A method of distributing electricity across an electricity distribution network

Abstract

Apparatus for and method of distributing electricity across an electricity distribution network including: providing a voltage adjustment device 22 located between a power generation site 12 in the el

Description

TITLE: A method of distributing electricity across an electricity distribution network FIELD The invention relates to an electricity distribution method and apparatus for implementing such a method. BACKGROUND Electrical distribution networks are designed to supply electricity at a voltage that lies within a tolerance band of a predetermined voltage. This allows for fluctuations in demand, available generating capacity and losses within the distribution network. In the UK, for example, the predetermined target voltage is 230Vac, although the actual voltage supplied may be within +10% and -6% of this target. In many instances, the actual voltage supplied to consumers is approximately 242Vac. Other countries or regions have different target voltages, and may have different tolerance bands. Electrical energy can be generated by a number of different sources, and a single distribution network may distribute electrical energy generated by one type of source, or by many types of sources. Example sources include fossil fuels such as coal, petroleum, or gas; renewable energy sources such as solar energy wind energy or hydropower; or nuclear sources such as nuclear fission. To produce electrical energy from fossil fuels, the fuel is burnt to generate heat. This heat is in turn applied to a source of water to generate steam. The steam generated by this process is in turn used to drive a turbine (or multiple turbines). The turbines are driven at a predetermined nominal target frequency, which in turn produces alternating current (AC) power. In the UK, this predetermined nominal target frequency is 50Hz, although it may actually be suppled within £1% of this (i.e., +0.5Hz) The electricity generated by these sources is often transmitted over long distances and transmission is carried out at relatively high voltages, to reduce losses. Electricity transmission is typically carried out by overhead power cables. Electrical distribution networks typically include transformers at substations which step down the voltage for local distribution to connection points, e.g. homes, offices, street furniture, etc. A local substation may step down the voltage from approximately 11kV to approximately 400V (3-phase), for example. In high load areas, for example densely populated areas, it is known to provide multiple feed cables from different transformers. A significant portion of the existing electrical distribution infrastructure was constructed at a time when many modern sources of power generation where not commonplace and consumer usage habits were significantly different to those of the present day. For example, most consumers now own a relatively large number of electrical appliances, and many consumers own electrical vehicles (EVs) which require frequent charging. In addition, the increasing adoption of homeworking has not only served to increase domestic power consumption, but has also altered the times of the day when consumption may be expected to peak. As a result, the evolving demand on electricity distribution network continues to have a detrimental effect on its ability to distribute electricity to consumers in a stable manner. The present invention provides an electricity distribution method and apparatus as set out in the appended claims. BRIEF DESCRIPTION OF THE FIGURES In order that the present disclosure may be more readily understood, preferable embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: FIGURE 1 is a schematic view of an electricity distribution network in accordance with the present disclosure; FIGURE 2 is a schematic view of a part of the electricity distribution network of Figure 1; FIGURE 3 is a graph showing the change in voltage over time of electricity generated by a power generation site and electricity consumed by at least one consumer; FIGURE 4a is a graph showing the change in a characteristic over time of electricity generated by a power generation site and change in a characteristic over time of electricity injected into a transmission network by a power stabilisation device; FIGURE 4b is a graph showing the change in a characteristic over time of electricity generated by a power generation site and change in a characteristic over time of electricity injected into a transmission network by a power stabilisation device; and FIGURE § is a schematic view of a part of the electricity distribution network of Figure 1 with three- phase supply cables. DETAILED DESCRIPTION OF THE DISCLOSURE Referring to Figure 1, there is shown an electricity distribution network 10, including a power generation site 12, a transmission network 14 and a consumer distribution network 16. It will be appreciated that the electricity distribution network 10 may include a plurality of power generation sites 12. The power generation site 12 may be operable to generate electrical energy in any manner, including through the use of renewable and / or non-renewable energy sources. For example, a power generation site 12 may include a synchronous generator connected to a steam turbine. The steam turbine may be driven by steam which is produced using heat generated from any appropriate source, such as the burning of fossil fuels or through renewable sources. The process of driving the turbine, and thus the synchronous generator, is carefully controlled and maintained at a specific rotational frequency. In the UK, this rotational frequency is approximately 3000 rpm, which equates to a nominal mains frequency of approximately 50 Hz. Electrical energy generated at the power generation site 12 may be transmitted at a relatively high transmission voltage, e.g. between 400kV and 275kV, via a transmission apparatus 15 which may form part of the transmission network 14. The transmission apparatus 15 may be suitable for transmitting electrical energy over long distances. The transmission apparatus 15 may include, for example, overhead power lines, step-up transformers for elevating the voltage of the electricity produced by the power generation site 12 to the required transmission voltage and step-down