GE's Guard III Harmonic Mitigating Transformers Eliminate Damaging Harmonics

Plainville, CT - Invisible intruders wreak havoc for consulting engineers and managers of industrial, commercial and educational facilities. The culprits-harmonics-overheat electrical systems, causing less capacity, more noise and shortened lives for transformers. Guard III Harmonic Mitigating Transformers from GE Consumer & Industrial curb harmonic currents that K-factor transformers do not, reduce transformer heating caused by harmonics and improve upstream power quality, all while maintaining the NEMA TP-1 standard for energy efficiency.

"Harmonics are everywhere," says Bill Forsythe, product manager, GE Consumer & Industrial. "Unlike K-factor transformers, which merely reduce transformer heating due to poor power quality, Guard III transformers from GE help to improve power quality, extend transformer life and reduce premature transformer failure."

Power quality problems increase substantially with the use of sophisticated controls and equipment deployed today in education, healthcare, manufacturing, telecommunication, gaming and commercial settings.

Examples of non-linear loads that produce harmonic currents include electronic lighting and ballasts, electric arc furnaces, electric welding equipment, industrial process controls, medical equipment, adjustable speed drives, personal computers and other office equipment, solid state rectifiers, UPS systems and solid-state elevator controls.

Most North American electrical power operates at a frequency of 60 Hz, sometimes called the fundamental frequency. Harmonics are always at a higher frequency than 60 Hz (2nd harmonic = 120 Hz, 3rd harmonic = 180 Hz). If harmonics are introduced into the electrical system, they can combine with the standard 60 Hz frequency and distort it. The addition of any harmonic will create distortion. Every piece of equipment that converts AC to DC creates some harmonic distortion.

The Guard III Harmonic Mitigating Transformers, which accomplish harmonic mitigation by providing good source impedance and sine wave phase shifting, round out GE's line of power quality product offerings. A Guard I transformer is any GE transformer, other than a K-factor transformer, that incorporates an electrostatic shield. A Guard II transformer incorporates the same electrostatic shield as the Guard I, while featuring components to enhance spike and surge suppression. Guard I, II and III are selected based on the type of building or installation.

Harmonic mitigating transformers (HMTs) come in specific phase shifts of 0, 15, 30 and 45^°. Using a drive installation as an example, phase shifting transformers are useful for configurations where multiple drives can be placed into tow, or 4 groups where the total drive power within each group is about the same. By using 2 groups of drives, 1 group on a 0° phase shift, and the other on a 30° phase shift, it's possible to cancel most of the 5th and 7th harmonics, mimicking a 12-pulse system. The same is true with 15° and 45° phase shift transformers. With 4 groups of drives, placing a group onto each of the four phase shifts will cancel most of the 5th, 7th, 11th and 13th harmonics, mimicking an 18-pulse system. If some of the drives were stopped, there would be less cancellation. The worst-case condition for voltage distortion is when all of the drives are at full load.

Guard III, in addition to eliminating harmonics, provides these benefits:

• Compliant for LEED building specifications;
• Can save energy by reducing losses caused by harmonics;
• Eliminates transformer overheating and high operating temperatures;
• Reduces maintenance and equipment replacement costs;
• May reduce building cooling costs;
• Maintains energy efficiency even when harmonics are present in the electrical system;
• Helps eliminate power quality problems that K-factor transformers do not;
• Meets CAS C22.2 #47, UL 1561, NEMA ST20;
• Meets IEEE C57.110 (harmonic mitigation).

"Failure to address the harmonics issue in sensitive applications could result in transformer overheating, premature failure, building damage or costly downtime," says Forsythe. "It also could damage or reduce the life of electronics, computers and other equipment at the location. Guard I, II and III transformers provide an excellent solution for end users and consultants faced with the growing problem of poor power quality."

SOURCE: GE Consumer & Industrial