A30076 — Power unit: thermal overload internal braking resistor alarm

A30076 is the power unit's warning that the energy absorbed by the internal braking resistor has exceeded the alarm threshold of 80 %. The condition matters while the power unit operates in generator mode: if generation continues unchanged, the absorbed energy can climb to the shutdown threshold. To avoid overheating of the braking resistor, the drive inhibits its use and outputs alarm A30077. Depending on how the drive is configured, the same condition can also be output without a reaction. The message value itself tells you how much energy the resistor has absorbed, so you can read the actual load directly from the alarm.

• The energy absorbed by the internal braking resistor has exceeded the alarm threshold of 80 %.
• The power unit is being operated in generator mode; if it keeps operating in generator mode, the absorbed energy can reach the shutdown threshold.

1. Read the alarm value in r2124 (interpret decimal): it shows the energy absorbed by the braking resistor in Ws.
2. Reduce the power when generating.
3. With a DC link coupling, take the generating power of all of the coupled power units into consideration.

• The message value (%1) is the alarm value in r2124; interpret it as a decimal number. It contains the energy absorbed by the braking resistor in Ws.

• r2124 — alarm value of this message: read the energy absorbed by the braking resistor (in Ws) here, interpreting the value as a decimal number.

No acknowledgement is required for this alarm, and the manuals describe no separate reset step. What they call for is an operational change: reduce the power when generating, taking the generating power of all of the coupled power units into account on a DC link coupling. To protect the braking resistor from overheating, its use is inhibited and alarm A30077 is output.