Handbook of Energy Storage for Transmission or ... - W2agz.com

EPRI Proprietary Licensed Material
The company initially focused on energy storage flywheels for telecom applications, and
developed the highest stored-energy, commercially available flywheel products in the
world. Its high-energy telecom flywheel systems are operating in about a dozen field
locations in North America, South Africa and Israel. Beacon recently began marketing
high-power flywheel systems for UPS applications. Beacon is also proposing an
innovative flywheel power station that can deliver megawatts for high-power distributed
generation applications. Beacon offers flywheel technologies over a range of low and
high power, from 2 kW to 250 kW.
For low power, they have a 6-kWh flywheel that delivers up to 2 kW, for a long period of
time–up to 3 hours at full rated load for remote terminal telephone and cable applications,
longer at reduced power. These flywheels are designed for very low power loss (~60 W)
and totally maintenance free operation for 20 years. The system uses a composite rotor
on magnetic bearings, spinning in a patented self-contained vacuum environment and
operating at 22,500 rpm in float. Because of the low power applications, these flywheels
can efficiently deliver power down to approximately 7,000 rpm. The flywheel is
typically installed underground, which minimizes real estate requirements and provides
increased security.
For high power, Beacon offers a 250 kW flywheel that delivers high power for short
duration. This flywheel is designed to economically provide longer run-time than other
available flywheels; up to 25 seconds at 250 kW vs. the typical 12-15 seconds. This type
of flywheel delivers a relatively small amount of energy (e.g. 250 kW for 25 sec is only
1 kWh). The rotor is considerably smaller than the 6 kWh wheel used in the low power,
long duration telecom applications. This family of flywheels operates at a float speed in
the 36,000-rpm range. Depending on the load, the cut-off speed is limited by current
draw through the electronics and ranges between 18,000 and 24,000 rpm.
Hitec Power Protection
Hitec (formerly known as Holec Power Protection) is a Dutch company that has been
manufacturing its Continuous Power Supply (CPS) for over thirty years. Recent versions
of the CPS have incorporated an unusual system using a flywheel within an inductive
coupling to provide bridging power.
The CPS is composed of four parts: a diesel engine, a free-wheel clutch, an induction
coupling, and a synchronous generator. The generator is connected to the AC utility line
in parallel with the load. The clutch disengages the generator from the diesel engine,
allowing the generator to spin, as a motor when utility power is available. The generator
is connected mechanically to the induction coupling, which consists of two concentric
rotors. The outer rotor is directly connected to the generator on one side and to the diesel
engine, via the clutch, on the other, and contains ac and dc windings that couple it to the
freewheeling inner rotor.
When the ac windings are energized the outer rotor, spinning at 1800 rpm, becomes a
two-pole stator as in an induction motor. And this induction acts on the inner rotor,
spinning it up to nearly 5400 rpm, where it acts as a flywheel. When utility power is lost
the dc windings of the other rotor take over and hold the generator shaft at 1800 RPM by
coupling with the inter rotor and controlling the slip as it is decelerating. This provides
enough time for the diesel generator to turn on, come up to speed and pick up the load via
Flywheels Page 18