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Technical Articles

Determine Primary Side of Transformer in Solar PV Applications
When a transformer is energized, a large inrush current occurs for a few cycles as the transformer energizes the core. Typically the outer windings are considered the primary windings.  If the inner (secondary) windings are used to initially energize the transformer, much larger inrush currents can occur due to the inner coils closer proximity to the transformer’s core.  Click here to see more

Harmonic Mitigating Transformer Broadcasting Application Case Study
The length and size of a power cable makes a difference in the voltage harmonic distortion.  We will examine a real life situation of a TV station in Montreal. The problem can be simplified with this one line diagram of the electrical installation.  A 112.5 kVA transformer feeds a series of panels and sub-panels which feed several studios. The loads are non-linear with some minor exceptions. Click here to see more

How Harmonic Mitigating Transformers Outperform K-Rated Transformers
It is quite commonly known that harmonics generated by non-linear loads can cause serious overheating problems in standard distribution transformers.  Even under much less than fully loaded conditions, transformers have been known to fail catastrophically.  One of the main reasons for this is that harmonic currents will dramatically increase the eddy current losses in a transformer. Click here to see more

Introduction to Power Quality
More and more, electricity is being considered a product.  Ideally, the AC voltage wave is a sine wave alternating from a positive peak to a negative peak 60 times per second (60 Hz) without any deformations, spikes or surges.  In reality, different factors influence the quality of the wave.  Certain disturbances come directly from the power source, such as lightning.  Other disturbances come from loads; in particular, from electronic equipment which are non-linear loads that produce harmonics, mostly because of their switching power supply. Click here to see more

K-Factor vs. H-Factor in Drive Applications
H-factor is defined under ANSI/IEEE C57.18.10 and also referenced under C57.110. K-factor is a UL classification and is not appropriate, nor covered by ANSI or IEEE, for transformer construction based on drive isolation transformer applications. To be in full compliance with ANSI and IEEE standards, a manufacturer must be able to provide an H-factor classification for the transformer. Click here to see more

Load Reactor Applications
The name “Line Reactor” immediately brings to mind that this inductive device is used on the line (input) side of the VFD.  However, that same or de-rated line reactor can often be used on the load (output) side of a VFD as it delivers power to the motor. Click here to see more

Simulate a 12-Pulse VFD Using Two 6-Pulse VFD’s
Many variable frequency drive (VFD) manufactures currently offer 18-pulse VFD’s that meet IEEE-519 THDi if the point of common coupling (PCC) is defined as the VFD itself.  Using a method that gives slightly lower cancellation called 12-pulse can aid in meeting IEEE-519 when the PCC is defined as the more traditional utility service entrance. Click here to see more

Sizing Solar Transformers
There are two main effects to consider when sizing transformers fed from inverters powered by PV arrays. Click here to see more

Transformers, Harmonic Currents
Harmonic currents are omnipresent in electrical distribution systems and can cause a variety of problems. It is therefore important to understand which solutions are available to us.  In this article, we will review various ideas that will be useful for solving problems related to power quality. Click here to see more

U.L. vs. CSA Listings
U.L. stands for Underwriters Laboratory.  U.L. is an NRTL (Nationally Recognized Testing Laboratory) and SDO (Standards Development Organization) that can test for both the United States and Canadian standards of equipment safety. Click here to see more

Vacuum Pressure Impregnation: VPI vs. VPE
A common transformer construction method is Vacuum Pressure Impregnation, usually referred to as VPI.  Another insulation term is VPE which can have two meanings, most commonly Vacuum Pressure Epoxy.  VPE can also mean Vacuum Pressure Encapsulation. To better clarify this discussion, VPE Epoxy will be referred to as VPEx and VPE Encapsulation will be referred to as VPEn. Click here to see more