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The US EPA http://www.epa.gov/dfe/pubs/wire-cable/wirecable-factsheet.pdf life cycle factsheet for wire and cable outlines the four following stages for Life Cycle Assessment (LCA):

When dealing with transformers and inductors, we find it helpful to call attention to an additional stage:

The re-manufacturing/downcycling stage fits into the chronology after Product use/maintenance and before End-of-life disposition. It's important for designers to be aware of the re-manufacturing/downcycling stage early in the product development process.

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Have you tried the spec tool yet? It´s pretty fun. Check it out.

Our programmers are calling this the alpha version of the spec tool. We think it´s good enough to share and we know there are some bugs. You´re invited to help direct the process of improving the tool. Please share any fixes or features that you´d like to see. We´ll continue to rely on your opinions to guide future tool upgrades. Thanks for sharing your thoughts.

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Image: Flickr user Toni F.

Designing transformers to take advantage of low duty cycle applications can save on physical size and potentially reduce the initial hardware investment. But this approach can quickly lead to component failures and loss of investment, particularly in cases when the specifying engineer miscalculates duty cycle.

1.) On-Off cycle must be considerably shorter than the thermal time constant of the transformer.

• Thermal time constants for transformers are usually expressed in hours.
• A 50 KVA, 100% duty cycle transformer has a thermal time constant of approximately 6-8 hours.
• If the On-Off cycle is less than 60 seconds, you can consider taking advantage of the reduced duty cycle approach in such a case.

2.) How to calculate Duty Cycle:

• Duty Cycle (As a Percent) = [Cycle On Time / (Cycle On Time + Cycle Off Time)] x 100

Example: On-Time = 6 seconds, Off-Time = 14 seconds, Duty Cycle = [6 / (6 + 14)] x 100 = 30 Percent

3.) How to Calculate Relative KVA size:

Relative KVA size is calculated by multiplying the 100% Duty Cycle KVA size by the square root of the duty cycle.

Example (Single Phase Application):

• Duty Cycle = 30.0 Percent
• Load during the On-Time = 50 KVA
• Therefore, Design KVA = 50 KVA x SQRT(0.300) = 50 x 0.548 = 27.4 KVA Design.

For easy calculation, assume the On-Time load is 100 Volts and 500 Amps (50 KVA).

• "Continuous" (100% DC) Design Current is 27.4 KVA / 100 Volts = 274.0 Amps.

A transformer designed to deliver a continuous current of 274.0 will perform well in an application designed to provide 500 Amps, operating at a 30.0 percent duty cycle.

Continue reading "Reduced Duty Cycle Transformer Designs" »

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Saturable reactors are not common electromagnetic components. Here is a brief overview of why saturable reactors are occasionally referred to as magnetic amplifiers.

Saturable reactors are considered magnetic amplifiers because they can use a relatively small amount of DC volt-amps to control the transfer of a significant amount of AC volt-amps. The DC input is referred to as the control.

The relationship between the DC control volt-amps and AC volt-amps is called the amplification factor. The amplification ratio is often expressed as a ratio: output volt-amps divided by the control volt-amps.

Continue reading "Saturable Reactors are Magnetic Amplifiers" »

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