Patent Publication Number: US-2022231507-A1

Title: System for frequency regulation on a power distribution network

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 16/759,248, which is a National Stage Entry of PCT/EP2019/057439, which claims priority and benefit of EP Application No. 18208637.1 and EP Application No. 18163594.7, each of which are expressly incorporated by reference herein in their entireties. 
    
    
     FIELD 
     The present disclosure relates to a system for and a method of frequency regulation on a power distribution network, and to devices for use in such a system. 
     BACKGROUND 
     An increase in renewable power generation connected to the distribution network has created a more active network where bi-directional power flows are increasingly common. Such renewable generators include but are not limited to wind power generators, solar power generators and tidal generators, for example, provided both in power generation plants and in domestic and commercial premises (i.e. through the installation of solar panels on residential buildings, for example). These active networks present a challenge for traditional methods of voltage regulation which are tailored toward passive, load dominated networks and which aim to maintain constant voltage on the output terminals of transformers. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       We now describe features of embodiments of the invention, by way of example only, with reference to the accompanying drawings of which 
         FIG. 1  is a diagrammatic representation of a portion of a power grid and system according to aspects of the invention, 
         FIG. 2  is a diagrammatic representation of a voltage control device according to aspects of the invention, and 
         FIG. 3  is a diagrammatic representation of a network control device according to aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     An expected increase in the demand for electricity, over time, may erode existing network capacity margin at grid and primary substations. When responding to such changes, a distribution network operator (DNO) must assess if the increase is permanent and warrants immediate intervention, or will be eventually offset by distributed generation so that network reinforcement (i.e. provision of additional generators) can be avoided or delayed. In order to operate networks safely in the interim without potentially expensive interventions, techniques have been proposed to enable short-term rapid rises in peak demand to be adequately managed and met using existing assets. These techniques can allow short-term changes in demand to be managed while deferring the acquisition of additional power-generating resources until it is known that capacity is clearly an issue. 
     It has been demonstrated that electricity network demand (i.e. the total electrical power usage across a network at a given time) can be both reduced and increased by changing the voltage on the public electricity supply network. The operation of primary transformers in a staggered tap configuration can provide a flexible means of absorbing reactive power in a network and controlling over-voltage situations. 
     In general terms, premises are supplied with electrical power from the network. Electrical devices operating within each those premises require a specific voltage to operate in a fully effective operating state. Slight variations in voltage supplied to the device may affect the operation of the device, but in most cases a very small variation in voltage is not noticeable to the users operating the device. For example, a refrigeration unit or air conditioner operating with a voltage that is supplied within a small margin of error of the specified voltage may not operate at full efficiency, but the difference in operating efficiency is most likely to be largely undetectable. Those devices will still operate as required by the user. 
     Research and associated field trials examining voltage regulation of active networks reveal that voltage control schemes (Automatic Voltage Control, or AVC) are able to regulate voltages supplied to the network, but that they also act as a constraint on the connection of additional Distributed Generation. 
     In addition, such systems assist in avoiding unacceptably high voltages on a network, which might otherwise occur on networks during periods when high distributed generation output coincides with low local demand. 
     There has also been an increasing probability that the available generation within a network may exceed the demand or network capacity, leading to unacceptable network conditions and the need to constrain the generation output. This constraint acts to decrease the efficiency of the generation and hence drive up costs to customers. 
     Power providers have overseen a change in the types of generator being used to provide power to a network, with increased amounts of low inertia intermittent generation connected to the system along with large nuclear generating units. As a consequence, over time, there will be an increased need to access system reserves to maintain overall system stability to help avoid cascade tripping events. Owing to the high financial and carbon cost of conventional spinning reserve, fast acting and flexible demand management for frequency, and system balancing is expected to become an increasingly important part of future system operation. This is of particular benefit for local power balancing within a DNO network, and also offers potential advantages for future distributed system operator network management. 
     All alternating current (AC) electricity networks have an inherent system frequency. The frequency is measured in Hertz (Hz) and represents the rotating speed of synchronous electricity generating plant connected to the network. In the United Kingdom the frequency is typically 50 Hz. 
     As additional demand is connected to a network the frequency reduces. Conversely as the demand falls or additional generation is added to the network, the frequency increases. System frequency must, for technical reasons, be maintained within strict operating limits. Typically the frequency must be maintained within plus or minus of a few percentage points of the nominal or target frequency (i.e. 50 Hz in the UK). For example, in a network with a target frequency of 50 Hz, the electricity must be supplied at a frequency between 49.5 Hz and 50.5 Hz. 
