Energy Suppliers and Conservers… The Flywheel
Energy, the basics on which any electrical or mechanical device functions. Basically energy is the backbone of all electro mechanical systems. But as they say, along with exploitation of energy for the useful needs, there comes a part of saving energy for the future needs.. to conserve energy so that it can be used again and again, Important fascinating yet a question to ponder on how can we achieve this ain’t it……!!!!
Well as they all say, every problem comes with a solution of its own… And thus came a device which could do both…. the functions of storing the energy if in excess or the function of supplying energy in the times of need…. THE FLYWHEEL…..!!!!
What is a Flywheel…..????
A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed.
Since a flywheel serves to store mechanical energy for later use, it is natural to consider it as a kinetic energy analogue of an electrical inductor. Once suitably abstracted, this shared principle of energy storage is described in the generalized concept of an accumulator. As with other types of accumulators, a flywheel inherently smoothens sufficiently small deviations in the power output of a system, thereby effectively playing the role of a low-pass filter with respect to the mechanical velocity (angular, or otherwise) of the system. More precisely, a flywheel’s stored energy will donate a surge in power output upon a drop in power input and will conversely absorb any excess power input (system-generated power) in the form of rotational energy.
The mechanics of energy storage in a flywheel system are common to both steel- and composite-rotor flywheels. In both systems, the momentum (the product of mass times velocity) of the moving rotor stores energy. In both types of systems, the rotor operates in a vacuum and spins on bearings to reduce friction and increase efficiency. The rotor, loaded with magnets, is effectively part of an electromagnetic motor/generator that converts energy between electrical and mechanical forms. Steel-rotor systems rely mostly on the mass of the rotor to store energy and composite flywheels rely mostly on speed.
Components of a flywheel energy storage system
A flywheel has several critical components.
a) Rotor — a spinning mass that stores energy in the form of momentum. The rotor, as the energy storage mechanism, is the most important component of the flywheel energy storage system. The design of the rotor is the most significant contributor to the effectiveness and efficiency of the system. Rotors are designed to maximize energy density at a given rotational speed, while maintaining structural integrity in the face of rotational and thermal stresses. Rotor designs can be divided into two broad categories of low-speed, vertical or horizontal shaft and high-speed, usually vertical shaft rotors. Both types of rotors have advantages and disadvantages, and the two find uses in different applications.
b) Bearings– pivots on which the rotor rests. The bearings support the flywheel rotor and keep it in position to freely rotate. The bearings must constrain five of the six degrees of freedom for rigid bodies, allowing only rotation around the axis of the rotor. The construction of the bearings is important in flywheel performance. Speed of the flywheel is limited in large part by the friction on the bearings, and the resulting wear on the bearings often defines the maintenance schedule for the system. Magnetic bearings are required for high-speed flywheel systems. These bearings reduce or eliminate frictional force between the rotor and its supports, significantly reducing the intrinsic losses.
c) Motor-Generator — a device that converts stored mechanical energy into electrical energy, or vice versa. Motors convert electrical energy into the rotational mechanical energy stored in the flywheel rotor during charge, and generators reverse the process during discharge. In many modern flywheels the same rotating machine serves both functions. The machine is called a motor alternator or motor generator and consists of a wound- or permanent magnet rotor, usually revolving within a stator containing electrical winding through which charge (or discharge) current flows. Note that this machine, along with any power electronics, limits the power rating of the flywheel system. And in some practical systems the generator for discharging the wheel is higher power than the recharging motor. Thus at full power charging the wheel will require more time than discharging. The starter motor and alternator or generator are connected to the flywheel via the same steel shaft and may be either a single machine or two different machines. In both cases the rotor becomes part of the flywheel mass. When separate, the starter motor is typically a simple induction motor that is able to produce starting torque.
