MicroVersaTripPius™ and PM™ Trip Units
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 downstream
protective devices. There a re three time delays that provide
delays from 100 ms to 350 ms of 1 (MI N), 2 (I NT), 3(MAX).
l't
OUT
Short-time delay wit h 12t OUT
Selectable Short Time (2t Function
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u
l r
ll
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Selectable short-time l2t is a lways provided with the short
time option. The l2t helps the solid-state trip unit coordinate
with downstream thermal magnetic devices or fuses. This
function i mpacts the shape of short-time and short-time
delay time current curves, and may be programmed either
I N or OUT.
t'·i
Short-time delay with l2t I N
H igh-Range I nstantaneous (Optional)
The high-range instantaneous function is for special applica
tions where all coordination is based on adjustments of long
and short time. The instantaneous trip setting is fixed at "H"
- breaker's short-time withstand rating.
Normal Ground-Fault Protection (Optional)
Ground-Fault Protection
A g round fault is an unintentional current flow from a circuit
through a conductive path to g round. Ground faults usu
ally have intermittent or very low values of current flow,
as depicted in G ra ph A, and are not detected by long-time
overload protection.
18
Some g round-fault trip systems may not detect this typ e
o f fault because t h e intermittent nature o f the fault never
exceeds the trip threshold as illustrated in Gra ph B.
The MicroVersaTrip Plus™ and MicroVersaTrip PM™ trip units
detect and integrate (add a series of a rcing and intermittent
current pulses) the low-level current of a ground fault. This
integration function provides a memory response for g round
faults to achieve preferred g round fault protection as shown
in G raph C.
The N EC requires that the maximum g round-fault settin g not
exceed 1200 amps. G round-fault protection includes pickup
setting, ground-fault delay settings and selectable l2t func
tion.
Ground fault memory circuit
Ground fault pickup and ground fault time delay
G round-fault pickup settings a re based on multiples 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 a m ps.
There are three ground-fault delay bands of 1 ( M I N), 2 (I NT) 3
(MAX) ranging from 100 ms to 350 ms. The l2t function adds
an 12t slope to the square corner of the ground-fault time
current curve transition, from pickup to the constant delay
bands, to improve coordination with downstream devices.
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