Prepared for the worst
The Summer of 1998 threatened brownouts. Next time, don’t just hope for the best – be prepared for the worst. Here’s how
BUILDING ELECTRICAL SYSTEMS AND EQUIPMENT NEED TO OPERATE properly with clean, stable power supplied by the electric utility. Variations in this supply can mean system downtime, increased maintenance costs and, in some cases, costly equipment failures. With the widespread use of computers in facilities and the systems used to operate those facilities, it is even more critical that power be reliable. Variations in electrical supply can result in corrupt data, system shutdowns and component failures.
Electric utility systems have grown so reliable we often take them for granted. Aside from the occasional power interruption during spring and summer thunderstorms, or temporary power outages resulting from rare distribution system component failure, utility companies have a high success rate for supplying facilities stable electricity. The interconnection of different utility companies into a nationwide grid has improved system reliability by providing backup capacity for individual utility companies in the event of unusually high demand or system failure.
Despite these safeguards, interconnections and backup systems, electrical systems occasionally experience problems that affect facility professionals. One of the most significant is the electric brownout. Brownouts are periods when the utility is forced to reduce voltage in the lines by 5 percent or more. When demand for electricity exceeds the utility’s ability to supply or purchase it elsewhere, the utility risks the collapse of its generation and distribution network. Since capacity is limited and the utility cannot control the load connected to the system, the only option is to reduce system voltage.
Often the circumstances leading to a utility reducing its distribution voltage are a combination of isolated events that – had each occurred separately — would not have resulted in a brownout. For example, take the events this June in a large section of the Midwest. A record-setting heat wave that lasted nearly a week created an unexpectedly high demand for electricity. One utility serving the area had several units off-line for scheduled maintenance and couldn’t generate at full capacity. Another utility was unable to supply power to the region under an exchange contract. A tornado destroyed several miles of lines of another utility serving the region, further reducing the capacity available.
The combined effect was a situation where electrical demand came very close to exceeding the ability of utilities in the region to supply electricity. Larger customers were notified of the potential for a brownout and asked to reduce their electrical loads. Radio and television stations carried announcements notifying all customers of the potential for a brownout. In the end, a break in the weather, combined with the efforts of customers to reduce their loads, averted the need to reduce system voltages.
STARK REMINDER. Although a
brownout was avoided, this should serve as a reminder that the threat of brownouts is real and must be planned for. While the circumstances that created the near brownout conditions in the Midwest may seem unusual, they are typical of the events leading up to an electrical brownout. And these events occur more frequently than facility professionals may realize. Portions of New England have faced brownouts for a good portion of the summer as the result of record electrical demand levels. Other portions of the country have experienced similar conditions in past summers.
If facility professionals are to deal effectively with electrical brownouts, they must first understand how brownouts affect the operation of their facility, then develop a plan for minimizing the impact.
The impact brownouts have on facility equipment is underrated and misunderstood. Brownouts may seem a minor inconvenience because there is no actual interruption in service. Some loads may have to be cut, but all other building equipment will continue to operate at the reduced voltage with no noticeable negative effects. What some facility professionals fail to realize is that power brownouts can have a serious impact on electrical equipment, leading to damage, decreased life and equipment failures.
There are two types of building equipment particularly susceptible to damage from operating during brownouts: motors and computers.
All NEMA-rated motors are designed to operate at under- and over-voltage conditions of up to 10 percent. This rating leads many to believe that the undervoltage conditions which occur during a brownout will not impact motor operation. But while the NEMA rating assures the motor will operate at reduced voltage, it does not imply the motor will operate at its rated performance at less than nominal voltages.
There are three primary impacts on performance when an electric motor is operated at reduced voltage. Reduced operating voltages reduce the starting torque of the motor. Motors that drive certain loads may not start during brownout conditions. Even if they do, it may take a long time to accelerate the load to normal operating speed. Long acceleration times cause excessive heating in the motor’s windings, damaging the winding’s insulation and resulting in early motor failure.
Reduced operating voltages also reduce the running torque of motors. Motors sized close to the load they are driving may not have sufficient torque to operate at their rated speed, resulting in increased slip and heating of motor windings. Even motors that are oversized for their connected load will operate at higher temperatures as a result of the decreased operating torque.
Reduced operating voltages also increase the operating temperature of the motor’s windings, even when the motor has sufficient torque to start and run the connected load. Increased winding temperatures accelerate the deterioration of the winding’s insulation, shortening its life. For every 10 degree Centigrade rise in the temperature of the windings, the rate of deterioration of the insulation doubles. While the insulation will not immediately break down, it is this slow deterioration over time that contributes to many premature motor failures.
Reduced operating voltages also affect the operation of computer and other electronic equipment. Unless the voltage reduction is large, typically greater than 10 percent, the threat of damage to the equipment itself is small. Regulated and protected power supplies used by the equipment will protect it from damage. The real threat is data corruption. Reduced operating voltage increases the frequency of data errors and system lockups.
