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Engines and energy

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Understanding energy flow in electrical power: The system and its state

Energy can be most conveniently described as the capacity to do work. Work in turn can be defined as the energy transferred by a force applied through a displacement. The amount of work done in a given time or the rate of doing work is known as power. Pushing a car on the road by people is a straightforward scenario. But to explain how the energy used in a power station being transferred through out the whole electricity grid until used by its customers is a very complicated process.

An important principle to note here is the conservation of energy. This principle in essence states that energy can never be created or destroyed. It is only ever transferred. What this means is that the energy exists in many forms and can change from one form to another, but the total amount of energy in an isolated system (e.g. our universe) is always the same. In fact, Einstein, through his famous equation showed that all matter that has mass is a form of energy. However, to access matter directly for energy would be the future generation's job. What we have been doing is lot more simpler. We have many other type of energy sources that can be used. For example, hydrocarbon fuel can release energy through combustion. Engine is the mechanical device to extract energy by thermal expansion. The gas expansion force will be used by engine to do work. This is a topic we have further discussion in our free book.

The energy that is consumed by almost all the machines and devices we use at home, in our offices and in industries, is electrical energy. Electrical energy is obtained by transforming energy from other forms into electricity. These other forms of energy can be fossil fuels, kinetic energy in wind and water, solar energy, energy from nuclear reactions, etc. These forms of energy are converted in to electrical energy by electrical generators. It is important to note here that during the conversion of energy from one form to another, not all of it is converted. Part of the energy becomes useful electrical energy, whereas the rest is dissipated as heat, which is referred to as an energy 'loss'. A useful parameter may be introduced here called efficiency. Efficiency here can be defined as the ratio of useful electrical energy produced as output of a generator to the total energy taken as input into the generator.

For a better understanding on energy waste due to heat lost caused by bad engine designs, you should read our book. We think thermal engine designs are full of flaws. In one of our projects, we will design a engine capable to extract thermal heat energy through two heat reservoirs, of which temperature difference is no more than 30 degrees. The project itself demonstrates many consideration of engine designs.

Electrical generators use the principle of electromagnetic induction to essentially create a current. Rotating a conductor between magnets creates a current in the conductor. The current created is such that it reverses its direction of flow (i.e. electron flow) once for every full rotation which is known as alternating current. Two types of generators exist viz. are Direct Current (DC) and Alternating Current (AC) generators. Both generators produce alternating current but the DC generator has a component called the commutator which converts the alternating current into a direct current which does not change its direction. AC generators were invented by Nikola Tesla and are the most widely used type of generators. The AC generators are considered better than DC generators as the AC voltages and currents they produce can be modulated into higher or lower values. To understand this, we must revisit the concept of 'power'.

Power in the context of electricity can be defined as a product of voltage and current:

Voltage is the difference in potential between two points and current is a measure of the amount of flow of electrons. By extension of this, electrical energy can be defined as the amount of power used in a given time:

This energy is what we pay for in our electricity bills.

Going back to voltage and current transformation, since it is the power consumed over time that consumers pay for, the power delivered to a consumer is most important. This power can be delivered as a product of high voltage and low current or a product of low voltage and high current without changing the amount of power delivered. It is more beneficial to use high voltages and low currents as this enables the transfer of electric power over large distances owing to lower losses during power transfer.

The AC generators consist of two major components i.e the stator and the rotor. The Stator is a stationary cylinder consisting of wound conductors. The rotor is a rotating component made of magnet(s) and consists of a conductor winding. The rotor fits inside the stator and is attached to a prime mover.

The prime mover is usually a mechanical device coupled with generator. The energy released from primary source is guided through this device using particular medium carrying energy, which interacts with the mechanical device and pass medium internal energy into prime mover's mechanical energy. Steam turbines, hydro turbines, wind turbines etc., are all belong to prime mover. In the case of fossil fuels or other hydrocarbon fuel, combustion is a violent chemical reaction, of which heat is the main source of energy that can be passed to medium such as water to generate steam. Steam at high temperature creates high pressure. The disparity of steam pressure and the environment, when passing through a turbine, steam molecules will impact turbine blades to make the whole turbine rotate along with generator as a consequence. The efficiency of this process, notably lower than 50%, is quite low. This is mainly due to steam energy can not fully coupled through the turbine. By comparison, hydro turbines do have much higher energy conversion rate. This is because water flow is purely gravitational energy. Water, when passing through hydro turbine, doesn't have phase change like steam. Steam, when expanded, the dominated energy is thermal, which must be fully isolated in a confined environment. The expansion also must be on directional and should be regulated. With a turbine, all these conditions are unable to enforced.

