GB2476396A

GB2476396A - Controlling groups of energy producing and/or consuming devices in an electricity network

Info

Publication number: GB2476396A
Application number: GB1100859A
Authority: GB
Inventors: Robert Alastair Fraser Currie; Graham William Ault
Original assignee: University of Strathclyde
Current assignee: University of Strathclyde
Priority date: 2007-11-16
Filing date: 2008-11-17
Publication date: 2011-06-22
Anticipated expiration: 2028-11-17
Also published as: GB201100859D0; GB2476396B

Abstract

A regulated group of energy producing and/or consuming devices in an electricity network is controlled by applying one or more trigger levels that, when exceeded, cause the devices to either stop or start, reduce or increase producing or consuming power, or to be disconnected. The trigger levels may be fixed or variable sequential trigger levels, and the devices may be individually and sequentially disconnected from the network. Reset trigger levels may be provided which when breached cause the energy producing and/or consuming devices to restart producing and/or consuming power. The trigger levels may be applied according to monitored parameters.

Description

Active Network Majgernent The present inventIon relates to an active network management (ANM) scheme to facilitate increased connection of energy producing/consuming devices to electricity networks.

sKawid of they on The increased expansion of renewable and distributed generation is posing new technical, economic and regulatory challenges to the electricity industry The growth in renewable energy sources is crucial to meeting electricity sector emissions reduction targets It is often the case however, that the renewable resource exists in rural areas supplied by relatively weak distribution networks Distribution networks were not designed to accommodate high levels of renewable or distributed generation (DG) and so can act as a significant barrier to the connection and operation of DG units. Active Network Management (ANM) is emerging as a preferred solution to the connection and operation of DG units.

ANM concerns the technical challenges that can result from the connection snd operation of DG units to distribution networks: power flow management, voltage control and fault level management. ANM has emerged primarily in the UK through the work of the UK Government Embedded Generation Working Group (EGWG) which later became the Distributed Generation Coordination Group (DGCG), An important outcome of one of the work streams of the DGCG was the publication of Solutions for the Connection and Operation of Distributed Generation" DTI Distributed Generation Programme (Contractor EA Technology, Authors Collinson A Dai F, Beddoes A Crabtree, J), K/EtJ00303/00f0 1/REP 2003 This report is often referred to as the Sasic Active Management" or SAM report and describes solutions to the technical issues of voltage control, power flow management and fault level management for the connection and operation of individual distributed generation (DG) units. The main categories of the solutions proposed for power flow management are pre-fault constraints, post-fault constraints cnrect ntertnpprng generator trip based on power flow measurements and generator power output control based on power fiow measurements.

Power flow management based on pre-fault constraints implies the limitation of power flows to that which can be accommodated for the next circuit outage. During normal operation the worst case first circuit outage (FCO) is the N-i contingency (the loss of the laroest of N nirniiit\ Pra..fiit rnna+rn;n+r r'-nrr'..

used to monitor power flows and issue maximum output instructions to the wind farms in a particular area of the transmission network Both preventive and corrective control actions are considered based on the offline calculation of transfer limits through the rnnnpct,r4 frnc,rniccrtn n,,r.Ja-r;, lEE Proceedings Generation, Transmission and Distribution May 2006, and G W Ault, ft A. F. Currie, J. ft McDonald; "Active Power Flow Management Solutions for Maximising DG Connection Capacity", IEEE PES General Meeting, Montreal, Invited Panel Paper, 2006.

Although ANM schemes are known, much of the work in this area has been theoretical and does not address the design, operat!on and deployment of an ANM scheme to electricity networks.

Summary of he Invention

According to the present invention there is provided a method for defining one or more ANM zones in an electricity network, the method compnsing determining the maximum power and/or current transmittable to or from a node or branch in the network; determining the maximum capacity of power and/or current transmittable through that node or branch; and defining a zone including the node or branch and generator unit(s) that requires to be actively managed, in the event that the maximum power and/or current transmittable to the node or branch exceeds the maximum capacity of power and/or current transmittable through it. The ANM zone is an area of the electricity network where the connection and operation of one or more energy producing/consuming devices: must be managed to prevent technical constraints on the network being breached.

By analyzing the network to determine where the net transfer may exceed the capacity that the infrastructure can handle, the location of constraints on the network can be identified and an ANM strategy implemented.

Once the location of the energy producing/consuming devices to be actively managed is known or agreed each device must be considered according to the princrples of access to capacity (i e individually in turn or collectively as required) To determine a zone, the electrical node where the new energy producing/consuming device connects is identified, as is the power lmport/export routes and power produced/consumed at the electrical node. Once this is done, the maximum power and/or current transmittable to or from the node or branch is determined and compared with the maximum capacity of pOwer and/or current transmittable through it, If the maximum power and/or current transmittable to orfrom the node or branch exceed the maximum capacity, then an ANM zone boundary is defined.

