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3 phase motor power


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For an insight into why they have no neutral, it is because Three Phase motors are perfectly balanced at all times, therefore they don't put any current back down the neutral (hence not requiring one).


If you are running a Low Voltage system (e.g. Red Plug and Yellow Socket on the motor) then you can also save another core in the cable if you combine it into one cable (as the company I work for does). This is done by replacing the cee-form connectors with 1 x 7-Pin Socapex connector and 1 x 7 Core cable as opposed to 2 x 4 core cables (one for Three Phase and the other for LV control). This is done by combining the earth's that are used in the individual cee-forms. Also there are a fair few companies who now run the 7-Pin socapex system out there (I can think of 3 off the top of my head).





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I was asking a friend this the other day, but what I didn't ask is what is the Purpose/Advantages Between Star & Delta? ? ?

Thanks Joe


Delta wiring means that you do not have to supply a neutral which cuts down on installation costs, for instance with the super-grid EHT system.


A star wiring system means that you can produce a neutral point where the loads join at the centre point, excellent for those times where you need a neutral for single phase and unbalanced three phase loads. This wiring is used at the 11kV to 415V step-down points, i.e. the point where it comes from sub-grid to local distribution to houses etc.

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Consider also the voltage across the windings, for a star connected load, each winding sees 230V, where the delta connected winding sees 400V (assuming normal three phase mains), most smallish three phase motors have 230V windings so would be star connected for direct use on the mains in the UK, but many inverter drives (Particularly in the fractional HP class) only output 230V between phases, so these need a delta connection.


Regards, Dan.

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