3 Phase Power Question

[Waxman]

My wash has 3 phase power.

A customer with a woodworking shop was telling me about a house he bought to build a shop behind. The reason; it had access to 3 phase power. He said 3 phase power is cheaper power. I asked him why it was cheaper and he couldn't really tell me.

An electrician told me about making sure my power usage was balanced and that was easier to accomplish with 3 phase.

I still do not get it,

Can anyone explain? Thanks!

 

[pitzerwm]

My understanding that your motors (5HP +) run more efficiently and last longer, there probably is different rates for 3PH from the power company but kilowatts are kilowatts.

 

[ken-pro]

Waxman:

Three phase power is generally cheaper for three reasons: Lower demand amp draw for motor starting, higher efficiency of motors, and higher reliability of motors.

Three phase motors are very simple - Just a series of copper windings around a rotor - The three phases of supplied power allow the motor to start rotating from a dead stop easily. Three phase motors are usually cheaper than single phase motors.

Single phase motors require centrifugal switches and capacitors to start (Always part of the motor) - More parts means more problems. The capacitors are required to "Kick start" the motor at start-up, and then balance their power draw while running.

Any site with an automatic car wash will generally require three phase power, because 10 HP motors are typically the largest single phase motor available (Not enough for an automatic pump station)

Three phase services are fairly expensive to install, versus single phase services - If your woodworking customer has single phase shop tools, the benefit of having 3 phase power is non existent. The savings from three phase power come only from using large motors on a regular and consistent basis (Car wash is a prime example), and they must be three phase to gain any benefit. Supplying a house, or small shop with three phase power is not beneficial unless there is a large motor demand.

Of course your customer could be looking for an excuse to buy new tools as well

 

[Waxman]

So should I check all my motors to see if they're 3 phase?

 

[ken-pro]

I am 100% sure your motors on your auto are three phase. (Except possibly for chemical pumps or spot free rinse pumps etc... which are small motors anyways).

For your self serve - While there is not usually any harm having single phase motors with a three phase supply, 3 phase motors are almost always more efficient, and definitely more reliable. I wouldn't run out and replace the motors if they are single phase, but something to keep in mind if they ever need replacing.

 

[bigleo48]

I once read a better explanation of 3 phase power. It's rather simplistic, but I think you'll understand better. Single phase is like one hammer pounding a nail. Three phase is like having 3 hammers synchronized to pound the nail. So one hammer is making contact with the nail head, while another is starting to come down and the third is pulling back up. Hope this makes sense.

BigLeo

 

[Waxman]

Hmm.

Okay, I get it I think. And it is less expensive because it is more efficient?

 

[MEP001]

I keep getting conflicting info about the efficiency of 3-phase. I do know that I've seen the inside of several electric meters, and they aren't all the same. Some don't meter the "high" leg of power, so one would think that pulling only 12 amps on 3-phase when a single phase, 5-horse motor would pull 35 amps through the meter, it would cost less to operate 3-phase. Our power is 208, and all three legs are metered. If you go by math, it should in theory be cheaper to run 3-phase because 12 times three is much less than 35 times two.

Recently a friend's wash had the power shut off due to a billing issue. I passed by and noticed only one set of lights on, turns out when they pulled the meter it left one leg on. It was running some of the lights, the changer, one vacuum and his surveillance equipment without running up the meter.

 

[Joe Law]

single phase vs 3 phase

This is a good description of the difference between 3 phase and single phase.

http://www.federalpacific.com/univer.../chapter3.html

 

[mjwalsh]

I can't help but wonder if variable frequency drives is making the need less for 3 phase. I know that laundry equipment manufacturers have been kind of steering people more in the direction of VFDs as an alternative to 3 phase power. It seems like you can then use & get the use of 3 phase motors without using 3 phase power. Supposedly even more energy savings. As long as the added devices do not create more breakdown.

I do like our 3 phase that we have available. I just want to give everyone a heads up on the fact that the VFDs may have changed the landscape a bit. Maybe someone familiar with VFDs can shed a little more light on the consideration. I really do not have any first hand experience with VFDs so maybe someone else can be more precise.

 

[MikeV]

If you really want to save energy costs on a 3 phase motor, especially blower motors, have them wired for "Y-DELTA" start. I have some customers that I did this for that have blower motors that are well over 10 yrs old without a failure. Saves on electricity and motor wear.

 

[Waxman]

Will most any electrician know how to do this?

What is involved?

Thanks! I'm intrigued.

 

[MikeV]

There's the rub, most electricians don't have a clue. Find a good industrial electrician and he might know what you are talking about. Most confuse Y-Delta start with wye start/delta run. Basically you would use 3 motor starters, one for each set of windings on a 3 phase motor and start each one with a 1- 1 1/2 sec delay.This reduces start up torque and reduces a lot of stress on motors caused by starting.

 

[soapy]

Three phase power is generally billed in 2 ways. First they take the overall electricity used during the month. The second part of the bill is determined by how much peak power you use at any given time during the month. Peak will be determined by how much power is required during the month at the highest use time. Even if it is for only 5 minutes that will be your multiplier for the entire bill. Lowering the overall peak demand is the goal for staggered starts on equipment. When you check your vacuums do you put quarters in all of them at the same time so they are all running at once? Then someone uses your automatic at the same time and all your SS bays fire up with lights on. If so you may have created your high use demand for the month. THe more things you have on at any given point in time the higher the demand multiplier is.

 

[Kevin Reilly]

Soapy, that's how it's priced in California. My son has VFD's driving the blowers in his tunnel washes for that very reason. The VFD's ramp up slowly, and the computer is timed to keep the blowers on of there is a car close and if not shuts down. Long term it's the way to go.

 

[Earl Weiss]

There's the rub, most electricians don't have a clue. Find a good industrial electrician and he might know what you are talking about. Most confuse Y-Delta start with wye start/delta run. Basically you would use 3 motor starters, one for each set of windings on a 3 phase motor and start each one with a 1- 1 1/2 sec delay.This reduces start up torque and reduces a lot of stress on motors caused by starting.

With 3 motor starters versus one are you buying 3 starters that are the same size as if you used one, or are they each 1/3 the size or something like that? Any idea on overall cost of equip for say a 10 HP motor with 3 starters versus one?

 

[MikeV]

I used to get them from Hanna, that was several years ago, before they were bought out by Coleman. As I recall, the starters were a little smaller than if you used just one, but I will check and get back to you on that. I have a unit close to home that I will go look at.