APC Bypass Static User Manual download pdf (Page 10)

Page 10 10/05/09

1A/1B auxiliary contacts. The circuit breakers shall be equipped as part of a line-up-and-match

type battery enclosure.

B. Maintenance Bypass Cabinet (MBC):

1. The MBC shall provide power to the critical load bus from the bypass source, during times

where maintenance or service of the UPS is required. The MBC shall provide a mechanical

means of complete isolation of the UPS from the electrical wiring of the installation. The MBC

shall be constructed in a freestanding or wall-mounted NEMA 1 enclosure unless otherwise

stated in this Section.

2. As a minimum, the MBC shall contain the following features and accessories:

a. Circuit breakers of the appropriate size and withstand rating (maximum 25 kAIC rating), for

the system.

b. Minimum 1A/1B auxiliary contacts for the purpose of relaying status information of the

maintenance bypass circuit switch to the UPS.

3. The MBC shall be available in a minimum of two distinct types:

a. Wall-mount, three-breaker, NEMA 1 enclosure.

b. Line-up-and-match style enclosure. This option shall have pre-formed knock-outs for

purposes of top or bottom fed distribution. It shall be available as a standard cabinet, or

shall come equipped with a 42 pole distribution panel, or shall be equipped with an input

isolation transformer.

4. The MBC shall carry a UL 1778 agency listing.

C. Input Transformer Cabinet (XFM): The input transformer cabinet shall provide isolation or voltage

transformation for rectifier input and DC bus for ungrounded DC systems. The input isolation

transformers shall be housed in a line-up-and-match type enclosure.

D. Parallel Operation:

1. General: For purposes of load-sharing, the UPS shall contain, as a standard feature, the

ability to parallel up to four modules for either increased capacity, redundancy, or both. In this

mode of operation the output voltage, output frequency, output phase angle, and output

impedance of each module shall operate in uniformity to ensure correct load-sharing. This

control function shall not require any additional footprint and shall be an integral function of

each UPS.

2. Network: Communication between modules shall be connected in a multi-drop bus network

comprising of two parallel redundant buses so that the removal of any single cable shall not

jeopardize the integrity of the parallel communication bus.

3. Synchronization Bus: One UPS module shall operate as the master. The master unit shall

transmit a signal directly derived from its own phase lock loop (PLL) circuit as the sync clock

reference to the slave units to ensure effective synchronization of modules. In the event that

the master unit fails, the first slave unit to receive logic power shall assume the role as master.

4. Load-Sharing: A load-sharing circuit shall be incorporated into the parallel control

communications to ensure that under no load conditions, no circulating current exists between

modules. This feature shall also allow each UPS to share equal amounts of the total critical

load bus. A UPS module's influence over load-sharing shall be inhibited in any mode where

the UPS inverter is not supporting its output bus. Load-sharing communications shall be

galvanically isolated for purposes fault tolerance between UPS modules.

E. Parallel System Maintenance Bypass Cabinet (PSMBC):

1. The PSMBC shall provide power to the critical load bus from the bypass source, during times

where maintenance or service of the UPS modules is required. The PSMBC shall provide a

mechanical means of complete isolation of the UPS module from the electrical wiring of the

installation.

2. As a minimum, the PSMBC shall contain the following features and accessories:

a. Circuit breakers of the appropriate size and withstand rating (maximum 25 kAIC rating), for

the system and each UPS module.

Minimum 1A/1B auxiliary contacts for the purpose of relaying status information of all

PSMBC circuit breakers to the UPS.

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APC Bypass Static User Manual Page 10

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