Once consideration of the first node is completed, the next node in the direction of S power export is considered and the power import/export routes and power produced/consumed identified. The maximum power and/Or current transmittable to or from the node or branch is determined and compared with the maximum alowable capacity If the maximum power and/or current transmittable to or from the node or branch by the connected generators exceed the maximum allowed capacity, then an ANM zone boundary is defined, This process is repeated for each node in the direction of power export until the Grid Supply Point (GSP) or logical extent of network is reached Once thrs happens, the originating electrica' node, where the energy producing/consuming device is connecting, is reviewed to determine if an alternative route for power export exists. If it does, then each electrical node on this route is reviewed to determine whether a zone boundary should be applied, again until the Grrd Supp'y Point (GSP) or logical extent of network is reached Each time a new energy producing/consuming device connection is identified, the process is repeated.

Once the zones are identified, an ANM configuration is defined according to principles of access to capacity in each zone For the example of last in first out (LIFO) capacity access arrangements, the energy producing/consuming devices to be added to the network would be considered in order of connection date pnority, starting with the highest pnority device being the first to connect to the network The requirement for ANM zones would be considered for the connection of each subsequent device, but any higher priority energy producing/consuming devices would be included in the analysis.

After the ANM configuration is defined, the entire network is subject to electrical power flow analysis. This is performed individually, consecutively or collectively for each energy producing/consuming device connecting to the ANM scheme depending on the principles of access to capacity. The results of the power flow analysis are used to identify the real and reactive power flows in the system. The power flow studies identify any potential confhcts to the principles of access The approach to identifying zones can be performed to allow the system to be reconfigured either online or offline in the event one or more of: a change in the size or behaviour of all or part of the exisbng generation portfolio including the decommissioning/mothballing of generating units; a change in the size or behaviour of demand on the network a change in network topology or network components, addition of a new energy producing/consuming device According to another aspect of the invention, there is provided a method for controlling energy producing/consuming devices in an electricity network, the method comprising setting one or more fixed or variable tngger levels to trip inthvidual energy producing/consuming devices in the event that the trigger point is exceeded, wherein the energy producing/consuming devices are individually and sequentially disconnected from the power network until the trigger point is no longer exceeded.

By sequentially tripping individual energy producing/bonsuming devices, operational goals can be achieved without having to trip all energy producing/consuming devices.

The fixed or variable trigger levels are defined within one or more ANM zones of the network. as defined in the first sapect of the invention.

The method may involve applying one or more reset trigger levels which when breached reset the regulated energy producing/consuming devices to re-start producing /consuming power the reset level being lower than the sequential trigger level.

The method may involve applying one or more trim tngger levels, which when breached causes the regulated energy producing I consuming devices to reduce their producing / consuming power The trim level may be between the sequential tngger level and the reset level.

The method may involve applying a trip operating margin which when breached causes all of the regulated energy producing / consuming devices to stop producing / consuming power.

The method may involve varying one or more of the trigger levels. The one or more trigger levels may be varied by an amount dependent on a gradient of power export.

The gradient of power export may be influenced by ramp rates of one or more of: the regulated energy producing / consuming devices, energy producing/consuming devices that have unconstrained access to the network during the N and N-i condition (firm generation devices) energy Producing/consuming devices that are required to curtail output to meet network constraints during the N-I condition (non-firm generation), and the electrical load.

The method may further involve assessing a probability of certain pre-determined ramp rates of energy producing/consuming devices occurnng and using this to determine the one or more trigger levels.

The method may further involve monitoring one or more power system parameters, such as voltage and/or current, to determine whether the one or more trigger levels are breached.

According to another aspect of the nvention there is provided a system for controlling energy producing/consuming devices in a distribution network, the system comprising means for sequentially and individually tnpping or disconnecting the energy producing/consuming devices in the event that one or more trigger levels is exceeded According to another aspect of the invention there is provided a method for controlling energy producing/consuming devices on an electricity network and a system for implementing this, the method comprising: setting one or more trigger levels which when breached cause energy producing/consuming devices to stop Producing/consuming power, and setting one or more tngger levels which when breached reset energy producing/consuming devices to re-start or increase producing/ôonsuming power.

By resetting the energy producing/consuming devices to re-start producing /consuming power it is possible to maximize the use of available network capacity. The method 3 may also involve individually tripping the energy producing/consuming devices sequentially as required.

Preferably, the trigger levels are defined within one or more ANM zones of the network, as defined in the first aspect of the invention.

S

According to yet another aspect of the invention, there is provided a method for controlling energy producing/consuming devices on an electricity network, the method comprising: monitoring one or more power system parameters, such as voltage and/or current, and depending on the monitored parameters setting one or more trigger levels which when breached cause energy producing/consuming devices to stop or start or reduce or increase producing/consuming power In this way, the trigger levels can be varied to respond to changes in the network conditions and so the network can be actively and dynamically managed in real time According to yet another aspect of the invention, there is provided a system for controlling energy producing/consuming devices on an electricity network, the system comprising: means for receiving information on one or more power system parameters, such as voltage and/or current, and means for setting one or more trigger levels which when breached cause energy producing/consuming devices to stop or start or reduce or increase producing/consuming power depending on the parameters, The system may include one or more sensors or monitoring devices for sensing or monitoring the power system parameters.

