Thread: 2 phase 240 volts?

Originally Posted by Ivan in Oz

2 Phases, 180* between both 2 phases ................Specialised
480V Ph to Ph,
240V Phase to Neutral

This is not correct.

What you are talking about here is what is commonly used in the USA, which is called "split phase". It is not 2 phases. The word "phase" can only be used when electrical phase displacement is exactly 120 degrees.

The word "phase" can only be used when electrical phase displacement is exactly 120 degrees.

Not true. You can from a technical point of view have any number of phases and hence the displacement could be any number of degrees resulting from the number of phases divided into 360. In most practical applications however the number of phases in power generation is limited to 3 and hence 120 is the most common number of degrees.

Cheers

Originally Posted by juan

Not true. You can from a technical point of view have any number of phases and hence the displacement could be any number of degrees resulting from the number of phases divided into 360.

Jaun is quite correct.

Originally Posted by juan

In most practical applications however the number of phases in power generation is limited to 3 and hence 120 is the most common number of degrees.

I think the reason that three-phase is so prevalent is that three-phase is probably the effectivenesses of transmission. The use of three-phase and hence three active conductors (no neutral required) allows three times the power that can be transmitted over single-phase (one active and one neutral conductor). i.e a three-phase transmission line using 50% more copper allows 300% more power than single-phase.

Originally Posted by chrisp

Juan is quite correct.


I think the reason that three-phase is so prevalent is that three-phase is probably the effectivenesses of transmission. The use of three-phase and hence three active conductors (no neutral required) allows three times the power that can be transmitted over single-phase (one active and one neutral conductor). i.e a three-phase transmission line using 50% more copper allows 300% more power than single-phase.

My original statement

The word "phase" can only be used when electrical phase displacement is exactly 120 degrees.

was meant to be referred to the statement that Juan made,

In most practical applications however the number of phases in power generation is limited to 3 and hence 120 is the most common number of degrees.

Advantages of a 3 phase system.
1. For any one machine frame, the output is;

1 phase - about 65%.
2 phases - about 90%.
3 phases - about 96%.

2. The power delivered to or taken from a 3 phase system is more constant. In a single phase system, the power curve pulses at twice the line frequency. With 3 phases, the pulses are 6 times the line frequency & do not cross the zero axis like the single phase system (there is no "zero power" point). Since the power is more constant, the torque of a rotating machine is more constant, which results in less vibration.

3. With one type of 3 phase connection, there are 2 voltages available (Star).

4. A 3 phase machine can be smaller than a single phase machine for the same power output.

5. In a distribution system, the total quantity of material needed for 3 conductors is less than that required for the equivalent single phase system.