A motor is a device that converts any form of energy into mechanical energy, that mechanical energy may be rotational or linear.
This article is about the conversion of three phase alternating current electrical energy into rotational mechanical energy, its effects on the electricity supply and the control of the electrical energy as it affects that mechanical energy. In that respect any reference to a motor in this article is a motor with a rotational output of fixed nominal speed or speeds powered by three phase alternating current electricity.
Motors vary in output power from milliwatts to megawatts. A motor is rated by it’s output power in watts, or much less commonly in the modern world horse power, a watt as the unit of power is a SI (systemes international) standard unit, and is used throughout this article.
For those who still abide in the horse power world one horsepower equates to 745.6999watts in the UK and USA; and 735.4988watts for Continental Europe and Japan.
Now for the confusion since the motor output is in Watts and electrical energy that drives the motor is also measured in Watts it is necessary to differentiate between them. In this article Watts of mechanical energy that is motor output power will be shown as Wo.
An important point regarding the SI system of units, the base unit of power is the Watt some of the preferred sub units are the milliwatt (mW = Watt x 10-3), the kilowatt (kW = Watt x 103), the megawatt (MW = Watt x 106) and the gigawatt (GW = Watt x 109) it should be noted that the preferred units are in steps of 10±3 of the base unit.
Similarly the base unit of length is the metre (m) the preferred sub units are the kilometre (km = m x 103), millimetre (mm = m x 10-3) and micrometre (µm = m x 10-6). The centimetre (cm = m x 10-2) is not a preferred unit and its use is therefore deprecated which is why it is not used within this article.
It is a pity that teachers in England are in total ignorance of these preferred units since they persist in educating our students using centimetres, however this is not surprising given the appalling state of the education system in England. This is due to a mixture of poor quality teachers, the political dogma of the (British) Labour Party (ideology - from each according to his means, to each according to his needs : reality – those that can and do are taxed to pay for those that can’t and won’t : result – those that can’t and won’t enjoy a life of idle fecklessness and cost free breeding whilst those that can and do struggle to exist – for proof of this watch Jeremy Kyle) and the extremely low number of hours per year, less than 1000, (most other people work between 1680 and 1920hrs per year) that teachers actually spend teaching in England’s schools.
It also requires the students to be re-educated in the SI system when they have finished their education and enter the real world where they learn about life which is their most important lesson, a place most teachers have never experienced and certainly do not teach.
The BBC is a respected broadcasting organisation in England; although it must be remembered that they are the scum class chief advocate; they too use the term centimetre in their various broadcasts probably because their presenters are the products of the English education system and UK universities, unfortunately it gives the centimetre the credibility it does not warrant.
And let us not forget the other great influence on our lives, computer software. Most computer software, which is invariably American in origin, that utilises measurements invariably shows metric units in cm, which is the abbreviation for centimetres, a word the Americans cannot spell correctly so it should really be of no surprise that they are unaware of its lack of import in linear measurement.