Tapping Down Transformers 1

[140668]

What are the principles behind the reason tapping down your voltage on your HV/LV transformers actually reduces energy consumption.

 

[tinfoil]

Much connected load is constant impedance in nature (hot water tanks, space heaters, light bulbs, etc).

When you reduce supply voltages, you reduce the current through these impedances (Ohm's law, V=IR)

Therefore, you reduce the Power as well (P=IV)

Some of these loads will simply run longer to consume roughly the same amount of energy, as the water in the heater will still need to reach a setpoint before the tank turns off, but will use less peak power while doing so.

Some of these loads, like the light bulbs, will simply not be as bright while they are on, saving both energy and peak power.

So, voltage reduction DOES result in slightly less energy consumption, but more properly is used to reduce peak POWER by speading out the energy use over more time.

Care must be taken to ensure that these reduced voltages are not so low that equipment gets damaged as a result.

 

[WoodrowJWeen]

On the other hand, induction motors will draw more current at reduced voltage, so I'm not sure that overall any energy would be saved. I was under the impression that utilities today do not reduce voltage to reduce load.

 

[140668]

Guys

Thanks for the information it has been most helpful but can I ask one last question. Why would the induction motor draw more current?

 

[stevenal]

The mechanical load the motor is required to move does not decrease along with the applied voltage. Power is proportional to V and I, so if one decreases the other increases.

 

[ScottyUK]

addendum to stevenal's post:

If you reduce the voltage too far, you'll be in the market for a new motor. The higher slip - i.e. lower shaft speed - at the lower voltage causes excessive rotor heating and will accelerate motor failure.


----------------------------------

One day my ship will come in.
But with my luck, I'll be at the airport!