Power Problems and Voltage Regulator Technologies
Power quality problems come in all sorts of shapes and
sizes. They cost you any where from a couple hundred dollars to upwards of a million
dollars depending on the size and type of problem you have. Commonly, power problems are
defined as spikes, surges, sags, brownouts, outages, and harmonics. In the business world,
they are defined as burned-out motors, erroneous motion of robotics, lost data on volatile
memory, destruction of hard drives, unnecessary downtime, and increased maintenance costs.
Voltage Regulators are simple, cost-effective ways to deal with many of these problems,
which this article will introduce.
One thing needs to be stated from the start, the term "utility power problems" is a term used to classify power problems because AC power comes from the utility companies. Actually, a very small percentage of the power problems you experience are the fault of the utility company. In the United States, the power that is supplied from the utility lines to your facility is some of the cleanest power in the world. Facilities only begin to experience power problems once the power is used inside their building.
Before we get to the solution of power problems, we must first understand the five major power problems and what causes them. The most common type of power problem is Electrical Noise or Transients. These disturbances are high frequency voltage spikes, typically in the micro-second range. Electrical Noise or Transients are magnified by poor grounding of plant equipment and caused by arcing, lightning hits, or use of certain types of equipment such as welders, elevators, copiers, etc..
The next major power problem is a fluctuating voltage situation. Fluctuating voltages can also be termed voltage sags or surges. These type of disturbances are short-term under or over voltage conditions that can last from one cycle to several cycles. This occurs when motors start-up suddenly drawing current from the line, lightning strikes, fault clearing, and from power factor switching.
Brownouts are another of the major power problems. Brownouts happen less frequently than transients or fluctuating voltage, but are much more noticeable when they occur. Brownouts seem to be popular on those hot and muggy days in the dead of summer when everybody has their air conditioner turned as high as it will go. Brownouts are defined as longer term under voltage conditions lasting from several seconds to several hours, depending on the cause. This type of disturbance can typically be measured with a standard digital or analog voltmeter. They are caused by faults, large changes in the load (air conditioners), long-term regulation problems, utility grid overload, or your particular position within the power grid.
With the increasing use of non-linear loads (PCs, variable frequency drives, industrial DC power supplies, etc.) comes the very real problem of harmonics. If your load is attached to the utility and distorts the input line currents as all non-linear loads do, high frequency or harmonic currents are generated. These harmonic currents travel along the surface of conductors, cutting down the cross-sectional area and therefore, effectively increasing the resistance of the conductor. Because the resistance has gone up, the power dissipated in the conductor goes up. The net effect is a fire hazard, because conductors are not sized for harmonic currents. The main culprits for this deadly power problem are switch mode power supplies (which are installed in virtually every computer), variable speed equipment, and other non-linear power supplies.
The last main power problem is out of the scope of this article but bears mentioning and that is Blackouts or Power Outages. Power Outages are a total interruption of electrical power. These problems are solved by additional means other than voltage regulators. The causes of power outages are overloads, faults, storms, internal or external power distribution failure, or something as unfortunate as a squirrel getting caught in a transformer.
The effects of these electrical anomalies can be devastating to a company's production facility. An example of the havoc power problems can play on a plant can be seen through this recent incident:
A Division of one of the Big 3 Auto Makers in Saginaw, MI faced a power disturbance that plagued the company for many years. The plant, which manufactures automobile rear disk rotors, experienced numerous explained and unexplained power problems that caused an average of 4 to 12 hours of downtime a month, and required the services of three electricians per incident to fix the problem. Although plant management tried numerous solutions and a variety of products, they couldn't pin down the problem. The division called in local manufacture of power quality equipment and found among other things a lack of regulated voltage. After installing a system that included both surge suppression and line voltage regulation, the electrical problems ceased. Plant management estimated that the Division saved $750,000 over a three-year period after the system was installed. Because of it's success, these systems were installed on all new CNC equipment and other critical plant electronic components.
