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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 three phase
conductors can pass. The most common ground fault Cts have a ratio of 50:5 or 50:1.
The MP-3000 carries UL 1053, Ground Fault Protective Device listing. 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 setpoints 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).
Obviously, 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,
considering the ct secondary voltage capability; and the total burden of the ct secondary 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.
Residual connection – 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 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 certain higher
harmonics, or other measurement errors producing false residual currents. Monitor the metered
ground current during various loading conditions to insure good margin between these error
currents and the ground fault trip current setting GFT, P3L1. Also, watch out for phase Cts which
saturate during motor starting - the saturation will produce a large residual current and a ground
fault trip. This may be a problem if the Cts have low voltage capability (e.g. C5 or C10), or if
they have long wiring runs or are otherwise heavily burdened.
9.2 Motor Cycle Monitoring
— This
refers to the MP-3000 functions that monitor the motor
during periods 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 supporting data in log books and history records.
The primary function of the MP-3000 is to alarm, and 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 next; and process load
shedding to reduce overload as explained in 9.1.5 above. Others can be programmed by
assigning a particular internal MP-3000 measurement to a contact output with output relay
setpoints.
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
Summary of Contents for 66D2032G01
Page 18: ...Page 18 I L 17562 PR 0 3 Effective 8 99 Figure 4 1 MP 3000 Pushbuttons...
Page 19: ...I L 17562 Page 19 PR 0 3 Effective 8 99 Figure 4 2 MP 3000 LED Indicators...
Page 72: ...Page 72 I L 17562 PR 0 3 Effective 8 99 Figure 6 1 Panel Cutout Dimensions...
Page 73: ...I L 17562 Page 73 PR 0 3 Effective 8 99 Figure 6 2 Faceplate Dimensions...
Page 74: ...Page 74 I L 17562 PR 0 3 Effective 8 99 Figure 6 3 MP 3000 Case Depth Dimensions...
Page 75: ...I L 17562 Page 75 PR 0 3 Effective 8 99 Figure 6 4 Universal RTD Module Mounting Dimensions...
Page 76: ...Page 76 I L 17562 PR 0 3 Effective 8 99 Figure 6 5 Rear Panel Terminals...
Page 78: ...Page 78 I L 17562 PR 0 3 Effective 8 99 Figure 6 7 Typical ac Supply and URTD Wiring...
Page 79: ...I L 17562 Page 79 PR 0 3 Effective 8 99 Figure 6 8 Alternatives for Discrete Input Wiring...
Page 80: ...Page 80 I L 17562 PR 0 3 Effective 8 99 Figure 6 9 RTD Wiring to URTD Module...
Page 100: ...Page 100 I L 17562 PR 0 3 Effective 8 99 Figure 9 1 Rotor Temperature Tracking...
Page 101: ...I L 17562 Page 101 PR 0 3 Effective 8 99 Figure 9 2 Motor Protection Curve...
Page 102: ...Page 102 I L 17562 PR 0 3 Effective 8 99 Figure 9 3 Underload Jam Protection Curve...
Page 104: ...Page 104 I L 17562 PR 0 3 Effective 8 99 Figure 9 5 Motor Protection Curve Example with RTDs...
Page 105: ...I L 17562 Page 105 PR 0 3 Effective 8 99 Figure 9 6 Motor Start and Run Cycles...
Page 109: ...I L 17562 Page 109 PR 0 3 Effective 8 99 P5L8 40 Incomplete Sequence time 1 60s OFF 1 240s...