Page 9-2
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IB02602002E MP-4000
The MP-4000 automatically calculates the correct motor protection
curve from nameplate or manufacturer values of full load amperes
(FLA, P1L1), locked-rotor current (LRC, P1L2), maximum allowable
stall or locked rotor time (LRT, P1L3); and service factor as used to set
ultimate trip current (UTC, P1L4). The following subsections describe
how such a typical curve is obtained.
Note that, for now, it is assumed that the three phase currents are
balanced and have proper 120 degree phase relationship (i.e.: only
positive sequence current). If negative sequence current reecting
unbalance is present, the MP-4000 gives much heavier weighting to
the heating effect of these currents, and tripping occurs sooner than
expected from balanced-current curves.
9.1.3.1 Instantaneous Over current Function
This function is intended mainly to trip for high-current faults. The ex-
ample instantaneous over current setting used in Figure 9.2 is 12 times
(1,200%) of FLA. In general, the instantaneous over current setting
(IOC, P3L4) should be at least 1.5 times LRC, well above the locked
rotor current normally seen at the moment of a start.
CAUTION
MOST CONTACTORS ARE NOT RATED TO INTERRUPT HIGH-
CURRENT FAULTS. FREQUENTLY, THE MOTOR CONTROL CEN-
TER ALSO CONTAINS FUSES, WHICH CAN INTERRUPT THESE
FAULT CURRENTS.
THE MP-4000 TRIP COMMAND IS INTENDED TO OPEN ALL
THREE PHASES VIA THE CONTACTOR AND BLOCK FURTHER
STARTING, BUT THE FUSES MUST INTERRUPT THE LARGE CUR-
RENT IN FAULTED PHASE(S). IF THE CONTACTOR INTERRUPT-
ING RATING IS EXCEEDED WHEN THE MP-4000 TRIPS WITHOUT
THIS FUSE BACKUP, THE CONTACTOR OR MOTOR CONTROL
CENTER COULD BE DESTROYED IN A HAZARDOUS OR EXPLO-
SIVE CASCADING FAULT SITUATION.
ANOTHER ACCEPTABLE APPLICATION IS TO CONNECT THE
MP-4000 TO DIRECTLY TRIP A CIRCUIT BREAKER THAT HAS AN
INTERRUPTING RATING EXCEEDING THE HIGHEST AVAILABLE
BOLTED-FAULT CURRENT.
IOC should trip fast; no run or pickup delay is provided. A start delay
(IOCSD, P3L5) is set at a minimum of two cycles, or more if needed
to block IOC tripping on magnetizing inrush when the motor is rst en-
ergized. Note that the entered IOCSD value is the total IOC trip time,
including pickup time of the basic IOC measurement algorithm, and
cannot be set below two cycles.
9.1.3.2 Locked-Rotor Function
The family of curves shown in Figure 9.2 is based upon a locked rotor
current setting (LRC, P1L2) of 6.1 times (610%) of FLA (P1L1) and a
family of locked rotor or stall time settings (LRT, P1L3).
All curves shown in Figure 9.2 are based on a maximum allowable stall
time from a cold start. The nameplate LRT used for setting is normally
a cold start value. Since the thermal algorithm actually retains recent
operating history as reected in the thermal bucket level, it is not
necessary to program the MP-4000 for hot starts because hot start
protection is automatic. Note that the effective limit curve for a hot start
is actually more restrictive, (i.e.: more limiting in time and current, than
the cold-start curve in Figure 9.2).
The Emergency Override function, if invoked, lowers the thermal
bucket to cold level, regardless of recent history, and restores the cold
start curve. Use this only for a real process emergency because it
defeats the thermal modeling protection, and the motor is at risk.
9.1.3.3 Ultimate Trip
The setting for the ultimate trip function is the value of current above
which the motor can be damaged over time. Figure 9.2 shows a
setting of 100%, reecting a nameplate service factor of 1.0 and an
ambient temperature that does not rise above 40°C (104°F). If the
motor has a service factor different from 1.0, the ultimate trip current
level is adjusted accordingly. Other common service factors are 0.85
(UTC=85%) and 1.15 (UTC=115%).
As explained above and in Section 5, UTC sets the upper continuous
limit if stator RTD temperature measurements are not available. The
time to trip after the UTC threshold is crossed depends on recent
operating history, and on the thermal bucket size dened by settings.
With stator RTDs reporting acceptable temperature, the algorithm can
allow sustained operation above UTC. Make sure the winding direct
thermal trip temperature setting (WD T) is not turned OFF, or the algo-
rithm reverts to strict use of UTC.
9.1.3.4 Underload Functions
When the motor is running, a current reduction might indicate a
malfunction in the load. Underload protection recognizes mechanical
problems, such as a blocked ow or loss of back pressure in a pump,
or a broken drive belt or drive shaft.
Refer to the underload protection limit - the left vertical line in the
Underload Jam Protection Curve example in Figure 9.3. Here, the
underload trip is set at 60% of FLA. The MP-4000 has settings for un-
derload alarm (ULA, P4L5), and underload trip (ULT, P3L9). Each can
be disabled by setting it to OFF. These would be represented by two
such vertical lines, both below the normal load current. Be sure to set
the alarm level above the trip level. Both trips and alarms are held off
by start delay (ULSD, P3L10). Each has its own run or pickup delay
(ULTR, P3L11 and ULAR, P4L4). Use the start delay to block tripping
until the load stabilizes after a start. Use run delays to avoid nuisance
alarms or trips for load transients.
Note: Underload protection is also available via the Under Power
function described in Subsection 5.20.
9.1.3.5 Jam Functions
When the motor is running, a current increase above normal load
might indicate a malfunction in the load. Jam protection recognizes
mechanical problems, such as broken drive gears.
Refer to the jam protection limit - the right vertical line in the Under-
load Jam protection curve example in Figure 9.3. Here, the jam trip is
set at 150% of FLA. The MP-4000 has settings for jam alarm (JMA,
P4L3) and jam trip (JMT, P3L6). Each can be disabled by setting it to
OFF. These would be represented by two such vertical lines, both well
above the normal load current. Be sure to set the alarm level below
the trip level. Both trips and alarms are held off by start delay (JMSD,
P3L7). Each has its own run delay (JMTR, P3L8 and JMAR, P4L4).
Use the start delay to block tripping until the motor current drops to
continuous load level. Use run delays to avoid nuisance alarms or
trips for load transients.
9.1.4 Complete Motor Protection Curves
To illustrate the protection features of the MP-4000, two sample
curves are given. Using specic motor data, typical motor protection
curves for the MP-4000 without RTDs are shown in Figure 9.4. The
use of RTDs is assumed in Figure 9.5. The following data were used:
Balanced currents during start and run cycles;
Instantaneous over current limit IOC of 12 times FLA;
Locked-rotor amperes of 6.1 times FLA;
Maximum allowable stall or locked-rotor time of 15 seconds,
cold start;
Ultimate trip level of 100% of FLA (service factor = 1.0);
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