A plurality of Controllers may be provided throughout the network for causing the energy producing/consuming devices to stop or start or reduce or increase producing/consuming power depending on the trigger levels and the measured parameters. Each controller may comprise a programmable logic controller or microprocessor based system, According to yet another aspect of the invention, there is provided a system for controlling energy produdng/consuming devices that have to be regulated on an electricity network, the system adapted to: receive information on one or more measured power system parameters, such as voltage and/or current within one or more zones that have to be actively managed; apply one or more trigger levels to each zone; and cause the energy producing/consuming devices in a zone to stop or start or reduce or increase producing/consuming power when the one or more trigger levers are breached in that zone.

The system may include at least one sensor or monitoring device for sensing or monitoring the power system parameters.

The system may comprise one or more controflers or processors for receiving the information; applying the parameters and controlling the regulated energy producing/consuming devices.

Communication means may be provided for communicating the sensed parameters from the energy producing/consuming devices and/or for communicating control instructions to the energy producing/consuming devices.

The one or more trigger levels include one or more of: a trip operating level at which all the regulated energy producing/consuming devices are disconnected; a sequential trip operating level, at which regulated energy producing/consuming devices are sequentially disconnected; a trim operating level, at which the output of regulated energy producing/consuming devices is reduced; and a reset trigger level, at which any disconnected regulated energy producing/consuming devices are reconnected to the network.

According to another aspect of the invention, there is provided one or more computer programs having code or instructions for implementing any of the methods of the invention. Preferably, the computer program is provided on a data carrier or computer readable medium. The computer program may be implemented in hardware or software.

flefDescripfion of the DrawJ!jg Various aspects of the invention will now be described by way of example only and with reference to the accompanying drawings, of which: Figure 1(a) is a schematic of a typical radial distribution network; Figure 1(b) shows ANM zones applied to the network of Figure 1(a); Figure 2(a) is a schematic of a typical interconnected distribution network; to Figure 2(b) shows ANM zones appUed to the network of Figure 2(a); Figure 3 shows various active network management operating margins; Figure 4 is a simplified representation of the capacities for DC connection on a distribution network, and Figure 5 is a block diagram of an ANM system.

Pfita ii ad Dese riflo of theD in S The present invention relates to various aspects of active network management1 including the setting up and monitoring of zones in the network that have to be actively managed to ensure that network constraints are complied with This is generally done as and when new producing/consuming devices are added to an existing network for example new renewable energy sources The first step is to identify the first new energy producing/consuming device and the node to which it is to be connected Then power import/export routes and the power produced/consumed at the electrical node are determined and an ANM zone boundary condition applied to assess whether the export route node capacity could be exceeded, By comparing the maximum power/current that can be transmitted with the maximum capacity of the node being considered, zones that have to be actively managed can be identified The invention takes as its formulation the application and adaptation of kirchoffs current law In doing so, issues relating to coincident constraints on an electricity network are addressed. The method for determining the boundaries of zones can be expressed using the following ANM zone boundary condition: S wa4 + rnd&c d > 5rnx (1) Where, = Maximum transfers or contributions from n nested zones or other network areas (A or MW or MVA) = Maximum summated rated output of n energy producing devices within zone or MW or MVA) Summated minimum demand of n energy consuming devices within zone (A or MW or MVA) = Maximum capacity at zone irnport/expoil boundary (A or MW or MVA if the resulting net transfer is greater than the static, seasonal or dynamically determined export capacity from the node being considered (Srn) then an ANM zone is defined If the net transfer is below the static seasonal or dynamically determined export level then an ANM zone ls not required, Once the first node is assessed the next node in direction of power export has to be considered and the process repeated until the Grid Supply Point (GSP) or logical extent of the network is reached This process is then repeated for each export route for current and power from the electrical node being considered and each new generator At this stage, an ANM configuration is defined according to principles of access to capacity in each ANM zone. To ensureS that the principles of access are adhered to, power system. studies are performed for the connecting energy producing/consuming device(s). Techniques for doing such power system studies are known in the art and therefore will not be described in detail.

ANM zones can be nested within one another, or exist in isolation; The contribution of nested ANM zones or other network areas to the net transmittable current or power from an ANM zone is recognised in equation (1) by the term: 8tPQflXJèr This relates to any current or power flowing into or out of the electncal node being considered and so can be a positive or negative value.

