Page 151 - Power Quality in Electrical Systems

Uninterruptible Power Supplies 133

ML
Alternate
line
Thyristor
switch

Line Rectifier Inverter M G To load
MI MG set
contactors

Battery

(b)
Figure 9.2b MG UPS with load-commutated inverter and battery [9.1].

Types of UPS Equipment
Commercially available UPS equipment can be categorized into the fol-
lowing types, depending upon the manufacturer and the application.
■ Output Ratings
■ Power: 1 kVA single-phase to 1000 kVA three-phase per module
■ Voltage: 120 V single-phase to 208 V/120 V or 480 V three-phase
■ Design
■ Double: Conversion or Delta
■ Inverter: Power transistors, IGBTs. Pulse-width modulated with
output filter
■ Battery Charger: Input rectifier or separate charger
■ By-pass Circuit: Thyristors or IGBTs
■ Maintenance By-pass: Circuit breaker
■ Energy Storage
■ Batteries: Flooded, VLRA (value regulated lead acid)
■ Flywheels
■ Fuel cells
■ Typical Run Time
■ Batteries: 5 to 20 minutes at full load
■ Flywheels: 15 seconds, enough time to start E/G set
■ Fuel cells: 8 hours