Why LT Motors are Delta connected but HT Motors are Star?
In industries Low Tension i.e. low voltage Motors like Motors supplied by three phase 415 V are normally have Stator connected in Delta while High Tension i.e. Motors supplied by high voltage like 6.6 kV have Stator connected in Star configuration. The reason behind this is technical while making the Motor economical.
Following are the main reasons due to which high voltage Motors stator are connected in Star:
As the Stator winding of Motor is to be connected with high voltage, it is better to configure the Stator in STAR as in this configuration, the phase current remains the same as the line current but the phase voltage reduces by to Vph = Vline/1.732 which means that insulation requirement from phase winding will be less.
The second most important reason is that, starting current for Motors is 6 to 7 times of full load current. So start-up power will be large if HT motors are delta connected. It may cause instability i.e. voltage dip in case of small Power System. In STAR connected HT Motors starting current will be less compared to delta connected motor as voltage is Vph and current is line current. So starting power and starting torque are reduced.
As current is less in STAR configuration, copper (Cu) required for winding will be less.
Following are the main reasons due to which low voltage Motors stator are connected in Delta:
In Delta connection, the insulation requirement will not be problem as voltage level is less in LT Motors.
Starting current will not be problem as starting power in all will be less. So no problem of voltage dips.
Starting torque should be large, as motors are of small capacity and hence Stator should be connected in Delta to have more current and hence more starting torque.
Ramdevs Motors is leading manufacturer and supplier of LT motors in India. Ramdevs Motors manufacturing plants are located at Coimbatore, India.
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