While the electrical notation for apparent power (5) is used here, the most general meaning of S is implied through reference to current (in A), real power (in MW) and apparent power (in MVA), The actual calculations for S in equation (1) and subsequent equations, expressions and expanations must take into account the vector form of S. In many cases, S, is predetermined or known. However it could be a real time value I 2 determined by for example monitoring and evauatng dynamic hne ratings, which may in practice vary due to weather conditions and prior Ioadihg.

Establishing ANM zones for specific network types will now be described in detail with reference to Figures 1 and 2, which show a radial network and a interconnected distribution system respectively, although the method can be applied to different networks and network topologies includfng meshed systems The zoning method can be performed at the planning stage when the network is set up or as and when new generators are to be added. The zoning method can also be performed at the operation stage to respond to changes to network topology Figure 1(a) shows a typical radial distnbution network that has three FG units connected to a feeder via three buses 1, 3 and 4 The maximum capacityfor export for this network is 12MW The three FG units are FG1 (10MW) at bus 4, FG2 (2MW) at bus Sand FG3 (6MW) at bust The maximum rated FG output is equal to the capacity for export (12MW) plus the minimum load (6MW), which gives a total of 18MW The operation of all or any FO units will not overload the thermal rating of the distribution network on any section of the feeder Three RNFG units are to be connected to the radial distribution network introduced in Figure 1(a): RNFG1, RNFG2 and RNFG3. The first unit RNFG1 (2MW) is to be connected at bus 4, the second RNFG2 (4MW) at bus 3 and the third RNFG3 (4MW) at bus 1. It will be assumed that RNFG1 is the first to connect, followed by RNFG2 then RNFG3 To identify the zones to be actively managed in the network of Figure 1(a) RNFGI is added to the network at bus 4, where FG1 (10MW) is already connected Equation (1) is then applied to bus 4 giving 12-1=11 Since this is less than the maximum capacity for export, an ANM zone is not required at bus 4 Next equation (1) is applied to all of the electrical nodes connected to the feeder, in the direction of export from bus 4.

Doing this for buses 3 and 2 also results in no ANM zone being required, i.e. no condition of generation or load demand could result in the export from bus 3 or bus 2 exceeding the circuit thermal rating of 12MW. However, for bus I equation I results in 10+6-2=14, which is more than the maximum export capacity from bus 1, and so an ANM zone boundary is required at bus I This and the location of RNFG1 define a zone, which will be referred to as zone 1, as shown in Figure 1(b), requiring active network management.

Consider now the addition of R:NFG2 (4MW) at bus 3, The appHcation of equation (1) at bus 3 gives: 11+6-2=15 and 15>12, resulting in the requirement for an ANM zone boundary defining a zone, zone 2, which is nested within zone 1, as shown in Figure 1(b), FoHowing the export path from bus 3 involves the appflcation of Equation (1) at bus 2 and bus 1. This identifies that RNFG2 also contributes to the overloading of the export from bus I Therefore, RNFG2 has to be actively managed for access to available export capacity from bus I and bus 3 Consider now the addition of RNFG3 (4MW) at bus 1 Application of equation (1) identifies that RNFG3 compounds the existing overloading on the export circuits from bus 1 Therefore, RNFG3 has to be actively managed for access to capacity in zone 1 At each zone boundary a measurement device is located or an existing device in the appropriate position used, so that the net power and/or current can be monitored in real time To ensure that the maximum capacity at the network pinch point is never exceeded, an active network management controller (not shown) monitors these key measurements and uses them as an indicator to trigger preventative action, This will be described in more detail later.

Once the zones are defined, an ANM configuration is determined based on access to capacity criteria and the entire network is subject to electrical power flow analysis. This is performed individually, consecutively or collectively for each energy producing/consuming device connecting to the ANM scheme depending on the principles of access to capacity The results of the power flow analysis are used to identify the real and reactive power flows in the system In particular the power flow studies will identify any potential conflicts to the pnnciples of access The access to capacity criteria may be based on any agreed pnnciples for example a last in first out scheme (LIFO) scheme. In the example of Figure 1, because RNFGI is the first unit connected it is only liable for curtailment based on the measured export from bus 1 and is the last of the three RNFGs to be curtailed for the constraint at this location. In contrast, RNFG2 will be curtailed before RNFG1 is impacted and RNFO3 will be curtailed before either of RNFG1 and RNFG2.

Based on a LIFO scheme, the RNFG stack for curtailment in either zone of Figure 1(b) is given below in Table I.

TABLE I

RNFQ slACK FOR ZONE 1 AND ZoNE 2 iN FiGUAE 1(A) Zone RNFG Stack L2I1RRiNFFir:3iJ In this scenario, when the export from bus 1 is measured as exceeding the allowable limit, and so the constraint at zone Us breached, then the RNFG units will be curtailed indwduaHy or collectively according to LIFO in the order RNFG3 RNFG2 then RNFGI RNFG3 will be curtailed first; RNFG2 may be curtailed at the same time as RNFG3 (if RNFG3 is to be fully reduced) or after RNFG3 has been fully curtailed RNFG1 may be curtailed at the same time as RNFG2 (if RNFG2 is to be fully reduced) or after RNFG2 has been fully curtailed. RNFG2 will be curtailed for a breach of the constraint at zone 2.

