Motor Cycle Monitoring - Eaton MP-3000 Instruction Leaflet

IM02602002E
The unbalance is the ratio of negative sequence to positive sequence
current. If the motor can be started in either direction (P1L8 = REV),
the MP-3000 takes the larger of the two sequence currents at the time
of the start as the positive sequence current.
The sequence currents are accurately calculated according to the defi-
nition, which relates directly to heating. Note that significant negative
sequence current is present if the phase angles are not symmetrical,
even though the 3-phase current magnitudes are equal.
The unbalance trip and alarm functions can each be set from 4% to
40%, or OFF. A common start delay is provided (UBSD, P3L13), plus
separate trip (UBTR, P3L14) and alarm (UBAR, P4L8) run delays.
Use the run delays to ride through external-system unbalanced faults,
which could last for several seconds. Check the time curve settings
of feeder relays or fuses. Keep in mind that high-resistance or arcing
faults, which may take a longer time to clear, have less tendency to
severely depress voltage than a solid fault.
9.1.10 Ground fault Protection application
Use this fault-protection function with a flux-canceling ground fault
CT. This CT has a large primary window through which all 3-phase
conductors can pass. The most common ground fault CTs have a
ratio of 50:5 or 50:1.
The MP-3000 is recognized to UL 1053, Ground Fault Protective
Device standard. This may eliminate the need for a separate ground
fault protector in many applications that formerly required it.
Note that the ground fault trip and alarm current settings GFT, P3L1
and GFA, P4L1 are based on percentage of ground CT rated primary
current, not on FLA or the phase CT ratio. For example, setting 10%
gives a trip or alarm for an actual ground leakage current of 5 A with a
50:5 CT (GCT, P1L6 = 50).
This function is only useful for a grounded power system. The ground
return is normally made from the neutral of the secondary wire winding
of the supply power transformer. Resistance grounding is acceptable,
as long as the resulting fault current is at a level the relay can be set
to detect.
The ground CT, which provides sensitive protection for high-resistance
ground faults, may saturate for a robust heavy-current ground fault
in a solidly-grounded system. Minimize the saturation problem by
minimizing the burden. Use the shortest and heaviest leads possible
between the ground CT and the relay. The MP-3000 itself has very low
burden, usually much lower than the connecting wiring. Calculate the
current magnitude which saturates the ground CT. Consider the CT
secondary voltage capability and the total burden of the CT second-
ary winding itself, the connecting wires, and the relay. Make sure this
saturation current is well above the minimum sensitivity of the phase
IOC function and/or the motor fuses.
A residual connection – the wired summation of the phase CT circuits
through the ground CT input – requires a much higher GFT setting to
avoid false tripping. Thus, sensitivity is not nearly as good as with a
separate flux-canceling CT. If the MP-3000 relay is installed where a
residual connection is used, GCT should be set to the same value as
PCT. The User must then set the ground fault trip level at a high value
to avoid nuisance tripping from CT ratio errors, third harmonic and cer-
tain higher harmonics, or other measurement errors producing false
residual currents. Monitor the metered ground current during various
loading conditions to ensure a good margin between these error cur-
rents and the ground fault trip current setting GFT, P3L1. Also, watch
out for phase CTs that saturate during motor starting. The saturation
produces a large residual current and a ground fault trip. This may be
a problem if the CTs have a low voltage capability (e.g., C5 or C10),
have long wiring runs, or are otherwise heavily burdened.
Page 9-4
MP-3000

9.2 Motor Cycle Monitoring

This refers to the MP-3000 functions that monitor the motor during pe-
riods of normal operation. Normal operation includes the start cycle,
run cycle, and stop cycle. Trips may occur at any time. The MP-3000
time-tags many critical changes of state, and stores them with sup-
porting data in log books and history records.
The primary function of the MP-3000 is to alarm, as well as to trip
and block, the motor contactor for faults and abnormal or dangerous
operating conditions. It can also exercise some active control of a
normally functioning motor and/or its load. Active control functions
include transition control to full running voltage for a reduced-voltage
starter as explained in Subsection 9.2.1. Process load shedding that
reduces overload is covered in Subsection 9.1.5. Other functions can
be programmed by assigning a particular internal MP-3000 measure-
ment to a contact output with output relay settings.
9.2.1 Start Cycle and Transition Tripping
Figure 9.6 shows an example of how the MP-3000 reacts to a normal
operating-cycle current profile. Initially, the motor is stopped and the
current is zero. As long as the MP-3000 is not in a trip state, it permits
contactor energization by closing its trip contact in series with the con-
tactor. The contactor is energized by the operator or process control
system through a normal two-wire or three-wire motor control scheme,
external to the MP-3000. The MP-3000 declares a motor start when
it senses a motor current that exceeds 30% of the FLA setting (P1L1).
The message START is displayed and the transition timer (TRNT,
P5L6) begins to run. Also, the MP-3000 monitors the large starting
current, noting when the current falls below the transition level TRNC,
P5L5.
Using the TRN XXX setting P5L7, the User can select one of four
transition behaviors:
TRN TIME—Transition to RUN after time setting (P5L6) only. Current
is ignored.
TRN I—Transition when starting current drops below setting (P5L5)
only. If the time set in TRNT P5L6 expires before the current transi-
tion, the motor trips.
TRN T+C—Transition on time or current, whichever comes first.
TRN T/C—Transition on time and current. Both must occur, and the
current must drop below the setting before the time delay expires. If
the timer expires before the current falls below the set transition level,
trip the motor.
If there is no transition trip, and the MP-3000 relay declares a suc-
cessful transition, the display and data communications messages
indicate RUN. If P10L1 is set to TRN ON, the AUX 2 output relay
operates its contact when the transition is declared. This contact con-
trols a reduced-voltage starter, switching to full running voltage.
Even if the transition control output contact is not used, set the transi-
tion function to provide clear indications of the actual state of the
motor (START versus RUN) on the front panel display and via data
communications. A good way to do this is to use the settings of P5L7
= TRN T+C and P5L5 = 130% of FLA. Modify the latter, if needed,
to lie at a transition value between the starting current and post-start
maximum load current. Set the transition timer well beyond the nor-
mal start time to avoid a transition trip.
9.2.2 Start Delays
When the MP-3000 declares a START, all start timers of enabled
functions begin to time. Each of these timers blocks the respective
function until the set delay expires. These start timers are affected
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