GE MM2 Motor Manager Complete Guide

HOT/GOLD CURVE RATIO: defines the ratio of the hot and cold characteristics of a motor. If the known motor stalling time is 7 seconds in the hot state and 10 seconds in the cold state, then the ratio is set to 70%. Automatically calculate the heat capacity utilization rate based on the actual current during operation.

THERMAL CAPACITY ALARM: Provides a warning when the heat capacity exceeds the set percentage (e.g. 80%).

MINIMIZE RESET TIME: When enabled, MM2 will dynamically calculate the allowable reset point after overload tripping based on the heat capacity consumed during the last startup, instead of waiting for complete cooling.

2. Ground fault protection

Ground Fault CT INPUT: Select sensor type (50:0.025 CBCT/5A SEC CBCT/5A RESIDUAL).

ALARM LEVEL/TRIP LEVEL: For 5A CT, set as a percentage of the CT's rated value at one time; For 50:0.025 CT, set the absolute current value (0.1-15.0A).

DELAY ON RUN/ON START: Set the delay for running and starting respectively. The delay during startup can be shorter because the inductive leakage current at the moment of startup may be higher, but if a large grounding current occurs during startup, quick action is required.

3. Under voltage automatic restart (S4: Control)

When the control voltage drops below the threshold (80V threshold for 120V setting; 150V threshold for 240V setting), MM2 will save critical data and enter standby timing. After restoring power supply:

IMMED. RESTART POWER LOSS TIME: If the power outage time is shorter than this value (such as 200ms), restart immediately.

DELAY REST POWER LOSS TIME: If the power outage time is between the above values and this value, delay the REST TIME DELAY before restarting.

If set to UNLIMITED, the restart will always be delayed.

The backup processor is powered by a large capacitor and can continue to operate for about 1 hour, accurately recording the duration of power failure. This feature is crucial for continuous processes that do not allow for prolonged downtime.

4. Starter type (S1: STARTER)

MM2 supports up to 13 starter control logics, including:

FV NON-READING (direct startup)

FV REVERSING

WYE DELTA OPN TRANS (star delta open conversion)

TWO SPEED (Dual Speed)

Inverter (frequency converter)

AUTOTRANS OPN/CLS TRANS (autotransformer open/closed conversion)

SOFT STARTER

DUTY/STANDBY (main and backup motors)

Each type is equipped with corresponding contactor A/B timing, interlock delay, and feedback monitoring. For example, for star delta startup, it is necessary to set CHANGE OVER CURRENT and CHANGE OVER TIME: when the startup current drops below the set value and after a minimum conversion time of 25%, switch from star to delta.

Common troubleshooting and maintenance

Based on extensive on-site experience, the following table summarizes the most common problems and solutions encountered in the use of MM2.

Possible causes and solutions for the fault phenomenon

The motor stops within 1 second after starting and displays "OPEN CON CIRCUIT". Within 1 second after closing the contactor, no feedback signal is received from the auxiliary contact of the contactor (terminals 55/56). ① Check if the auxiliary contacts of the contactor are wired to the corresponding Status input; ② Check if the auxiliary contacts are truly closed after the contactor is engaged (mechanical failure); ③ If a two-wire control is used and the start signal is maintained, the OPEN CON CIRCUIT TRIP function can be enabled to prevent frequent shaking.

The motor status displays' UNAVAILABLE 'and cannot be started. ① There is an unreset trip; ② Stop input (terminal 51) not closed; ③ Process Interlock is configured with Startup Override Delay=0, but the Interlock input is not closed. ① Check A2: TRIP DATA to confirm the reason for the trip, press the RESET button or clear it through remote reset; ② Confirm that the Stop terminal has 120V AC; ③ Check the programmable input status and short-circuit or adjust the delay if necessary.

Communication cannot be established ① The master station protocol is not Modbus RTU; ② Wrong polarity of wiring; ③ Address, baud rate, and checksum do not match; ④ Missing terminal resistors or star shaped wiring. ① Confirm that the main station is using RTU mode; ② Check if all MM2's 39 (+) and 40 (-) are interconnected; ③ Verify the address, baud rate (default 9600), and checksum through S1: Communications; ④ Ensure that the chain path type is daisy chain, with a 120 Ω+1nF terminal network added at both ends.

Grounding fault false tripping/false alarm ① Improper CT selection (50:0.025 CT used in low impedance grounding system); ② The normal leakage current of the system is too high; ③ CT saturation. ① For low impedance grounding systems, use 5A CT residual connection or 5A zero sequence CT; ② Measure the actual leakage current and set the alarm/trip level slightly higher than the normal value; ③ Check if the CT meets the burden requirements of MM2 (see Appendix E).

The reset button is invalid after thermal overload tripping. ① The thermal capacity has not decreased to the allowable reset point; ② The MINIMIZE RESET TIME function requires waiting for cooling; ③ LOCKOUT RESET is not configured or used. ① Check A2: TIME TO RESET in TRIP DATA, wait; ② You can force a reset by configuring a programmable input as LOCKOUT RESET (use with caution); ③ Confirm that the OVERLOAD TRIP RESET in S2 is set to MANUAL or AUTO.