GE WavePro LVPCB Application Manual page 17

Short-Time Delay
Short-time delay is always provided when short-time pickup
is ordered. Short-time delay provides additional refinement
in providing coordination between upstream and down-
stream protective devices. There are three time delay bands
[1 (MIN), 2 (INT), 3 (MAX)] that provide delays from 100
ms to 350 ms.
2
I T IN
MIN
INT
MAX
MIN
INT
MAX
2
I T OUT
OUT
Short-time delay with I 2 t OUT
Selectable Short-Time I 2 t function
Selectable short-time I 2 t is always provided with the short-
time option. The I 2 t helps the solid-state trip unit coordinate
with downstream thermal magnetic devices or fuses. This
function impacts the shape of short-time pickup and short-
time delay time current curves and may be programmed
either IN or OUT.
2
I T IN
MIN
INT
MAX
MIN
INT
MAX
2
I T OUT
2
Short-time delay with I t IN
Ground-Fault Protection (Optional)
Ground-Fault Protection
Power+ trip units are field upgradeable to include ground
fault protection. To upgrade to the ground-fault option,
simply remove the rating plug that does not have the
ground-fault option and install a ground-fault rating plug.
I t
2
I t
2
IN
Trip Characteristics — Power+™ (cont.)
Once installed, the ground-fault function is enabled and
adjusted through the pickup and delay selector switches on
the rating plug. The optional Defeatable Ground Fault
includes an "OFF" setting on the ground fault delay selector
switch to allow ground fault to be temporarily disabled for
maintenance or testing purposes.
A ground-fault is an unintentional current flow from a cir-
cuit through a conductive path to ground. Ground faults
usually have intermittent or very low values of current flow,
as depicted in Graph A , and are not detected by long-time
overload protection. Some
ground-fault trip systems
may not detect this type of
fault because the intermit-
tent nature of the fault
never exceeds the trip
threshold as illustrated in
Graph B . The Power+ trip
unit detects and integrates
(adds a series of arcing and
intermittent current pulses)
the low-level current of a ground fault. This integration
function provides a memory response for ground faults to
achieve preferred ground-fault protection as shown in
Graph C .
The NEC requires that the maximum ground-fault setting
not exceed 1200 amps. Ground-fault protection includes
pickup setting, ground-fault delay settings and selectable 1
function. Ground-fault pickup settings are based on multi-
ples of S, the current sensor rating. The lowest setting is
20% of S, and the highest setting is based on current sensor
amp ratings, such that the maximum setting does not
exceed 1200 amps. There are three ground-fault delay
bands of 1 (MIN), 2 (INT), 3 (MAX) ranging from 100 ms
to 350 ms. The I 2 t function adds an I
corner of the ground-fault time current curve transition,
from pickup to the constant delay bands, to improve coordi-
nation with downstream devices.
(xS) .24 .26
.22
.28
.30
.20
.22
.20
MAX MAX
INT INT
MIN MIN
2 2
I T I T
IN OUT
Ground-fault pickup and delay
Ground Fault Curr ent
A
t
Ground Fault
Detection
B
t
Ground Fault
Trip
Detection
C
t
Ground-fault memory circuit
2
2 t slope to the square
Pickup
I t IN
2
Delay
t
15