     Frequency is typically regulated by increasing or decreasing the power output of a generating plant. Of course, as demand on the network grows, at some stage the generation capacity of the network is reached, such that it may not be possible to regulate frequency sufficiently by providing additional power to the network when required. Before this stage is reached, additional power generating capacity must be added to the network, to ensure that frequency on the network can be balanced as required. However, increasing the power output of a generating plant may not be quick or cost-effective to achieve, and relies on the short-term availability of additional power generating facilities. 
     The present invention seeks to ameliorate or reduce one or more problems associated with systems of the prior art. 
     Systems described herein relate to developments allowing the automatic regulation of voltage in response to the electricity system frequency. By this method demand is also automatically regulated which in turn counteracts the change in system frequency. Frequency regulation therefore constitutes an advantageous way to stabilise the frequency of the electricity network. 
     Such systems provide environmental benefits by allowing a mechanism for lowering power consumption, alongside the benefits of reducing the need for additional power generators in circumstances where the frequency and load requirements can be met using the existing infrastructure. 
     Such systems seek automatically to regulate the demand to counter any change in system frequency thereby maintaining frequency within the prescribed operational limits without the need for additional generating plants. Sensors are used to measure system frequency and then to activate a network transformer on load tap changes to change the network voltage. These voltage changes are co-ordinated through the technology to cause a prescribed and reliable change in system demand and hence stabilise system frequency to the desired value. 
     According to a first aspect a system for controlling voltage supply to a portion of a distribution grid, the portion of the grid including a substation providing one or more circuit elements operable to increase or decrease the voltage supplied to consumers within the portion of the grid, 
     the voltage control system providing a data set including a previously measured power consumption associated with previously measured values of at least one portion for a portion of the grid, the at least one property being one of voltage, current, frequency or load, and/or a combination thereof. The voltage control system providing a measurement device to measure the at least one property supplied within the portion of the grid. The voltage control system providing a processing device to determine from the previously measured values of the at least one property in the data set a most likely effect of altering the value of the at least one property from a first value to a second value, on the power consumption of those consumers. The reference to consumers as used herein may be to consumers within a portion of the grid. 
     A circuit element as used herein can refer to one or more of a tap changer, transformer, and/or capacitor. In at least one example, the circuit element can include two or more circuit elements each one of which can be selected from a tap changer, transformer, and/or capacitor. 
     The processing device may be configured to determine whether the power consumption of the consumers has reached a desired value. 
     The measured value of the at least one property and the associated measured power consumption values may be added to the data set. 
     The data set may include measurements of the at least one property and the measured power consumption which have been taken every: 
     60 minutes; 
     50 minutes; 
     40 minutes; 
     30 minutes; 
     20 minutes; 
     15 minutes; 
     10 minutes; 
     5 minutes; 
     4 minutes; 
     3 minutes; 
     2 minutes; or 
     1 minute. 
     The data set may include the day on which the property and power consumption were measured, for example, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday or Sunday, and wherein the day on which the property(ies) and power consumption were measured is used to assist in determining the most likely effect of altering the value of the property(ies) on the power consumption of those consumers. 
     The data set may include property(ies) and power consumption values measured over a period of time of at least: 
     1 year; 
     2 years; 
     3 years; 
     4 years; 
     5 years; 
     6 years; 
     7 years; 
     10 years; 
     15 years; or 
     20 years. 
     The data set may include seasonal information, for instance whether it is winter, spring, summer or autumn or Christmas day or a bank holiday, and wherein the seasonal information may be used to assist in determining the most likely effect of altering the value of the property(ies) on the power consumption of those consumers. 
     The most likely effect of altering the value of the property(ies) from a first value to a second value on the power consumption of those consumers may be determined by using one or more of the following: 
     numerical regression, 
     k-means clustering, 
     multivariate analysis, 
     neural network, 
     Bayes&#39; theorem. 
     The property may be voltage. 
     The voltage control system may be further operable to communicate instructions to the substation to alter the voltage within the portion of the grid from the first value to the second value. 
     Each transformer may include a primary and a secondary winding. The substation may provide circuit element connectable to a portion of the grid to alter the voltage supplied to the consumers within the portion of the grid. 
     The value of the at least one property and the power consumption are measured and added to the data set in response to capacitor connection or disconnection from the portion of the grid. 
     The value of the at least one property and the power consumption may be measured and added to the data set in response to an increase or reduction in windings of either winding of a transformer. 
     The transformer may include a primary and a secondary winding and wherein the data set may include the number of windings on one or both of the primary and/or secondary windings of the transformer. 
