I.L. 17562
Page 9
PR 0.3 Effective 8/99
2.2 Motor Starting and Control Functions
The MP-3000 Motor Protection relay includes logic to control the number of starts that can occur
on the motor in a given time period for cold and hot motor conditions. Settable timers are
provided to control the time between starts and to restart a motor after a stop. Additional logic is
included for transition control of reduced-voltage starters.
2.2.1 Start Control Timers
Motors typically have limits to the number of cold starts, starts per time period and time between
starts that are permitted without damage. The MP-3000 incorporates these checks to prevent
excessive starting the motor.
2.2.2 Reduced Voltage Starting
The MP-3000 provides a transition and incomplete sequence detection function for reduced
voltage starting. The user can select to transition based on four logical combinations of starting
current and time sequence. The incomplete sequence function can be used independently for
feedback indication from the process, to trip the motor if expected action doesn't occur.
2.2.3 Antibackspin Timing
For certain applications, such as pumping a fluid up a pipe, the motor may be driven backward
for a period of time after it stops. The MP-3000 provides an antibackspin timer (minimum time
between stop and restart) to prevent starting the motor while it is spinning in the reverse
direction. The relay displays the timer countdown from the moment a stop is declared by the
relay.
2.2.4 Load Shedding
The MP-3000 provides a mechanical load shedding feature that can be used to control the
driven process. The load shedding function closes a contact on an overload condition to stop
addition of load until the overload condition subsides by a set amount. Then the load shedding
contact opens and the load is restored.
2.2.5 Emergency Override
The MP-3000 has a user programmable feature that lets the operator reset certain trip conditions
including the jogging timers and thermal-model overload bucket. This function is for use in
emergency conditions only and may result in motor damage or failure. The override action is
logged with time-tag. The button is located behind a security door. The function can be
disabled.
2.2.6 Long Acceleration Motors
Large motors with high inertia loads, such as centrifuges and large fans, may experience starting
currents that greatly exceed the full load current for greater than the locked rotor time. The MP-
3000 has a timing feature which holds off thermal tripping during the long acceleration. Use this
with a zero-speed switch input.
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