question: How is electricity divided into different components in an electrical device / sub-grids when required power from each component varies?
comment: > If a resistor type is used, wouldn't the resistor heat up, and consume the otherwise unused power? Yes, it does. You can do this with low powered components like small LEDs, but dimming a large light bulb with a variable resistor (potentiometer) would be waste a lot of power. Stepping down the voltage is another way. There are step-transformers which have multiple output voltages, and this is one way you could regulate something like an AC motor. But today, this is usually done with semiconductors. A simple dimmer uses a type of switch called a triac, which only lets current flow for a fraction of the time. [This]( URL_0 ) diagram from Wikipedia shows fairly well how that looks: The shaded area shows the time where the triac closes and current flows. Because it's open part of the time, the total amount of power that flows through the light bulb is reduced. Now this doesn't work with all devices. Things like electric motors and fluorescent bulbs don't like a chopped up current like that. So a better way to achieve the same effect is to use a transistor that switches on and off extremely rapidly, thousands of times per second. The chopped up current is then smoothed by a capacitor, resulting in a clean AC or DC current of your desired voltage. This wastes a lot less power than either step transformers or resistors, and is an integral component of pretty much all power supply units in modern day electronics.
passages: Power systems deliver energy to loads that perform a function. These loads range from household appliances to industrial machinery. Most loads expect a certain voltage and, for alternating current devices, a certain frequency and number of phases. The appliances found in residential settings, for example, will typically be single-phase operating at 50 or 60 Hz with a voltage between 110 and 260 volts (depending on national standards). An exception exists for larger centralized air conditioning systems as in some countries these are now typically three-phase because this allows them to operate more efficiently. All electrical appliances also have a wattage rating, which specifies the amount of power the device consumes. At any one time, the net amount of power consumed by the loads on a power system must equal the net amount of power produced by the supplies less the power lost in transmission.
   Frequency control refers to the need to ensure that the grid frequency stays within a specific range of the nominal frequency. Mismatch between electricity generation and demand causes variations in frequency, so control services are required to bring the frequency back to its nominal value and ensure it does not vary out of range.
  
  If we have a graph for a generator where frequency is on the vertical axis and power is on the horizontal axis:
  
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   Coordinating generation units is a difficult task for a number of reasons:
  
  BULLET::::- the number of units can be large (hundreds or thousands);
  
  BULLET::::- there are several types of units, with significantly different energy production costs and constraints about how power can be produced;
   BULLET::::- generation is distributed across a vast geographical area (e.g., a country), and therefore the response of the electrical grid, itself a highly complex system, has to be taken into account: even if the production levels of all units are known, checking whether the load can be sustained and what the losses are requires highly complex power flow computations.
   BULLET::::- which units can be "modulated", i.e., their produced energy can be decided by the operator (albeit subject to the technical constraints of the unit), as opposed to it being entirely dictated by external factors such as weather conditions;
  
  BULLET::::- the level of detail at which the working of the electrical grid must be considered, ranging from basically ignoring it to considering the possibility of dynamically opening (interrupting) a line in order to optimally change the energy routing on the grid.
  
  Section::::Elements of unit commitment problems.:Management objectives.
   BULLET::::- whether the units and the grid are all handled by a Monopolistic Operator (MO), or a separate Transmission System Operator (TSO) manages the grid providing fair and not discriminatory access to Generating Companies (GenCos) that compete to satisfy the production on the (or, most often, several interconnected) energy market(s);
  
  BULLET::::- the different kinds of energy production units, such as thermal/nuclear ones, hydro-electric ones, and renewable sources (wind, solar, ...);
   where P is the change in power of the system. If we have multiple generators, each might have its own R. Beta can be found by:
  
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  The change in frequency due to a change in power can be found with:
  
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  This simple equation can be rearranged to find the change in power that corresponds to a given change in frequency. 
  
  Section::::Types of ancillary services.:Operating reserves.
  
  Since production and demand must match so perfectly (see Scheduling and dispatch), operating reserves help make up the difference when production is too low.
   There is therefore a physical requirement for a controlling agency, the transmission system operator, to coordinate the dispatch of generating units to meet the expected demand of the system across the transmission grid. If there is a mismatch between supply and demand the generators speed up or slow down causing the system frequency (either 50 or 60 hertz) to increase or decrease. If the frequency falls outside a predetermined range the system operator will act to add or remove either generation or load.
   BULLET::::- "production decisions": how much energy a unit is producing at any time instant;
  
  BULLET::::- "network decisions": how much energy is flowing (and in which direction) on each branch of the transmission and/or distribution grid at any given time instant.
  
  While the above features are usually present, there are many combinations and many different cases. Among these we mention:
   However, in practice, they are never run flat out simultaneously. Typically, some generators are kept running at lower output powers (spinning reserve) to deal with failures as well as variation in demand. In addition generators can be off-line for maintenance or other reasons, such as availability of energy inputs (fuel, water, wind, sun etc.) or pollution constraints.
  
  "Firm capacity" is the maximum power output on a grid that is immediately available over a given time period, and is a far more useful figure.
  
  Section::::Features.:Interconnectors.
   BULLET::::- Transient (fluctuations due to individual's actions, differences in power transmission efficiency and other small factors that need to be accounted for)
  
  There are currently three main methods for dealing with changing demand:
  
  BULLET::::- Electrical devices generally having a working voltage range that they require, commonly 110–120 V or 220–240 V. Minor variations in load are automatically smoothed by slight variations in the voltage available across the system.
  
