Improving Power Quality Wichita KS

As industrial automation continues to evolve with the introduction of computer-based control systems, the importance of AC power quality has never been higher. The inclusion of more sensitive electronic equipment in industrial processes demands the delivery of clean and stable power. Even the smallest service or process interruption can have a devastating effect on a company's production and profitability.

Voltage fluctuations and noise are common power disturbances present in any electrical environment that directly affect electronic equipment. These disturbances exist in numerous forms including transients, sags, swells, over voltages, under voltages, harmonics, outages, frequency variations and high frequency noise.

Harmonic distortion has emerged as a significant problem due to the increased use of electronic equipment. Electronic equipment draws current that is not linear to the voltage waveform. This non-linear current can cause high neutral current, overheated neutral conductors, overheated transformers, voltage distortion and breaker tripping. Loads such as solid-state controls for adjustable speed motors, computers and switched mode power supplies are sources of non-linear currents.

Reliable electronic system performance in the industrial environment requires an initial inspection of the wiring and grounding system. Without stable and dependable system wiring, reoccurring electrical problems are inevitable. Once the integrity of the wiring is established, power conditioning products can be effectively applied to protect critical equipment and processes.

Power Conditioning Equipment

Several types of power enhancement devices have been developed over the years to protect equipment from power disturbances. The following devices play a crucial role in developing an effective power quality strategy.

Transient Voltage Surge Suppressors (TVSS) provide the simplest and least expensive way to condition power. These units clamp transient impulses (spikes) to a level that is safe for the electronic load. Employing an entire facility protection strategy will safeguard the electrical system against most transients. Multi-stage protection entails using TVSS at the service entrance, sub-panel and at the point of use. This coordination of devices provides the lowest possible let-through voltage to the equipment.

Filters provide protection against low-voltage high-frequency noises. Filters are designed to pass the fundamental frequency (typically 50 or 60Hz) and reject higher frequency noise such as conducted electromagnetic interference (EMI) and radio frequency interference (RFI). Harmonic current filters prevent the harmonic content of non-linear loads from being fed back into the power source.

Isolation Transformers provide a degree of isolation and filtering. These devices effectively reduce conducted electrical noise by physical separation of the primary and secondary through magnetic isolation. Isolation transformers reduce normal and common mode noises; however, they do not compensate for voltage fluctuations and power outages.

Voltage Regulators correct voltage sags, swells and brownouts. Voltage regulators maintain output voltage at nominal voltage under all but the most severe input voltage variations. Voltage regulators are normally installed where the input voltage fluctuates, but total loss of power is uncommon. There are three basic types of regulators:

• Tap Changers: Designed to adjust for varying input voltages by automatically transferring taps on a power transformer. The main advantage of tap changes over other voltage regulation technology is high efficiency. Other advantages are wide input range, high overload current capability and good noise isolation. Disadvantages are noise created when changing taps and no waveform correction.
• Buck Boost: Utilize similar technology to the tap changers except the transformer is not isolated. Advantages are the units withstand high in-rush currents and have high efficiency. Disadvantages are noise created when changing taps, poor noise isolation and no waveform correction.
• Constant Voltage Transformer (CVT): Also known as ferroresonant transformers. The CVT is a completely static regulator that maintains a nearly constant output voltage during large variations in input voltage. Advantages are superior noise isolation, very precise output voltage and current limiting for overload protection. The lack of moving parts mean the transformer requires little or no maintenance. Disadvantages are large size, audible noise and low efficiency.

Uninterruptible Power Supply (UPS) systems provide protection in the case of a complete power interruption (blackout). They should be applied where down time resulting from any loss of power is unacceptable. UPS systems are designed to provide continuous power to the load in the event of momentary interruptions. They also provide varying degrees of protection from surges, sags, noise or brownouts depending on the technology used. There are three major UPS topologies each providing different levels of protection:

• Off-Line UPS (also called Standby): Low cost solution for small, less critical, stand-alone applications such as programmable logic controllers, personal computers and peripherals. Off-line UPS systems supply the load directly from the electrical utility with a limited conditioning. The unit provides power to the load from the battery during sags, swells and power interruptions. They offer some noise suppression through a filter/surge suppressor module. Advantages of off-line UPS are high efficiency, low cost and high reliability. The main disadvantage is that protection from high and low voltages is limited by the battery capacity. Other disadvantages are poor output voltage regulation and noticeable transfer time. To keep unit cost low, most off-line units utilize step-sine wave outputs when on battery power.
• Line-Interactive UPS: Provides highly effective power conditioning plus battery back-up. These units are ideal in areas where voltage fluctuations are frequent. The defining characteristic of line-interactive models is they can regulate output voltage without depleting the battery. Advantages are good voltage regulation and high efficiency. Disadvantages are noticeable transfer time and difficulty in comparing competing units. The output waveform can be either a sine wave or step-sine wave, depending on the manufacturer and model.
• True On-Line UPS: Provides the highest level of power protection, conditioning and power availability. True on-line technology, also called double conversion is unique in that the power is converted from AC utility to DC for battery charging and to power the inverter. The DC is then converted back to AC to power the critical load. Advantages of the on-line UPS include the elimination of any transfer time and superior protection from voltage fluctuations. Voltage regulation is achieved by continuously regenerating a clean sine wave. Disadvantages are lower efficiency and higher audible noise.

Suzette Albert is Product Marketing Manager for Sola/Hevi-Duty, member of the EGS Electrical Group and specialist in identifying and providing industrial power quality solutions. For more information, visit www.sola-hevi-duty.com