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So I don't understand a concept of mechanical to electrical energy conversion.

Let's assume I have a 3-phase generator and need X amount of mechanical power in order to get 200 Volts Phase-Neutral. Now suppose I add some windings etc. so that I have a hypothetical 6-phase system. Would I need more mechanical energy in order to get 200 V for each phase, or can I get it by same amount X? So basically, if I have more phases do I need more mechanical power?

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  • \$\begingroup\$ Conservation of energy. All else being equal, more phases with the same mechanical energy in does not equal to more power output except due to efficiency increases. Just smoother power. \$\endgroup\$
    – DKNguyen
    Commented Jan 22, 2020 at 23:17
  • \$\begingroup\$ Because you make no mention of electrical output power, it is hard to answer your question. Mechanical input power = electrical output power / efficiency. At the concept level, assuming 100% efficiency, number of phases makes no difference. Please note that large commercial generators and motors are in the mid 90% efficiency level. Smaller ones down to half a horsepower or so may be more like 75 - 80% efficient. Below that sometimes the motor efficiency is awful. \$\endgroup\$
    – user57037
    Commented Jan 23, 2020 at 1:18

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Let's assume I have a 3-phase generator and need X amount of mechanical power in order to get 200 Volts Phase-Neutral.

You are confusing the relationship between power and voltage. For a given winding arrangement the voltage will depend on the speed. The mechanical power input required when unloaded will be that only to overcome the mechanical resistance.

Now suppose I add some windings etc. so that I have a hypothetical 6-phase system. Would I need more mechanical energy in order to get 200 V for each phase, or can I get it by same amount X?

You don't need much power to generate voltage. You do need power to generate current at that voltage.

So basically, if I have more phases do I need more mechanical power?

No. You need more mechanical power if you draw more electrical power from the generator no matter how many phases you have. In general:

$$ P_{OUT} = P_{IN} \times efficiency $$

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  • \$\begingroup\$ Thanks for your answer. Voltage depends on speed because of induction? And so do energy providers increase mechanical power on their generators, so that they can satisfy high current requirements, like on peak times (evening)? \$\endgroup\$
    – Verman
    Commented Jan 22, 2020 at 23:28
  • \$\begingroup\$ You should be able to find the motor equations for whichever type of motor you're thinking of. They will give you the relationship between speed and output voltage. \$\endgroup\$
    – Transistor
    Commented Jan 22, 2020 at 23:30
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If it's a hypothetical generator, then if you put no load on the generator, it will take no effort to spin. Adding more windings then makes no difference. The voltage output also makes no difference, as there is no current being drawn.

Add an electrical load to the generator, and the mechanical load on whatever is driving increases by the same amount. Again, that's true regardless of how many windings you put on. If you double the windings and attach a load to each, then you double the mechanical effort.

Mechanical power in = electrical power out

Of course real generators aren't perfect. They have friction in the bearings and the windings get warm, all wasting power.

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The 0-120-240° three phase system is used because it utilizes the three wires as good as DC would. 100% of possible current and 100% of possible voltage without overloading either. A single-phase AC system in contrast only has an utilisation of 70% because of the zero crossings.

You cannot do better than 100%. That's why more phases are pointless.

There are systems with more phases for other reasons, for example for smoothing the output of a connected rectifier. But this is within a machine or building at most.

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