Maintaining power in remote locations
UPS systems ensure reliable power for oil and gas applications.
This article, originally posted May 1, 2015, was modified on Aug. 8, 2015, adding additional information on wind-power applications, and graphics about service life of UPS, as an “Online Extra” to a Control Engineering August Digital Edition Exclusive.
Although many people think of uninterruptible power supplies (UPSs) as being tucked away in environmentally-controlled environments, some units are designed to protect a variety of environmentally demanding applications that require the UPS to handle broad temperature ranges while maintaining 100% reliability. Double-conversion online UPS technology, through its continuous regeneration of new ac power, provides the highest level of power conditioning and protection. Online UPS technology is ideal for use as a combination high performance power conditioner and battery backup system. When used in a controlled environment, ranging from 0 to 40 C, any domestically available online UPS should meet this temperature requirement as most have been tested and listed for operation beyond this temperature range by a safety agency such as Underwriters Laboratories (UL).
However, UPSs are often needed to operate reliably in locations with -30 to 65 C temperature conditions. One example is providing critical backup power in remote oilfields, gasfields, and pipelines. A UPS is usually installed inside a NEMA-rated enclosure in outdoor locations with little or no thermal conditioning or protection.
In oil and gas applications, the backup power requirement is often essential to provide critical power to SCADA systems and to actuate control valves when there has been a loss of utility power. Product control is essential in this industry.
Uninterruptible power keeps the flow going
Hydrocarbons are under great pressure at the wellhead. To control the flow of oil and gas, a motor operated valve (MOV) is installed at the wellhead and controlled by the SCADA system. The control of the MOV is critical as it must always be secured in a closed position if the SCADA system detects abnormalities at the wellhead site. Due to the remote locations of many wellheads, either local utility or onsite generator power is made available to power the site. Power outages are not uncommon, which could result in the MOV being left in an open state and the flow of hydrocarbons left uncontrolled. The ramifications of an uncontrolled MOV could range from a costly oil spill cleanup to the total loss of the wellhead. To protect against this problem, an industrial high-temperature UPS is typically incorporated into the SCADA system and MOV control.
In addition to MOV control, the SCADA system monitors the wellhead pressure, controls onsite ground water and oil separation, monitors various containment tank levels, and acquires critical data from various site sensors. It continuously communicates the site status in real time to a central monitoring location via a cellular or a wireless transceiver. UPS backup power is essential to keeping the SCADA system communicating during a power outage.
Product control is paramount, in pipeline applications. Remote monitoring and flow control along the entire pipeline is essential to assure a timely product delivery and to prevent damage to the pipeline. Again, the remote monitoring and control is accomplished using a SCADA network. At these locations, reliable backup power is required to facilitate continued remote monitoring and to power valves to put that section of the pipeline into a safe state until utility power returns.
Even if a UPS is installed inside a weather-proof NEMA enclosure, not every UPS is up to the job. The operational temperature specification for the majority of UPS products on the market is stated as 0 to 40 C. Most UPS products have been designed to be used indoors in a temperature-controlled environment. Furthermore, they have undergone safety agency testing throughout the manufacturers’ stated temperature range and have received an ETL or UL listing for use over the stated range.
As part of the safety agency product evaluation, the temperature rating of key electronic components, displays, plastics, circuit-board materials, insulating materials, magnetics, and batteries are verified to remain within their stated temperature specifications while the UPS is operating. As a result, a UPS designed to provide reliable operation in an oilfield must have a strong design.
The majority of UPS products rated under 10 kVA use valve-regulated sealed lead-acid batteries as their source of backup energy. The operational temperature range of a battery used in a UPS having a 0 to 40 C rating should fit into the following ranges for its various functions between the recommended temperature ranges.
- Discharge mode (-15 to 50C)
- Recharge mode (-15 to 40C)
- While being stored (-15 to 40C)
- Battery plastic material (60 C Max)
A typical U.S. oilfield temperature range could be -30 to 60 C, so the manufacturer’s stated operational UPS temperature ranges are not broad enough to provide reliable operation in a -30 to 65 C application. Moreover, the battery manufacturer has received safety agency recognition certification for the battery over same-state temperature ranges.