transformers for providing electricity to large industrial sites. It will be appreciated that any appropriate apparatus for the transmission of electrical energy may be included in the transmission network 14. The transmission network 14 and associated transmission apparatus 15 may be a part of the overall electricity distribution network 10 which is closer to the power generation site 12. In general, the purpose of the transmission network 14 is to transmit electricity at the relatively high voltages described above to the consumer distribution network 16. The consumer distribution network 16 may be a part of the overall electricity distribution network 10 which is remote from the power generation site 12 and is closer to a at least one consumer 20, or a plurality of consumers 20, and may include a distribution apparatus 17. The purpose of the consumer distribution network 16 is to transmit electricity at a relatively lower distribution voltage, compared to the transmission voltage, to at least one consumer 20, or a plurality of consumers 20, as described in more detail below. The distribution apparatus 17 may include, for example, overhead power lines, underground power lines and any other appropriate apparatus for the distribution of electrical energy to consumers 20. The electricity distribution network 10 may include a substation 18. As shown in figure 1, the substation 18 provides a connection or interface between the transmission network 14, and the associated transmission apparatus 15, and the consumer distribution network 16, and the associated distribution apparatus 17. For simplicity, one substation 18 is shown as connected to a single transmission apparatus 15 and a single distribution apparatus 17. However, it should be appreciated that an electricity distribution network 10 may include any appropriate combination of a plurality of substations 18, a plurality of transmission apparatus 15 and a plurality of distribution apparatus 17. Electricity transmitted to the substation 18 may be distributed to a group of consumers 20 to which it is connected to via the distribution apparatus 17 contained within the distribution network 16 and / or it may distribute electricity to other parts of the distribution network 17 which may include further substations 18 which may be connected to other groups of consumers 20. At the substation 18, the value of the voltage of the electricity transmitted to the substation 18 may be adjusted to a value of voltage, i.e., a distribution voltage, which is suitable for safe distribution to the consumers 20. The adjustment of the transmission voltage to the distribution voltage is accomplished through the use of at least one transformer, as described below. The distribution voltage may be the mains supply voltage which may be set nationally, for example. The nominal distribution (mains supply) voltage in the UK is 230V (single-phase) and 400V (three-phase), and the nominal frequency is 50Hz. It should be appreciated that the substation 18 may be connected to, or otherwise in communication with, other substations 18 which may distribute electricity in a different phase arrangement. For instance, the substation 18 may distribute electricity via a three-phase supply to another substation 18 which distributes electricity to consumers 20 via a single-phase supply, or any other appropriate combination. For this purpose, the substation 18 may include a voltage adjustment device 22, or a plurality of voltage adjustment devices 22. The or each voltage adjustment device 22 may be operable to adjust the distribution voltage, and may be operable to increase or decrease the distribution voltage above or below a predetermined value. In addition, the or each voltage adjustment device 22 may be operable to stabilise the distribution voltage such that the distribution voltage is held substantially constant. For example, the or each voltage adjustment device 22 may be operable to reduce the transmission voltage to a distribution voltage. The or each voltage adjustment device 22 may also be operable to increase the distribution voltage by approximately 10%, i.e. to maintain the distribution voltage at a value approximately 10% higher than the nominal distribution voltage. The increased distribution voltage which is ultimately distributed or distributable to the consumers 20 must remain within an acceptable range, which, in the UK for example is approximately the nominal distribution voltage +10% / -6%, i.e. 216.2V-253V. In Europe, the nominal distribution voltage is 230V +10%, i.e. 207V-253V. It will be understood that the maximum permissible increase in the distribution voltage of the electricity which is ultimately distributed or distributable to the consumers 20 will be dictated by local (e.g. continental / national / regional) nominal voltages and associated tolerances. As shown in figure 2, the or each voltage adjustment device 22 may comprise a transformer 22a, or a plurality of transformers 22a. The or each of the transformers 22a may be operable to step-down the voltage from the relatively high voltage transmission voltages described above to a lower distribution voltage. For example, the or each transformer 22a may step-down the relatively high transmission voltage at a fixed ratio, for instance by using a transformer 22a with fixed primary and secondary windings. In another example, the or each transformer 22a may step-down the relatively high transmission voltage at a variable ratio, for instance by using a transformer 22a with a plurality of coil taps and a tap changing mechanism such as an on-load tap changing mechanism or an off- load tap changing mechanism, as is known in the art. The substation 18 may include any combination of a transformer 22a, or a group of transformers 22a, which step-down the relatively high transmission voltage at a fixed ratio, and a transformer 22a, or a group of transformers 22a, which step-down the relatively high transmission voltage at a variable ratio. As shown in figure 2, the voltage adjustment device 22, or plurality of voltage adjustment devices 22, may further include at least one voltage regulator 22b which may be used in conjunction with the or each transformer 22a described above. The or each voltage regulator 22b may include a tap-change auxiliary transformer which is in electrical communication