Based in Sydney Australia, RFL Alternators Pty Ltd is a world class manufacturer of high quality permanent magnet alternators for the power generation industry. With over 25 years of investment into research and development, RFL prides itself in continuing to develop new and efficient cutting-edge technologies and products which are at industry’s forefront, and manufactures alternators to the highest of quality standards.
The objective of the blog is to give a deep understanding of Permanent Magnets, the modern industrial applications, demand and supply drivers.
Why know about Permanent Magnets
Permanent magnets are a vital part of modern life. They are found in or used to produce almost every modern convenience today, from speakers in mobile phones to the electric motors in hybrid cars; air conditioners and washing machines. Permanent magnets are used increasingly in technological applications, including traveling wave tubes, Hall Effect sensors, high temperature-resistant permanent magnets, thin-film coating equipment and flywheel storage systems.
Magnets – Permanent vs Temporary
Centuries ago, it was discovered that certain types of mineral rock possessed unusual properties of attraction to the metal iron. One particular mineral, called lodestone, or magnetite, is found mentioned in very old historical records (about 2500 years ago in Europe, and much earlier in the Far East) as a subject of curiosity. Later, it was employed in the aid of navigation, as it was found that a piece of this unusual rock would tend to orient itself in a north-south direction if left free to rotate (suspended on a string or on a float in water). A scientific study undertaken revealed that steel could be similarly “charged” with this unusual property after being rubbed against one of the “poles” of a piece of lodestone or temporary magnets.
Unlike electric charges (such as those observed when amber is rubbed against cloth), magnetic objects possessed two poles of opposite effect, denoted “north” and “south” after their self-orientation to the earth. It was impossible to isolate one of these poles by itself by cutting a piece of lodestone in half: each resulting piece possessed its own pair of poles.
Induction – Permanent Magnets Vs Electromagnets
A Permanent Magnet is made from a hard-magnetic material whose atoms have been permanently aligned during manufacturing. Permanent Magnets maintain this intrinsic magnetism over long periods of time.
An electromagnet is created by running a current through conductive wire that is tightly wound around a piece of soft magnetic material. The magnetic field stops when the electrical current ceases.
The basic operation of generators and motors relies on Faradays law of induction which predicts how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF). A magnetic field is thus required to create electrical power in generator mode, or to create work in motor mode. These magnetic fields can be generated by either permanent magnets (PMs) or electromagnets. This blog will give a brief description on the differences between the two along with their associated advantages and disadvantages.
The main benefit to using an electromagnetic is in the ability to control the resultant magnetic flux. This can be done by either turning the magnet on and off or by adjusting the current through the coil. This is an ideal characteristic for maintaining voltage regulation where the electromagnet operates as a generator. Electromagnets also possess the ability to create greater pull strength than permanent magnets.
As the name suggests Permanent Magnets maintain a permanent magnetic flux, hence limiting the flexibility associated with voltage control whilst operating as a generator. A key benefit of PMs is that they are capable of operating at a peak efficiency at all times.
Loss of Magnetism – A myth or fact!
Deep Dive into ways Permanent Magnets are mounted in Alternators and Motors – Understanding limitations of Surface mount PMs and how our patented Imbedded design has proven success
It is a common notion that permanent magnets lose their magnetism over a period of time. Although this is not at all true, there are conditions which may result in loss of magnetic properties.
For this we need to understand the difference between Surface Mount Magnets and RFL’s patented Imbedded Design and the relation of magnetism to PM temperature rating
We conducted a lot of temperature tests on the RFL alternators and other alternators / motors using surface mounted design. The case temperature and the rotor temperature stabilize after about 1 Hour running at full load. The PM temperature range is about 120 degC and although our alternators are air-cooled, we have never registered temperatures beyond 100 degC.
However, this may not be the case with alternator design where the Permanent Magnets are surface mounted. At this temperature, the magnets can be susceptible to short circuit load conditions damaging the magnets. We have tested many other pm designs and have found these units to be prone to magnet damage under short circuit load conditions.
High loads or motor starting can demagnetize the magnets in surface mount pm designs even at magnet temperatures well below the PM temperature rating. For example – DOL motor starting of AC motors. This is effectively a short circuit and as such many PM designs have problems starting AC motors. The RFL design does not have these problems. The motor starting ability is equivalent to a standard induction alternator with a pm exciter. The patented positioning in the RFL Alternators means that magnets are protected from flux loss under short circuit loads, even at elevated temperatures. This is a key advantage of RFL design.
We have also tested the RFL design with magnet temperatures close to 100 degC, at short circuit conditions many times and no flux loss has been registered. Due to the patented imbedded design, The RFL unit does not have this problem. In fact, we have had zero rotor failures to date.
Our largest four pole customers are reefer industry generator set manufacturers. We have produced over 2000 units for these clients. This application requires constant starting of refrigeration compressors at high temperatures and for long periods of constant operation (weeks without stopping). RFL Permanent Magnet Alternators have had not a single failure in this application.
There are a number of major families of permanent magnets available for designers, ranging from ferrite, known for its low cost and low energy, to rare earth materials, which are more expensive and offer higher performance. Designers need to analyse magnetising field strength and magnetic output of magnetic materials prior to deciding on the appropriate magnet.
The design of Permanent Magnets is extremely flexible; they can be built longer and flatter, providing a large area of magnetic coverage. Due to the flexibility in Permanent Magnet sizing, the generators construction becomes more flexible. For example, a higher pole count can be achieved due to Permanent Magnets requiring a smaller