     The voltage control system may be operable 
     to determine from the previously measured values of the at least one property in the data set an effect of altering the value of the voltage supplied to consumer within a portion of the grid to each one of a plurality of different values, on the power consumption of those consumers within that portion of the grid, and 
     to determine a selected one of the plurality of values to be the second value. 
     The grid may include a plurality n of substations each providing one or more transformers operable to increase or decrease the voltage supplied to consumers within a respective portion of the grid supplied by that respective substation, and 
     the voltage control system may be operable to measure, for each of the n substations, the at least one property within the portions of the grid associated with that respective substation, and 
     wherein, for each of the n portions of the grid, determine from the previously measured values of the at least one property in the data set a most likely effect of altering the value of the of voltage supplied to consumers associated with that portion of the grid from a first value to a second value, on the power consumption of those consumers within that portion of the grid. 
     According to a second aspect we provide a method of controlling voltage supplied to a portion of a distribution grid, the method including 
     providing a data set as set forth in accordance with the first aspect 
     measuring at least one property within a portion of the grid supplied by a substation, and 
     determining from the previously measured values of the property(ies) in the data set an effect of altering the voltage supplied to consumer within the portion of the grid from a first value to a second value on the power consumption of those consumers. The property may be voltage. 
     The method may include measuring the value of the property(ies) and power consumption and storing the value(s) with the associated measured power consumption in the data set. 
     The method may further include communicating instructions to a substation providing one or more circuit elements operable to increase or decrease the voltage supplied to consumers within the portion of the grid, to alter the voltage within the portion of the grid from the first value to the second value. 
     The method may include measuring the value of the voltage and power consumption and storing the voltage value with associated measured power consumption in the data set in response to the operation of one or more of the circuit elements. 
     According to a third aspect of the invention we provide a system for controlling voltage supply to a portion of a distribution grid, the portion of the grid including a substation providing one or more transformers operable to increase or decrease the voltage supplied to consumers within the portion of the grid, 
     the voltage control system being operable (via a measuring device) to measure a first voltage supplied at a first time to the consumers within the portion of the grid and to measure or calculate an estimate of a first load being used by the consumers at that first time, and 
     the voltage control system being operable (via a processing device) to determine an estimate of the effect, of altering the voltage supplied to those consumers from the supplied voltage to a revised voltage, on the power consumption of those consumers. 
     The voltage control system may be further operable to communicate instructions to the substation to alter the voltage supplied to the consumers within the portion of the grid to the revised voltage, so that a second voltage, different to the first voltage, is supplied to the consumers at a second time. 
     Each transformer of the substation may provide a tap changer operable to increase or reduce the windings on one or both of the primary and/or secondary winding of the transformer so as to alter the voltage output from the transformer to the consumers within the portion of the grid. 
     The voltage control system may provide a voltage control device operable to measure the voltage supplied to the consumers within the portion of the grid, and to communicate the measured voltage to a network control device, the network control device being operable to determine the estimate of the effect of applying the revised voltage, and subsequently to communicate instructions to at least one of the substation and the voltage control device to apply the revised voltage. 
     The voltage control device may be operable to receive instructions communicated from the network control system to apply the revised voltage, and to communicate those instructions to the substation. 
     The voltage control system may be operable 
     to determine an estimate of the effects, of altering the supplied voltage to each one of a plurality of different voltages, on the power consumption of those consumers, and 
     to determine a selected one of the plurality of voltages to be the revised voltage. 
     The voltage control system may be operable to display the estimate of the effect of applying the revised voltage to a user, and the voltage control system is operable to communicate instructions to the substation to implement the revised voltage on receipt of an input from the user. 
     The estimates of the effects of applying each of the plurality of different voltages may be displayed to a user, and 
     the voltage control system may be operable to receive an input from the user representing a selected one of the different voltages, 
     the revised voltage being set as the selected one of the voltages. 
     The voltage control system may be configured to store indications of a plurality of predetermined voltages, wherein the plurality of different voltages for which estimates are determined is a subset of the stored predetermined voltages. 
     The voltage control system may be configured to receive an input of the revised voltage from a user, and subsequently to determine the estimated effect of applying that revised voltage. 
     The grid may include a plurality n of substations each providing one or more transformers operable to increase or decrease the voltage supplied to consumers within a respective portion of the grid supplied by that respective substation, and 
     the voltage control system may be operable to measure, for each of the n substations, a first voltage supplied at a first time to the consumers within the portions of the grid associated with that respective substation, and to measure or calculate an estimate of a first load being used by the consumers at that first time in that respective portion of the grid served by that substation, and 
     wherein, for each of the n portions of the grid, determine an estimate of the effect of altering the voltage supplied to the consumers within that portion of the grid from the supplied voltage to a respective revised voltage associated with that portion of the grid, on the power consumption of those consumers within that portion of the grid. 