with a transformer 22a, or plurality of transformers 22a, described above. The or each voltage regulator 22b may be operable to step-up and / or step-down the voltage of the electricity transmitted to it from the or each transformer 22a. For example, such a voltage regulator 22b may be connected to a transformer 22a which steps down voltage at a fixed ratio, with the voltage regulator 22b providing the necessary voltage adjustment described above. In other examples, the voltage regulator 22b may also include other devices such as capacitor banks and / or power semiconductor-based devices, or may utilize such devices in place of an auxiliary transformer. The physical location of the at least one voltage regulator 22b may be at the corresponding substation 18, or at a location near the corresponding substation 18. The substation 18 may include other devices in addition to those described above. For instance, the substation 18 may include equipment necessary for monitoring and measuring the electrical energy flowing through it, and may include safety features such as disconnect switches, circuit breakers and lightning arresters. In an electricity distribution network 10 including a plurality of substations 18, the network 10 may be capable of distributing electricity at a number of different voltages. For instance, a substation 18, or a group of substations 18, may include step-down transformers which step down the voltage from the transmission voltage to a distribution voltage which is higher than that of the mains supply voltage of 230V (single-phase) and 400V (three-phase). This relatively higher voltage may be more suitable for larger industrial applications such as manufacturing facilities or large commercial buildings, whereas the lower mains supply voltage may be more suitable for domestic applications such as powering homes and appliances belonging to consumers 20. Electrical energy is distributed from the or each substation 18 and any associated distribution voltage adjusters 22 to a plurality of consumers 20 via a distribution apparatus 17 at the distribution voltage set by the substation 18 and voltage distribution voltage adjuster(s) 22. Each consumer 20 may be a domestic or commercial consumer, for example. Each consumer 20 may be connected to the electricity distribution network 10 via a consumer connection point 21. Each consumer connection point 21 may include a meter, which may be a smart meter. The electricity distribution network 10 may also include one or more power stabilisation devices 23. Only one power stabilisation device 23 is shown in the figures, for the sake of simplicity. The or each power stabilisation device 23 may be associated with a voltage adjustment device 22, and may be in communication with it. The physical location of the power stabilisation device 23 may be at or near the location of the voltage adjustment device 22, or it may be remote from the location of the voltage adjustment device 22. The power stabilisation device 23 may include an input 23a and an output 23b. As shown in figure 2, the input 23a may be connected to, or otherwise in communication with, the substation 18 and the associated voltage adjustment device 22, or plurality of voltage adjustment devices 22. The input 23a may also be connected to, or otherwise in communication with, a part of the voltage adjustment device(s) 22 which is also connected to, or otherwise in communication with, the distribution network 17. The output 23b of the power stabilisation device 23 may connected to, or otherwise in communication with, the transmission network 14. For example, the output 23b may be connected to, or otherwise in communication with, the transmission apparatus 15 of the transmission network 14. In another example, it may be connected to, or otherwise in communication with, a part of the voltage adjustment device(s) 22 of the substation 18 which is / are also connected to, or otherwise in communication with, the transmission network 14 and the transmission apparatus 15. The power stabilisation device 23 may include power semiconductor-based devices, such as thyristors, power MOSFETS, power diodes and insulated-gate bipolar transistors (IGBTs) in addition to other devices such as capacitor banks or supercapacitor banks. In use, the power stabilisation device 23 may be operable to modify at least one characteristic of the electricity it receives at the input 23a, such that the electricity distributed from the output 23b differs from the electricity received at the input 23a. In examples, the characteristic may include, but not be limited to, the voltage, current or frequency of the electricity. In addition, the power stabilisation device 23 is able to modify a phase angle ¢ between the electricity it receives at the input 23a and the electricity distributed from the output 23b. As the electricity received at the input 23a may be substantially in-phase with the electricity flowing through the transmission network 14, it is thus also possible to modify the phase angle ¢ between the electricity distributed from the output 23b and the electricity flowing through the transmission network 14, as will be described in more detail below. As described above, the value of distribution voltage must remain within an acceptable predetermined range, and ideally close to a predetermined nominal value. The voltage adjustment device 22 described above may be used to stabilise the distribution voltage to an extent. However, situations may arise whereby conditions elsewhere within the electricity distribution network 10 are such that the voltage adjustment device 22 may not be able to stabilise the distribution voltage alone. For instance, in times of high demand when the consumption of electricity starts to exceed the supply of electricity being generated, the voltage and / or frequency of the electricity generated by the power generation site 12 will start to decrease. As shown in figure 3, the frequency of the electricity G generated by the power generation site 12 will reduce relative to the frequency of the electricity C consumed by the at least one consumer 20. Conversely, in times of low demand when the supply of electricity being generated starts to exceed consumption, the voltage and / or frequency of the electricity generated by the power generation site 12 will start to increase. In both