A wide temperature range UPS suitable for operation in an oilfield will have a minimum operational temperature range of -30 to 60 C (see diagram. This requires the use of batteries having a broader temperature range. These types of batteries are available, but due to their high cost are not typically installed in most commercial UPS products.
For applications that are within the battery’s operational temperature range, note the effects of elevated temperatures on both the battery’s service life and self-discharge rates. Battery manufacturers typically state their expected battery life at 25 C, which is the average temperature for use in a home, office, or computer room. Assuming the battery spends its entire life in the 25 C environment, the expected service life of this type of battery is 5 years. However, if the battery spends its life in a 50 C environment, the service life is reduced to less than 1 year. Heat greatly reduces the life of most batteries due to the acceleration of its internal chemical reactions.
Batteries are but one component in a UPS. Before a UPS can provide long-term, reliable operation when operating in a -30 to 60 C environment, every component used in its manufacturing process must be evaluated to ensure its thermal safe operating area is well within the UPS operational temperature range. The component temperatures must then be verified while the UPS is operating over the entire stated temperature range, while under full- and no-load conditions. Next, reliability testing over the temperature range must be performed to verify the long-term reliability of the UPS.
Depending on the location of the installation, other environmental conditions may have to be addressed by the UPS manufacturer prior to the UPS shipment. When being installed inside a NEMA 3R enclosure, dew point, moisture, salt air contamination, or the ingress of fire ants may require the manufacturer to apply conformal coating to the internal circuit boards and electronic components.
Finally, to ensure product safety, the high temperature UPS should be evaluated by a safety agency, such as UL over the manufacturers’ stated -30 to 60 C operational temperature range and receive a UL Listing mark. UPS products submitted to UL are evaluated against the UL1778 UPS standard. When a UPS is to be installed inside an industrial control panel, the UL1778 listing mark may not be enough. Industrial control panels and all of the equipment installed inside fall under, UL508. A UPS being installed into an industrial control panel should have the additional UL508 listing to prevent code compliance issues.
Advice to engineers
Never use a UPS that is not rated for a high-heat environment or properly prepared to maintain reliability in the environment of its intended installation. If you’re installing a UPS in a harsh environment, always select a UPS that has been designed and has a safety agency listing for operation in the installed environment.
Michael A. Stout is the vice president of engineering for Irwindale, Calif.-based Falcon Electric, Inc. He is an authority in the computer automation, power conversion and UPS industries with nearly two decades of experience in critical power systems. In his current position, Stout specifies and designs new UPS and critical power system products and evaluates emerging technologies.
This additional online text on UPS use for wind turbines and graphics on temperature effects on battery service life, depth of discharge, and trickle life discharge add to what appeared in the Control Engineering August 2015 Digital Edition.
Wind power reliability
UPS can be used to protect the unique and harsh demands of wind turbines. Electronic control systems for wind turbines range from simple control elements to complex state-of-the-art control systems that can operate in rough-weather conditions. Often, six months may go by before scheduled maintenance is conducted on components, which are mounted at the top of a 450-ft tower and are subjected to temperature extremes, lightning strikes, and other hazards. The most important task in wind turbine control is the continuous control of blade pitch and braking during short-term grid failure or utility loss.
This is essential for safe operation, since failure to assure this control can result in mechanical stress of the drive train and its tower, in addition to the possibility of loss of life.
To stop the turbine blades from turning, the angle of every blade (pitch) is adjusted so the edges of the blades are in line with the wind; eliminating the force of wind against the blades decreases rotor speed. Next, brakes are applied to stop and hold the rotor. If the brakes are applied before the rotor speed is below the allowed braking speed, the brakes will be damaged. The precise operation of the turbine’s control system necessitates that backup power be available and in the form of a UPS than can weather the environment. This is crucial as temperatures can reach up to 149 F or down to -22 F.
Original content can be found at Oil and Gas Engineering.