  BULLET::::- Power plants can be run below their normal output, with the facility to increase the amount they generate almost instantaneously. This is termed 'spinning reserve'.
   The electric power industry comprises electricity generation (AC power), electric power transmission and ultimately electric power distribution to an electricity meter located at the premises of the end user of the electric power. The electricity then moves through the wiring system of the end user until it reaches the load. The complexity of the system to move electric energy from the point of production to the point of consumption combined with variations in weather, generation, demand and other factors provide many opportunities for the quality of supply to be compromised.
   The price of electricity from the grid is complex. Most power sources in the developed world are generated in industrial scale plants developed by private or public consortia. The company providing the power and the company delivering that power to the customers are often separate entities who enter into a Power Purchase Agreement that sets a fixed rate for all of the power delivered by the plant. On the other end of the wire, the local distribution company (LDC) charges rates that will cover their power purchases from the variety of producers they use.
   In voltage signaling, the variation of voltage is used to increase generation. The power added by any system increases as the line voltage decreases. This arrangement is stable in principle. Voltage-based regulation is complex to use in mesh networks, since the individual components and setpoints would need to be reconfigured every time a new generator is added to the mesh.
   Section::::Types of ancillary services.
  
  Six different kinds of ancillary services:
  
  BULLET::::- scheduling and dispatch
  
  BULLET::::- reactive power and voltage control
  
  BULLET::::- loss compensation
  
  BULLET::::- load following
  
  BULLET::::- system protection
  
  BULLET::::- energy imbalance
  
  Section::::Types of ancillary services.:Scheduling and dispatch.
  
  Scheduling and dispatch are necessary because in most electrical systems energy storage is nearly zero, so at any instant the power into the system (produced by a generator) must equal the power out of the system (demand from consumers). Since production must so closely match demand, careful scheduling and dispatch is necessary.
   The modern electricity market is an important example of a two-sided smart market., Electricity markets clear every few minutes, and require coordination to ensure that power generation matches demand, and that power flows do not exceed network line capacities. Generators offer to supply tranches of power at a range of prices. Wholesale power distributors bid to buy tranches of power at a range of prices. To clear the market, the market manager solves a linear program in which the decision variables are how much power to accept from each generator, the flow of power on each line, and how much power to provide to each distributor. 
   In addition, there's often central control, which can change the parameters of the AGC systems over timescales of a minute or longer to further adjust the regional network flows and the operating frequency of the grid. For timekeeping purposes, the nominal frequency will be allowed to vary in the short term, but are adjusted to prevent line-operated clocks from gaining or losing significant time over the course of a whole 24 hour period.
   Section::::Elements of unit commitment problems.:Types of production units.
  
  In the context of UC, generating units are usually classified as:
   Markets for energy-related commodities trade net generation output for a number of intervals usually in increments of 5, 15 and 60 minutes. Markets for power-related commodities required and managed by (and paid for by) market operators to ensure reliability, are considered ancillary services and include such names as spinning reserve, non-spinning reserve, operating reserves, responsive reserve, regulation up, regulation down, and installed capacity.
   The line to neutral voltage is half the line-to-line voltage. Lighting and small appliances requiring less than 1800 watts may be connected between a line wire and the neutral. Higher wattage appliances, such as cooking equipment, space heating, water heaters, clothes dryers, air conditioners and electric vehicle charging equipment are connected across the two line conductors. This means that (for the supply of the same amount of power) the current is halved. Hence, smaller conductors may be used than would be needed if the appliances were designed to be supplied by the lower voltage.
   Section::::History.
  
  Before the use of automatic generation control, one generating unit in a system would be designated as the regulating unit and would be manually adjusted to control the balance between generation and load to maintain system frequency at the desired value. The remaining units would be controlled with speed droop to share the load in proportion to their ratings. With automatic systems, many units in a system can participate in regulation, reducing wear on a single unit's controls and improving overall system efficiency, stability, and economy.
   Depending on the area, the consumer may have two electricity meters, one for normal supply ("Anytime") and one for the load-managed supply ("Controlled"), with Controlled supply billed at a lower rate per kilowatt-hour than Anytime supply. For those with load-managed supply but only a single meter, electricity is billed at the "Composite" rate, priced between Anytime and Controlled.
  
  Section::::Examples of schemes.:France.
   A distinction should be made between the voltage at the point of supply (nominal voltage at the point of interconnection between the electrical utility and the user) and the voltage rating of the equipment (utilization voltage). Typically the utilization voltage is 3% to 5% lower than the nominal system voltage; for example, a nominal 208 V supply system will be connected to motors with "200 V" on their nameplates. This allows for the voltage drop between equipment and supply. Voltages in this article are the nominal supply voltages and equipment used on these systems will carry slightly lower nameplate voltages. Power distribution system voltage is nearly sinusoidal in nature. Voltages are expressed as root mean square (RMS) voltage. Voltage tolerances are for steady-state operation. Momentary heavy loads, or switching operations in the power distribution network, may cause short-term deviations out of the tolerance band and storms and other unusual conditions may cause even larger transient variations. In general, power supplies derived from large networks with many sources are more stable than those supplied to an isolated community with perhaps only a single generator.
   While historically large power grids used unvarying power plants to meet the base load, there is no specific technical requirement for this to be so. The base load can equally well be met by the appropriate quantity of intermittent power sources and dispatchable generation.
  
  Unvarying power plants can be coal, nuclear, combined cycle plants, which may take several days to start up and shut down, hydroelectric, geothermal, biogas, biomass, solar thermal with storage and ocean thermal energy conversion. 
   The U.S. National Electrical Code provides rules for technical power installations. The systems are not to be used for general-purpose lighting or other equipment, and may use special sockets to ensure only approved equipment is connected to the system. Additionally, technical power systems pay special attention to the way the distribution system is grounded.
  