     According to a fourth aspect of the invention we provide a method of controlling voltage supplied to a portion of a distribution grid, the method including 
     measuring a first voltage supplied at a first time to consumers within a portion of the grid supplied by a substation, 
     measuring or calculating an estimate of a first load being used by the consumers at that first time, and 
     determining an estimate of the effect of altering the voltage supplied to those consumers from the supplied voltage to a revised voltage on the power consumption of those consumers. 
     The method may further include altering the voltage supplied to the consumers within the portion of the grid to the revised voltage, so that a second voltage, different to the first voltage, is supplied to the consumers at a second time. 
     The voltage supplied to the consumers may be altered by operating a tap changer provided by the substation to increase or reduce the windings on one or both of the primary and/or secondary winding of the transformer. 
     The method may include using a voltage control device to measure the voltage supplied to the consumers within the portion of the grid by the associated substation, 
     communicating the measured voltage from the voltage control device to a network control device, 
     estimating the effect of applying the revised voltage using the network control device, and subsequently 
     communicating instructions to at least one of the substation and the voltage control device, from the network control device, to apply the revised voltage. 
     The method may further include receiving at the voltage control device instructions to apply the revised voltage, communicated from the network control system, and 
     communicating those instructions to the substation. 
     The method may include 
     determining an estimate of the effects of altering the supplied voltage to each one of a plurality of different voltages on the power consumption of those consumers, and 
     determining a selected one of the plurality of voltages to be the revised voltage. 
     The method may include displaying the estimate of the effect of applying the revised voltage to a user, 
     receiving an input from a user confirming the revised voltage is to be applied, and subsequently 
     communicating instructions to the substation to implement the revised voltage. 
     Displaying the estimate of the effect to the user may include displaying the estimated effect of the effects of applying each of the plurality of different voltages, 
     receiving an input from the user representing a selected one of the different voltages, and 
     setting the revised voltage equal to the selected one of the voltages. 
     The method may include storing indications of a plurality of predetermined voltages, from which the plurality of voltages used to estimate effective changes in power consumption are selected. 
     The method may further include receiving an input of the revised from a user, and subsequently determining the estimated effect of applying that revised voltage. The method may include measuring a first voltage supplied at a first time to consumers within respective portions of the grid each supplied by a respective one of a plurality of n substations, 
     measuring or calculating an estimate of a first load being used by the respective consumers of each portion of the grid at that first time by each respective substation, and 
     determining, for each of the n portions of the grid, an estimate of the effect of altering the voltage supplied to the consumers in that portion of the grid from the supplied voltage to a respective revised voltage associated with that portion of the grid, on the power consumption of those consumers within that portion of the grid. 
     The method may include measuring the power consumption after the revised voltage is applied, and storing to a data set the revised power consumption and the associated voltage (and/or other measured property values). 
     According to a fifth aspect of the invention we provide a voltage control device for use in controlling the voltage supplied to consumers within a portion of a grid supplied with electrical power by a substation, the device providing a measuring device for measuring the voltage supplied to the consumers, and the voltage control device being configured to measure or to calculate an estimate of a load being used by the consumers at that first time, and providing a communication interface for communicating the measured voltage and the measured or estimated load to a remote network control device. 
     According to a sixth aspect of the invention we provide a network control device for use in controlling the voltage supplied to consumers within a portion of a grid supplied with electrical power by a substation, the device providing 
     a communications interface for receiving an indication of a measured voltage and a measured or estimated load, and 
     a processor configured to determine an estimate of the effect, of altering the voltage supplied to those consumers from the measured voltage to a revised voltage, on the power consumption of those consumers. 
     The voltage control device and network control devices may be configured to operate with the voltage control system according to the first aspect of the invention. 
     In broad terms, a circuit element can be implemented to increase or decrease the voltage supplied to consumers within a portion of the gird. One example, of a circuit element that can increase or decrease voltage supplied to consumers within a portion of the grid is a capacitor. Additionally, another circuit element that can be implemented is a transformer that can increase or decrease voltage supplied to consumers within a portion of the grid. In at least another example, a tap changer can be implemented as the circuit element. In yet other examples, the circuit element can include two or more elements that can be selected from the above. The use of circuit element as used herein is not limited to a single element, but can include one or more elements. Furthermore, there are combination of the devices described above that can be implemented a single device. transformers transfer electrical energy between two circuits through electromagnetic induction. As known in the art, a varying magnetic field is produced by varying current in a coil of the transformer, in turn causing a voltage in the second coil. In this way power is transferred between the two coils via the magnetic field. Transformers are deployed at various positions within an electrical power grid  10 . For example, transformers  18  are used on the transmission grid  12  in which power generating resources  16  (such as power stations) are located, to convert the electrical supply to a suitable lower voltage for transmission on the distribution grid  14  to consumers. Transformers  20  are also provided at local substations on the grid, to further lower the voltage to a level suitable for consumption in residential, commercial and industrial premises, for example (i.e. 240V in the UK). 