scenarios, if this change in the voltage and / or frequency of electricity is left unchecked, the voltage and frequency of the electricity may exceed safe limits and may disrupt the entire electricity distribution network 10. In addition, faults may occur within the electricity distribution network 10 which may rapidly alter the availability of electricity transmitted throughout parts of the network 10, or the entire network 10. Such faults may have a cumulative effect as they may cause power lines in other parts of the network 10 to fail due to overheating and / or they may cause entire power generation sites 12 to disconnect from the network 10 to prevent severe damage. There are also factors which are not directly related to the amount of consumption of supply, or lack of supply caused by faults. For example, the type of consumption and the type of supply within parts of the network 10 may also present issues further upstream the network 10 towards or at the generator 12. One way in which stability of the voltage and frequency of the electricity distribution network 10 may be supported is by the generation and absorption of reactive power. The electricity produced by the power generation site 12 and distributed to consumers 20 across the electricity distribution network 10 is consumed by appliances used by the consumers 20. These appliances may range from large industrial equipment to lighting of commercial building to electrical appliances in domestic applications. The electricity consumed by these appliances which provides useful work, such as the illumination of a lightbulb, is referred to as real power or active power. For example, an appliance which is a purely resistive load may consume only real power, some of which may produce useful work and some of which may also be dissipated as light and / or heat. However, many appliances do not consume all of the electricity they receive to produce useful work. Many appliances may include inductive or capacitive components which may draw electrical energy, but do not use that electrical energy to perform useful work in the manner described above. An example of this may be an appliance which includes an electrical motor, whereby a portion of the electrical energy provided is used to produce a magnetic field which enables the motor to function and consume real power. This non-resultant power drawn by capacitive or inductive components of appliances is called reactive power. This reactive power circulates back and forth between the source and the load. For example, the source may be a power generation site 12 and the load may be an appliance of the consumer 20. Both the generator at the power generation site 12 and appliances of the consumer 20 may generate and absorb reactive power. The generation and absorption of reactive power is not necessarily limited to the power generation site 12 and the appliances of the consumer 20. Other parts of the electricity distribution network 10 may be capable of generating and absorbing reactive power, including parts of the transmission apparatus 14 and the distribution apparatus 18 and transformers located within the network 10. Therefore, the stability of the voltage and frequency of the electricity distribution network 10 may be supported by balancing the degree to which reactive power is generated and absorbed within the network 10. However, due to the changes in the type of consumption and the type of supply within parts of the network 10 described above, balancing reactive power and overall stability of the voltage and frequency of the electricity within the network 10 is becoming increasingly difficult. In addition, as the vast majority of consumers 20 are located remotely from a power generation site 12, the reactive power resulting from the consumer appliances must travel long distances to the generator 12 which is inefficient. As shown in Figure 1, if a number of consumers 20 are each provided with a consumer optimisation apparatus 24, the appliances within their property may no longer be capable of feeding reactive power back into the network 10. The consumer optimisation apparatus 24 may be configured such that the voltage provided to the consumer 20 is maintained at a substantially constant value, which may result in a reduction or complete elimination of available reactive power. Thus, what was at one time an abundant source of reactive power has begun to see a decline in availability. Localised renewable energy sources are also becoming increasingly commonplace which results in consumers 20 being less dependent on, or isolated from, the electricity distribution network 10. In addition to this, the supply of voltage from larger scale renewable energy sources, such as wind farms and solar farms, may be intermittent as they are switched in and out of the network 10. The power stabilisation device 23 described above may be used to provide reactive power support to the electricity distribution network 10. Use of the power stabilisation device 23 to stabilise the voltage and frequency of the electricity distribution network 10 will now be described by way of example. As described above with reference to figure 3, in times of high demand when the consumption of electricity starts to exceed the supply of electricity being generated, the frequency of the electricity G generated by the power generation site 12 may start to decrease. However, the frequency of the electricity C consumed by any connected network, such as the distribution network 16 and any connected consumers 20, may not decrease by the same amount, or may not decrease at all. As a result, and as shown in figure 3, a lag in the frequency between the electricity G generated by the power generation site 12 and the electricity C to be consumed is created — which can be expressed as a phase angle ¢, as known in the art. If this reduction in the frequency of the electricity G generated by the power generation site 12 is not mitigated and / or if the demand continues to increase, the frequency can continue to reduce until it is now below acceptable and safe limits. In such a situation, the voltage of the electricity G generated by the power generation site 12 may also start to decrease. Accordingly, to counteract this drop in the voltage of the electricity G generated by the power generation site 12, the operators of the grid