The Case for Redundant SCADA Communications
In mission critical Industrial applications such as Oil and Gas Production & Pipelines there is often the need for Redundant SCADA Communication.
When SCADA Communications fail, operations cannot continue to operate unmanned due to safety or environmental concerns. Sometimes sites are configured to shutdown if there is extended SCADA Communications outage for these reasons. Custody transfer measurement data may be lost if there is extended SCADA communications outage.
In these cases there is need to repair communications within a set time frame.
Redundant SCADA Communications can help prevent unwanted shutdowns and emergency repair situations.
Master Stations/Repeater Sites
Many SCADA Systems have Point to Multipoint Communications where multiple sites in a network are accessed from a single Master Site, via Master Station Directly or Via Repeater Systems. If the Master Station or Repeaters Systems Fail, multiple or all Remote site communications fail.
The first level of Redundancy to be considered would be redundancy of the Master or Repeater Site since failure at these sites will impact all sites.
Redundancy at Critical or High Value Remote Sites
Remote sites with high environmental impact such as high H2S levels sites or block valve/leak detectdion sites protecting rivers/lakes may required redundancy. Sites with high production rates often a candidate for redundant communication.
Difficult to Access Sites
Sites that are difficult to access may need rendundacy communications. These sites may be helicopter, skidoo, argo or ice road accessible only; or very far away.
Repeater Sites are commonly hard to access since they may be located on top of mountains or hills making for difficult access during heavy snow or rain conditions.
Equipment Redundancy
Communication Systems can fail due to equipment failures including the Communication Device (Radiomodem/Transceiver), the Antenna Systems, or the Power System. Repair of the systems involves identifying the problem and replacing the failed component.
Redundant Equipment can be implemented as cold standby or hot standby.
Cold standby may be spare equipment that is left at site to be changed out when there is a failure. Equipment should be preconfigured and tested.
Hot standby redundancy involves having that equipment that can be immediately switched on or our automatically switched on when communications failure is detected. Hot standby requires logic to detect communication failure. This could be ping type mechanisms in IP SCADA Communications networks to detection of serial communications in serial based SCADA Communications. Hot standby requires also mechanism to turn transceivers on/off approriately and to connect antenna systems to operating transmitter.
Typically hot standby equipment are fit for purpose systems designed for this purpose. An example of Equipment designed for hot standby are the Master Stations by GE MDS – GE MDS SD4. This equipment is provides for for manual or automatic failover.
Hot standby systems should be configured and periodically tested to ensure availability when required. Cold standby should only be used if the operating company has trained technicians on staff to ensure that repair can be made in a timely manner.
RF Path Redundancy
RF Path Redundancy can be used to to protect against RF Fade or Interference; and/or Carrier Outage (Cellular, Satellite). RF Path Redundancy can be SCADA Host Controlled, or via Network Controlled. SCADA Host Redundancy relies on the SCADA host application to control connectivity. Path is Network Controlled when Router Fail-Over is used.
The SCADALink SatConnect provides RF Path Redundancy by using Cellular and Starlink Satellite Links.
