Harmonic Cancellation Transformer
What is a Harmonic Cancellation or Harmonic Mitigation?
Harmonic cancellation is performed with harmonic canceling transformers also known as phase-shifting transformers. A harmonic canceling transformer is a relatively new power quality product for mitigating harmonic problems in electrical distribution systems. This type of transformer has patented built-in electromagnetic technology designed to remove high neutral current and the most harmful harmonics from the 3rd through 21st. Electronic nonlinear loads as the reason for the generation of harmonics. Nonlinear loads range from the little plug-in power sources to the massive automation equipment in factories. Harmonics slowly erode the electrical environment causing high maintenance, premature failures and fires. It is important that they are addressed.What problems do harmonics create in a electrical distribution system?
- Large load currents in the neutral wires of a 3 phase system. Theoretically the neutral current can be up to the sum of all 3 phases therefore causing overheating of the neutral wires. Since only the phase wires are protected by circuit breakers of fuses, this can result in a potential fire hazard.
- Overheating of standard electrical supply transformers which shortens the life of a transformer and will eventually destroy it. When a transformer fails, the cost of lost productivity during the emergency repair far exceeds the replacement cost of the transformer itself.
- High voltage distortion exceeding IEEE Standard 1100-1992 "Recommended Practice for Powering and Grounding Sensitive Electronic Equipment" and manufacturer’s equipment specifications.
- High current distortion and excessive current draw on branch circuits exceeding IEEE Standard 1100-1992 "Recommended Practice for Powering and Grounding Sensitive Electronic Equipment" and manufacturer’s equipment specifications.
- High neutral-to-ground voltage often greater than 2 volts exceeding IEEE Standard 1100-1992 "Recommended Practice for Powering and Grounding Sensitive Electronic Equipment."
- High voltage and current distortions exceeding IEEE Std. 519-1992 "Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems."
- Poor power factor conditions that result in monthly utility penalty fees for major users (factories, manufacturing, and industrial) with a power factor less than 0.9.
- Resonance that produces over-current surges. In comparison, this is equivalent to continuous audio feedback through a PA system. This results in destroyed capacitors and their fuses and damaged surge suppressors which will cause an electrical system shutdown.
- False tripping of branch circuit breakers.
How do harmonics affect a site or facility?
Voltage distortion and voltage drop as mentioned in above items #3 and #6 cause the equipment connected to the branch circuit to draw more current to maintain the power rating (watts) of the unit. The bigger the current draw from the unit, the more it produces excess heat within the unit that was not factored for by its original design. In turn, the excessive heat causes premature component level failures within the unit. Additionally, you will experience computers locking up and other operational malfunctions that are unexplainable. Think about how many times we have experienced the "no problem found" syndrome with our computers! The excessive heat produced can directly contribute to downtime. Therefore, downtime is identified as any event that incurs or contributes to lost productivity, lost revenues, lost savings, and more importantly lost time. As we all have heard in the business world, "Time is Money".In special facilities such as call centers or data centers, the excessive heat produced due to the large concentration of monitors and PCs will also cost money in energy dollars. The air computer room (CRAC) or building air conditioning system will run longer or harder, therefore requiring more energy to maintain the desired temperature.
Telecommunications cabling is commonly run right next to power cables. If harmonics are above normal tolerances (more than 5% THD) as outlined in IEEE Standard 519-1992, then high frequency harmonics can be induced into phone lines and data cabling. The end result is noisy phone lines and unexplained data lose or data corruption in your LAN or WAN.
Why are harmonics unknown or untreated in electrical distribution systems?
The electrical distribution system of most sites or facilities was never designed to deal with an abundance of non-linear loads. It’s a problem that has only recently begun to be recognized in the building industry. Within the last decade, the widespread use of computers and SMPS equipment is turning modern office buildings, factories, and industrial plants into high-tech computer environments. Even older buildings that are renovated are not retrofitted with modern harmonic treatment or cancellation. The end result is a building or facility unable to fully support today’s technology and the high-tech problems that it brings along with it. Obviously, given the problems harmonics can cause, it is imperative that today’s electrical distribution systems be designed for non-linear electronic loads, not just linear electrical loads. Unfortunately standard building codes and engineering designs do not meet the requirements of today’s technology. With the advent of newer SMPS equipment the harmonic problem will continue to get worse along with inadequate facility grounding.How can we wire electrical distribution systems for harmonics?
These are recommended ways to wire for the harmful effects that harmonics cause. However, these recommendations only keep the electrical distribution systems safe. These wiring recommendations do not eliminate or cancel high levels of harmonics.- Use double-size neutral wires or separate neutrals for each phase.
- Specify a separate full-size insulated ground wire rather than relying on the conduit alone as a return ground path.
- On a branch circuit use an isolated ground wire for sensitive electronic and computer equipment.
- Segregate sensitive electronic and computer loads on separate branch circuits all the way back to the electrical panel.
- Run a separate branch circuit for every 10 Amps of load.
- Install a comprehensive exterior copper ground ring and multiple deep driven ground rods as part of the grounding system to achieve 5 ohms or less resistance to earth ground.
- Oversize phase wires to minimize voltage drop on branch circuits.
- Shorten the distance on branch circuits from the power panel to minimize voltage drop.
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