may implement measures which increase the voltage which is ultimately delivered to the consumer. For instance, the operator of the power generation site 12 may operate the generator 12 to increase the voltage of the electricity G generated by the power generation site 12 as shown in figure 3, or the operator of a substation 18, or other transformer on the network 10, may increase the voltage as described above. The purpose of increasing this voltage may include the reduction of current consumption by consumers 20, the increase of the average RMS voltage supplied to the consumer 20 to protect their appliances, and to assist in the generation of reactive power which may be reflected back to the generator 12 by consumer devices as described above. Therefore, the consequence of an increase in demand may result in a reduction of the frequency of the electricity supplied to the consumer and may also result in an increase in the voltage. As described above, the power stabilisation device 23 is connected to, or otherwise in communication with, a voltage adjustment device 22, with the voltage adjustment device 22 being capable of raising or increasing the mains supply voltage as desired. By virtue of the connection of the input 23a of the power stabilisation device 23 to the voltage adjustment device 22, it may extract a portion of the electricity from the voltage adjustment device 22. For example, if the voltage adjustment device 22 increases the mains supply voltage of 230V by 10% to approximately 253V, the power stabilisation device 23 may be operable to extract a portion of the electricity at a value of approximately 23V (i.e., 10% of the value of the mains supply voltage). In another example, the voltage adjustment device 22 may increase the mains supply voltage of 230V to a desired voltage which may equate to an increase by desired percentage of the mains supply voltage (i.e., 5%, 6%, or any other percentage), and the power stabilisation device 23 may be operable to extract a portion of the electricity at a value which equates to the increase by the desired percentage. For instance, the mains supply voltage of 230V may be increased by 5% to approximately 241.5V, and the power stabilisation device 23 may be operable to extract a portion of the electricity at a value of approximately 11.5V (i.e., 5% of the value of the mains supply voltage). In a further example, the power stabilisation device 23 may be operable to extraction a portion of the electricity at a value which is different to the value by which the mains supply voltage has been increased. For instance, the mains supply voltage of 230V may be increased by 10% to approximately 253V, and the power stabilisation device may be operable to extract a portion of the electricity at a value of approximately 11.5V (i.e., 5% of the value of the mains supply voltage). In the above examples, the electricity not extracted by the power stabilisation device 23 does not decrease in voltage. For instance, if the voltage adjustment device 22 increases the mains supply voltage of 230V to 253V (a 10% increase), the voltage of the electricity to be distributed to the consumers 20 is maintained at approximately 253V whilst the extracted portion of electricity which is to be injected into the transmission network 14 is maintained at an effective value of voltage of 23V. In other words, use of the power stabilisation device 23 with a voltage adjustment device 22 results in the creation of two streams or paths of electricity which may be connected to different parts of the electricity distribution network 10, with the first stream or path having a first voltage value and the second stream or path have a second voltage value. Due to the connection between the power stabilisation device 23 and a part of the transmission network 14, the power stabilisation device 23 may inject this extracted portion of electricity having an effective value of voltage as described above into the transmission network 14. For instance, this may be injected into the transmission apparatus 15 which forms a part of the transmission network 14. As described above, the power stabilisation device 23 is also operable to modify the phase angle ¢ between a characteristic of the extracted portion of electricity which it receives at its input 23a, and a characteristic of the electricity on the part of the electricity distribution network 10 to which the power stabilisation device 23 is connected to, such as a part of the transmission network 14 and the voltage adjustment device 22. As would be understood by the person skilled in the art, the phase angle ¢ may be expressed as the phase angle ¢ between the voltage of the portion electricity extracted by the power stabilisation device 23 and the voltage of the electricity on the part of the electricity distribution network 10 to which the power stabilisation device 23 is connected (such as the voltage adjustment device 22 and the transmission network 14). Alternatively, it may be expressed as the phase angle ¢ between the current of the portion electricity extracted by the power stabilisation device 23 and the current of the electricity on the part of the electricity distribution network 10 to which the power stabilisation device 23 is connected. It may also be expressed as the phase angle between voltage of the portion electricity extracted by the power stabilisation device 23 and the current of the electricity on the part of the electricity distribution network 10 to which the power stabilisation device 23 is connected, or it may be expressed as the phase angle ¢ between the current of the portion electricity extracted by the power stabilisation device 23 and the voltage of the electricity on the part of the electricity distribution network 10 to which the power stabilisation device 23 is connected. The phase angle ¢ between a characteristic of the portion electricity extracted by the power stabilisation device 23 and a characteristic of the electricity on the part of the electricity distribution network 10 to which the power stabilisation device 23 is connected (such as the voltage adjustment device 22 and the transmission network 14) may be selected such that the characteristic of the extracted portion may either lead or lag the characteristic of the electricity on the part of the network 10 to which the power stabilisation