Three Phase or Single Phase for instruments

[satxx]

Hi,

i have a question regarding selection of electrical instruments like compressors, fans, etc.
The compressors are available in both three phase and single phase according to the datasheet. How do we select which type we need if we are designing a system from scratch (ie both three phase and single phase supply is available). Is there any determining factor like:

Three phase is more efficient than single phase for a compressor. If so, could you please explain the logic behind it.

Thank you

 

[Geoff1946]

Depends on size to start with. Anything above (say) 1hp is probably best 3 phase.
Then there are various trade offs, cost of purchase, cost of installation and operation, reliability.
Too many variables for a simple answer.

 

[roys]

If 3 phase is available then use it, the 3 phase motor is generally more efficient and more reliable than single phase motors. A 3 phase motor is just 3 sets (or multiples of) coils of wire, this creates the rotating magnetic field which a motor requires to rotate.
A single phase motor due to the fact that it is only single phase has to use other method of creating a rotating magnetic field, to do this they tend to use capacitors ( other methods are available) and often centrifugal switches, more bits = less reliable, also with capacitor life anything over 10 years is a bonus.
In simple terms more bang for your buck with 3 phase machines. However Infrastructure, protection and control is more than involved with 3 phase.
This is a very rough and simplistic overview.

 

[binky]

Chances are total demand is likely to exceed a single phase supply with heavy draw equipment, so 3 phase tends to be better, plus cable sizes can be smaller making for easier installation.

 

[Marvo]

With small fractional horse power items it often doesn't make much difference and you often find single phase versions will be cheaper due to economy of scale with the higher number being sold.

As motors get larger the 3-phase versions become cheaper than their single phase counterparts because often they run direct on line so they don't need start gear such as large expensive capacitors and centrifugal switches etc.

Also with larger single phase motors the cable size required to handle the inrush current without presenting a detrimental volt-drop become a factor.

Any motor that is in an application that requires high starting torque would generally be better as a 3-phase and once you get larger than 3 or 4 kilowatts in size you're almost always going to be using a 3-phase motor.

 

[satxx]

Hi,

i have a question regarding selection of electrical instruments like compressors, fans, etc.
The compressors are available in both three phase and single phase according to the datasheet. How do we select which type we need if we are designing a system from scratch (ie both three phase and single phase supply is available). Is there any determining factor like:

Three phase is more efficient than single phase for a compressor. If so, could you please explain the logic behind it.

Thank you

With small fractional horse power items it often doesn't make much difference and you often find single phase versions will be cheaper due to economy of scale with the higher number being sold.

As motors get larger the 3-phase versions become cheaper than their single phase counterparts because often they run direct on line so they don't need start gear such as large expensive capacitors and centrifugal switches etc.

Also with larger single phase motors the cable size required to handle the inrush current without presenting a detrimental volt-drop become a factor.

Any motor that is in an application that requires high starting torque would generally be better as a 3-phase and once you get larger than 3 or 4 kilowatts in size you're almost always going to be using a 3-phase motor.

Thank you for the detailed explanation