Although continuous electrical power can be taken for granted in contemporary business life, an unbroken supply cannot always be depended on. This fact is driven home every time there is a major blackout, like the one that occurred in New York City in July of 2006, affecting 174,000 people in the northwest section of Queens. This particular blackout caused estimated business losses of tens of millions of dollars, in addition to the airport and transits delays and cancellations.

An Electric Power Research Institute (EPRI) study on recurring U.S. energy problems found that more than 90 percent of manufacturing facilities will experience utility voltage sags greater than 20 percent from nominal. The study also states there will be more than 30 dips of over 10 percent per year. 2 Adding to the problem is the unpredictable nature of power outages. In the United States there is a significant variation in the number of complete blackouts by region:

 

• Areas with high Kuronic rates (lightning strikes) experience more naturally caused power losses than areas with lower incidences of thunderstorms.

• Industries that are at the end of long feeder routes are at higher risk for outages than facilities that are closely coupled to electrical substations.
• Buildings in older parts of a city or suburb might experience higher failure rates due to equipment aging or poor maintenance.

It was clear that the electrical power infrastructure was in need of upgrades, even before these major blackouts. The complexity of the U.S. grids means that even a small glitch in a local supply station, if not attended to in time, can cause an outage affecting millions of customers. In its Power Delivery Infrastructure Challenge, EPRI states, “The existing radial, electromechanically controlled grid needs to be transformed into an electronically controlled, smart electricity network in order to handle the escalating demands of competitive markets in terms of scale, transactional complexity, anti-power quality…These reliability and power quality limitations already cost the U.S. economy more than $30 billion each year. The upgraded system is not a luxury, nor even an option for the future. Rather, it is imperative to build productivity and ensure global competitiveness in the $8+ trillion U.S. economy.” Unfortunately, the program to update the U.S. electricity delivery system is on a 50-year plan, leaving American businesses with distinct limitations due to the lack of its reliability.

The globalization of the American economy has created a lower tolerance for power delivery problems. Competition with manufacturers around the world has pushed even the smaller production facilities in the U.S. to attempt to increase factory productivity by relying on ever-increasing levels of automation and computerized control of processes, communication and materials flow. Thus, a full array of electronic equipment is now commonplace on the factory floor.

 Unfortunately, most of the computerized tools that enhance competitiveness are vulnerable to the same power quality issues that have threatened more traditional computer applications while being subjected to additional environmental factors — including temperature extremes, high airborne particulate density and more frequent electricity dips and sags. As processes become more precise, and as more and more sensitive electronic equipment is used to control manufacturing machinery, the issue of power quality problems increases.

 What’s at Risk

Some processes cannot tolerate an electrical disturbance without loss of a batch or run of materials. For example, in the semiconductor industry, certain diffusion steps are so critical that an incorrect temperature or loss of a timer can turn an entire production lot into very expensive scrap. Also, in certain serially integrated extrusion processes, power failure results in both a lost batch of finished product and serious equipment damage as machines can become choked with raw material if a heating function fails or a motor controller trips off-line. In many applications, these motor controllers are found in continuously running processes, such as paper mills, where many are used on a single production line. Tripping one adjustable speed drive or nonsequential tripping of the total motor population can cause a huge increase in waste materials and the need for significant human involvement to get the process back in operation. There is more than one approach to alleviating such quality issues.

First, there is a growing trend toward providing multiple sources of electrical power to an entire operation. Electrical feeders from two or more substations might be used, or electricity might be generated locally by engine-generators or cogeneration plants.

In other instances, manufacturers have placed small uninterruptible power supply (UPS) on the controls portion of numerically controlled machines or installed energy storage devices on the DC bus of the motor controllers. Often, diesel generators are used, but they are not always well coordinated with total power needs and are usually put in use only after a plant experiences an unexpected shutdown. Until recently, there was no well designed and integrated solution for the industrial market that would provide reliable protection for any type of equipment and keep the factory running through a power loss.