For example, when the supply voltage decreases sufficiently, energy management system panels and temperature control systems frequently lock up or assume there has been a power outage and attempt to reset themselves. Both result in HVAC system malfunctions and interruption of services.
REPARING FOR BROWNOUTS.
When a utility is forced into brownout conditions, customers get only a few hours of warning. In most cases, the utility will first notify customers that the potential for a brownout exists. This potential may extend for several days. If conditions do not improve and demand approaches the supply capacity, the brownout will be initiated. If possible, the utility will send out a notice that the brownout is being initiated.
Due to the relatively short notice that accompanies brownouts, the only way facility professionals can prevent damage to motors and sensitive electronic equipment is to have a program in place well in advance of a brownout.
For electric motors, the program must identify motors most likely to be damaged when operated under reduced voltage conditions. These include motors that are heavily loaded, or that must start and accelerate high torque loads. While it would be ideal to survey all motors in the facility, the sheer number makes this nearly impossible. Start the survey with two groups of motors. The first is those with horsepower ratings of 5 and above or those critical to the operation of the facility. The second is those with horsepower ratings of less than 5 or those not critical to facility operations.
With the first group of motors, measure the current draw of each motor to identify those that are heavily loaded. Motors operating at 90 percent or more of their rated load should be considered to be heavily loaded and susceptible to damage from a brownout.
The second group of motors, ones that must start and accelerate high torque loads, are commonly found in building chiller and compressor applications. Measure the current draw of these motors. Those operating at 80 percent of their rated load during normal operation are susceptible to brownout-induced damage.
Develop a list of the motors with the greatest risk of being damaged during a brownout. Identify their size, the load they drive and their location. While turning off all of these motors prior to the start of the brownout is the best protection, not all can be shut down due to the nature of the load they power. Motors have thermal cutoff mechanisms so they shut down before overheating. For the most part, you are at the mercy of built in protection mechanisms such as these.
For motors that can be turned off during a brownout, rank them according to the need to protect them and the ability to turn them off, and assign the responsibility for turning them off to a particular group of workers. Also identify who is responsible for turning the motors back on once the brownout has ended.
Developing a plan for preventing damage to motors during brownouts is straightforward, but developing one for computer-based energy management and temperature control systems is not. In many cases, the control system will continue to operate without problems. In other cases, problems will occur randomly. Two identical computer-based control systems may respond differently to the same brownout conditions. There are, however, steps facility professionals can take to minimize the impact of the brownout.
Work with the manufacturer of the equipment installed in the facility. Determine the tolerances of their system to undervoltage conditions. If their equipment can tolerate undervoltages of 5 percent, most brownouts should pose no problem to the operation of the system. If the equipment cannot tolerate undervoltages of 5 percent, there are two options: shutting down the equipment or protecting it with an uninterruptible power supply (UPS).
Small-scale UPS systems are ideal for protecting critical energy management and building temperature control systems from both brownouts and power interruptions. The systems convert the incoming alternating current to direct current, then back to alternating current. A small battery pack connected to the direct current portion of the UPS maintains constant voltage output to connected equipment during the brownout or power interruption. A side benefit is that they protect the connected equipment by filtering voltage spikes and noise from the power line. Small UPS systems are well-suited for use on both field-installed microprocessors and central energy management computer equipment.
For systems that are not protected by UPS systems and cannot tolerate undervoltage conditions, such as computers and direct digital temperature control systems, develop a plan for protecting the operation of the systems they control. In most cases, this requires switching those systems to manual operation mode – or turning them off altogether, provided the facility can run temporarily without them. Develop a list of equipment and systems that must be switched or turned off. Assign responsibility for implementation to key maintenance groups. Make certain those same groups are responsible for returning those systems to automatic control once the brownout has ended.
HEDDING LOADS. Perhaps the most impotant step in preparing for a brownout is identifying electrical loads that can be shed. When the utility issues a warning of approaching brownout conditions, they will request that customers reduce their electrical loads as much as possible. If loads are reduced sufficiently, as they were in the Midwest this past June, the brownout can be avoided.
Survey the facility for non-critical loads that can be readily disconnected. Lighting systems, HVAC systems, elevators and process equipment all include electrical loads that can be turned off without major disruptions to facility operations. This is not to say, shut these systems down completely. Turning down the lights to reduce loads and shutting down all but one elevator will be inconvenient at worst – but the facility will still be operational.
Identify the loads that can be reduced, and assign responsibility to specific maintenance groups for turning them off and back on again once the brownout conditions have passed.
With careful planning and a little effort, most facilities can minimize the disruption and potential damaged caused by electrical brownouts. With rapid implementation, they may even be able to avoid the brownout altogether.
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Copyright Trade Press Publishing Company Oct 1998
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