Does 3 phase save energy

[Rodney Koop]

does 3 phase save energy on linear circuits like electric heat, and how about non linear like a motor.

 

[Rockyd]

Think about motors this way in regard to their usage of power and efficiency. Each phase will be a person.

So for a 120 volt motor, that is equal to just one person standing there, spinning a motor from one spot.

So for 208 or 240 motor (single phase but two lines), you'd have two people opposite each other, spinning the motor.

So for 480 three phase motor, you'd have three people standing 120 degrees apart in a circle, spinning the motor.

The standard "improvement" for bringing along an extra person is 1.73 times work done per person.

There is tremendous savings in wire used (size), and wire savings (amount) also.

This is the easiest 101 I can spit out before coffee...

 

[al hildenbrand]

does 3 phase save energy on linear circuits like electric heat, and how about non linear like a motor.

A 3 kW resistance heating element is still a 3 kW load, unchanged, whether supplied by single phase, 3 ?, or any other number of phases.

A horsepower delivered to the shaft of a motor takes roughly a kVA of input energy. Think about that. And let me ask you, what are the differences in construction between a single phase and a 3 ? motor?

 

[coulter]

Rodney -

Three phase motors are more efficient than single phase motors. Take a look at the FLA tables in 430. These will give an approximation of the difference in required KVA for single phase vs three phase.

Other efficiencies are as Rocky and al noted

carl

 

[Rodney Koop]

I understand that 3 phase takes smaller wire, breakers, pipe, fittings, steel lead copper zinc and smaller power plants. But I always taught that 3 phase was more efficient not just a smaller load such as amps or obviously smaller transformers. But is there an energy savings. I dont see one on linear loads such as heat because kw is kw and at 100% it is also kva. I realize that power companies have to adjust with demand and power factor meters due to power factor corrections so they dont get taken advantage of by low power factor equipment that takes energy but doesnt spin the meter as fast but am I or my customer saving money on the electric bill. Does 3 phase take less energy than single phase. there may be a price difference from the power company but does it take less. I'm beginning to think not. Rodneoy

 

[al hildenbrand]

Consider a 1 HP 208 Volt motor.

Single phase, Table 430.248 tells us the FLA = 8.8 Amps.
Three phase, Table 430.250 tells us the FLA = 4.8 Amps.

208 x 8.8 = 1830 VA (single phase)

208 x sqrt 3 x 4.8 = 1728 VA (three phase)

 

[brian john]

I had an instructor that summed it up this way, "VATTS is VATTS". he had a slight accent.

 

[jtester]

Efficiency is a reduction in I**2xR. If the current is cut in half, current squared usually goes down faster than R goes up. Therefore there is a savings even though Watts are still Watts.

Jim T