit
breakers with electronic trip devices.
This setting is used when I
4
t Long Delay
Time is selected.
4B. I
2
t Response
I
2
t in: For coordination with fuses and
thermal magnetic breakers.
Instantaneous (I)
5.
Instantaneous Pickup
Determines the level of fault current
which will actuate a trip with no time
delay.
Ground Fault (G)
6.
Ground Fault Pickup
Determines the level of fault current at
which the ground fault trip delay count-
down is actuated.
7.
Ground Fault Delay
Determines the amount of time the
breaker will carry a ground fault before
tripping.
7A. Flat Response
I
2
t Out: For coordination with other cir-
cuit breakers with electronic ground fault
settings.
7B. I
2
t Response
I
2
t In: For coordination with zero
sequence ground fault relays.
Programmable Dependant Curve Shaping
Digitrip OPTIM 750 and 1050 trip units offer
programmable dependent curve shaping via
ten curve shaping choices that are pro-
grammed electronically into the trip unit. The
trip curves are interactive so that changing a
long delay setting (Ir) moves the whole curve
including the short time portion to provide
closer protection for bus and cables. Depen-
dent curve shaping provides a wider range of
available settings. OPTIM offers virtually infi-
nite settings to allow the user to optimize co-
ordination for a selectively coordinated
distribution system. Time-current set points
can be downloaded via a handheld program-
mer or a communication system from a cen-
tral personal computer. Digitrip OPTIM is
normally applied to electrical power systems
where system integrity is very important.
Zone Selective Interlocking
Zone selective interlocking capabilities are
available with Digitrip OPTIM 750 and 1050
trip units. Zone selective interlocking pro-
vides positive system coordination by allow-
ing the breaker closest to the fault to trip
without any preset time delays. This is
achieved by setting up the distribution sys-
tem as shown in Figure 2. The hard wired
connection between the trip units sends a re-
straining signal upstream allowing the break-
er closest to the fault to interrupt instan-
taneously, while the upstream breaker times
out per its programmed settings. Zone selec-
tive interlocking reduces stress on the distri-
bution system by isolating faults without
time delays, and provides the ultimate in sys-
tem selective coordination.
I
n
= Rating Plug Rating
I
r
= LDPU Setting
* Varies with Breaker Type and Frame –
See small table this page.
10 Curve Shaping Adjustments
Function
Multiplier/
Setting
Setting Range
Overload
1. Long Delay Pickup
XI
n
0.4 - 1.0
2A. Long Delay Time I
2
t
@6I
r
2 - 24 sec.
2B. Long Delay Time I
4
t
@6I
r
1 - 5 sec.
Short Circuit
3. Short Delay Pickup
XI
r
1.5 - S max.*
4A. Short Delay Time Flat Response
XI
r
0.1 - 0.5 sec.
4B. Short Delay Time I
2
t Response
XI
r
0.1 - 0.5 sec.
5. Instantaneous
XI
n
2.0 - M max.*
Ground Fault
6. Ground Fault Pickup
XI
n
0.25 - 1.0 (1200 A max)
7A. Ground Fault Delay Flat Response
XI
n
0.1 - 0.5 sec.
7B. Ground Fault Delay I
2
t Response
XI
n
0.1 - 0.5 sec.
Breaker Type
Frame
S max.
M max.
SPB
SPB
DSII
400A - 3000A
4000A - 5000A
All
8
6
10
10
6
12
7B
7A
6
T
ime
5
1
4B
4A
2A
2B
2
3
Current in Amperes
4
7
Figure 1. OPTIM Trip Curve Settings
