February 2013, Vol. 240 No. 2
Features
Power Conditioning, Backup Protection Of Pipeline SCADA Systems In Harsh Environments
The management of complex gas and oil pipeline systems demands constant, reliable system-wide control. Typically this is accomplished with system-wide monitoring and control using sophisticated System Control and Data Acquisition (SCADA) equipment.
The remote sensors, related Programmable Logic Controllers (PLCs) and client software are vital to the reliable supervision of product flow control, pipeline and manifold internal pressures, product measurement, etc. The location of remote SCADA PLCs and sensors are in some of the harshest environments on earth. Many are responsible for the monitoring and control of critical functions requiring absolute reliability.
A reliable source of computer-grade primary and backup power is an essential element to ensuring system reliability. Backup power is essential to maintain monitoring and control functions in addition to assuring the pipeline’s infrastructure and safety. Without the SCADA systems continuous measurement and control, pumps and valves that control pressures within the pipeline and its manifolds could result in increased pressures potentially bursting the pipe causing costly hazmat spills and cleanups.
Moreover, on steep slopes, check valves could remain open during a loss of power to pumps causing damage to pipes and valves on the downhill side. To further compound the problems, SCADA system PLCs are often sensitive to power pollution such as voltage spikes, sags, surges and common mode noise. These problems can result in unreliable PLC operation or failures. The solution to these problems is the addition of an on-line double- conversion uninterruptible power supply (UPS).
Power Protection For Harsh Power Environments
The double-conversion online UPS technology, through its continuous regeneration of new AC power, provides the highest level of power conditioning and protection (figure 1). Online UPS technology is ideal for use as a combination high performance power conditioner and battery backup system.
When used in a controlled temperature environment ranging from 0 degrees C to 40C (32F to 104F), most domestically available online UPSs can meet pipeline usage requirements as most have been tested and approved for operation over this temperature range by a safety agency such as Underwriters Laboratories (UL). However, in remote locations where SCADA monitoring equipment is located, the use of online UPS technology is required. Many remote outdoor installations are situated in harsh power environments where power-sensitive PLCs and online UPSs may be installed inside buildings without any climate control systems, or in protective NEMA-rated enclosures. For example, the outdoor temperature in Phoenix, AZ in the summer can exceed 120F, while the low temperature in Prudhoe Bay, AK can be below -22F (30C). Even though the online UPS is protected from the remaining elements, attempting to use an off-the-shelf UPS in these extreme temperature environments is a poor decision and often results in a UPS failure.
A standard off-the-shelf online UPS having a UL or ETL Listing for operation over a 0C to 40C temperature range typically has been submitted by the manufacturer to a safety agency for an engineering evaluation. As part of the evaluation, a temperature profile is taken of the highest heat-generating components and heatsinks to ensure they do not exceed their maximum temperature ratings while the UPS is operated at the maximum temperature specified by the manufacturer. A UPS incorporates many high power components that can overheat and not only cause the UPS to fail, but present a risk of an internal UPS fire.
The safety agency also reviews the types of circuit board and plastic materials used in construction of the UPS with regards to their temperature ratings and limits. Due to the largest part of the UPS market demand being for products rated for use in temperature-controlled environments, most online UPS manufacturers design their products for operation in the standard 0C to 40C operating environment and submit them to the safety agency for evaluation over the same operational temperature range.
Installing this UPS in a building or NEMA enclosure without proper temperature control in the summer in Arizona would be using the UPS outside safety agency’s product listing status. In many cases, since the UPS was designed for use in a limited temperature environment, internal components that were near their temperature limits when tested could exceed their maximum temperature ratings. This will result in the UPS having a greatly reduced reliability and service life, or an outright failure.
At the higher temperatures of Arizona, plastics used in the UPS construction and battery can become deformed or cracked. The standard UPS battery used is typically not rated for temperatures above 40C to 50C. Further, per the battery manufacturer’s rated 50C temperatures, the battery service life can be severely reduced from five years to a few months.
Battery Weakness
Temperatures below 0C present their own set of unique problems. Due to the electro/chemical design of most Valve Regulated Lead-Acid (VRLA) batteries in temperatures below -20C, depending on the battery design, can impair the batteries’ ability to deliver sufficient current to power the UPS properly. The amount of battery runtime can be reduced to less than 50% of its normal time when operated at 25C.
Below -40C the electrolyte inside electrolytic capacitors used in the circuitry of the UPS can greatly lower the capacitor’s capacitance or even freeze causing capacitors to rupture. This can cause the internal electrolytic capacitors to slowly dry out, resulting in eventual UPS failure.
Below -40C, if not rated for this low temperature, some integrated circuits and optical isolator devices can function improperly causing the UPS to go to an alarm condition until warmed up. Again, a full UPS failure can result. At this low temperature, batteries can also freeze along with the plastics used in their case material becoming brittle and subject to cracking.
As the battery electrolyte freezes it expands the plastic case and can cause the batteries to leak acidic electrolyte inside the UPS when the ambient temperature raises enough to allow the batteries to thaw out. This often renders the UPS unusable, requiring it to be replaced. A standard online UPS having an operational temperature rating of 0C to 40C should not be installed in protected outdoor locations having temperature extremes outside its rated limits, yet it is often attempted.
To meet the demand for wide temperature range UPS and power conversion products, a few manufacturers are designing products specifically to not only survive in these difficult environments, but to provide superior performance while greatly reducing the servicing requirements. The wider-temperature range products may be found in standalone UPS units or prepackaged turnkey systems from the manufacturer that are packaged into NEMA rated enclosures and cabinets. These systems are ready for immediate installation and operation and reduce the associated project engineering costs.
Typical Application
The pipeline starts at the wellhead and is an ideal example of how rugged, wide-temperature power protection equipment is installed and used. New drilling and well reprocessing techniques such as fracking have the potential to revitalize many of the played-out oil and gas wells in this country.
The process involves drilling down an existing well and at a specified depth turning the drill 90 degrees and drilling across the oil deposit. Fluid is pumped down in to the well at very high pressures, about 1,000 pounds per square inch. Since the fluid in the well is under such high pressure, should the utility power be lost to the pump it is imperative that the valve be closed at the wellhead to prevent the fluid from coming back out of the well and causing a very expensive hazardous materials cleanup.
To eliminate this problem, a wide-temperature Uninterruptable Power Supply (UPS) is installed into a NEMA 3R-rated enclosure on site. As the enclosure is located outside, the UPS is subjected to the wide range of temperatures experienced at the specific location. The UPS is used to provide backup power to both the onsite SCADA client system in addition to providing the power to close the wellhead valve.
SCADA Security
Due to the critical nature of gas and oil pipelines there is great concern that the SCADA network may become the target of a terrorist or foreign government attacks. UPS systems pose the threat of providing a potential backdoor into the network, or at a minimum, the remote control of a UPS powering a critical element in the pipeline system.
For instance, a UPS powering a PLC responsible for controlling a key pipeline valve or pump control may be subject to outside sabotage through its unsecured SNMP/HTTP, Telnet, SMTP and other ports on the network Ethernet interface. When connected to the SCADA network using unsecure SNMP/HTTP agents it could compromise a portion or the entire pipeline system. The need for password hashing, data encryption and the ability to turn off or secure unused communications ports is essential to ensuring an adequate level of security. Ethernet-based MODBUS interface is also supported by several manufacturers as most PLCs support direct MODBUS connectivity.
In conclusion, the double conversion online UPS, rated for proper operational temperature ranges, provides the ideal solution to utility power-related problems. It can be used as an active surge protector, battery backup, precision voltage and frequency regulator and if programmable, much more.
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