     In a typical power network the system voltage is regulated by altering the tap position of transformers  18 ,  20 . A tap changer is used to alter the turn ratios on one or both coils of the transformer in discrete steps. A variable turns ratio is enabled by connecting a number of additional taps on either the primary or secondary winding of the transformer  18 ,  20 , to increase or decrease the ratio of turns between the primary and secondary windings. By increasing and decreasing the ratio, the voltage output from the transformer is altered. For example, the default setting of the transformer may convert a high voltage input to a lower voltage output, by providing 80 coils on a primary (i.e. input) winding, and 20 coils on a secondary (i.e. output) winding, to create a drop to 4 to 1 ratio of input to output voltage. By increasing the ratio of coils between the two windings (e.g. by adding tapped coils to the primary winding), the ratio of input to output voltage is increased, resulting in output voltage being decreased. The tap changers can be automated or may be manually operated. 
     Additionally or alternatively, one or more capacitors may be operable to alter (increase or decrease) the voltage supplied to consumers with a portion of the grid. As indicated above, a combination device such as a capacitor voltage transformer or capacitor-coupled voltage transformer can be implemented as the circuit element operable to increase or decrease the voltage supplied to consumers within a portion of the grid. 
     Many substations include a pair of transformers working in parallel. Where illustrated in the figures, a substation  20  is represented by a single transformer  20 , but it should be understood that a substation typically provides a pair of transformers working in parallel. Each tap of each transformer  20  changes the voltage by about 1.5%, with a typical tap range of about 20% available on each transformer  20 . A pair of transformers  20  feeding 20,000 customers will tap up and down typically between 2-20 times every day during the course of normal operation, to maintain an even output voltage given variation in the input voltage received from the transmission grid  12 . The resultant changes to voltage are so small as not to be noticeable by customers. 
     If a pair of transformers  20  supplying a group of premises are operated at different tap positions, i.e. with “staggered taps”, a circulating current is introduced around the pair. The circulating current decreases the network power factor and effectively absorbs reactive power from the upstream distribution grid  12 . The consequential increase in reactive demand reduces network voltages higher up in the grid but leaves customer voltages unaffected. This technique is highly effective in controlling potential unacceptable high voltages. 
     This paired arrangement for transformers  20  can also be used to deliver a very fast demand response which can automatically balance a network in the event of loss of a large generation in feed. For example, if one of the pair of transformers  20  is disconnected, supplies are still maintained to all premises in the group by the second transformer  20  but the voltage supplied to the group will instantaneously reduce by between 4-8% triggering a similar instantaneous demand reduction in the group. When aggregated across many substations, this response is sufficiently large to counteract the loss of a major power generator  16 . The system of the present invention allows a response of this nature to be delivered in a coordinated and controlled manner. 
     A significant drop in demand (of 20-40%, for example) may be enabled under certain conditions—such as when all available sources of reserve generation have been exhausted and the only option available to balance the system is to reduce demand. Demand reduction can be achieved either through voltage reduction or direct disconnection of loads. A voltage reduction of a 3% typically provides a 5% demand reduction and a 6% voltage reduction provides a 10% demand reduction. To meet these demand reduction requirements, a 1.5% voltage change from transformer tap operation delivers a predictable and controlled demand response which when aggregated at a point in a network is adequate for demand management, whether locally or on a wider national grid whilst at the same time not impacting on the quality of supply to customers. 
     With reference to  FIG. 1  of the drawings, the distribution grid  12  is connected via substations  20  that provide transformers (in pairs, as described above) for converting the transmitted voltages to lower voltages for supply to consumers  22 , for example. In general terms, the power is supplied locally to consumers at premises such as residential, commercial, or industrial units, for example. A single substation  20  may supply power to a single or to multiple consumers  22 . In a residential neighbourhood, for example, a substation may provide power to hundreds, or thousands, of properties. In the case of residential premises, the consumers  22  draw a relatively small amount of power each—in the order of a few kW. However, the power consumed within each subsection of the grid served by a substation  20 , varies constantly. While the consumption follows certain general patterns, there is no certain method of predicting how much power will be required at a specific time or over a future time period, and therefore the load placed on the substation  20  cannot be known accurately in advance. 
