Three Phase Dual Voltage Motors. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Bookman · 29th Jun 2018, 8:04 pm

The use of Star & Delta nomenclature in relation to three phase A.C. motors refers to their ability to be connected in that format to permit "Star/Delta" starting.
In this it must be borne in mind that all motors under start conditions will give rise to a starting current that will generally be 600% as a minimum of full load current. The problems this causes are substantial for all applications.
There are several ways to reduce the starting current from an application point of view; all of which involve some form of mains supply Voltage reduction. However, there is a need for care as torque is directly proportional to Voltage squared.
Electrically a simple switching application is undertaken. All one need do is connect all of the motor windings in a way that they will be configured in a star format under start conditions. Note, there is no separate neutral connection so any reference to root 3 derivatives of the mains supply are purely notional; i.e. no 230V supply. However, the simple ratio of 1/3 of rated motor power will apply in its star connection.
A timer is then used in a way that will automatically switch from Star to Delta (415V) and the motor will then run at mains voltage and at its rated capacity.
When considering these problems think of multiple motor process applications. For example if the motor run load is 1MW then without reduced Voltage start the start Power requirements would be 6MW but with reduced Voltage would be 2MW.
VVVF (Variable Voltage Variable Frequency) motor starters are now available that permit most such Voltage reduction to be undertaken electronically; most specifically for Water Treatment works and Petrochemical industrial networks.
It used to be a fascinating aspect of heavy engineering.

29th Jun 2018, 8:04 pm	#21
Bookman Hexode Join Date: Aug 2017 Location: Taunton, Somerset, UK. Posts: 318	Re: Three Phase Dual Voltage Motors. The use of Star & Delta nomenclature in relation to three phase A.C. motors refers to their ability to be connected in that format to permit "Star/Delta" starting. In this it must be borne in mind that all motors under start conditions will give rise to a starting current that will generally be 600% as a minimum of full load current. The problems this causes are substantial for all applications. There are several ways to reduce the starting current from an application point of view; all of which involve some form of mains supply Voltage reduction. However, there is a need for care as torque is directly proportional to Voltage squared. Electrically a simple switching application is undertaken. All one need do is connect all of the motor windings in a way that they will be configured in a star format under start conditions. Note, there is no separate neutral connection so any reference to root 3 derivatives of the mains supply are purely notional; i.e. no 230V supply. However, the simple ratio of 1/3 of rated motor power will apply in its star connection. A timer is then used in a way that will automatically switch from Star to Delta (415V) and the motor will then run at mains voltage and at its rated capacity. When considering these problems think of multiple motor process applications. For example if the motor run load is 1MW then without reduced Voltage start the start Power requirements would be 6MW but with reduced Voltage would be 2MW. VVVF (Variable Voltage Variable Frequency) motor starters are now available that permit most such Voltage reduction to be undertaken electronically; most specifically for Water Treatment works and Petrochemical industrial networks. It used to be a fascinating aspect of heavy engineering.