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December 12, 2016

We are pleased to announce that Power Equipment Sales has been named as the exclusive Sales Representative Firm for Harmonics Limited Inc. in New England.

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September 19, 2016

Harmonics Limited featured in High-Profile Magazine

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Core Technology

TransMax vs Zig-Zag Transformers

It has been suggested that  TransMax® Harmonic Suppression Systems (HSS®), using Blockade™ Technology, can be replaced with a Harmonic Mitigating Transformers (HMT). (Harmonic mitigating transformers come under many trade names. Whatever the name, these transformers are all basically zig-zag transformers that have a very low secondary impedance to zero sequence harmonic currents.) The HMTs are claimed to be equivalent to the HSS. Outlined in the following are numerous reasons why HMTs are not equivalent and should be rejected.

1. Harmonic cancellation:
a. The HSS operates by blocking the flow of 3rd harmonic current in the neutral wire. This prevents the flow of harmonic currents in both phase and neutral wires from the transformer out to the furthest outlet. The 3rd harmonic currents are never formed in the system.
b. The HMT operates by canceling the 3rd harmonic current in a specially wound zig-zag secondary winding. This prevents the harmonic current from circulating in the transformer delta primary winding, but has no effect on the phase and neutral currents flowing in the electrical system down stream of the transformer. The 3rd harmonic currents flow in every phase and neutral wire, every circuit breaker, , and to every outlet in the system. These currents are mitigated only within the transformer itself.

2. Special wiring
a. Since 3rd harmonic currents never exist in an electrical system using the HSS, there is no need to increase wire size, double neutral wires, or run an individual neutral wire for each phase wire.
b. The HMT permits 3rd harmonic current flow throughout the electrical system and double or individual neutral wires are recommended. The transformer is constructed with double lugs for the neutral wire.

3. Increased useable capacity
a. The HSS, by removing 3rd harmonic currents from the entire electrical system reduces the rms current throughout the system. Since the system is rms-current limited, use of the HSS results in increased useable system capacity. (More electrical loads can be connected without overloading the system.)
b. Since the HMT permits the continued flow of 3rd harmonic currents, its use provides no increase in the number of loads that can be connected.

4. Lower heat production
a. With the 3rd harmonic currents removed from the entire electrical system, the I2R losses due to high harmonic current flow in wires, switchgear and transformers are lowered. Transformer temperatures are reduced. (Transformer temperature reduction of as much as 39°C has been observed in the field.)
b. Since the HMT does not prevent 3rd harmonic current flow throughout the electrical system, and removes these currents only within the transformer windings, I2R losses are high and transformer operating temperatures are high.

5. Transformer impedance
a. The standard transformer used with the HSS has an impedance of 4% to 6%. In a refereed paper1 presented at the International Conference on Harmonics and Quality Power (ICHQPS) conference this September, it is shown that the lower the impedance of a transformer serving harmonic-producing loads, the higher the harmonic currents flowing in the system.
b. The HMT has an extremely low (0.95% to the 3rd harmonic and 3.2% to the fundamental) impedance. Data show that the zig-zag transformer permits more harmonic current to flow in the system than a standard transformer.

6. Energy consumption
a. A system using the HSS has been documented to use less energy than the same system using a zig-zag transformer.2 (When the HSS was added to an already-installed zig-zag transformer, energy consumption decreased by over 4%.)
b. Due to the fact that the HMT permits high 3rd harmonic currents to flow in the distribution system, energy consumption of such a system is significantly higher than that in a system using the HSS.

7. Summary
a. The HSS reduces 3rd harmonic current throughout the entire electrical distribution system from the transformer to the furthest outlet. Useable system capacity is increased, heat losses are reduced, and energy consumption is lowered. There is no need for special k-rated transformers or increased wire size.
b. The HMT does not reduce 3rd harmonic current throughout the entire electrical distribution system, and may, in fact, increase harmonic currents. There is no increase in useable system capacity, no reduction in energy consumption, and special wiring, including double neutrals, is recommended.

There is no supporting evidence for the supposition that the HMT is the equivalent of the HSS for harmonic mitigation in an electrical system serving computer loads. All evidence shows that the HMT is not equivalent to the HSS with Blockade Technology.