device 23 is connected. In other words, the peak and / or zero value of the waveform of a characteristic (such as the voltage or current) of the extracted portion of electricity may either lead or lag the peak and / or zero value of the waveform of a characteristic (such as the voltage or current) of the electricity on the part of the electricity distribution network 10 to which the power stabilisation device 23 is connected. The result of this is that the power stabilisation device 23 is operable to inject or feedback electrical energy back into the network 10 not only at a desired value of voltage, but also such that the waveform of the electrical energy leads or lags the waveform of the electrical energy already flowing through the relevant part of the electricity distribution network 10, such as the transmission network 14. As described above, electrical energy within a part of the network 10, for instance electrical energy which is not utilised as real power by inductive or capacitive loads at the consumer end, which is not in phase with the electrical energy produced by the generator 12 flows through the network as reactive power. Thus, the capability of altering the phase angle ¢ as described above for the power stabilisation device 23 allows the power stabilisation device 23 to inject or feedback electrical back into the electricity distribution network 10 in the form of reactive power. This reactive power may be used to support the stability of the generator 12, and the electricity distribution network 10 as a whole. This capability of the power stabilisation device 23 to inject or feedback reactive power back into the network 10 at a desired value of voltage and a desired phase angle ¢ means that the power stabilisation device 23 can provide reactive power support to the generator 12 in response to changes in the operating characteristics of the generator 12. In other words, if the frequency and / or voltage of the electricity generated by the generator 12 increases or decreases outside of the predetermined safe limits, or is increasing or decreasing towards these limits, reactive power may be injected or fed back into the network as appropriate to counteract this increase or decrease to stabilise the generator 12. As would be appreciated by the person skilled in the art, characteristics of the electricity being distributed across the electricity distribution network 10 may be measured and monitored. For instance, characteristics of the electricity being generated at a power generation site 12 may be measured and monitored by the operators of the power generation site 12. Characteristics of the electricity being distributed may also be measured and monitored at other locations across the network 10, such as at or near substation 18, at or near consumer connection points, and at points along the transmission network 14 and the distribution network 16. The power stabilisation device 23 may therefore be used inject or feedback reactive power into the network 10 based on, i.e., in response to, measurements taken from one part of the electricity distribution network 10, or from multiple parts of the network 10. In a first example, if the measurements taken from the network 10 indicate that the frequency of the generator 12 has reduced beyond, or is reducing towards, unsafe limits, the power stabilisation device 23 may inject or feed electricity S into the transmission network 15 having a waveform which leads the waveform of the electricity G produced by the generator 12. As described above, the waveform may be representative of a characteristic of the electricity, such as voltage or current. With reference to figure 4a, the peak PS of the electricity S outputted by the power stabilisation device 23 may lead the peak PG of the electricity G produced by the generator 12. Injecting or feeding this electrical energy into the transmission network 14 means that reactive power may flow between the generator 12 and the power stabilisation device 23, such that the generator 12 is now supported by the reactive power and the frequency of the generator 12 can return to safe limits (i.e., the reactive power support allows the generator 12 to speed up). Injecting or feeding electrical energy into the electricity distribution network 10 which leads the electrical energy produced by the generator 12 may therefore be implemented when consumer demands exceeds, or is tending towards exceeding, the supply of electricity available within the network 10 and produced by the generator 12. The power stabilisation device 23 may adjust the value of the voltage and the phase angle ¢ between the electrical energy injected into the network 10 and the electrical energy produced by the generator 12 to optimise the amount of reactive power such that the generator 12 may be stabilised quickly and may be able to respond quickly to additional changes in the operating conditions of the network 10 and / or the generator 12. In a second example, if the measurements taken from the network 10 indicate that the frequency of the generator 12 has increased beyond, or is increasing towards, unsafe limits, the power stabilisation device 23 may be operable to inject or feed electricity S into the transmission network 15 having a waveform which lags the waveform of the electricity G produced by the generator 12. With reference to figure 4b, the peak PS of the electricity S outputted by the power stabilisation device 23 may lag the peak PG of the electricity G produced by the generator 12. Injecting or feeding this electrical energy into the transmission network 15 means that reactive power may flow between the generator 12 and the power stabilisation device 23, such that the generator 12 is now supported by the reactive power and the frequency of the generator 12 can return to acceptable or desirable limits (i.e., the reactive power injected into the network 10 may cause the generator 12 to slow down). Injecting or feeding electrical energy which lags the electrical energy produced by the generator 12 may therefore be implemented when the supply of electricity within the network 10 and produced by the generator 12 exceeds, or is tending towards exceeding, the consumer demand for electricity. The power stabilisation device 23 may adjust the value of the voltage and the phase angle ¢ between the electrical energy