UNDERSTANDING UPS OPERATION
The emergency bypass consists of a momentary−duty static switch, a wraparound bypass breaker, and a backfeed protection contactor K5. The bypass breaker is located in parallel with the static switch. The backfeed protection contactor is located in series with the static switch. Bypass breaker CB4 is used for manual transfers to bypass without using the static switch. The static switch is armed and ready during both types of transfers.
On an UPS configured as an Input Output Module (IOM), bypass circuitry is not installed. This configuration is primarily used in multiple UPS parallel systems that do not need a bypass for each UPS and use a separate System Bypass Module (SBM) to provide system bypass capabilities.
6.2Single UPS
A single UPS operates independently to support an applied load from the inverter, providing conditioned and uninterruptible AC power to the critical load from the output of the module. During an outage, the inverter continues to operate, supporting power to the load from the battery supply. If the unit requires service, applied loads are transferred to the internal bypass, continuous−duty static switch either automatically or manually. With the exception of a battery cabinet, no other cabinets or equipment are required for the single UPS to successfully support its applied loads.
6.2.1Modes
The Powerware 9395 UPS supports a critical load in three different modes of operation:
SIn Normal mode, the critical load is supplied by the inverter, which derives its power from rectified utility AC power. In this mode, the battery charger also provides charging current for the battery, if needed.
SIn Bypass mode, the critical load is directly supported by utility power.
SIn Battery mode, the battery provides DC power, which maintains inverter operation. The battery supports the critical load.
The UPS can automatically use all three modes, as required. The following paragraphs describe the differences in the three UPS operating modes, using block diagrams to show the power flow during each mode of operation.
6.2.2Normal Mode
Figure 6-2 shows the path of electrical power through the UPS system when the UPS is operating in Normal mode.
During normal UPS operation, power for the system is derived from a utility input source through the rectifier input contactor K1. The front panel displays indicating the incoming power is within voltage and frequency acceptance windows. Three−phase AC input power is converted to DC using IGBT devices to produce a regulated DC voltage to the inverter. When contactor K2 is closed the battery is charged directly from the regulated rectifier output through a buck or boost DC converter, depending on the system voltage and the size of the battery string attached to the unit.
The battery converter derives its input from the regulated DC output of the rectifier and provides either a boosted or bucked regulated DC voltage charge current to the battery. The battery is always connected to the UPS and ready to support the inverter should the utility input become unavailable.
6−2 | EATON Powerware® 9395 UPS |
