Battling Brownouts, Blackouts
What are the latest advances in uninterruptible power supplies? Has the Northeast outage of last summer resulted in power systems with greater reliability? Professionals on the front line provide answers. Consulting-Specifying Engineer: In the news of late, we've head a lot about dealing with blackouts, but what about brownouts? Specifically, what types of facilities are most prone to these occ...
What are the latest advances in uninterruptible power supplies? Has the Northeast outage of last summer resulted in power systems with greater reliability? Professionals on the front line provide answers.
Consulting-Specifying Engineer : In the news of late, we've head a lot about dealing with blackouts, but what about brownouts? Specifically, what types of facilities are most prone to these occurances and what's the best way to protect against them?
BATTISH : In answer to the first question, facilities and geographic areas that require high power usage, such as data centers, manufacturing plants and metropolitan areas with high power consumption—such as New York, Los Angeles, Chicago, Houston and Boston—are prone to brownouts. Brownouts occur when the utilization equipment requires more power than what is available. Brownouts occur during peak loads, such as hot summer days when equipment is running at full capacity. Brownouts can also occur during cold winter months when electric heating is running on high.
ROBERTS : Traditionally, data-processing and telecom facilities have been recognized as the most vulnerable to utility power disturbances. However, these days, semiconductor wafer fabrication plants rival that level of criticality. In general, any industrial end user with an automated critical process sees an impact when voltage drops in excess of 20% occur. And with increased use of PLCs and motor drives, more power quality problems are occurring.
BATTISH : As far as your second question is concerned, it's hard to design a facility to completely protect against brownouts, because these events are caused by the cumulative effect of multiple buildings. Typically, except for large industrial facilities, an individual building isn't the sole cause of a brownout.
What a design professional can do to address such a situation is to provide standby power. Although brownouts typically last for less than 20 minutes, in severe cases, they may last longer or even become rolling blackouts. Sufficient fuel capacity should be provided for back-up generators for proper protection. Also, the design professional should consider planning for non-critical loads to be shed during the brownout. Equipment intolerant to low-voltage conditions should be shut down or operated by a standby power source.
It is also important to gather historical data on the frequency and duration of brownouts in the area where a facility is to be built so that the end user will be aware of how this problem could affect his or her facility's operation.
CSE : What's the best way to protect against such a problem—UPS?
MOCK : Not necessarily. UPS are designed primarily for dealing with power outages. It's true that brownout protection, to a degree, is inherent in the design of a double-conversion UPS, but it's probably not the most cost-effective solution for just this specific problem. A good line conditioner, for example, will give adequate protection over a wider voltage range and at less cost.
Specifically regarding UPS, a standby or line interactive UPS will probably track the reduction, but a double conversion UPS or a good line conditioner will provide 1% output voltage regulation if the brownout is no greater than 8%.
CSE : Switching gears to blackout concerns, describe some of the recent technological advancements you're seeing in regard to UPS.
BATTISH : From my perspective, the main goal of technological advancements is to provide greater power reliability, as compared to traditional parallel-redundant systems. So one new system I'm interested in uses two or more UPS modules with internal static-switch bypass to parallel with each other, producing redundancy at both the UPS module and the static-switch bypass.
Another advance is the use of front-end IGBT [insulated-gate bipolar transistor] technology with generators.
MACK : This advancement is really about UPS input section. In other words, a change made from a diode/SCR rectifier front end to an IGBT active front end has improved the UPS input power factor to 0.98, reducing the current total harmonic distortion to less than 3%. This allows the UPS to work with a generator on a 1:1 sizing ratio instead of having to follow the traditional sizing rule of thumb that a generator must be 2.5 times larger than the UPS.
MOCK : This is a very positive step, because changes in the design of UPS in recent years, in my opinion, have focused more on inverter or output technology, rather than on the input of the UPS. Most UPS still have some form of single or double full-wave, bridge-style of rectifier with harmonic filters. Their voltage acceptance range is, and has been, +10% to -15%—quite a wide range—and should cover most brownouts, getting back to our original subject. At the input of the UPS, most of the design effort has been toward reduction of harmonic current demand and improving the input power factor over a wider range of loading.
ROBERTS : I'm going to digress somewhat, because I think the biggest single technological advancement that has occurred in the last 10 years is better power quality monitoring. Virtually all electrical switchboards installed today are equipped with sophisticated power monitors that document power quality disturbances. This allows users to correlate events and more accurately pinpoint financial losses caused by power problems. Better data means better decisions as to what type of power quality solution is most cost effective.
CSE : How about in the area of transient voltage surge suppressors?
BATTISH : In the case of TVSS, a hybrid technology of silicon avalanche diodes (SAD) and metal oxide varistors (MOV) are utilized to provide balanced transient protection. SADs operate to correct lower power, and fast transients and MOVs are used for more brute force applications.