In order to decide the level of reduction or curtailment an ANM scheme is required that wilr calculate a reduction in output from the RNFGs that will return the export to satisfactory levels The delivery of an output reduction signal will preferably involve the application of operating margins implemented within an ANM scheme This will be described in more detail later.

Figure 2(a) shows another network to which ANM can be applied This is an interconnected distribution network. The electrical load at buses 3, 5 and 6 (a total peak of 15MW) can be met for the loss of either circuit between buses 3 and 2, or buses 6 and 7. There is additional electrical load at bus 2 (a peak of 14MW). Firm Generation (FG) has been allocated on the network at bus 6 (FGI, 15MW) and bus 3 (FG2, 8MW), these FG units can operate for the loss of either circuit between buses 3 and 2, or buses 6 and 7 without overloading the remaining circuits on the distnbutron network. Regulated Non-Firm Generation (RNFG units are to connect to the network at bus 3 (RNFGI, 30MW) and at bus 5 (RNFG2, 10MW). RNFGI is first to connect, followed by RNFG2. The size of RNFGI and RNFG2 require them to have their output regulated in real-time during normal operation and not just be inter-tnpped dunng the first circuit outage.

To identify ANM zones, equation I is applied to each RNFG unit in turn. Consider firstly connection of RNFGI. In this case, 30MW of generation capacity is added to bus 3. In this case, there are two possible export routes either between bus 3 and bus Z or bus 3 and bus 5. Applying Equation (1) to the export from bus 3 to bus 2 gives - 15+38-2 = 21. Since the maximum capacity is exceeded, an ANM zone is required on the export route between buses 2 and 3 This ANM zone is shown in Figure 2(b) as zone 1 Applying Equation (1) to the export from bus 3 to bus 5 gives a similar result and so zone us extended to cover this boundary with measurement points defined on the export route from bus 3 to bus 5 and bus 3 to bus 2 Following each export route to each of the GSPs and applying Equation (1) at each bus in turn, there are no further ANM zones required on the interconnected network for the connection of RNFG1.

Consider now connection of RNFG2 to bus 5 Equation (1) is apolied to bus 5 The maximum export from bus 5 includes the full export from bus 3 of 15MW and so is 15+10-3 = 22. This is greater than the maximum capacity of 15 and so an ANM zone, zone 2, is required at bus 5, as indicated in Figure 2(b) Moving one node in the direction of power export, bus 6 has to be considered. According to equation (1), the maximum export = 15+15-3 = 27. This is greater than the maximum capacity of 24.

Therefore, an ANM zone, zone 3, is required at bus 6, as shown in Figure 2(b). During intact network operation, no other ANM zones are required on the network for the RNFG units considered.

At each zone boundary, a measurement device is located or an existing device in the appropriate position used, so that the net Dower and/or cuirent can be monitored in real time, for example between buses 3 and 2, buses 3 and 5 and buses 5 and 6 To ensure that the maximum capacity at the network pinch point is never exceeded an active network management controller (not shown) monitors these key measurements and uses them as an indicator to trigger preventative action For example, when the export from bus 5 and/or bus 6 is measured as exceeding the allowable limit, the ANM calculates a reduction in output from RNFG2 based on the level of overload experienced. This will be described in more detail later, Once the zones are defined, an ANM configuration is determined based on access to capacity criteria and the entire network is subject to electrical power flow analysis to ensure that the principles of access could not be violated. As an example. ft the access to capacity is based on an LIFO scheme, the RNFG stack for curtailment in the zones of Figure 2(b) is given below in Table 2.

TABLE 2

RNFG STACK FOR ZONE 1, Zoi 2 AND ZONE 3 iN FIGURE 2(B) Zone RNFG Stack 1

RNFGI

L 2 RNFG2H RNFO2 In this scenano1 when the export from bus 3 is measured as exceeding the allowable limit, and so the constraint at zone 1 is breached, then RNFG1 is curtailed If export from bus 5, or zone 2, is exceeded, RNFG2 is curtailed. Likewise, if export from bus 6, or zone 3, is exceeded, RNFG2 is curtailed, Both RNFG1 and RNFG2 could also require to be disconnected in the event of an outage on the system, through an intertripping arrangement from branch protection systems.

For the sake of simplicity, a LIFO access scheme is described above in the two illustrative examples. Howeveç the principles of access to capacity can be varied to accommodate a number of situations, these include: some from of traded access rights to capacity for participating energy producing/consuming devices some variation of nodal pncing for energy and network access such as locational marginal pnces, access to capacity shared proportional to the size of each participating energy producing/consuming device and/or relative to the size of the entire portfolio of participating energy producing/consuming devices (i e requiring the control of all participating energy producing/consuming devices rather than individual devices) and access based on the technically and economically optimum and most effective (in terms of generator response characteristic) energy producing/consuming device or devices to respond to a breach in network constraints.

