Page 162 - Power Quality in Electrical Systems

144 Chapter Nine

NTWED

Figure 9.14 External appearance of 4.5-kW fuel cell UPS [9.23].
[© 2000, IEEE, reprinted with permission]

Ultracapacitors
Ultracapacitors can substitute for batteries in low-power UPS. Their fea-
tures include

■ Construction: These capacitors utilize electrodes of highly porous
carbon to achieve large values of capacitance per unit weight. Zorpetta
2
quotes surface area of 1500 m /g; a typical electrode of 250 g would
2
have an area of 375,000 m [9.25].
■ Ratings: Maxwell Technologies offers ultracapacitors ranging from
5 to 10 F to cylindrical 2700 F, rated 2.5 V DC per cell [9.26]. Storage
amounts to 3 or 4 Wh/kg [9.25].
■ Applications: One manufacturer offers UPS modules rated 1.6 and
2.3 kW, replacing batteries, employing 2300 F of ultracapacitors [9.27].
M. L. Perry describes a 5-kW fuel cell standby power unit in which
three banks of ultracapacitors provide the energy while the fuel cells