Influence of fluid selection on synchronous generators power output in compressed air energy storage systems

The use of intermittent sources of energy in modern power grids makes frequency support more challenging. In case of contingent events, fast instantaneous reserve systems should be employed in order to restore the frequency. One of the promising solutions is the use of rapidly accelerated synchronous generators with hydraulic drive-trains. They are driven by energy from compressed gas in pneumo-hydraulic accumulators. To reduce the cost of recharging, nitrogen which is used in these accumulators, can be replaced with air. However, this has the potential to create a dangerous flammable mix of air and mineral oil within the accumulator. This paper investigates the effects of replacing mineral oil with a water-glycol blend in a hydraulic drive-train coupled to a 100 kW, 415 V, 3-phase synchronous generator. We find that water-glycol blends represent a useful approach to reduce the risk of an explosion at facilities where electro- hydraulic drive-trains are employed.