Power transfer at constrained locations (i.e. ANM zone boundaries) on the electrical network that results from the connection and operation of energy producing /consu.ming devices requires to be limited within the capacity of the circuit(s). This is done using operating margins, which are designed with network security in mind. The operating margins determine the capacity between different trigger levels, the breaching of which trigger ANM control instructions to be sent to energy producing/consuming devices.

The operating margins can be calculated if the behaviour of the load and existing energy producing/consuming devices is known, monitored or can be assumed. For the application to managing real-time power flows, the ANM scheme can require RNFG units to achieve a set-point and desired ramp rate for both increasing and reducing power output; the desirable ramp rate can be set at the planning stage or in operational timescales, Figure 3 specifies the order of the export trigger levels that correspond to specific control instructions and the associated operating margins for an electricity network that has firm generation units (FG); non-firm generation units (NFG) and regulated non-firm generation units (RNFG). There are six export revels or margins of interest, the first for when the system approaches real danger, i.e. a dangerously high current is flowing in the circuit with implications for safety, continuity of service, asset health and asset lifetime. At this point, the export from the zone has breached all trigger levels, the ANM scheme, NFG intertripping and protection systems have failed to act, exposing the asset to extremely high current, potentially damaging the asset and posing a threat to safety. This is an extreme condition that the distribution network is designed not to reach through careful coordination and setting of protection systems.

The second export level or margin is defined as the level at which protection systems will act to open circuit breakers and remove a circuit from operation. This level is set as part of a coordinated protection scheme for overcurrent protection and the circuit is tripped by branch protection systems due to the measurement of a persistent overcurrent. The real danger and circuit trip trigger levels are employed on existing systems; it is the operating margins and the trigger levels defined below these points that are the focus of the ANM scheme, For practical implementations of operating margins, on one or more intact parallel circuits, due recognition of the relative impedance of each circuit will be required.

The third margin is the NFG intertrip trigger level. When this is exceeded, NIEG units are tripped to remove any subsequent overload due to a fault on a parallel circuit or due to the net export from the zone in excess of the margin. The NFG trigger point must be applied to both circuits in the case of two parallel circuits at a zone boundary, as described in: 8NF6 I = -(v -1)2 (2) = -(ti -(3) Where, Level of export in circuit I to trigger intertrip of NFG if circuit 2 is on outage (A or MW or MVA) SqrQ Level of export in circuit 2 to trigger intertrip of NFG if circuit 1 is on outage (A or MW or MVA) = Total combined capacay of intact circuits (A or MW or MVA) (jv -= Export capacity lost due to outage on circuit I (A or MW or MVA) (N -= Export capacity lost due to outage on circuit 2 (A or MW or MVA) The next level or margin is the global RNFG trip margin. This is the level at which all RNFG units are tripped to prevent the NFG units being tripped as a result of persistent and excessive RNFG output. The global RNJFG trip could also trip all RNFGs for the loss of a parallel circuit at a zone boundary. The trigger level must be applied to each circuit, Equations (4) and (5) can be used to calculate the global RNFG trigger level for the example of parallel circuits given above.

°1Thp (4) = S Nm2 -OAt7. (5) Where, = Level of export in circuit I that will cause a global trip of RNFG units (A or MW or MVA) Level of export in circuit 2 that will cause a global trip of RNFG units (A or MW or MVA) oM,= Trip Operating Margin (A or MW or MVA) The next level or margin is the sequential RNFG trip trigger level, This is used to trip individual RNFG units in consecutive order, as required to remove the breach of the sequential trip margin. This can occur when efforts to trim the RNFG have failed to reduce the export and the export continues to rise towards the Global RNFG tnp1 The sequential trip trigger level is calculated using:.

= (i/oh Tr OMyeq (6) SseqThp2 G/o&trIp2 -OM3, (7).