The rotating turbine is attached to the prime mover which rotated the rotor inside the stator. The winding in the rotor is supplied with a small DC current and this current when rotated inside the stator induces voltages in the stator windings. This process was demonstrated by Michael Faraday and is known as Electromagnetic Induction.

The voltages induced in the stator windings can be used to supply power to electrical 'loads' through a connection which can carry currents.

Electrical loads here refer to any device or machine that consumes electricity. Light bulbs, computers, refrigerators, industrial machines, etc. all contribute to the total electrical load of an electrical system. The electrical system is composed of the generators, the loads and a network of conductors connecting the generators to the loads. The network of conductors is known as the electrical grid. This grid can be classified into two networks, the transmission network that carries bulk power from generators to bulk supply points and the distribution network that carries power from the bulk supply points to individual consumers.

An important point to note here is that the AC generators produce alternating voltages and currents as mentioned previously. This is done in most systems such that the current and voltage polarity reverse direction 50 or 60 times for every one second. This is known as the system frequency (given in Hertz). As a result all electrical devices are produced to function with a power supply at this frequency. A deviation in the system frequency can be dangerous as it may damage the machines and devices using electricity and it creates disturbances in the system.

One source of system frequency deviation is an imbalance in the demand for electric power and the supply of it. The nature of the electric power system is such that the total demand for power created by all the loads connected to the grid must be almost exactly met by the generators. This means that the generators in combination must produce the electric power as required by the loads connected to the grid on-demand. In reality, this is not done on-demand but is done using a predictive approach. The designated system operator (usually government appointed body) predicts the amount of energy that will be required by all the loads and dispatches that amount of power by directing generators to operate as required.

electricity-demand-and-flua

An implication of this nature of the electric power systems is that connection of new generators is not straightforward. A new generator to be connected to the grid must be able to meet the requirement of producing stable electricity at a frequency of 50/60 Hz so that it does not create disturbances in the system. The criterion is not easily met by distributed generation (DG) sources and renewable energy sources as they rely on unstable and unpredictable primary sources such as wind and sunshine. To make breakthrough in this stalemate, energy storage must take over the bridging role to decouple such interference. But don't bet any energy storage in low energy density solutions. Make no mistake, human beings are smart. But the physics and scientific rules are the boundary we try not to challenge. If Tesla motor battery energy density is just 0.5% of liquid fuel, that is a long way to catch. To make battery as future family electricity storage products, someone is trying to fool the public for profiteering game.

Localised generation at a small sale with similar technologies used by big generators is also problematic as it creates power flow issues and causes disturbances in the system. These issues become increasingly important when the safety of the system is considered. Every power system has a protection system built into it which comes into play in case of equipment failure, harsh weather conditions, unpredictable faults, etc. When there are small scale generators connected to the grid and a fault occurs, the protection system will operate and the small scale generators in such cases may cause significant issues in the entire system.

When all these issues are considered, the generation of electric power at a small scale in geographically distributed points (Distributed Generation) is significantly problematic and faces resistance from utility companies. This resistance is justified as the current power systems with its control issues planned at the investment stage is not designed for DG. In order for DG to become a viable option, much change in the power system is needed as we move into the next stage of its evolution.

The solution seems to me would be go back DC instead of AC. After all, some many cars can offer their engines to supply electricity if the network is DC based. Thomas Edison can rest peace in his grave when that happens.

DCfor21st

With 21st century technologies, we believe if a highly energy efficient technology can address electricity grid issues, then the technology must be good enough for average family. It is our view that power grid is not a long term solutions because its underline operational cost. Moreover, the behaviour of profiteering nature by utility business will force people who wish to cut down their energy cost with green and sustainable energy sources other than fossil. This would be one "luxury" normal energy companies won't have: to harvest fuel without considering cost. People who embrace such off-grid electricity technology can access so much free fuel, they are very cost effective. Instead of waiting to see a shrinking market share and profit bottomline, energy companies should consider transfer their business practice to reflect the trend and future. Instead of sending energy through the copper wires, they should provide solution to people and business to live with Blue Energy.

References:

[1] Electric Machinery fundamentals by Chapman
[2] http://www.dg.history.vt.edu/ch1/introduction.html
[3] http://www.reliance.com/mtr/images/mtfig8.gif (image)

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Blue Energy

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