Input Phase Loss

What does PHF mean?

This fault occurs when one or more phases of the incoming power supply to the drive are lost or are significantly unbalanced, typically detected when the drive is under load. Potential causes include blown input fuses, incorrect wiring (e.g., 3-phase drive on a single-phase supply), or an unbalanced line. Operating with input phase loss can damage the drive's input rectifier and lead to erratic performance.

• Blown fuse or tripped circuit breaker on one or more incoming power phases (L1, L2, L3) supplying the drive.
• Loose electrical connection at the main disconnect switch, input reactor, or the drive's input terminals (R, S, T).
• Significant voltage unbalance (e.g., >2%) or loss of a phase from the utility power supply.
• Internal failure of the drive's input rectifier bridge, preventing proper conversion of AC to DC power.
• Intermittent contact in an upstream power switching device (e.g., contactor) causing a momentary phase loss.

Click steps to track your progress.

1. 1

   1. Measure the incoming line voltages (L1-L2, L2-L3, L3-L1) at the drive input terminals (R, S, T) using a true RMS multimeter. Verify they are balanced within 2%.

2. 2

   2. Inspect and test all fuses or circuit breakers in the main power supply path to the drive. Replace any blown fuses or reset tripped breakers.

3. 3

   3. Check the tightness of all input power connections at the main disconnect switch, input line reactor (if present), and the drive's input terminals (R, S, T).

4. 4

   4. Monitor the DC bus voltage at the +DC and -DC terminals while the drive is attempting to operate (should stabilize at nominal DC bus voltage, e.g., 560VDC for 400V input).

5. 5

   5. If voltage unbalance persists, contact the utility provider to investigate potential grid supply issues at the facility.