In today’s competitive industrial environment, maximization of operations is essential, and companies cannot risk system malfunction or potential failure due to power disruptions. The end result can be disastrous, ending in loss of production, profits, clientele, and ultimately, complete operational failure. This makes the quality of power of vital importance. Consequently, heavy duty applications require power filtering and maximum protection and should only utilize surge suppression with the highest caliber of reliability and performance standards. Besides essential quality, engineered placement of these Surge Protection Devices (SPDs) is equally critical to the protection solution.
LIGHTNING & TRANSIENTS VS. ELECTRONICS
Dating before Benjamin Franklin’s famous kite experiment in 1752, lightning has long been a devastating natural adversary to human invention. Around the world there are 100 lightning strikes per second (or 8,640,000 times per day), and lightning incurs billions of dollars worth of combined electronic and property damage. However, it should be noted that these strikes are only a fraction of the constant threats facing electronic equipment, as around 80% of the spikes and surges in a facility’s electrical systems are internally generated. Operations such as the turning on and off of loads, rotating of motors, and transformer switching are often the main causes of internally generated transients. Lightning induced or internally generated transients are known to cause electronic equipment failure. Additional organizational costs can include: business operational downtime, replacement equipment delivery time, maintenance repairs, electrical repairs, etc. Power filtering and power protection is best accomplished when proper quality Surge Protection Devices (SPDs) are applied utilizing the cascade protection approach. Much like how the quality of water improves with multi-layering filtering techniques, power quality is enhanced with a cascaded application of transient filtering devices on an industrial process control system. An example of the cascade protection design approach, which is often preferred in industrial settings, is illustrated in the following article.
CASCADING CASE STUDY
Boscan oil field is located in Maracaibo City, Venezuela and operated by Chevron. In an area confirmed by NASA to be one of intense isokeraunic activity, Boscan’s operations were experiencing continuous system downtime after repeated lightning storms. With the majority of Boscan wells pumping heavy crude oil and using several different processes, the Variable Speed Drives that feed the electro-submersible pumps were found to be those with the highest levels of vulnerability. After a lightning storm, many of these drives failed due to damage to the electronic boards.
In this comprehensive case study, the cascade protection method was chosen to monitor 60 wells at the Boscan field. The purpose of selecting this particular method was to decrease system downtime while providing critical yet cost-sensitive protection of the most susceptible electronic components within the drive cabinet. The cascade protection approach proved to be the most effective and provided a more secure and stable electrical environment where a single SPD device was determined to be insufficient. An explanation of the cascade protection approach and an illustration of how to best implement this methodology is provided below.
PROTECTION OF DRIVERS
The use of various types of drives to control motors is very common. The purpose of the drive is to increase the efficiency or to manage the speed of the motor being controlled. Through various processes and control mechanisms, the drive often reshapes the sinewave to provide a signal to the motor that allows for greater efficiency or varies the frequency of the signal to control the speed of the motor. Applying SPDs to a drive system mitigates the damage that can occur due to voltage surges.
Figure 1 illustrates a typical drive layout. Often, the incoming voltage is 480V, but other voltages may be used. The incoming power is usually stepped down to a lower voltage that provides power to the control circuit. The control circuit contains sensitive electronics. Once the power is acted upon by the drive, the output is fed to the motor. There are five opportunities for protecting the typical drive system, each of which are labeled in Figure 1 with a circled number and are described below.
1. Drive input.
Protecting the drive input is an essential step in protecting the drive system. Providing protection at this location prevents surge damage due to events propagated on the electrical system from upstream sources, external events such as lightning and switching surges created by the electric utility, and the interaction of multiple drives on the same system.
At this location, a parallel connected, voltage responsive circuitry device is appropriate (one without frequency responsive circuitry). Frequency responsive circuitry is not recommended for this location due to the fact that this location is typically more susceptible to switching induced transients as opposed to frequency transients. This environment is classified as IEEE Category C where the exposure of transients is greatest. ANSI/UL 1449 3rd Edition Type 1 SPD is recommended for this location.
2. Inverter input.
The inverter input is one of the extremely sensitive and critical areas of the drive itself. It is at this location that care must be taken and the proper power quality analysis be conducted. You may install a parallel connected, frequency responsive circuitry device provided you have confirmation that within this drive no additional capacitors have been installed to mitigate harmonic currents.
