Quite often, the indications of motor problems are similar to those of a defect in the frequency converter itself. To determine whether the problem is internal or

external to the frequency converter, disconnect the motor from the frequency converter output terminals. If the three voltage measurements are balanced, the

frequency converter is functioning correctly. The problem therefore is external to the frequency converter.

If the voltage measurements are not balanced, the frequency converter is malfunctioning. This typically means that one or more output IGBT is not switching on

and off correctly. This can be a result of a defective IGBT or gate signal from the gate drive card.

5.2 Internal Frequency Converter Problems

The vast majority of problems related to failed frequency converter power components can be identified by performing a visual inspection and the static tests as

described in the test section. There are, however, a number of possible problems that must be diagnosed in a different manner. The following discusses many of

the most common of these problems.

5.2.1 Overtemperature Faults

Overtemperature faults in the drive are typically the result of blocked airflow or a faulty cooling fan. The overtemperature alarm message displayed indicates

where the fault exists.

Alarm 244, Heatsink Overtemperature. This normally indicates a heatsink fan not functioning. While an overtemperature alarm message is displayed, all cooling

fans should be operating at full speed. Check the fans prior to resetting the drive to determine the fault location.

Alarm 247, Power Card Overtemperature. This normally indicates that the ambient temperature inside the drive enclosure is too high. Check all air passages to

ensure that nothing is obstructing the air flow. Also check the filters for the door fans and clean or replace if necessary.

With either of these alarms, the report value in the Alarm Log displays which module experienced the overtemperature condition.

5.2.2 Open (Blown) Fuses

Open (Blown) Fuses

The drive contains fuses protecting internal circuits from excessive damage in the event of a component failure. It must be emphasized that an open fuse is an

indication of a problem in that circuit. Do not replace an open fuse and apply power to the drive without checking for short circuits or component failures. See

the following descriptions for details.

Mains Input Fuses

An open mains input fuse typically indicates that there is a shorted power component in either the rectifier or inverter circuits. Perform the static test procedures

to locate the failed component(s).

Soft Charge Fuses

Each soft charge card contains three fuses which are in series with the AC input to the card. This AC input powers the soft charge circuit. It also connects to the

power card in each inverter module to supply power for the fans.

An open soft charge fuse can indicate a short in either the soft charge rectifier or the fan transformer supplied by that soft charge card. To locate the source of

the problem, perform the static test procedure for the soft charge rectifier and the fan continuity test.

Fan Fuse

The fan fuse on each inverter module protects the fan circuitry from excessive damage in the event of a failure in the heatsink or door fans. Perform the fan

continuity test to determine the location of the defective fan.

DC Supply Fuse

The DC bus connection to each power card contains a fuse in the positive DC lead. This is to protect the logic circuitry from damage should a fault occur in the

SMPS circuitry. It is not recommended to replace an open DC supply fuse without checking and possibly replacing the power card in that module.

DC Bus Fuses

The DC bus connection to each inverter module is fused to prevent excessive damage due to a shorted IGBT in the inverter section. Typically, an open fuse indicates

a shorted or failed IGBT in the module.

Note, however, that an IGBT fault may fail the DC bus fuses in adjacent inverter modules due to the quick discharging of the DC capacitors through the shorted

IGBT. Perform a static test on all inverter modules if one or more of these fuses are found to be open.

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