Engineers at Kinetic Traction Systems Inc. in Chatsworth, Calif., (www.kinetictraction.com) are developing flywheels to store energy recouped from braking trains. The flywheels can also store energy that can be used to stabilize voltage levels in areas prone to low-voltage sag. In both cases, the flywheels would be mounted beside the tracks. To capture energy from braking, the flywheels would also be located near train stations where trains would be braking. Being near train stations would also let the flywheels off- load stored energy to trains as they pull away, a time when they can use the energy boost. The devices can deliver more than 1,150 charge-discharge cycles per day for 20 years with minimal maintenance.
The company's flywheel was first developed by Urenco Power Technologies. When that company closed, Kinetics Traction Systems purchased the technology, which they improved and updated. But basically, the device has three major components, including a main cylinder that houses the flywheel, a permanent magnet, brushless, dc motor generator, and a separate power electronics module that feeds power into the flywheel or can be used to take power out of the flywheel. The flywheel consists of a composite rotor running on magnetic and hydrodynamic bearings. A vacuum cooling subsystem cools the flywheel motor.
The flywheel would capture and store the energy normally wasted to resistor banks during braking, thus cutting energy use by eliminating unnecessary resistor heat production and HVAC demands to remove that excess heat.
The normal operating speed range of the flywheel is from 430 to 630 Hz (25,800 to 37,800 rpm). Usable energy is approximately 6 MJ or 1.7 kWh. On the input side, the minimum under-voltage threshold is 450 Vdc and the minimum charging current is 5 A dc. Average standby power consumption is less than 400 W. The device operates in temperatures from 32° to 104°F.
Some of the older Urenco flywheels are still in operation, including several at a wind farm run by Fuji Electric. All units used for railways have been decommissioned. Engineers at Kinetics Traction System are working to increase the energy-storage capacity of the flywheel while management pursues prospects to place units with mass transit agencies.
Kinetic Traction Systems Inc.
Chatsworth, Calif., www.kinetictraction.com