Energy Control Systems
November  24, 2008
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Are harmonics in your building's power system costing you money?Harmonic currents, generated by non-linear electronic loads, increase power system heat losses and power bills of end-users. These harmonic-related losses reduce system efficiency, cause apparatus overheating, and increase power and air conditioning costs. As the number of harmonics-producing loads has increased over the years, it has become increasingly necessary to address their influence when making any additions or changes to an installation.
 
Harmonic currents can have a significant impact on electrical distribution systems and the facilities they feed. It is important to consider their impact when planning additions or changes to a system. In addition, identifying the size and location of non-linear loads should be an important part of any maintenance, troubleshooting and repair program.
 
The trouble with harmonics in modern power systems...
 
Harmonics are a distortion of the normal electrical current waveform, generally transmitted by nonlinear loads. Switch-mode power supplies (SMPS), variable speed motors and drives, photocopiers, personal computers, laser printers, fax machines, battery chargers and UPSs are examples of nonlinear loads. Single-phase non-linear loads are prevalent in modern office buildings, while three-phase, non-linear loads are widespread in factories and industrial plants.
 
Most power systems can accommodate a certain level of harmonic currents but will experience problems when harmonics become a significant component of the overall load.
As these higher frequency harmonic currents flow through the power system, they can cause communication errors, overheating and hardware damage, such as:


Overheating of electrical distribution equipment, cables, transformers, standby generators, etc.
High voltages and circulating currents caused by harmonic resonance
Equipment malfunctions due to excessive voltage distortion
Increased internal energy losses in connected equipment, causing component failure and shortened life span
False tripping of branch circuit breakers
Metering errors
Fires in wiring and distribution systems
Generator failures
Crest factors and related problems
Lower system power factor, resulting in penalties on monthly utility bills


Solutions to compensate for and reduce harmonics

 Use Powerware power distribution units (PDUs) with harmonic-mitigating transformers.

 The K-rated, dry-type transformer is widely used in electrical environments, but there have been more recent advancements in transformer design that offer even better performance in
reducing voltage distortion and power losses due to current harmonics.

Eaton's energy-efficient Harmonic Mitigating Transformer (HMT) is designed to handle the non-linear loads of today's electrical infrastructures. This transformer uses electromagnetic
mitigation to deal specifically with the triplen (3rd, 9th, 15th, etc.) harmonics. Secondary windings of the transformer are arranged to cancel zero sequence fluxes and eliminate primary winding circulating currents. This transformer also addresses the 5th and 7th harmonics by using phase shifting.

Using these two electromagnetic techniques, the Eaton HMT allows loads to operate the way their manufacturers designed them, while minimizing the impact of the harmonics to energy
losses and distortion. Eaton HMTs exceed NEMA TP-1 efficiency standards, even when tested with 100-percent non-linear loads. Wherever a K-rated transformer is specified, an equivalent HMT is a direct substitute.

Powerware PDUs equipped with HMT transformers are efficient and effective at mitigating the harmonics generated by computer equipment and other non-linear electronic loads.

Key Advantages of using Powerware PDUs with HMT transformers

Prevents voltage flat-topping caused by non-linear loads
Reduces upstream harmonic currents
Eliminates transformer overheating and high operating temperatures
Eliminates primary winding circulating current
Saves energy by reducing harmonic losses
Maintains high energy efficiency even under severe non-loading conditions
Treats power quality harmonic issues that K-rated transformers do not address
Suitable for high K-factor loads without increasing in-rush current
Improves power factor

20081124A
In This Issue
Trouble with Harmonics
Harmonic Solutions

Harmonic currents can have a significant impact on electrical distribution systems and the
facilities they feed. It is important to consider the impact of harmonics when contemplating
additions or changes to a system. In addition, identifying the size and location of non-linear
loads should be an important part of any maintenance, troubleshooting and repair program.
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Call us at 1.800.383.6956 or visit www.ecsintl.com for more information!
 
Jeff Edwards
Energy Control Systems
800.383.6956