     In broad terms, a system is provided for controlling voltage supply to portions of the distribution grid. Each portion can be thought of as providing a respective substation  20 , having one or more transformers operable to increase or decrease the voltage supplied to consumers within that portion of the grid. In general terms, a voltage control system measures a first voltage supplied at a first time to the consumers within the portion of the grid. The system also measures (or calculates based on other readings) an estimate of the load being used by the consumers at that point in time—in other words, how much electricity is being consumed. Using this data, the voltage control system determines an estimate of the effect, of altering the voltage supplied to those consumers from the supplied voltage to a revised voltage, on the power consumption of those consumers. In other words, if the voltage to that portion of the grid is reduced, what is the corresponding drop in power usage likely to be as a result of that voltage reduction? Similarly, if the voltage rises, what effect is that likely to have. Such variations in power consumption effect the frequency of the grid, and therefore having knowledge of the effect of such rises and reductions prior to making them, provides important information used to manage the grid and react to fluctuations in frequency. 
     The voltage control devices  26  form part of a voltage control system which may include multiple voltage control devices  26  each being associated with a respective substation  20  and set of consumers  22 . One or more network control devices  28  also form part of the voltage control system, the network control devices  28  being configured to communicate with the voltage control devices  26 , to receive data from those devices, and to determine ways in which to regulate frequency on the grid by controlling the respective substations  20 . 
     Each voltage control device  26  may provide a relay  48 , for example, to disconnect the consumers  22  from the powered network in the event of a fault occurring, by activating a circuit breaker to trip the powered connection. 
     In embodiments, and particularly in residential and commercial settings, a single voltage control device  26  may connect one or more premises to the substation  20 , and preferably, the voltage control device  26  provides a power connection between the substation  20  and a plurality of consumers  22 . In industrial settings, or for single consumers creating large power consumption (such as a hospital, for example), a single voltage control device  26  may connect a substation  20  to what is effectively a single consumer  22 . 
     Each consumer  22  may use a plurality of powered devices, each drawing electrical load from the network. For example, residential properties may include tens or even hundreds of devices requiring electrical power. Factories or commercial premises may provide tens or hundreds of power-consuming units  24  such as air conditioning systems, refrigeration systems, storage heaters, or the like. 
       FIGS. 2 and 3  illustrate a voltage control device  26  and a network control device  28  according to embodiments of the invention. The voltage control device  26  includes a measuring device  44  operable to measure the voltage of the electricity supplied (see input line  42 ) to its respective consumers  22 . The measuring device  44  or a further measuring device is also operable to measure or calculate the load drawn on the network by the consumers  22  forming its subsection of the network. The measuring device  44  (or in at least one example, another measuring device) may be operable to measure the frequency of the network. 
     In embodiments the voltage control device  26  includes a processor  46  for controlling operation of the device, the processor  46  being connected to a data storage device  50  (either internal to the device or via a data link to a remote device or cloud resource, for example). The storage device  50  may be used to store operating instructions to configure the processor  46  to operate the relay  48  when certain operating conditions are detected. For example, the relay  48  may be tripped in the event that an over-voltage is detected by the measuring device  44 . 
     The measurements of voltage and/or current made by the voltage control devices  26  are communicated to the network control device  28 , and received via a network communication interface  32 . The measurements may also be stored locally on the storage device  50 . The voltage control devices  26  provide a communications interface  52  for sending data to and receiving data from the network control device  28  via a communication channel  54 . The communication channel  54  may be provided by a direct wired link or via a wired or wireless network, via internet protocol (e.g. via a cloud-based server), or by any other suitable means of communication as is known in the art. The network control device  28  provides a respective communication interface  32  for sending and receiving data to and from the voltage control devices  26  and/or substations  20 . 
     In embodiments the network control device  28  further provides a dashboard functionality—in other words, providing an interface for a user to oversee and/or control the operation of the various distributed voltage control devices across the network, and/or to control the transformers operating at the various substations  20  on the network. The terms network control device  28  and dashboard are used interchangeably herein. 
     The network control device  28  provides a processor  36 , operable to control and configure the voltage control devices  26  and transformers at local substations  20  on the network, via the communications interface  32 . The network control device  28  further provides a network storage device  38  for storing operating data and/or operating instructions and settings. The network storage device  38  may be formed integrally with the network control device  28  or may be hosted elsewhere on the network or on cloud-hosted remote storage, for example. In such cases, the storage device  38  may be accessible via the communications interface  32 . 
     In embodiments, the network control device  28  may itself provide a measuring device  34  for measuring aspects of network operating conditions, such as voltage, current or frequency conditions in a part of the network. 
