Powerware 9395 UPS 10001100 kVA - Manuel (Page 108)

UNDERSTANDING UPS OPERATION
EATON Powerware ® 9395 UPS (1000–1100 kVA) Installation and Operation Manual S 164201764 Rev 1 www.powerware.com 6−4
The internal bypass is comprised of a solid−state, silicon−controlled rectifier (SCR)
static switch (SSW), a motorized wraparound bypass breaker CB4, and a backfeed
protection contactor K5. The static switch is rated as a momentary−duty device that is
used instantaneously anytime the inverter is unable to support the applied load. The
static switch is wired in series with the backfeed protection contactor, and CB4 is
wired in parallel with this combination. Together they are wired in parallel with the
rectifier and inverter.
The static switch, being an electronically−controlled device, can be turned on
immediately to pick up the load from the inverter while bypass breaker CB4 closes
and inverter output contactor K3 opens to isolate the inverter. When breaker CB4
closes, the static switch stops conducting. The backfeed protection contactor is
normally always closed, ready to support the static switch unless the bypass input
source becomes unavailable.
If the UPS transfers to Bypass mode from Normal mode due to any reason other than
operator intervention, the UPS automatically attempts to transfer back to Normal
mode (up to three times within a ten minute period). The fourth transfer locks the
critical load to the bypass source and requires operator intervention to transfer.
Static
Switch
K5
Rectifier Inverter
K1 K3
Battery
Converter
Battery
Battery
Breaker
Main Power Flow
Trickle Current
Energized
De−Energized
Closed
Open
Breakers Contactors
K2
Bypass Input
Rectifier
Input
Output
Bypass
Breaker
(CB4)
Input
Breaker
(CB1
Figure 6-3. Path of Current Through the UPS in Bypass Mode
6.2.4 Battery Mode
The UPS automatically transfers to Battery mode if a utility power outage occurs, or if
the utility power does not conform to specified parameters. In Battery mode, the
battery provides emergency DC power that the inverter converts to AC power.
Figure 6-4 shows the path of electrical power through the UPS system when
operating in Battery mode.