Energy and Power: Production, Distribution, and Society/Distribution of Electric Energy
- 1 Generating Station
- 2 From Generator to Transformer to Transmission line
- 3 From Transmission line to Transformer to Substation
- 4 Substations
- 5 The grid
- 6 From substation to transformer
- 7 From transformer to industrial plants and to other users of electricity
- 8 Electricity distribution in buildings
- 9 Wires and cables
- 10 See also
Basically this is a transformation at this station of one kind of energy (coal, gas, waterpower, nuclear energy, wind, solar energy, etc.) into electrical energy, often via steam. While the electricity fed into the grid (see below) is Alternating Current (AC), some of these sources of energy are used to charge batteries; all batteries supply only Direct Current (DC). Converters and inverters are available to change DC into AC, and rectifiers change AC into DC. Many industrial firms, also hospitals and other emergency operations have their own emergency generators that automatically switch themselves into the circuits if the normal electricity supply fails. These emergency generators usually are powered from petroleum based fuels. Also most cars include a small generator, called an alternator, that charges the car's battery and provides electrical power to the vehicle while the engine is running. The battery is disconnected from the generator while the engine is not running, or if otherwise the generated voltage is too low, such as, for example, when there is a breakage of the fan belt. In order to get a lot of energy into the power grid, a lot of energy is needed to drive the generators, and in case there is a disconnection of the generator from its load the input energy must be removed immediately, or else the generator would speed up more and more, and a lot of destruction would be the result.
To restore small generators to service they could be started up as motors, with the normal energy source supplying no energy at all at first, but then that energy is added slowly back to driving the generator normally. While power at the beginning is taken from the grid into the generator (actually it is a motor at that time), with the power flow then in the negative direction, the direction of power flow soon is reversed to normal. No synchronization is needed in that case.
In restoring large power generators a major problem could be the time taken for the heat source to reach normality. This can take days in case of nuclear plants.. In the meantime severe restrictions on electricity availability must be expected. That is why many firms have their own generators that are switched on automatically if there is a power failure.
From Generator to Transformer to Transmission line
From Transmission line to Transformer to Substation
Substations usually contain transformers in order to change voltage levels; they are connnected to a "bus" via a circuit breaker.
What is a "bus"?
Think of an airport. There is a long corridor from which you can reach many platforms via doors. In a substation that long corridor is called a bus, and each door is a large circuit breaker connecting one or more transmission lines and/or one or more transformers and/or one or more generators or one or more loads (such as a distribution network of electric energy to users) to one or more busses, at one or more different voltages, in rare caes even at different frequencies.
What are circuit breakers doing in a substation?
- The circuit breakers can be operated from the main switching console, or they can be operated automatically from a protection relay or some other protection device. This will ensure that in case of a local overload the circuit breaker(s) concerned will open immediately, thus disconnecting the circuit and stopping the current, which is higher than a given limit, from doing any damage, even from starting any fires. If the protection device discovers that the problem is outside the local area, then a time delay is activated to permit the problem area to do its switching first, however after that set time delay the relevant circuit breaker, as a backup, will be operated to switch off here if the problem still continues.
- Other protection devices may be activated automatically if the voltage is not within a given set range, or "load shedding" could be activated in case of a local overload. This will switch off a predetermined portion of the distribution system, while leaving on only hospitals, security areas, and other high-priority loads.
- A "reclosing feature" is usually also a part of the power system automation. It is an important feature to deal with very short local problems, such as lightning strikes, tree branches and/or other weather-related problems, even, perhaps, an animal causing a temporary short circuit. A reclosing of one or more circuit breakers may be activated immediately after a disconnection has occurred, but only once, and often at that time everything is back to normal; if not, then a second, permanent, disconnection is activated.
- Some substations also include a synchronizer to ensure automatic synchronization before two circuits can be connected together. This happens in substations, for example, before generators can be connected to a bus that is connected to the grid and that synchronizer ensures the proper phase and voltage relation between the two circuits to be connected together. Because it takes a short time for a circuit breaker to actually effect the connection, that time delay must be taken into consideration by the synchronizer. The speed of a generator is related to the frequency of its output, and that speed is changed as required by the synchronizer to ensure both sides of the circuit breaker are at very nearly the same frequency, within set limits, before the "connect" signal is sent by the synchronizer to the circuit breaker.
This enables various operations to be carried out from a remote location, such as the operation of circuit breakers, the transmission to remotely located human operators of vital data from unmanned substations, such as voltage, current, power magnitude and power direction at various points of the substation. Even automatic synchronization can be effected remotely, if necessary, before two circuits are connected together by a circuit breaker at just the right time in the cycle.
A transmission grid is a high-voltage network for long-distance electric power transmission;
A distribution grid is a medium- and low-voltage network for local distribution of electric power to end-users;
Usually the grid contains many substations that are connected via transmission lines to one another. These substations contain protective equipment that in case of problems can automatically operate circuit breakers, disconnecting certain portions of the grid from the grid
.......... How transformers, located at generating stations and substations are used as a part of the grid:
See also more about Transformers
From substation to transformer
From transformer to industrial plants and to other users of electricity
Electricity distribution in buildings
There are a number of gauges (a certain number assigned to that wire size), with wires and cables sold per that gauge number, not by its diameter. Different gauges exist.
