ITS Designs & Implements a Siemens PCS7 Control System Based on PCS7 Architecture for National Grid

National Grid’s Churchover site currently receives gas from the North only. This gas is compressed and piped off the station for delivery to Wales and the South West via the National Transmission System. National Grid is installing new facilities to enable the supply of natural gas from the Milford area of Wales to the National Transmission System.

The Challenge

AMEC won the overall contract to install the gas compressor unit, new gas metering and new multi-junction valves including upgrades to the Fire & Gas, Station Protection and Station Control Systems to support the new bi directional flow of natural gas. AMEC awarded Industrial Technology Systems Ltd (ITS), a Siemens solution provider, a contract to design, configure, implement and test the PLC and SCADA hardware and software for the Siemens PCS7 control system based on Siemens PCS7 architecture.

The new control solution, designed by ITS’ engineers, is fully dual redundant and consists of the Fire & Gas, Station Protection and Station Control Systems. The solution consists of two Siemens PCS7 servers, three Siemens dual redundant PCS7 controllers on a fault tolerant industrial ethernet network, two operator stations, dual redundant I/O and power supplies.

The Result

The Fire & Gas System is required to monitor all air spaces where a fire or accumulation of a potentially flammable gas may occur, to detect any hazardous events, to alert personnel and initiate timely executive actions in order to minimise the consequences of an event. Connected to a number of detectors, the Fire & Gas System interfaces with the Station Protection System to initiate the automatic shutdown of the plant should a hazardous event occur. The system monitors and collects Fire & Gas activity data such as flame, gas, rate of rise of temperature, and smoke detectors, and provides the facility to expand this data into a Management Information System for reporting purposes.

The new Station Protection System will shut down the gas compressors in the event of a hazardous situation being detected by the F&G system. It will continue to operate independently regardless of failures of any individual compressors. The purpose of the protection system is to place the plant into a safe condition when the potential exists for an event to escalate into a catastrophic incident. The main hazard associated with gas compression facilities is loss of containment of the gas following a consequential explosion. The Station Protection System will act as a defence against such an occurrence as a gas escape, by disposing of the gas inventory contained within the equipment via the control system.

The Station Control System provides control and monitoring of the process gas flow between upstream and downstream stations, such that the operation of the whole station is controlled in a safe manner. The Station Control System also has executive control over the gas compressors and an interface with existing control systems, flow computers and a telemetry system.

The Safety Integrity Level required for each function in the plant control, shut down and control systems was assessed, designed and implemented in accordance with SIL 2, IEC 61508 and 61511 principles.