Will K rated Transformer helps to mitigate Harmonic generated by SMPS ?
Will K rated Transformer helps to mitigate Harmonic generated by SMPS ?
Personal computers, photocopiers communication equipment and other office equipment that forms large part of the electrical loads in buildings.These SMPS contain from 30% to 60% current harmonics.
The 3rd harmonics (150Hz) being the predominant one is the most harmful as its amplitude is bigger in magnitude and can be 3 times additive to neutral because these loads are non linear in nature their load currents are rich in harmonics 3rd, 5th 7th 9th and so on they can be a potential fire hazard.
The normal tendency is to install K rated Transformer with input delta and output star.
The ill effects due to current harmonics generated by these non-linear loads include:
1. Large currents in the neutral wires of the power distribution system. The neutral current will generally be larger than the current in any of the phase wires. Because only the phase wires are protected by circuit breakers or fuses, this is a very real fire hazard.
2. Overheated electrical supply transformers. Overheating shortens the life of a transformer and will eventually kill it. When a transformer fails, the cost of lost productivity during the emergency repair time far exceeds the replacement cost of the transformer itself.
3. Poor power factor. The harmonic currents caused by the non-linear loads do not carry any real power (kW) even though they do increase the volt-amperage (kVA). This lowers the power factor (PF = kW/kVA) at the building electrical service entrance. Electrical utilities have a monthly penalty charge for major users with a power factor less than 0.9.
4. Lowered reliability of computer systems. Distorted 120VAC supply voltage and increased the neutral-to-ground voltage may cause hardware problems which often appear at first to be software problems. IEEE Std. 519-1992 recommends that the voltage distortion for computer use be limited to a maximum of 5% total harmonic distortion (THD) and that the largest single harmonic not exceed 3%.
The electrical industry’s first response to these four problems was to double the ampacity (current carrying capacity) of the neutral conductors so that they would not burn-up. This is becoming a standard design practice in office buildings.
The second response was overheating shortens the lifetime of a distribution transformer and will ultimately kill it. These transformers are now known as K rated Transformers. The k-factor is a mathematical formula which predicts that the eddy current losses in a transformer will be increased in direct proportion to the sum of the products of each harmonic current amplitude squared multiplied by its harmonic number squared.Doubling the neutral and using a K rated Transformer will solve the electrical safety half of the harmonics problem.
In order to ride over the probable the solution is Harmonic mitigating transformer or phase shifting transformer with dual output one supplied to 50% of the building load and another half to other 50% load.A 30 degree phase shift is done in one output of the transformer and 180 degree phase shift done in another output. This can be the most cost effective solution for mitigating 3rd , 5th, 7th, 9th, 11th, 13th and 17th harmonics. This is an ideal way from protecting the building rich in harmonics from a potential fire hazard, and also save substantial energy saving.
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