As is pretty evident, power problems lead to serious problems in a production facility. These problems surface as erroneous motion of robotics, equipment failure and ultimately lost production. To find out how critical it is for your particular plant to have the maximum level of uptime, facilities managers have to ask themselves a few questions:
Because the answer in terms of dollars to these questions are usually significant, the ROI for a power protection system such as a voltage regulator is the first time it prevents downtime.
Now that the problems and effects are evident what can we do about them? There are a few different types of solutions for these electrical anomalies, but voltage regulators are the most popular. Voltage regulators come in three forms: Tap-Switching, Ferroresonant, and Electronic. Each type of voltage regulator has its own characteristics and is better suited for differing applications.
The first voltage regulator we will discuss is the Tap-Switching Voltage Regulator with a multi-shielding transformer. The Tap-Switching voltage regulator regulates line voltage by automatically switching taps on the isolation transformer. This solves the fluctuating voltage, sag and surge problems. It also removes transients, noise, high frequency impulses with multi-shieldeding and output filtering.
The advantages of using a Tap-Switching system is high efficiency rating, fast correction time (1.0 cycles typical), and the ability to package larger KVA rated systems into a relatively small enclosure. Although it addresses a large number of power problems, it can be an expensive solution for single phase and lower KVA rated applications. It also does not address harmonic currents, except for the third harmonic when using a Delta-Wye three phase system.
The best utilization of the Tap-Switching Voltage Regulator are industrial or commercial applications that are three phase or need larger KVA sizes. This is to take advantage of the Tap-Switcher's ability to pack a large KVA size into a smaller footprint.
Ferroresonant Voltage Regulators have been around a long time because they operate very simply. The Ferroresonant regulates line voltage by operating in the saturation region of the transformer design. A large change in input voltage will produce negligible change in output voltage. Virtually any waveform input (square, trapezoid, etc.) will produce a true sine wave on the output. The Ferroresonant voltage regulator also can ride out a short term (up to 1 cycle) power outage because of the stored energy from saturation in the magnetic field and capacitor.
The Ferroresonant system is unmatched in power conditioning and filtering of line noise and transients. The increased physical displacement between the primary and secondary windings virtually eliminates noise pollution from the output. Because of it's simple design (no moving parts), the Ferroresonant Voltage Regulator has the highest MTBF of the three voltage regulator technologies. Another advantage of the Ferroresonant is that it attenuates both line and load generated harmonic currents. Disadvantages the Ferroresonant system faces are that it is 5-7% less efficient than the Tap-Switching Voltage Regulator and is somewhat heavier with a larger footprint than either of the other technologies.
The Ferroresonant system is popular to use under single phase conditions because of it's cost effectiveness and overall high level of power protection. It is used in industrial settings, commonly protecting PLCs and critical instrumentation in overall bad power environments. The Ferroresonant is also popular in medical applications due to low leakage current to ground.
The final system to discuss is the Electronic Voltage Regulator. The Electronic system is often used in conjunction with a transformer to offer protection for all power problems excluding power outages. The Electronic system regulates line voltage to within very close tolerances of ± 1% by utilizing an add and subtract winding driven a precision electronic control system. This eliminates fluctuating voltages, as well as, sags and surges.
The biggest advantage of the Electronic Voltage Regulator is that it offers the tightest regulation (± 1%) of all three technologies. This system can also deliver 1000% fault clearing current to downstream breakers. The user can easily raise or lower the output voltage by ± 10% by adjusting a control potentiometer.
The Electronic Voltage Regulator has it's disadvantages as well. It is physically larger and heavier than the Tap-Switcher, and doesn't have the same degree of power conditioning as the Ferroresonant. The correction time of the Electronic system (typically 3-5 cycles) is somewhat slower than the Tap-Switching unit.
The Electronic Voltage Regulator is almost exclusively used
in industrial settings. It is best used with motor loads and other high inrush devices.
The Electronic system is also a good alternate bypass source of industrial grade UPS