STARTING METHODS FOR GAS TURBINES

Gas turbines are usually started by a DC motor or an air motor. Either system is available for most turbines up to about 20 MW. Occasionally AC motors are used. Beyond 20 MW, when heavy industrial machines tend to be used, it becomes more practical to use air motors or even diesel engine starters. DC motors require a powerful battery system. The DC motor and battery systems tend to be more reliable and less space consuming, which is important for offshore systems. Air motors require air receivers and compressors. The compressors require AC motors or diesel engines. Air start and diesel start systems are more popular for onshore plants especially remote plants, e.g. in the desert. This is partly due to the fact that batteries tend to suffer from poor maintenance in hot, dry locations. Air systems require regular maintenance and must be kept fully charged in readiness for a quick start. Air system receivers can become very large if more than three successive starting attempts are required. More starts can probably be obtained by a battery system that occupies the same physical space.

Occasionally process gas can be used instead of air to drive the air/gas starter motor. This eliminates the need for receivers and compressors. However, there should always be a reliable source of gas available. The exhaust gas from the starter motor should be safely discharged e.g. into a ventilating pipeline.