A continuous move over the past 10 years toward automation and better enterprise efficiencies has been paying dividends for oil and gas companies. U.S. refineries are running at record levels in response to robust domestic and international demand for motor gasoline and distillate fuel oil. In July, the four-week average of U.S. gross refinery inputs surpassed 18 million barrels per day for the first time on record.
Downstream operators in the U.S. are examining ways to increase their plant utilization rates without having to invest heavily in new equipment. Operations and maintenance (O&M) optimization plays into this environment as well, with refineries finding that new bolt-on applications can help trim unneeded maintenance routines.
Refineries, like many industrial plants, have enormous power requirements and can experience service interruptions caused by power surges or undervoltage conditions (defined as a power drop within 90 percent of peak). Interruptions could also be caused by something internal, like a sudden spike in demand in a particular area of the plant or a temporary problem with a transformer. Even a lightning strike or disconnection from a breaker could wreak havoc on critical applications within the refinery.
Responding to a request from a major operator of oil and gas refineries looking for a better way to handle critical application restarts, ATC Diversified Electronics, a division of Marsh Bellofram and a supplier of isolated switches and alternating relay products, developed a way to reduce downtime caused by minor power outages—undervoltage events—affecting pumps in production areas throughout a plant. The MAR Series motor auto-start relay targets these intermittent power outages and overrides motor switches to keep highly valuable refinery production processes running while reducing O&M inspections.
“At a large refinery, the process may include various pumps tied to the distillation process circulating to crackers,” ATC’s refinery customer says. “When there’s a temporary power interruption, O&M staff moves into the plant to determine the process flow situation and actions required due to the interruption.”
Refineries rely on a complex series of pumps to move crude through the refining process. With hundreds of pumps at a single refinery, the task of restarting all those pumps manually after every small power blip is a daunting one. And ATC’s customer was experiencing about 12 of these brief power outages—lasting milliseconds to seconds—a year. Besides downtime, the interruptions can mean work in process (WIP) is lost, or a product becomes unfinished or discarded. “The resulting downtime of these small power failures and pulling O&M resources off their assigned task to restart pump motors cost close to $1 million in one calendar year—approximately $83,000 for each instance,” the refiner says.
Enter the auto-start relay system that recognizes very narrow parameters determined by the refiner to actuate the motor starter when an undervoltage occurrence arises. It also provides a staggered restart option to avoid thermal overload conditions for restarting multiple motors.
“The relay series fits into an existing control cabinet with the starter and connects to the start/stop control circuit,” says Phil Storey, national sales manager of ATC Diversified Electronics. “The relay becomes part of that control circuit of that specific pump or motor.”
The auto-start relays can address various undervoltage delay range requirements, and all ATC models are specifically designed for a power interruption period of no greater than 4, 6 or 10 seconds in duration.
When control voltage drops below the undervoltage trip point while the motor is running, the undervoltage delay begins. If the control voltage returns above the restart voltage point before the delay expires, the relay recognizes that power is back, and the adjustable restart delay begins. To restart the motor, the relay in the control circuit bypasses the start switch and goes directly to the motor starter coil.
ATC added an overload neutral disconnect feature to the relay series in the event a thermal overload relay sensed a high-current or high-temperature condition. This would result in a subsequent closure of the circuit via the overload relay and would not cause an automatic restart.
This relay can also distinguish between control voltage failures and stop pushbutton operations. A stop pushbutton operation de-energizes the output relay and terminates the timing sequences to prevent an automatic restart.
Since ATC developed this specific terminal relay more than a year ago, several refineries have implemented the device, with refineries ranging in size from 50,000 to 250,000 barrels per day. But the company has discovered that it has potential beyond refineries as well. “Any industry that has a production process with critical components is a candidate, as long as the process is not in a hazardous area and doesn’t have permissive circuits,” Storey says.
