N Ormal G Round-Fault Protection - GE Power Break II Manual

Power+™ Trip Units
Short-Time Delay
Short-time delay is a lways provided when short-time picku p
is ordered. Short-time delay provides a dditional refinement in
providing coord ination between upstream and downstrea m
protective devices. There a re three time delay b ands that
provide delays from 100 ms to 3 5 0 ms of 1 ( M IN). 2 (I NT). 3
(MAX).
S hort-time delay with l2t O U T
Selectable Short-time l2t Function
S electa ble short-time l2t is a lways provided with the short­
time option. The l 2t helps the solid-state trip unit coord inate
with downstream thermal magnetic devices or fuses. This
function i mpacts the shape of short-time and short-time
delay time current curves, and m ay be p rogrammed either IN
or OUT.
Short-time delay with l2t IN
Normal G rou nd-Fa u lt Protection (Optional)
G round-Fault Protection
The ground-fault function in the Power+™ trip unit is field up­
g radeable. It i s enabled and adjusted through the rating plug.
To upgrade to the g round-fa ult option, sim ply remove the
non-ground fa u lt rating plug that does not have the g round­
fa u lt option and insta ll a g round-fault rating plug. A g round­
fault is an unintentional cu rrent fiow from a circuit through
a cond uctive path to ground. Ground fa ults usually have
intermittent or very low va lues of current fiow, as depicted in
G raph A . and a re not detected by long-ti me overload protec­
tion.
12
Some ground-fa u lt trip systems m ay not detect this type
of fa ult because the interm ittent nature of the fault never
exceeds the trip thresh old as illustrated in G raph B.
Th e Power+ trip unit detects and integrates (adds a series of
a rcing and intermittent current pulses) the low-level cur­
rent of a g round fa ult. This integration function p rovides a
memory response for g round fau lts to achieve p referred
g round-fault p rotection as shown in Graph C.
�!!e_c!�!'
Ground Fault
... .. .............. ............... .. . .. . ..
_ _
Ground-fault memory c i rc u it
The NEC requires that the maxi mum g round-fa ult setting not
exceed 1200 a mps. G round-fa u lt protection incl udes pickup
setting, g round-fa u lt delay settings and selecta b le 12t func­
tion.
G round-fault pick-up settings a re based on multiples of S ,
the current sensor rating. The lowest setting is 2 0 % o f S, and
the highest setting is based on current sensor a m p ratings,
such that the maxi m u m setting does n ot exceed 1200 a m ps.
There a re three g round-fault delay bands of 1 (M IN). 2 (I NT). 3
( MAX) ranging from 100 ms to 3 5 0 ms. The l2t function adds
an 12t slope to the square corner of the g round-fault time
current curve transition, from pickup to the constant delay
bands, to improve coordination with downstream devices.
.24 .26
(xS)
.20
G rou nd-fault pickup and g round fault time delay