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2.3.3Input Contactor: The Inverter shall have a line contactor to isolate the rectifier in case of a line problem and allow for a smooth transfer/retransfer to and from bypass.

2.3.4Input Transformer:  An input transformer shall be factory installed inside the standard Inverter cabinet. It shall be located in the lower part of the cabinet, with a barrier separating it from the electronics section, to provide isolation between the line and the rectifier/inverter circuit.

2.3.5Rectifier:  A solid state circuit design, converting incoming AC power to regulated DC    bus voltage for the input to the inverter and battery charger.

2.3.6Inverter Heat Sink Assembly:  The inverter shall feature pulse-width modulation (PWM) design utilizing high frequency (15 kHz) switched IGBTs. It shall use a true double conversion system, generating rated AC output from the utility power or the batteries when in back up mode. The unit shall have a heat sink and power IGBT’s assembly for reduced switching noise and maximum reliability. The assembly shall come as a FRU (Field Replaceable Unit) and its design and mounting location shall facilitate easy maintenance. It shall be located on the electronics shelf with direct access when the door is open and should be replaceable using only a screwdriver within 15 minutes.

2.3.7Charger: A separate battery charger circuit shall be provided. It uses the same IGBT’s as in the inverter and provides constant voltage and current limiting control. The battery float voltage is programmable for the applicable kVA and DC bus ratings. Full recharge of the batteries shall be in accordance with UL 924. The battery charger will be part of the Heat Sink Assembly FRU to increase the ease and safety of service. The Heat Sink Assembly FRU will also include the power circuit board, rectifier, inverter, IGBTs and driver subassemblies.

2.3.8Static Bypass:  100% rated, Continuous Duty

The bypass serves as an alternate source of power for the critical load when an input line failure or abnormal condition prevents operation in inverter mode. It consists of a fully rated, continuous duty static switch for high speed transfers and features two back-to-back SCRs to allow make before break transfer. The design shall include a manual bypass switch, protected within the locked cabinet. It shall be accessible only to authorized personnel, allowing the unit to stay in bypass at all times for safe work on the unit. Manual transfer to bypass shall not cause unit trip, nor transfer into battery backup mode. The static switch shall be able to be powered up by an optional separate power source such as a generator or other power supply for dual input capabilities. to Bypass:  Will initiate automatically under the following conditions:        

Critical DC bus voltage out of limits

Low Battery

Over temperature

Inverter problem Transfers to Bypass shall be inhibited for the following conditions:

Bypass voltage out of limits (+/- 10 % of nominal)

Bypass frequency out of limits (+/- 3 Hz)

6005-033 Rev. B                                                        Page 4 of 12

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