Transmittal of generator prepurchase specifications, March 1998

NYC 9/11 Public Portal Document

PPS-Generators

A data keypad type operator interface shall be provided to enter the above data^nto the system's PLC. This unit shall also be usable as a field monitoring device for the PLC's I/O. The unit shall not be capable of changing any user values unless a keyswitdi located at the PLC enables its use.

m. Master PLC Redundancy

1) Total System control unit shall contain a master PLC (Programmable Logic Controller). PLC shall be capable of controlling the entire Emergency Power System, including engine generators and controllable loads, for all operations

2) The total system PLC shall have a redundant PLC and they shall back each other up. Each PLC shall have a central processing unit (CPU) each PLC shall share the intelligent input/output (I/O) system that monitors/controls all necessary functions of the system. The I/O shall communicate over a twisted pair to and from the CPU at 153.6Kbaud. Both CPUs shall have identical programs, read inputs and shall solve their algorithms simultaneously. However, the primary and intelligent I/O system will only update its output per the primary CPU's command, the primary and secondary CPU's shall be arbitrarily assigned such that if the I/O system does not sense an update from the primary CPU the I/O system will temporarily hold the current state of the outputs. If after three communications scans, approximately 20 ms, the primary PLC is not recognized, the I/O shall transfer control over to the secondary CPU. the I/O system shall then update it's outputs accordingly.

3) In this application, since both programs are identical there will be a "bumpless" transfer between CPU's. When the primary CPU has been restored, and is communicating correctly, the I/O system shall reverse the process to transfer control back to the primary CPU.

n. Provide a manual override panel to allow an operator to a manually load add/shed the loads in the event of a master PLC failure, or loss of the master cubicle 2 and V DC power supply.

OEM PPS-35 Generators 7 WTC March 20, 1998

NYC-WTC_000166910