Allen-Bradley Flex-I/O PLC.
The SCR Drive Assignment Contactors are fitted in the armature and are actuated by Allen Bradley PLC logic; through Allen Bradley flex I/O located in the SCR drive bay. The flex I/O communicates through a dual loop Profibus configuration to a processor for the first five SCR bays and a second matching configures for the next five SCR bays. The assignment configuration is such that any motor is assignable in three locations with any motor capable of assigning to the first five SCR bay or the second set of five SCR bays.
Each drive can support 4 different motor parameter sets. All the SCR Drives on the Frontier Driller shall be configured accordingly to the motors that they will support.
This architecture offers flexibility and reliability through redundancy in case of SCR drive failure. Should such an event occur the operator simply turns off the motor on the faulted SCR drive and turns back on allowing the PLC to assign to the next available SCR drive. Each motor is assignable to three different SCR drives with a total of twenty (20) SCR drives in the system.
The SCR Drives are controlled from consoles via profibus loop circuit to the dual redundant Logix 5561 CPU Allen Bradley PLC system. Overview of the SCR distribution with SCR PLC.
By use of the dual 5561 Allen Bradley processor (CPU) in the PLC system either processor can fail with no loss of operation. Communications to the drives is done by Profibus loop directly to the Siemens 6RA70 and flex I/0 locate each SCR bay. The flex I/O receives input and from devices outside the drive such as armature contactor feedback, drive cooling fan overload, circuit breaker status and the OFF/DRILL/MARINE selector switch. The flex I/0 receives output commands outside of the 6RA70 control for contactor assignments. The Siemens 6RA70 SCR drive sends and receives data as per the supplied manual, which controls operation of the motor and gathers operating information for logic control. All control signals from SCR to PLC shall be communicated through PROFIBUS DP field bus protocol, with the exception of the Emergency Stops, which shall be hardwired directly to the SCR Drive breaker for safety.
Signals exchanged between an SCR and its respective PLC are the same for each SCR. Apart from standard control/status signals, signals related to assignment and power management need to be exchanged.
This architecture offers flexibility and reliability through redundancy in case of PLC or communication failure. Should such an event occur, the communication cable could with stand one break in any loop and complete failure of either PLC1-A or PLC1-B with no loss of operation.
There is a PROFIBUS DP communication network for each SCR drive to the two PLC racks located in the generator cubicles. Each network is completely independent from the other with communications that are loop and able to be controlled by either CPU. The PLC racks located in the Driller’s Console and in the Mud Pump Console are networked by Ethernet Fiber optic loop to a MOXA module to convert the fiber signal. The two screens in the driller’s console are networked on this same loop with both screens able to display the same screens and status. There are two more MOXA modules connected in the same loop to supply data to the two workstations to enable data collection and trouble shooting of the complete system. There are two more MOXA modules on the same loop connected to PLC3A and PLC3B in the field supply cabinets, which in turn are connected to all the MCC, by Profibus fiber optic loop for control and status of all the required motor starters. Overview of the SCR PLC PROFIBUS DP and Ethernet communication network.
The PROFIBUS DP network in this application is based on 3 different mediums and topologies. A standard bus or line topology network with standard PROFIBUS DP RS-485 cable is established between an SCR PLC and its respective SCR drives. Each SCR is fitted with a CBP2 PROFIBUS communication board. Each one has its own address to differentiate between the various SCR Drives on the network. A redundant optical ring topology is established between all PLC racks via MOXA hub modules to form the Ethernet network. The third communication loop is Profibus fiber optic to all the Hirschmann Hub modules in the MCCs and the same type loop collecting data from the generator controls. MOXA modules and Hirschmann hub modules convert electrical signals to optical signals.
As of July 2007 we have completed the manufacturing portion of this project and have started testing the communications of the 5 remaining SCR Drive bays along with the Generator bays, Driller’s Console, Mud Pump Console & SCADA System. We have already shiped 5 DC drive bays and 1 of the 2 Isolation Switch bays and will ship the remaining equipment after completion of testing and DNV approvals.
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