What are the detailed electrical, thermal, mechanical, and environmental factors that can lead to IGBT thermal runaway in Siemens SINAMICS drives (such as G120, G130, G150, S110, S120, and MV series), and how do issues related to switching frequency, carrier modulation, overcurrent conditions, inadequate cooling, heatsink contamination, thermal interface degradation, DC link instability, load imbalance, harmonics, poor ventilation, or incorrect drive parameter configuration contribute to progressive junction temperature rise that ultimately results in IGBT overstress or failure?
IGBT thermal runaway in SINAMICS drives happens when the IGBT becomes hotter than it can cool down. This usually happens because of too much switching, high carrier frequency, or running the drive with heavy load for a long time.
The most common reason is bad cooling — blocked airflow, dust on the heatsink, slow or weak fans, or old/dry thermal paste that stops heat from moving out.
When the temperature goes up too fast, the SINAMICS drive tries to protect itself by lowering output or derating. But if cooling is very bad or the motor is too big for the drive, the heat rises faster than the drive can control.
This causes thermal runaway and the drive gives an over-temperature fault and shuts down.
To avoid this, keep the drive clean, make sure air can flow properly, use the right motor size, and set the drive parameters correctly.
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