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Isolation transformers are used to isolate sensitive loads from transients and noise derived from the mains. In some cases (Delta-Wye connection), isolation transformers keep harmonic currents generated by loads from getting upstream of the transformer.
The particularity of isolation transformers is a grounded shield mode of nonmagnetic foil located between the primary and the secondary.
Any noise or transient that comes from the source is transmitted through the capacitance between the primary and the shield, on to the ground, and does not reach the load. This is called the Ultra Isolation Transformer (see right side).
In recent years, there has been an increased concern about the effects of nonlinear loads on electric power systems. Harmonic currents adversely affect virtually every component in the power system.
The harmonic currents flowing through the power system impedances result in harmonic voltage drops, which are observed as voltage distortions. Severe voltage distortions may occur when the power system's inductive and capacitive reactance happen to be equal (parallel resonance) at one of the nonlinear load's significant harmonic current frequencies (typically the 5th, 7th, 17th, or 13th harmonic).
Even without resonance, harmonic currents cause losses in normal power system components. Due to skin and proximity effects, wiring experiences additional heating beyond the normal I2R. Harmonics also cause overheating of the neutral conductor due to the additive nature of triple harmonics (3rd, 9th, 15th, etc.) on three-phase, four-wire systems serving nonlinear loads with line-to-neutral connections.
Harmonic load currents cause additional heating in NORMAL isolation transformers, primarily through additional winding eddy current losses. IEEE C57.110 provides methods to de-rate a transformer for any given harmonic load profile
K-factor transformers are specifically designed to accommodate harmonic currents and have an additional thermal capacity within known limits, allowing operation up to nameplate capacity without de-rating.
K-factor transformers are designed to be operated fully loaded with any harmonic load having a K-factor equal to or less than their K-rating
For K-factor transformers, UL also requires that the neutral terminal and connections be sized to accommodate twice the rated phase conductor size (double the minimum neutral capacity) of standard transformers. Standard transformers, i.e., those not marked with a K-factor rating, may have some tolerance to nonlinear loading, but their capability is unknown to the user and is not certified by a third party such as UL. Currently, marking a transformer with a K-factor rating is not required by UL.
Magna Power Technology Pvt Ltd is part of a Rs. 200-crore group and specialises in the design, manufacturing, and support of a wide range of power conditioning equipment.
2, 3rd Cross Street, First Floor,
Singaravelan Road, Neelankarai,
Chennai , Tamil Nadu -600 041
Phone : 9789146400
Mail : sales@magnapower.in