The Unreliability of Batteries

Contemporary UPS systems provide both power conditioning and a source of temporary electricity for periods when the principal electrical source has been compromised or lost. It is common to include a short-term energy source in or as a part of the UPS system. This source of energy is generally assembled as an in-series string of lead-acid batteries. Unfortunately, these batteries have many undesirable traits, most notably including:

 

• The more they are used, the faster they wear out. A typical lead-acid battery is exhausted after 250 complete discharges. Even though they are typically warranted for 20 years pro rata, they are routinely changed out about every four to five years.
• Lead-acid batteries can be unreliable. Post-seal problems, corrosion and case swelling due to excessive sulphation can all cause leaks, and regardless of maintenance or repeated load testing, there is no way of knowing if an aging battery will survive a full load discharge.

• A significant amount of maintenance is required for lead-acid batteries to come close to the predicted mean time between failure (MTBF). Unfortunately, this stored-energy failure rate (1/MTBF) can be significant because most available UPSs use 10 or more 12-volt batteries in series, causing string failure rate to be multiples of the individual battery failure rate.
• Installation of battery systems can be expensive. Large systems may require spill containment systems, hydrogen monitoring, epoxy acid resistant floor coating, eyewashes and a completely separate battery room. In addition, there are dozens, if not hundreds, of costly copper connections and DC cable runs, as well as separate air conditioning with high air exchange to meet some local, state, and federal codes.
• UPS battery strings must be kept at or near 77 degrees Fahrenheit to balance performance and life expectancy. For every 10 degrees above 77 degrees, this is cut in half. For example, at 87 degrees, a 10-year battery quickly becomes a 5-year battery, and at 97 degrees it becomes a 2.5-year battery. For temperatures below 77 degrees, life expectancy is extended, but expected performance (measured by protection time) drops below required performance levels.

 

There is no question that the benefits of having stored energy on hand in an attempt to ride out a power outage have been proven. However, more traditional battery solutions have many challenges. In fact, a major user of UPS systems analyzed all the service actions on his UPS configuration over an extended period and found that the battery string alone caused over 90 percent of these forced actions.

 Flywheel-based Technology

Some manufacturers have addressed all these problems by eliminating batteries from its UPS. Instead, the company has integrated flywheel-based technology into the system to provide a value optimized power quality solution. An integrated system including a UPS permits support through any power disturbance or outage from sub-cycle to blackouts. The flywheel-based technology supplies energy for all power quality needs, depending on the load profile and the system chosen. For all outages or disturbances beyond that stored energy capacity, the engine-generator is brought on-line and continues to supply electricity through the UPS for as long as there is fuel for the engine. These systems offer protection from transient over-voltages, dips and sags to total power outages — with no time constraints. System benefits include:

 

• A useful service life in excess of 20 years with minimal maintenance.
• The rugged flywheel-based technology eliminates all battery reliability issues.
• Maintenance for a flywheel-based UPS system consists of changing bearings once every 30 months and the cleaning of the permanent air filters quarterly.
• Flywheel-based UPS systems generally take up less space than battery systems, saving valuable space for plant operations.

• Flywheel-based UPS systems are impervious to high cycling or temperatures up to 104 degrees.
• Eliminating batteries from the system does away with environmental and safety issues.
• The additional installation costs associated with lead-acid batteries are avoided with the flywheel-based UPS systems.

 

Battery-free UPS systems are being applied with rapidly growing popularity as the means to assure power reliability and quality in many applications around the world. The investment in a flywheel-based UPS system ensures that critical processes are not interrupted. This technology translates to significant cost savings when critical data loss, damage to manufacturing equipment, loss of product and dropped sales or service calls are at risk. Flywheel-based UPS systems ensure clean, continuous power for your mission critical operations.

For more information on Caterpillar UPS systems, or to find the local Cat dealer nearest you, please visit us on the web at www.cat-electricpower.com or e-mail cat_power@cat.com. For specification sheets, visit http://go.cateps.com/pr.

1. “An Assessment of Distribution System Power Quality,” EPRI, TR 106249, May 1996.

2. “Performance Testing of Flywheel-Based Uninterruptible Power Supply Report,” EPRI, 1004444, July 2002.