Where, = Trigger point in circuit 1 when the ANM scheme begins sequentially tripping one or more RNFG units in the ANM zone (A or MW or MVA) 5&aJrq2 = Tngger point in circuit 2 when the ANM scheme begins sequentially tripping one or more RNJFG units in the ANM zone (A or MW or MVA) = Sequential trip operating margin (A or MW or MVA) The next level or margin is the trim RNFG When the export breaches the Trim RNFG level, the set point issued to participating units is changed to curtail the RNFG units with the goal of reducing the export to below the tReset' level. The RNFG units are approached individually or collectively as required, the trim RNFG trigger level is calculated using: SirioJI = -(5) = -(9) Where, = Level of export in circuit I that will cause tnmming of RNFG unit(s) (A or MW or MVA) STPIm?= Level of export in circuit 2 that will cause trimming of RNFG unit(s) (A or MW or MVA) OM?,= mm operating margin (A or MW or MVA) The last of the margins is the reset operating margin, this is the target for the trimming of RNFG units and is designed to prevent hunting around the trim RNFG export level The reset trigger level is calculated using: = Sirpji -A/:IRcSe/ (10) 87nm2 (11) Where, Level of export in circuit 1 that will initiate the release of capacity to RNFG units (A or MW or MVA) S2 = Level of export in circuit 2 that will initiate the release of capacity to RNFG units (A or MW or MVA) = Reset operating margin (A or MW or MVA) The example distribution network shown in Figure 4 will now be used to demonstrate the calculation of operating margins and trigger levels for the ANM scheme to perform real power flow management. The limit of the existing FG connection capacity ih the distribution network is 26MW, based on a previous minimum local demand of 6MW (the network has since experienced load growth) and an outage of one of the two largest circuits (20MW), Additional generation connection capacity (21MW) beyond this limit has been made available to NFG, whereby NFG will only be permitted to operate when both of the largest circuits are in service lnter-tnpping arrangements will disconnect NFG for loss of either of the largest circuits and if the total export exceeds the capacity of the remaining cable Thus, further generator connections are constrained by a lack of available connection capacity according to established practice For real power flow (MW) management, the global RNFG trip operating margin can be calculated for a worst case scenario in terms of how quickly the export from an ANM zone can rise Equation (12) provides a method of calculating the trip operating-margin. The maximum increase in export will occur when the FG, NFO and RNFG units are ramping up at the maximum rate and there is a drop in electrical demand on the network at the maximum rate that can be experienced. The addition of these rate-of-change values for a!l DO units and loads provides the gradient of the export from the zone. This gradient is multiplied by the total time taken to achieve the control action.

This is a combination of the time it takes the ANM scheme to measure and process the breach of the trip margin (the ANM time delay. TD) and the time it takes to trip all the RNFO units (IT). t 11

= U$ d) k di)) X(TD+TT) (12)

E

£VFGi\ di kfH di.) Where, Maximum FG ramp rate (MW/mm) di t (»=J= Maximum NFG ramp rate (MW/mm) NhiJL di) E Minimum RNFG ramp rate (MW/mm) RNFG1 Maximum load drop (MW/mm) di) TD = Time delay (minutes) TT= Trip time (minutes) Equation (13) provides a method of calculating the sequential trip margin. Equation (13) is in the same format as Equation (12) but instead of the trip time the sequential trip time (SI) is added to the ANM time delay (ID) The sequential trip time is the time it takes the ANM scheme to trip an individual RNFG unit which may be staged at particular time intervals.

7 p Jfl >\\ ( 0 (1/) \ Elitmi El-l = di)) UirnL di) x(TD+sr) (13) (dP

Z I 1

Where ST = Sequential trip time (minutes) The trim operating margin can be calculated using Equation (14) which acknowledges that when the ANM scheme is taking measurements processing data and issuing control instructions there is no reduction from the RNFG units. There is also the inherent inertia within a generator controf scheme pnor to achieving a set point reduction. The maximum increasing gradientof the export from a zone is multiplied by the ANM time delay (ID) pftis the time it takes the RNFG unit to begin ramping down power production, defined here as the ramp time delay (RID),. Added to this value is the export gradient from the zone when the RNFG is ramping down at full capability, which is then multiplied by the time allocated to the ramp response, defined here as the ramping time factor (RTF). This means that the trim operating margin accounts for how long the ANM scheme takes to measure, process and issue a set point then provide the RNFG unit(s) with time to respond.

-TU'.i -W(;-i -, QMrrm,4Z + t (14) LL / .L'.l rrç:i&)Jnt)J j PiT t L cit)) d Where RTD = Ramp time delay (minutes) and RTF Ramp time factor (minutes) The reset-operating margin is calculated using equation (15), which adopts the same approach as the trip and sequential trip margin, except this time the reset time (RT) is added to the ANM time delay (ID). The reset time ensures that, the RNFG units are not released too' close to the trim trigger level. The reset-operating margin will ensure that the time between the RNFG units being released and the trim operating margin being breached will be at least equal to the reset time.

xftD+Rr) (15) 4 di di Where RT = Reset time Figure 4 illustrates the FG, NFG and RNFG unit capacities being Considered in this example. Provision of a similar level of capacity increase by conventional means would require installation of new circuit capacity. The cost associated with this could pose a significant financial barrier to further DG connections. The size of time delay and operating margins employed can impact on the economic viability of RNFG connections.

Equations (2)-(15) are now applied to the scenarios: shown in Table UI to demonstrate how to set the operating margins and trigger levels required for the ANM scheme to manage power flows.

