IM02602002E
Page 9-2
www.eaton.com
MP-3000
Note that, for now, it is assumed that the 3-phase currents are bal-
anced and have proper 120 degree phase relationship (i.e., only
positive sequence current). If negative sequence current reecting
unbalance is present, the MP-3000 gives much heavier weighting to
the heating effect of these currents, and tripping occurs sooner than
expected from balanced-current curves.
This function is intended mainly to trip for high-current faults. The ex-
ample instantaneous overcurrent setting used in Figure 9.2 is 12 times
(1,200%) of FLA. In general, the instantaneous overcurrent 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.
-
-
-
-
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.
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-3000 for hot starts - 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 - it defeats the
thermal-modeling protection, and the motor is at risk.
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.
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-3000 has settings for
underload 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.
Underload protection is also available via the Under Power
function described in Section 5.20.
When the motor is running, a current increase signicantly 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-3000 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.
To illustrate the protection features of the MP-3000, two sample curves
are given. Using specic motor data, typical motor protection curves
for the MP-3000 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 overcurrent 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)
Motor running; normally loaded at 90% of FLA
Underload protection at 60% of FLA with a 5-second run
delay
Jam protection at 180% of FLA with a 5-second run delay.
The MP-3000 recognition of the transition from start to run has no
impact on this protection curve, but denes when the displays and
indications change from START to RUN. For a reduced-voltage
starter, the transition function also denes when the AUX2 output relay
•
•
•
•
•
•
•
•
To Next Page
Loading...
