Page 158 - Power Quality in Electrical Systems

140 Chapter Nine

speed slows to 70 percent and that the flywheel generator and converter
efficiency is 0.90, the calculated flywheel stored energy must be 6.3 kWh
at full speed.
Applications. Applications of flywheels include the following:

■ No-break engine-generator set with flywheel and clutch [9.15]. The fly-
wheel provides energy to the generator when the utility source fails,
until the engine starts and reaches operating speed.
■ AC UPS, which delivers AC power to the load when the utility source
fails, as shown by Lawrence in Figure 9.10 [9.15].
■ Battery substitute in UPS, as shown by Takashi in Figure 9.11 [9.16].
■ Support medium voltage distribution network, as described by
Richard against voltage sags and interruptions [9.17].

Profactors primarily comparing flywheels to batteries include the
following:

■ Maintenance-free, bearings might need service in three to five years
[9.18]. Bearing-free flywheels utilizing magnetic levitation have
been built.
■ Long life—for example, three times that of batteries [9.16].
■ Can provide typically 15 s of power for engine, or turbine-generator
start [9.18].
■ Short recharge time; depends on power available—for example, for
one-tenth the discharge power, approximately 20 times the discharge
time [9.19].
■ Smaller footprint than batteries [9.19].

Utility 480 V AC Protected
supply load
Static
switch
Inverter

Low speed
flywheel

Figure 9.10 Block diagram of flywheel UPS with static switch,
inverter [9.15].
[© 2003, IEEE, reprinted with permission]