CHAPTER 5: SETPOINTS PROTECTION ELEMENTS
MM300 MOTOR MANAGEMENT SYSTEM – INSTRUCTION MANUAL 5–51
Fuse failure If one or two of the three phase voltages drops to less than 70% of nominal, and at the
same time any of the three voltages is greater than 85%, either an alarm or a trip and
block start will occur after a one second delay. The 70% threshold allows for the possibility
that the voltage downstream from a blown fuse is pulled up above zero by devices
connected between the open fuse and another phase.
NOTE:
Fuse failure protection is available only when a type IO_B option card (3 × VT) is specified in
the order code.
The following setpoints are available.
VT Fuse Fail
Range: Disabled, Alarm, Trip
Default: Trip
This setpoint selects the fuse failure action.
Sensor protection
Select the Home > Setpoints > Protection > Sensor page to edit the mechanical
protection setpoints.
RTD protection The MM300 can support up to six 100-R RTDs, each of which may be configured to have a
trip temperature and an alarm temperature. The alarm temperature is normally set
slightly greater than normal running temperature, and the trip temperature is normally set
at the insulation rating. Trip voting has been added for extra security in the event of RTD
malfunction. If enabled, a second RTD must also exceed the trip temperature of the RTD
being checked before a trip will be issued. If the RTD is chosen to vote with itself, or OFF, the
voting feature is disabled.
The following table shows the RTD resistance versus temperature. RTDs configured as
stator types are also used by the thermal model for determining the RTD bias.
Table 5-4: RTD temperature vs. resistance
Temperature Resistance (in ohms)
°C °F 100 Pt
–50 –58 80.31
–40 –40 84.27
–30 –22 88.22
–20 –4 92.16
–10 14 96.09
0 32 100.00
10 50 103.90
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