injected into the network and the electrical energy produced by the generator to optimise the amount of reactive power such that the generator may be stabilised quickly and may be able to respond quickly to additional changes in the operating conditions of the network 10 and / or the generator 12. In both examples, the reactive power injected or fed into the network 10 may absorbed by the generator 12, the transmission equipment 15, or any combination of the two. As described above, electricity may be distributed to parts of the electricity distribution network 10 in the form of a single-phase supply, or as a three-phase supply. The power stabilisation device 23 may be used with both forms of power supply. For example, the input 23a of the power stabilisation device 23 may be connected to, or otherwise in communication with, a single-phase supply cable, and the output 23b may be connected to, or otherwise in communication with, a part of the electricity distribution network 10 via a single-phase supply cable. In another example the input 23a of the power stabilisation device 23 may be connected to, or otherwise in communication with, the voltage adjustment device 22 via a three-phase supply cable, and the output 23b may be connected to, or otherwise in communication with, a part of the electricity distribution network 10 via a three-phase supply cable. When used in conjunction with three-phase supply cables, the power stabilisation device 23 may be operable to extract electricity from the voltage adjustment device 22 such that it extracts electricity from two of the three phases of the three-phase power supply at the input 23a of the power stabilisation device 23. It may extract the electricity equally from the two selected phases. The power stabilisation device 23 may then be operable to modify the phase angle ¢ relative to the electricity flowing through the transmission network 15, or other part of the electricity distribution network 10 to which it is connected. This arrangement is shown in figure 5. The voltage adjustment device 22 may be connected to the transmission network 14 via a first three-phase supply cable 31. The input 23a of the power stabilisation device 23 may be connected to the voltage adjustment device 22 via a second three- phase supply cable 32, and the output 23b of the power stabilisation device 23 may be connected to a part of the transmission network 14 by a third three-phase supply cable 33. The third three- phase supply cable 33 may be connected to any appropriate part of the transmission network, or to any appropriate device which is in communication with the transmission network 14. Each of the three-phase supply cables 31, 32, 33 includes at least three strands or cores, each corresponding to a phase of the three-phases of electricity flowing through the wire. The first three-phase supply cable 31 has a first phase 31a, a second phase 31b and a third phase 31c. The second three- phase supply cable 32 has a first phase 32a, a second phase 32b and a third phase 32c. The third three-phase supply cable 33 has a first phase 33a, a second phase 33b and a third phase 33c. With reference to figure 5, the power stabilisation device 23 extracts a portion of electricity from the first phase 32a and second phase 32b of the second three-phase supply cable 32 connected to the input 23a. The power stabilisation device 23 then modifies the phase angle ¢ of the electricity extracted from the first phase 32a and second phase 32b such that is no longer in-phase with the electricity flowing through the transmission network 14, in the manner described above. The phase shifted electricity extracted from the first phase 32a second phase 32b may then be injected into the third phase 33c of the third three-phase supply cable 33 connected to the output 23b of the power stabilisation device 23 and to a part of the transmission network 14. Advantageously, utilisation of the power stabilisation device 23 using the methods described above means that the operators of the electricity distribution network 10 are able to provide dynamic reactive power support to the power generation site(s) 12 to which the power stabilisation device 23 may be connected to, or otherwise in communication with, via the transmission network 14. Such support assists in maintaining the performance and stability of the network 10. This support can be provided without affecting or impacting the voltage performance and stability of the distribution network 16. It also enables the electricity distribution network 10 to generate reactive power support when traditional sources of reactive power support are unavailable, due to changing consumer habits and optimisation of voltages at the consumer end. In addition, locating the source of reactive power support further upstream, towards the power generation site 12, improves the efficiency of the transmission of the reactive power support as it is injected into the transmission network 14 where electricity is transmitted at a higher, and hence more efficient, voltage and also reduces the distance over which the reactive power support is transmitted. Use of the power stabilisation device 23 serves to improve the reactive power support available to the network 10, with minimal modification of the network 10. For instance, power stabilisation devices 23 can be installed at or near substations 18 and require minimal modification to the substation 18, and to the transmission apparatus 15 connected to the substations 18 and power stabilisation devices 23. This reduces the cost and complexity of installation, increasing the likelihood that operators of the network 10 and the substations 18 will adopt the power stabilisation devices 23. 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 invention may also broadly consist in the parts, elements, steps, examples and / or features referred to or indicated in the specification individually or collectively in any and all combinations of two or more said parts, elements, steps, examples and / or features. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiment(s) described herein. Protection may be sought for any features disclosed in any one or more published documents referenced herein in combination with the present disclosure. Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and / or to encompass equivalents.