     The network control device  28  further provides a control interface  40  for connection to a grid management system  30 , which is operable to oversee grid operations and performance. The grid management system  30  is operable to provide feedback of operating conditions to users operating and overseeing the grid network, via a user interface  32 . The user interface may be hosted locally at the network control device  28  or via a network connection on a remote terminal, or via a web-based portal hosted on a server for example. 
     Primarily the network control device  28  is operable to receive data transmitted from the voltage control devices  26 , indicating details of the voltage of the electricity supplied from its associated local substation  20 . The information received may include one or more measurements of voltage, current drawn by the consumers  22  on that portion of the grid, the operating current conditions, and frequency. In this way the voltage control system is able to use the information of the voltage being supplied to the portion of the grid, and the operating conditions on that respective portion of that grid including the load being drawn, to estimate the effect (in terms of change of power consumption at least, from which a corresponding change in frequency may be inferred) of changing the voltage before any such change is made. The voltage control system then communicates instructions to the substation  20  to alter the voltage supplied to the consumers  22  within the portion of the grid to the revised voltage. 
     The transformer(s) of the substation  20  typically provide tap changers as described above, operable to increase or reduce the windings on one or both of the primary and/or secondary winding of the transformer so as to alter the voltage output from the transformer to the consumers within the portion of the grid. The instructions to alter the voltage are sent either by the network control device  28  directly to the substation  20 , or from the network control device  28  via the voltage control device  26  associated with that substation  20 . 
     The circuit elements of the substation can be connectable to a portion of the grid to alter the voltage supplied to the consumer(s) within the portion of the grid. The value of the property(ies) and the power consumption are measured and added to the data set in response to a circuit element connection or disconnection from the portion of the grid. 
     The capacitor(s) of the substation can be connectable to a portion of the grid to alter the voltage supplied to the consumer(s) within the portion of the grid. The value of the property(ies) and the power consumption are measured and added to the data set in response to a capacitor connection or disconnection from the portion of the gird. 
     As detailed herein, a circuit element can include one or more elements. Additionally, the circuit element can be capacitor voltage transformer or capacitor-coupled voltage transformer. 
     In embodiments, the network control device  28  is programmed to carry out automated responses to situations arising on the network, either locally at subsections of the network served by particular substations  20  and/or voltage control devices  26 , or at a network-level, where the responses of multiple voltage control devices  26  and/or substations  20  on the network are controlled centrally to achieve a particular grid-level response. 
     In embodiments, the network control device  28  is configured to determine a suitable change in voltage to apply, where a frequency event or the like is detected, indicating that a change in voltage is required. For example, with a sudden peak in frequency, the network control device  28  may determine that a drop in voltage is required to reduce the power consumed in a portion of the grid. Alternatively, a user of the system (via the dashboard and user interface  32 ) may review a potential voltage drop prior to putting it into effect, to determine its likely outcome. The network control devices  28  may either select a candidate voltage from a predefined set of voltages saved on the storage device  38 , or may calculate a candidate voltage based on the data readings (i.e. present voltage, load on the portion of the grid, and optionally frequency on the grid or frequency response to be achieved). In embodiments, a plurality of different voltages may be considered, each providing a different change in power consumption, and associated frequency response. The estimates of the change in consumption are displayed to a user, or are calculated and reviewed by the network control device  28 , so that a preferred candidate may be selected as the revised voltage to be used. Instructions are then sent accordingly, and in the case where user input is required, confirmation is requested prior to the instructions being sent. 
     Of course, the network control device  28  receives information from a plurality of voltage control devices  26  across the grid, and is operable to select between different portions of the grid before making a choice of which substation needs remedial action. The system may compare the estimated effects of altering the voltages provided to different portions of the grid, each being subject to different loads, and potentially having different frequency response characteristics. In this way, a system operator may compare the effects of applying voltage changes to different portions of the grid, to make an educated assessment of which substation transformers to operate (i.e. to change the voltage supplied). 
     In embodiments, the system may include a data set which includes a previously measured power consumption which is associated with a previously measured value, or measured values, of a property, or properties. This property, or properties, may be one of voltage, current, frequency or load, or a combination thereof. This property, or properties, is measured by the measuring device as described above. 