CSE : Have you observed any trends in the increase of packaged power systems which incorporate multiple units and/or systems to address power reliability and power quality?
ROBERTS : The concept of packaged power systems is growing as the complexity of solutions increases. Particularly for very large-scale systems, more end-users want a turnkey approach involving total integration of UPS, backup generators and associated switchgear.
MOCK : All vendors have made some efforts at packaging power solutions for customers. Buyouts of related products, OEM relationships and alliances are all part of the effort to be a one-stop shop for the customer. Server farms have driven much of this effort, because they are so power-intensive and critical. Requirements for high levels of protected power availability at the load have driven the industry to integrate UPS, static switches, automatic transfer switches and power distribution modules into a system that will provide protected power to the server farm 24/7, regardless of operating conditions. One vendor, to date, has developed a totally integrated power package that includes not only the power elements, but also monitoring, cooling, racks and cabling.
MACK : The big trend in UPS are vendors pushing the concept of N+1 to the IT/MIS market. But in reality, the UPS MTBF for more than 200,000 hours is very reliable without the N+1 concept.
BATTISH : It's true that there is a surge of pre-packaged units. Typically, these units incorporate generators, UPS, switchgear, TVSS, etc., in a package with the hopes of saving the client real estate and simplifying the construction of a facility.
However, I have not seen many applications of such technology simply because the design of a facility incorporates so many variables. By simplifying the systems into a single package, it's not possible to meet the specific requirements for each client. In addition, most large corporations have specific standards that have been proven to work for them. Therefore, to develop a limited pre-packaged system to address everyone's needs is not feasible.
A pre-packaged system may also encounter resistance from local inspectors. Typically, jurisdictions follow the national codes, but there is always room for interpretation. A pre-packaged system that could be utilized in one part of the country may have to be radically redesigned for another region.
CSE : What differences have you noticed, if any, in the mentality of end users regarding power reliability as a result of the major blackout this past August?
MACK : The main thing that occurred was a wakeup call that made people realize the UPS is only as good as the batteries. This has motivated many people to buy new batteries and to begin having routine UPS and battery PM performed.
ROBERTS : The August blackout in the U.S. and the September blackout in Italy scared a lot of users with critical processes. Since then, there has been a lot of activity in adding backup power to sites with just UPS. In addition, numerous companies are seriously starting to look at adding UPS and backup generators to insure total power protection.
BATTISH : Power reliability concerns escalated in areas affected by the blackout and areas where Hurricane Isabel hit the hardest a month later. For example, an agency we are working with wanted to increase the reserve time for batteries on their UPS systems that serves critical equipment from the industry standard of 20 minutes to one hour.
MOCK : For several years there has been a strong move in the data processing industry toward disaster recovery. I think the blackout will intensify that movement, but the push will be toward complete duplication of facilities, not just an increase in power protection. Apparently, the power blackout raised more awareness of the need for longer protection times, rather than the need for additional protection devices. Generators and bigger batteries will be the beneficiaries of the great blackout.
CSE : In the realm of brownout protection, what do you see evolving over the next couple of years?
MACK : Many users are going to start to look at how low of a brownout their UPS can handle before batteries are discharged. Many UPS switch to battery when the utility voltage drops below minus 15%. In reality, end users should request a UPS that can support a minus 30% drop in utility voltage before switching to battery power, thereby preserving battery life for actual power outages, and not simple brownouts.
ROBERTS : Over the next two to three years, the options will increase. Higher power electronic devices are allowing prices to come down and performance and reliability to increase.
With technological growth in all industries, especially telecom, the market will require a certain level of power quality protection. For example, smaller servers are being deployed that draw a lot more watts in very small packages. Data centers with power densities at or above 200 watts per sq. ft. are a reality. This will definitely change the way power protection is applied to mission-critical facilities.
Rajan Battish , P.E., Senior Electrical Engineer, RTKL Associates, Baltimore
Greg Mack , Business Unit Manager, Toshiba UPS, Houston, Texas
John Mock , Senior Consultant, Powerware, Raleigh, N.C.
Bradford Roberts , Director of Power Quality Systems, S&C Electric Company, Franklin, Wis.
"Brownouts" Falling Out of Use
As a general comment, the term "brownout" is used very little in the power quality community today. The main issues are brief voltage sags, transients, short momentary outages and long-term outages. A brownout is the slow decline of the average voltage due to heavy loading, with the utility allowing the voltage to decline as a way to reduce the overall load. Because this can cause a lot of damage to end-user loads, the condition is rarely allowed to occur in the United States. To deal with such a situation, most utilities would initiate "rolling blackouts" instead of brownouts.