Claims

1. A method of distributing electricity across an electricity distribution network including:providing a voltage adjustment device located between a power generation site in the5 electricity distribution network and at least one consumer connection point, the voltage adjustment device being connected to the power generation site by a transmission network;providing at least one power stabilisation device in communication with the voltage adjustment device and the transmission network;providing electricity to the voltage adjustment device at a first voltage;10 measuring a characteristic of the electricity from at least one point in the electricitydistribution network;wherein, if the measured characteristic of the electricity is not within a predetermined range, the method includes using the power stabilisation device to extract a portion of the electricity provided to the voltage adjustment device, the extracted portion of the electricity having a second voltage, and15 injecting the extracted portion of the electricity into the transmission network.2000 CM2. A method according to claim 1 wherein the measured characteristic is a frequency of the electricity.

3. A method according to claim 2 wherein the predetermined range for the frequency is approximately 49.5Hz to 50.5Hz.

4. A method according to claim 1 wherein the measured characteristic is a voltage of theelectricity.

255. A method according to claim 4 wherein the predetermined range for the voltage isapproximately 216.2V to 253V, or approximately 207V to 253V.

6. A method according to any preceding claim, using the power stabilisation device to modify30 a phase angle between a characteristic of the extracted portion of electricity and acharacteristic of the electricity provided to the voltage adjustment device to a non-zero value.

7. A method according to claim 6, wherein the characteristic of the of the extracted portion of electricity leads the characteristic of the electricity provided to the voltage adjustment device.

8. A method according to claim 6, wherein the characteristic of the of the extracted portion of electricity lags the characteristic of the electricity provided to the voltage adjustment device.

9. A method according to claim 7 or 8 wherein the characteristic of the electricity provided to the voltage adjustment device is the voltage or current, and wherein the characteristic of the extracted portion of electricity is the voltage or current.5 10. A method according to any preceding claim including using the voltage adjustment device toraise the voltage before using the power stabilisation device to extract a portion of the electricity provided to the voltage adjustment device and injecting the extracted portion of the electricity into the transmission network.10 11. A method according to any preceding claim wherein the voltage adjustment device isconnected to the transmission network by a first three-phase supply cable, and wherein the power stabilisation device is connected to the voltage adjustment device by a second three-phase supply cable and is connected to the transmission network by a third three-phase supply cable.152012. A method according to claim 11 including using the power stabilisation device to extract a portion of the electricity provided to the voltage adjustment device from two of the three phases of the second three-phase supply cable, and injecting said portions into the third of the three phases of the third three-phase supply cable.

13. A method according to claim 12 wherein the voltage of the portion of electricity extracted from the first of the three phases is equal in magnitude to the voltage of the portion of electricity extracted from the second of the three phases.

14. A method according to any preceding claim wherein the voltage adjustment device includes a transformer.

15. A method according to any preceding claim wherein the power stabilisation device includes a power semiconductor.3016. A method according to any preceding claim wherein a portion of the electricity not extracted by the power stabilisation device is distributed to one or more consumers.

17. A method according to any preceding claim further including providing one or more of the 35 consumers with a consumer optimisation apparatus which is operable to adjust the supplyvoltage provided to the consumer dependent upon consumer demand.

18. An electricity distribution network including a power generation site, a transmission network for providing electricity from the power generation site to a voltage adjustment device, a 40 distribution network for distributing electricity from the voltage adjustment device to a pluralityof consumer connection points, and a power stabilisation device in communication with the voltage adjustment device and the transmission network;wherein the power stabilisation device is operable to extract a portion of the electricity distributed to the voltage adjustment device and inject the extracted portion of electricity into5 the transmission network.

19. An electricity distribution network according to claim 18, wherein the power stabilisation device is operable to modify a phase angle between a characteristic of the extracted portion of electricity and a characteristic of the electricity provided to the voltage adjustment device 10 to a non-zero value.

20. An electricity distribution according to claim 19 wherein the characteristic of the extracted portion of electricity leads the characteristic of the electricity provided to the voltage adjustment device, or wherein the characteristic of the extracted portion of electricity lags 15 the characteristic of the electricity provided to the voltage adjustment device.LO CM 20CO CM 2521. An electricity distribution network according to any of claims 18 to 20, wherein the voltage adjustment device is operable to adjust the voltage of the electricity to be distributed to the plurality of consumer connection points above or below a nominal value of voltage.

22. An electricity distribution network according to any of claims 18 to 21 wherein the voltage adjustment device is connected to the transmission network by a first three-phase supply cable, and wherein the power stabilisation device is connected to the voltage adjustment device by a second three-phase supply cable and is connected to the transmission network by a third three-phase supply cable.

23. An electricity distribution network according to claim 22 wherein the power stabilisation device is operable to extract a portion of the electricity provided to the voltage adjustment device from two of the three phases of the second three-phase supply cable, and inject said30 portions into the third of the three phases of the third three-phase supply cable.

24. An electricity distribution network according to any of claims 18 to 23 wherein the voltage adjustment device includes a transformer and wherein the power stabilisation device includes a power semiconductor.

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