Motor Book
Introduction:
Welcome! This motor book will provide you with a wealth of information about electrical motors, how they work, what they can be used for, and so on. But before we delve into detailed explanations of the world of electrical motors, we should perhaps spare a brief thought for the purpose of these motors. After all, motors are always designed to carry out specific tasks. As this is a Grundfos publication, it is only natural that we should pay special attention to motors used for pumps – although much of the information contained within these pages will benefit all those with an interest in electrical motors.
If we start by casting our minds back in history, Archimedes discovered that water can be lifted or moved – what we call "pumping" today – by means of a rotating screw. Today, Grundfos honours this venerable pioneer of pumping in our company logo.
Rotation is an essential part of the act of pumping. This means that the motor is an essential part of any pump. Without the motor, there would be no rotation - and the water would not be moved anywhere.
The purpose of the electric motor is to create rotation – that is to convert electric energy into mechanical energy. Pumps are operated by means of mechanical energy. This energy comes from electric motors. In the process of converting energy from one kind to the other, magnetism plays a major role. In the following section we will present the basic principles of magnetism.
Some basic motor concepts:
This section will look at how motors work. The objective is to provide basic information to serve as a background for more detailed studies. We will take a look at the concepts of magnetism, AC (alternating current), electromagnetism, motor construction, and torque.
All magnets share two characteristics: they attract metals such as iron and steel, and they will move to point north-south if nothing obstructs them. Another very important feature of magnets is that they all have a north pole and a south pole: unlike poles attract each other, whereas like poles repel each other.
We can visualise the magnetic field – the invisible force that makes magnets behave the way they do – as lines of flux moving from the north pole to the south pole. In some cases, the north and south poles are not as easily identifiable as in the classic bar or horseshoe magnets. This is certainly the case with electromagnetism.
A magnetic field is created around an electrical conductor when an electric current is passed through it. This is known as electromagnetism, and the physical rules for ordinary magnetism also apply here. The magnetic field moves around the conductor.
The magnetic field around electrical conductors can be strengthened by winding them into a coil around an iron core. When the wire is wound into a coil, all the flux lines produced by each turn of wire join up to form a single magnetic field around the coil.
The greater the number of turns of the coil, the greater the strength of the magnetic field. This field has the same characteristics as a natural magnetic field, and so also has a north and a south pole. But before we dig any further into the world of magnetism, let us have a closer look at the main components of an electric motor: the stator and the rotor.
Rotor:
The rotating part of the motor, rotates with the motor shaft by moving with the magnetic field of the stator.
Stator:
The stator is the stationary electrical part of the motor. It contains a number of windings whose polarity is changed all the time when an alternating current (AC) is applied. This makes the combined magnetic field of the stator.
Conclusion:
The objective of motor maintenance is to reduce unplanned and expensive downtimes thus reactive maintenance, which affects the manufacturing process Preventative maintenance can without no doubt improve the motor efficiency and consequently the plant efficiency Predictive maintenance helps determine when the time has come to replace a motor with a more energy efficient kind Last but not least, reactive maintenance is necessary when preventive and predictive maintenance have not been carried out properly or when the motor is not designed correctly or installed with material or production errors Reactive maintenance is unwanted maintenance because it leads to motor damages or a burned motor and consequently production downtime.