d) Power Electronics — an inverter and rectifier that convert the raw electrical power output of the motor/generator into conditioned electrical power with the appropriate voltage and frequency. Most flywheel energy systems have some form of power electronics that convert and regulate the power output from the flywheel. As the motor-generator or alternator draws on mechanical energy in the rotor, the rotor slows, changing the frequency of the AC electrical output. The main function of these devices is to allow energy to be taken from the wheel before its frequency and power output drop below usable levels. In fact the low-end (i.e., end-of-discharge) cutout speed at which the flywheel is considered discharged is primarily dependent on the current carrying capability of the electronics (or electromechanical coupling) and the size of the load. For example, most flywheels have output current proportional to load and inversely proportional to speed. This means a lighter load can go to a lower speed before the system cuts out on maximum current.
e) Controls and Instrumentation — electronics which monitor and control the flywheel to ensure that the system operates within design parameters
Flywheel systems require some controls and instrumentation to operate properly. Instrumentation is used to monitor critical variables such as rotor speed, temperature, and alignment. Rotor speed and alignment are also often controlled variables, through active feedback loops. The latter is especially important for systems with magnetic bearings, and most magnetic systems have complex controls to reduce precession and other potentially negative effects on the rotor. In many systems, other instrumentation is used to monitor performance or design parameters related to failure modes. In some composite flywheel systems, for example, instrumentation is used to measure deformation of the rotor over time, alerting operators when the rotor shape indicates possible failure in the future.
f) Housing — Containment around the flywheel system, used to protect against hazardous failure modes. It is sometimes also used to maintain a vacuum around the rotor to reduce atmospheric friction.
Now as we know what a flywheel is.. there must be different types of flywheel to suit the industrial needs and the applications….
Solid Disc Type Flywheel
The Simple Solid Disc Flywheel is shown in the above figure as follows. The Moment of inertia of these flywheels can be given as
The angular velocity of these type of Flywheels comes between 30000 rpm to 60000 rpm which may even be adjusted up to 100,000 rpm. They contain magnetic levitation bearings and need less maintenance. They are lighter in weight if compared size/capacity wise to low-velocity flywheels. They are costly in comparison to Low-velocity Flywheels.
The angular velocity of these type of Flywheels comes up to 10000 rpm. They are bulky and heavy if compared to high-velocity Flywheels. They need periodic maintenance and does not use magnetic levitation bearings. Their installation needs special concrete construction to support its weight. They are cheaper in comparison to high-velocity Flywheels.
Difference between flywheel and governor
Many people confuse between flywheel and governor, but they are totally two different things. Here are some differences between them.
- A flywheel is used to mitigate cyclic fluctuations in available energy but a governor is used to adjust the supply of fuel as per the load.
- The energy stored in the flywheel is kinetic which is 100% available but the governor mechanism involves friction.
- The flywheel is not used when cyclic fluctuation of energy is small or negligible.
- While a governor is necessary for all the types of engines because it limits the fuel supply as per demand.
- If we have constant load then the governor will remain idle but due to cyclic fluctuations in energy available, the flywheel will always work.
- Governor has no influence in cyclic fluctuations in energy and flywheel has no influence on the mean speed of an engine.
- Governor controls mean speed of the engine and flywheel controls cyclic fluctuations in energy.
Advantages of flywheel
- Less overall cost
- High energy storage capacity
- High power output
- They are safe, reliable, energy efficient, durable
- It is independent of working temperatures
- Low and inexpensive maintenance
- High energy density
There is an ever-growing selection of new flywheel products on the emerging on the coattails of advances in technology. Consequently there are also a number of applications that now propose using flywheels as the energy storage medium. These include inrush control, voltage regulation and stabilization in substations for light rail ,trolley, microturbine and wind generation. Still the majority of products currently being marketed by national and international-based companies are targeted for power quality(PQ) applications. And the number one application in power quality is short-term bridging through power disturbances or from one power source to an alternate source.
Flywheels are being marketed as environmentally safe, reliable, modular, and high-cycle life alternatives to lead-acid batteries for uninterruptible power supplies (UPSs) and other power-conditioning equipment designed to improve the quality of power delivered to critical or protected loads.