Rockwell Automation 1333 Drive, 3/4-5HP, 230-575V Series D - Manual (Page 110)

Preventive Maintenance and
Troubleshooting Common Drive Problems
Appendix B
B-3
Over Voltage Protection -- OU Displayed
The Reason When DC bus voltage rises above a preset level due to high
incoming line voltage or excessive regenerative energy, this protective
circuit stops transistor operation and annunciates the condition as shown.
Precheck Procedure
1. Check and correct the incoming line voltage. Refer to Chapter 3 ––
Specifications for acceptable voltage levels.
2. An extremely short deceleration time is the primary cause of excessive
regenerative line energy. Setting Parameter 18 to 1 or increasing
Parameter 2 will guard against OU nuisance trips. It may also be
necessary to add the Heavy Duty Dynamic Braking option.
Low Voltage Protection -- LU is Displayed
The Reason When incoming line voltage falls below 90% for 15 ms, this
protective circuit stops transistor operation to guard against incorrect drive
operation.
Precheck Procedure If the momentary power failure is less than 15 ms,
operation is not interrupted. If more than 15 ms, the drive will trip and line
voltage must be restored by cycling power. If automatic restart of the drive
is required, set Parameter 48 to 1 or 2 as detailed in Chapter 5.
Over Temperature Protection -- OH is Displayed
The Reason When heat sink temperature rises above + 50 °
C, this protective
circuit stops transistor operation and annunciates the condition as shown.
Precheck Procedure Check the drive ambient temperature. For 7 1/2-20 HP
(5.5-15 kW) units, check the cooling fan.