Core Technology

TransMax vs Zig-Zag Transformers

It has been suggested that TransMaxTM 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.