Page
9-6
www.eaton.com
IB02602002E
MP-4000
For a complete supply interruption, the nominal ride-through rating is
13 cycles. The relay typically continues to operate for 13 to 20 power
cycles, depending on power supply loading variables:
Number of output relays picked up;
Current being delivered by the 4-20 mA analog transducer
output port;
Type of PONI communications module powered by the MP-
4000, if any; and
Electrical URTD communications (using recommended opti
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cal communications lowers this burden slightly).
The one load that may depress the MP-4000 ride-through times below
13 cycles is the use of an Eaton Ethernet PONI (EPONI) for commu
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nications, particularly the EPONI with optical fiber communications. In
this case, ride-through could fall to below 10 cycles. However, this is
easily remedied by powering the EPONI from its own optional external
power transformer. The MP-4000 ride-through then returns to its 13 to
30 cycle range.
In applying this ride through capability, consider these external factors.
Typical utility feeder fault tripping and reclosing systems on
overhead medium- or high-voltage feeder lines up to
161 kV cause interruptions of 15 to 20 cycles, especially
during thunderstorms.
For higher or extra-high voltage supply circuits to large
plants, interruptions may be longer, up to 30 cycles. De
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termine if the power system has special mitigating features
like multiple well-separated sources, or local paralleled
generation.
Conventional motor contactors drop out in 3 to 5 cycles,
stopping the motor.
Special delayed-dropout contactors that store energy are
available, and ride through interruptions of 15 to 20 cycles.
Latching contactors or motor breakers may also be used.
They trip only by active unlatching or trip coil energization.
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The MP-4000 declares a motor stop after about 20 cycles of no current.
The only way to extend this time is to assign the MOTOR STOP func
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tion to one of the discrete inputs, and connect an external stop-indicat
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ing contact (refer to Subsection 5.6.1 for details).
If the ac supply returns after the stop declaration, but before the
MP-4000 microprocessor shuts down, the MP-4000 relay can go
through another start cycle and return to the RUN state without ever
tripping the motor. However, this on-the-fly restart declaration won’t
happen if the relay has anti-backspin or other jogging timer blocking in
effect. The relay trips at the moment the MP-4000 declares a stop.
WaRNING
BEWaRE OF RE-ENERGIZING MaNy laRGER MOTORS aFTER
aN INTERRUPTION OF MORE ThaN 20 CyClES, BUT lESS ThaN
SEVERal SECONDS. ThE INDUCED ROTOR CURRENT DECayS
SlOWly, yET ThE ROTOR SlOWS ITS ROTaTION aND DEVEl-
OPS a laRGE aNGUlaR DIFFERENCE FROM ThE DISCONNECT-
ED STaTOR FIElD. WhEN ThE STaTOR IS REENERGIZED aFTER
30 TO 40 CyClES, ThE SUDDEN TORQUE ShOCK CaN BREaK
a ShaFT KEy, OR DO MORE SERIOUS MEChaNICal DaMaGE.
USE a CONTaCTOR WITh aN aPPROPRIaTE DROP OUT DElay.
Summary of Contents for MP-4000
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