- For example the Radio Engineer's Pocket Book by F.J.Camm, published by George Newnes Limited, London, lists on pages 79–32 that relationship between the gauge number and the actual diameters in inches as well as in millimeters for different gauges. On pages 77 to 78 is a list related to copper wire, giving the number according to the "Standard Wire Gauge" (SWG), the diameter of the wire in inches, its resistance in Ohms per yard, in Ohms per pound weight, the number of pounds per Ohm, per 1000 yards, yards per pound, and the number of turns per inch for coils, using different insulation materials: Enamel only, single silk, double silk, single cotton and double cotton.
- For example the number 10 is assigned to its gauge by the American Wire Gauge (AWG) to a wire having 0.101 inches diameter (=2.565 milimeter), but that same number 10 is assigned under the British SWG label to a wire having a diameter of 0.128 inches.
- http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/wirega.html and
A thin piece of wire can be connected in series with the load. The current flowing will heat that wire, and if the current is too high that wire will melt and therefore will disconnect the current flowing into the load. The maximum amount of current such a wire can carry without melting depends on the outside temperature and also to what extent the surrounding air will cool the wire, but wire supply companies have published tables showing the approximate maximum current a particular wire can be expected to carry without "burning out".
- For example the fuse wire table published by the London Electric Wire Company and Smiths, Limited (LewcoS) lists
- for 1 Ampere: Copper: 0.0020 inches diameter, Aluminum/Aluminium: 0.0028, Tin: 0.0076, Allo-Tin and Lead: 0.0084
- for 15 Ampere: 0.0124, 0.0164, 0.044, 0.048
- for 60 Ampere: 0.032, 0.040, 0.110, 0.128
Modern fuses have the fuse wire enclosed, and are sold with a specific Ampere rating.
See also Fuses, also Fuses in Wikipedia.
When wires are bent often then they very likely will break eventually. If a power cable is going to be subject to movement, then usually Stranded Conductors are used, meaning that a bunch of wires are used in parallel, ensuring that if one of them breaks very little, if anything, will be affected by that single breakage. Cables should be regularly inspected to find such breakages, if any.
- The LewcoS (The London Electric Wire Company and Smiths, Limited) wire tables provide multiplying constants for stranded circular conductors; their sectional area, weight and resistance.
- For example, if there are 3 strands, then the diameter of the bunch as a whole is multiplied not by 3, but by only 2.155; the sectional area by 2.94118, the weight by 3.06000, and the resistance (reactance can be neglected at power frequencies) by 0.340000 of those of one of these wires (also called "strands") alone. Assuming we have a bunch of 3 wires, each with a diameter of 0.029 inches, and we want to know the combined area of 3 of these wires as a bunch, then we multiply the cross-sectional area of one of the wires having that diameter (0.0006605 square inches) by 2.94118 to get 0.001943 square inches for the bunch.
- The multipliers are for DIAMETER, AREA, WEIGHT, RESISTANCE:
- for 3 strands: 2.155, 2.94118, 3.06000, 0.34000
- for 7........: 3.000, 6.88235, 7.12000, 0.145299
- for 19.......: 5.000, 18.6471, 19.3600, 0.0536278
- for 37.......: 7.000, 36.2941, 37.7200, 0.0275527
- for 61.......: 9.000, 59.8235, 62.2000, 0.0167158
- for 91.......:11.000, 89.2353, 92.8000, 0.0112063
- for 127......:13.000, 124.529, 129.520, 0.00803023
- for 169......:15.000, 165.706, 172.360, 0.00603479
Large diameter wires are also listed up to a carrying capacity of 648 Amperes, for 127-strands of 0.103 inch diameter stranded wire made of standard annealed copper.
The LewcoS Wire Tables provide data for 3 kinds of Resistance Wire: No.1 and No.2 Nickel Chrome, and also for Eureka resistance wire. These tables provide Gauge (SWG), diameter (inches and millimeters), the resistance in Ohms per 1000 yards while the wire temperature is 15.5 °C, 500 °C and 1000°Celsius. As current passes through/thru that wire it heats it, and the tables show the current in Amperes that will increase the wire's temperature by 100 °C, 500 °C and 1000°Celsius. The tables also show the weight of the wire in pounds (lbs) per 1000 yards.
- For example: Many houses have a limit of 15 amperes on their room circuits, and we find in the tables that in order to obtain a temperature rise of about 1000 °C with about 14 Ampere flowing No.2 Nickel Chrome Resistance Wire should be used, having a diameter of 0.032 inches or 0.81 millimeters, which is gauge 21 (SWG). The resistance of that wire at 1000 °C is 2114 Ohms per 1000 yards. Given the applied voltage, and the required current, the required wire length can be calculated approximately. "Fine tuning" for each specific application may be advisable.
The LewcoS wire tables provide also information on enamelled copper wire. Often close-wound coils with insulation coverings of enamel only, enamel plus single silk, enamel with ordinary single cotton, single silk only, double silk, ordinary single cotton and ordinary double cotton are used, and the number of turns per inch of coil length obtained are also listed.
- For example about 26 turns per inch, side by side, are available if gauge No.20 (SWG) wire (0.036 inches diameter) is used with only enamel insulation on it.