F07801 — Drive: Motor overcurrent

F07801 is raised when the drive detects that the motor current has exceeded the permissible motor limit current. The manuals print the limit as: Limit current = 2 x minimum (p0640, 4 x p0305 x p0306) >= 2 x p0305 x p0306. On the S120/S150 with servo drive objects the limit is defined differently: 1.3 x p0323 for a synchronous motor and 1.3 x r0209 for an induction motor. The drive trips with OFF2 — the motor coasts down — and the fault must be acknowledged before the drive will start again.

• The effective current limit is set too low.
• The current controller is not correctly set.
• U/f operation: the up ramp was set too short or the load is too high.
• U/f operation: short-circuit in the motor cable or ground fault.
• U/f operation: the motor current does not match the current of the power unit.
• The drive was switched onto a rotating motor without the flying restart function (p1200).

On the S120/S150 with servo drive objects the list differs in two points: the motor was braked with an excessively high stall torque correction factor, and the motor current is compared against the current of the Motor Module rather than that of the power unit.

1. Check the current limits (p0640). On the S120/S150 with servo drive objects, check p0323 as well.
2. Vector control: check the current controller (p1715, p1717).
3. U/f control: check the current limiting controller (p1340 ... p1346).
4. Increase the up ramp (p1120) or reduce the load. On the S120/S150 with servo drive objects, reduce the stall torque correction factor (p0326) and increase the up ramp (p1318).
5. Check the motor and motor cables for short-circuit and ground fault.
6. Check the motor for the star-delta configuration and rating plate parameterization.
7. Check the power unit and motor combination; on the S120/S150 with servo drive objects, check the Motor Module and motor combination.
8. If the drive was switched onto a rotating motor, choose the flying restart function (p1200).

• p0640 (Current limit) — the first setting to check: its value enters the limit-current formula given above.
• p0305 (Rated motor current) and p0306 (Number of motors connected in parallel) — check the rating-plate parameterization; the limit current is at least 2 x p0305 x p0306.
• p1715 (Current controller P gain) and p1717 (Current controller integral-action time) — check the current controller when the drive runs with vector control.
• p1340 (I_max frequency controller proportional gain) and p1346 (I_max voltage controller integral time) — check the current limiting controller under U/f control.
• p1120 (Ramp-function generator ramp-up time) — increase the up ramp if acceleration is too fast for the load.
• p1318 (U/f control ramp-up/ramp-down time) — the up ramp to increase on the S120/S150 with servo drive objects.
• p1200 (Flying restart operating mode) — choose it so the drive can be switched onto a motor that is still turning.
• p0323 (Maximum motor current) — the synchronous-motor reference of the servo limit current (1.3 x p0323); check it.
• r0209 (Power unit maximum current) — the induction-motor reference of the servo limit current (1.3 x r0209).
• p0326 (Motor stall torque correction factor) — reduce it when the motor was braked with an excessively high factor (servo drive objects).

The drive responds with OFF2: the motor coasts down, and the fault must be acknowledged immediately before the drive will start again. Work through the checks above, then acknowledge the fault and restart the drive.