The Hard Wired Backup System is used to terminate fuel flow, steam flow or electricity to the driver under emergency situations and is independent of the train control system hardware and control logic.

When activated by any of several inputs, the system ensures that critical field devices transition to a safe shutdown position. This includes closing of the fuel and block valves and starting of the emergency lube pumps and any other subsystems required for emergency shutdown operation.

Inputs to the backup system for a typical driver/compressor package, as seen in Figure 1 are as follows:

• Two overspeed switch contacts per shaft.
• One PLC, CPU failure contact as sensed by a watchdog circuit. *
• One train vibration summary shutdown contact. *
• One fuel governor summary shutdown contact. *
• One fire shutdown contact. *
• All ESD shutdown contacts.

Under normal conditions, the hard wired system is energized with all input contacts closed. If any of the inputs listed above opens, the relay will de-energize thus immediately opening contacts in series with the fuel shutoff mechanism to terminate fuel flow, steam flow or electricity to the driver. This action safely shuts down the machinery.

* May be incorporated in the PLC and not require a separate input to the Safety Shutdown System.

During the design of a safety shutdown system, all hazards associated with the mechanical equipment as well as the causes and effects of control and shutdown system failures are identified as they relate to the packaged equipment. The safety shutdown system is then designed to provide the required level of safety and protection necessary to protect personnel, the equipment and the environment.

The Hard Wired Backup System is supplied using Dresser-Rand Control Systems' proven safety standards which have undergone rigorous design qualification and testing.

The relay based safety shutdown system shown in Figure 2 is a hard wired system which is independent of the controlling PLC.

Critical shutdown signals are input directly into the relay based safety shutdown system thus bypassing all programmable devices. This system is supplied in addition to the PLC based control system.

The system is classified as FAIL SAFE due to the fact that there is no programming involved and because all the contacts are energized in the normal operation mode.

In the event of a loss of control power or a loss of the PLC control system, the relay based system is designed to ensure a safe transition to the proper shutdown state.

The system also initiates the operation of lube oil pumps and other subsystems which are required to operate to protect the machinery in a shutdown condition.