If they have, then at this location, a parallel connected, voltage responsive circuitry device is appropriate (one without frequency responsive circuitry). This environment is labeled as IEEE Category B where there are both switching induced transients and frequency transients. ANSI/UL 1449 3rd Edition Type II SPD is recommended at this position.
3. Control circuit.
The control circuit is the most sensitive and can be damaged by even small voltage frequency transients. Protection at this location is essential. A series connected SPD with frequency responsive circuitry is recommended for this location. Filtering capabilities of series mounted devices is extremely good providing low let-through voltage. This location is categorized as IEEE Category A where there are maximum levels of exposure to frequency transients. ANSI/UL 1449 3rd Edition Type III SPD is recommended at this site.
4. Drive output.
Protecting the immediate drive output is recommended when the length of the connection between the drive and the motor is longer than 50 ft (15m) or if the connection is routed along an external wall or outdoors. One reason for protecting at the immediate output when the length of the connection to the motor is long is due to reflected waves that can occur as the signal (often higher frequency) from the output of the drive reaches the motor and is then reflected back and forth between the drive and the motor. This action can create “voltage piling” — the reflected voltage adds to the nominal voltage and other reflected waves. The SPD will aid in reducing the voltage peaks of the reflected waves.
More importantly, if the connection between the drive and the motor extends outdoors, along a path that is exposed to the environment or close to the building’s steel structure, protection at this location is important to diminish the effects of direct lightning or induced voltage surges due to nearby lightning. These surges can cause damage to the drive, even if protection is provided at the motor input. This location is similar to the drive input when the exposure of transients is compared.
At this location, a parallel connected, voltage responsive circuitry device is appropriate (one without frequency responsive circuitry). IEEE classifies this environment as Category C where there are the highest levels of switching induced transients. Here, ANSI/UL 1449 3rd Edition Type 1 SPD is recommended.
5. Motor input.
Protecting the motor input is an essential step in protecting the drive system and the motor itself. Providing protection at this location prevents surge damage due to events propagated from the drive output to the motor input. Providing protection at this location aids in extending the life of the motor as the SPD helps to prevent damage to the windings and bearings of the motor due to surges.
The environment at the motor input can be classified as IEEE Category C if the motor is located 50 feet from the drive output. If less, the environment can be classified as IEEE Category B. ANSI/UL 1449 3rd Edition Type 1 or Type II SPD would be recommended.
CONCLUSION
Sophisticated and highly susceptible microprocessor based electronics and data communication networks are integrated across every sector of today’s fast-paced business world. Preserving these mission-critical systems from the damages of surges, spikes, and transients ensures that these systems are protected from equipment destruction, disruption in service, and from costly downtime.
REFERENCES
1. Bustamante, F., Biternas, J., Borjas, J., Viloria, L, Edwards, J., and Chavez, J. (August 2006). Cascade Protection with Transient Voltage Surge Suppressors (TVSS) in Variable Speed Drive for Electro-Submergible Pumps. IEEE Explore Digital Library. Retrieved March 25, 2010 from http://ieeexplore.ieee.org/search/freesrchabstract.jsp?tp=&arnumber=4104519&queryText%3DCascade+Protection+with+Transient+Voltage+Surge+Suppressors+.LB.TVSS.RB.
+in+Variable+Speed+Drive+for+ElectroSubmergible+Pumps%26opened
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2. IEEE Power Engineering Society (2002). IEEE Guide on the Surge Environment in Low-Voltage (1000 V and Less) AC Power Circuits (IEEE Std. C62.41.1-2002). New York, NY.
3. IEEE Power Engineering Society (2002). IEEE Recommended Practices on Characterization of Surges in Low-Voltage (1000 V and Less) AC Power Circuits (IEEE Std. C62.41.2-2002). New York, NY.
4. IEEE Power Engineering Society (2002). IEEE Recommended Practice on Surge Testing for Equipment Connected to Low-Voltage (1000 V and Less) AC Power Circuits (IEEE Std. C62.45-2002). New York, NY.
5. IEEE Power Systems Engineering Committee (2005). IEEE Recommended Practice for Powering and Grounding Electronic Equipment (IEEE Std. 1100-2005). New York, NY.
6. Underwriters Laboratories Inc. (2006). UL Standard for Safety for Surge Protective Devices, UL 1449 Third Edition. Northbrook, IL.
Harshul Gupta, Vice President of Engineering MSEE & Six Sigma GB, Alltec Corporation, Asheville, NC