     Using such a data set has been found to be advantageous in predicting responses in large networks, and in particular in portions of the grid including a combination of constant power and constant impedance loads. Examples of loads in such a portion of the grid are motor controllers, generators and other power loads/sources that respond substantially independently to either counteract or amplify the change in power consumption. Previously systems have relied on formula driven models (i.e. theoretical models), such as described in US2011/0251732, which produce the same response for a given set of inputs (since the formula provides one outcome for a defined set of inputs). Often these models are provided with tuneable parameters to try and match the formula driven model as closely as possible to the portion of the grid which the model is modelling. Furthermore, such models are bound by a finite and usually small set of parameters, providing a theoretical prediction of power output response. In contrast, by using a data set which includes previously measured power consumptions, and/or changes in power consumptions, associated with property(ies), and/or changes in property(ies), of the portion of the grid, or the consumers, and other factors having an input on power consumption, it is possible to predict reliably how the power consumption of the portion of the power grid, or the consumers, will change for a given change in the property(ies). In other words, rather than making a theoretical prediction based on a fixed set of parameters, the system bases its estimation of change in power consumption (i.e. the effect of altering the value(s) of the property(ies)) and/or voltage supplied on recorded observations of similar scenarios or identical scenarios in relation to the network, or a network under similar or identical conditions or experiencing similar or identical changes in conditions. In embodiments, in this way, the system provides adaptive behaviour so that its response differs according to observations or past behaviour and the results of that behaviour. 
     As described above the system may include a processor, or processing device. In embodiments including the data set the processing device may determine from the previously measured values of the property(ies) in the data set an effect of altering the value(s) of the property(ies) and/or voltage supplied from a first value to a second value on the power consumption of those consumers. 
     The processing device may be configured to determine whether the power consumption of the consumers has reached a desired value. This may be advantageous in ensuring the portion of the grid is drawing the amount of power that is expected. 
     The measured value of the property, or values of the properties, and the measured power consumption may be added to the data set. This may be advantageous as it provides more data in the data set for the processing device to interrogate in determining the effect of altering the value(s) of the property(ies) and/or voltage supplied from a first value to a second value on the power consumption of those consumers. 
     The data set may include measurements of the property, or properties, and the measured power consumption which have been taken every: 60 minutes; 50 minutes; 40 minutes; 30 minutes; 20 minutes; 15 minutes; 10 minutes; 5 minutes; 4 minutes; 3 minutes; 2 minutes; or 1 minute. This is advantageous as this improves the accuracy of the data set and thus the accuracy of the most effect of altering the value of the property, values of the properties, and/or voltage supplied, on the power consumption of consumers. 
     The data set may include the day on which the property(ies) and power consumption were measured, for example, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday or Sunday. The day on which the property(ies) and power consumption were measured may be used to assist in determining the effect of altering the value of the property(ies) and/or voltage supplied on the power consumption of consumers. 
     The data set may include property(ies) and power consumption values measured over a period of time of at least: 1 year; 2 years; 3 years; 4 years; 5 years; 6 years; 7 years; 10 years; 15 years; or 20 years. This may be advantageous in providing a robust data set which improves the accuracy of the data set and thus the accuracy of the effect of altering the value of the property, values of the properties, and/or voltage supplied, on the power consumption of consumers. 
     The data set may include seasonal information associated with the measured property(ies) and measured power consumption. For instance the data set may include whether the measurements were made in winter, spring, summer or autumn. The data set may also include whether the measurements were made on a public holiday. The seasonal information may then be used to assist in determining the effect of altering the value of the property(ies) and/or voltage supplied on the power consumption of consumers. 
     The data set may include environmental information associated with the measured property(ies) and measured power consumption. For instance, the data set may include the temperature at the time the measurements were made. The data set may include the weather at the time the measurements were made. This may be advantageous because it may enable a closer match between presently measured property(ies) and previously measured property(ies) which may in turn provide a more accurate determination of the effect of altering the value of the property(ies) and/or voltage supplied from a first value to a second value on the power consumption of consumers. 
     The data set may include the number of windings on the primary and/or secondary windings of the transformer when the measurements were made. This may be advantageous as this improves the accuracy of the data set and thus the accuracy of the effect of altering the value of the property, values of the properties, and/or voltage supplied, on the power consumption of consumers. 
     The effect of altering the value of the property(ies) and/or voltage supplied from a first value to a second value on the power consumption of those consumers may be determined by using one or more of the following: numerical regression; k-means clustering; multivariate analysis; a neural network; Bayes&#39; theorem. This may be advantageous as this improves the ability of the system to interrogate the data set. This in turn improves the system ability to determine the most suitable previous measurements on which to base the effect of altering the value of the property, values of the properties, and/or voltage supplied, on the power consumption of consumers. 
     While example embodiments of the invention are described herein, it should be understood that features of different embodiments may be combined with one another, in isolation from one another or in any combination, unless stated otherwise. 
     When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. 
     The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.