AboutDave Nyce Expertise I have been an electronics engineer for 25 years. I can answer questions on analog and digital circuits and my specialty is sensors.
Experience I am the inventor on 23 US patents, and also some foreign ones. Developed sensors for over 25 years. Licensed private pilot (airplane and rotorcraft), have HAM radio license. I'm not an expert in computer networking.
Expert: Dave Nyce Date: 10/8/2003 Subject: Electrical Transformer
Question Sir,
I just want to know that why the TRANSFORMERS are rated in VA ( please explain in details )
and also that why we can not use them for the DC
and if we use that with the DC then what actually the result will be?
Answer A changing magnetic field induces energy into a nearby conductor, this is called the Faraday effect. If the magnetic field is constant, as produced by a DC current in a coil, there is no energy induced into a nearby conductor. That's why transformers don't work for DC. Energy is trnsferred from the primary to secondary of a transformer by a changing magnetic field.
There is a maximum current level in a transformer when the core becomes saturated, but the voltage and current may not be in phase in an AC circuit (eg. current lags voltage in an inductive circuit). The phase angle between current and voltage is called power factor. That's why transformers are rated in VA (volt-amps) rather than watts (because the highest voltage may not occur at the same time as the highest current).
