Overcurrent trip during constant speed

Was bedeutet E.OC2 ?

This overcurrent trip occurs during constant speed operation when the inverter output current reaches or exceeds approximately 230% of its rated current. It often signals a sudden increase in load, an ongoing overload condition, or an electrical fault during steady-state operation. The inverter trips to prevent damage.

• Sudden increase in mechanical load on the motor (e.g., material jam, sudden impact load) exceeding the motor's and inverter's continuous current capability.
• Motor operating at a frequency or voltage that causes it to exceed its continuous current rating for the given load.
• Damaged or improperly sized motor (Pr. 3, Pr. 5) for the application's continuous operational load, leading to sustained high current.
• Intermittent short circuit between motor phases or a phase-to-ground fault occurring during operation in the motor or motor cable.
• Inverter control loop instability (e.g., poor tuning of gain parameters like Pr. 120 (Current control gain)) causing current oscillations at constant speed.

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1. 1

   1. Monitor the actual output current (e.g., using inverter's monitor function or an external clamp meter on output terminals U, V, W) and the mechanical load at the moment of trip to identify the specific event causing the current surge.

2. 2

   2. Verify that the motor's rated current (Pr. 3) and capacity (Pr. 5) in the inverter parameters match the motor's nameplate data. Ensure the inverter is correctly sized for the motor and application's peak loads.

3. 3

   3. Inspect the driven machinery for any potential for sudden load changes or intermittent jamming conditions. Clear any obstructions or adjust process parameters to prevent overload.

4. 4

   4. With power disconnected and DC bus discharged, perform a Megger test (insulation resistance test) on the motor windings (U, V, W to ground, and U-V, V-W, W-U) and motor cable to detect insulation breakdown.

5. 5

   5. If field-oriented control (FOC) is used, consider slightly decreasing current control gain (e.g., Pr. 120 (Current control gain)) to improve stability, but monitor for sluggish response.

6. 6

   6. Check for loose or corroded connections on the motor terminals (U, V, W) and in the motor junction box which can increase resistance and lead to localized heating and current spikes.