TABLE Hi

SCEN&g OS USEO TO CALC L fe OPELAi t4G MARON E'AMi [cc [k!!pieSLnario1 Scuwto.f Sceirmo 3 Scenario 4 mm iO%fmm 20%/mm 40%/mm

-

E I --5 A/mm 10%/mm 20%/mm 40%/mm Vbt._ \ C 5%/mm iO%/min 20%/mm 40%/mM CM 1 > 1--1 510 20 and 40%/mm for acii scenario £WCML\ a// The assumptions regarding the various SANM time factors used in equations (10)-(13) are provided in Table IV.

TABLE IV

1 IMF DELAVS USED TO C4LQi rEopEMn1o IAROIN EXM4°I LS rjçj Time Facij Time (Seconds) I _____Ti) 2

_____ TT

ST

-WED 10 The capacity of FO, NFG and RNFG units used in the calculations is as shown in Figure 4 The results of the scenario analysis of operating margins are presented in

Tables V-VIIL

Table V presents the results of scenario I and shows that a low variability of FO, NFG and local load (5%/mm) results in low operating margins allowing the network to be operated close to its full rated capacity The tnm trigger level varies between 92 5% and 95.1 % for RNFG ramp rates of 5%/mm and 40%/mm respectiv&y, The ANM scheme will start releasing capacity back to RNFG units at 86% to 88.2% of rated capacity dependent on the ramp rate of the RNFG unmts. interestingly, the highest reset trigger point occurs at the lowest trim RNFG trigger point. This is also the case for scenarios 2 to 4. This means that the higher ramp rate of the RNFG unit(s) then the higher the export can be prior to taking action, but the lower the reset trigger due to the quicker rampwp of RNFG unit(s) post-curtailment.

TABLE V

______________ TRR.)OER LEVELS FOR SCENARIO I Trigger Point (% of raRe RNIO RNF'G RNFG RNFC ______ caieut /a/mln 10%/mm 20%/mm 40"o/rnoi NEG lntertri 1000 1000 1000 11)00 C'iobal RNFCI Tn 994 993 99 1 98 8 SLqRiPG Tn 988 986 983 975 -fnmR\EG 925 929 936 951 Reset 882 -872 Table VI presents the: results of the analysis of scenario 2. Scenario 2 considers a more vanable FG and NFG output and local load of 10% It can be seen that this results in larger operating margins and lower trigger levels for tripping, tnmming and releasing RNFG units The trwn trigger level now varies from 84 6% to 87 2%, around 8% lower than for scenario 1 The reset tngger level has reduced by a similar amount to 74.5% to 76.6%. Therefore, RNFG units in scenario 2 would experience more curtailment than in scenario 1.

TABLE VI

______ TRIGGER LEVELS FOR SCENARIO 2 Ii gger Point (% RN IC3 PNFQ RNFt RNIG of rate�gpneitv) 5%'min 10% mm 20%/mm 40%/minJ fjtenri l0Q_J9Q 0 1Q00 WOO C;IoFOTri 89 988 986 98.3 Seq RNFGIrip 978 -97 97 Trm RNPG 846 8)0 E_ Reset 763 Scenario. 3 considers an even more variable FG and NFG output and local load. It can be seen that this results in much reduced trigger levels due to the requirement for larger operating margins As can be seen in Table VII, the global RNFG trip and sequential RNFG trIp are stiU above or around 95% but the tnm and reset trigger levels are much reduced. The trim trigger level varies from 68,8% to 71.4% and the reset trigger level from 51.4% to. 53.6%..

TABLE vii

_______ _______ FRIGGER Ln r LS roE SCF'..ARWI I Trigger Poml (% RNFCI RNEG I R"4P0 RNFG orreapIt)j " s/mw 10%/mm 20%/ruin 40%_J Nrolatr 1000 1000 1000 1000 1 G1I& RNIQ{Lp 979 978 __ Sc, RNFO Id 95.9 957 95.3 94.6 mEG69[ jn Scenario 4 is the most extreme in terms of the variability in FG and NFG output and local load. For each of the RNFG ramp rates specified itis assumed thatthe FO, NFG and local load vary at 40%/min It can be seen in Table VIII that this results in greatly reduced trigger levels for the ANM scheme The global and sequential RNFG trip tngger levels are still above 90%, but the tnm trigger level varies from 37 2% to 39 8% This shows that if the FO NFG and local load are highly variable then the capability of the RNFG units does not impact much on the sizeof trim operating margin required. It can also be seen in Table VIII that the situation is so severe that capacity will not be released to the RNFG units until an export is measured of 5.3% to 7.5%.

TABLE VIII

________ ______TRIGGER LEVELS FOR Scn'ARIo4 Trigger Point % RNFG ENECI RNPQ RNFGfl of rated capao %Jmin 10%! r in 20%/win 40%'rn in J Nfl) 1ntcrtrp 1000 1000 _j9Q0 100 0_J uIohaiRNPoTIL 96P °59 937 953 Seq RNFUTrp 9' ?.L_2±2_ 914 906 Trim RNFO 37.2 37.6 k 3&3 39.8 Rese r 72 (6 It can be seen in Table. V -VIII that the behaviour of existing DG units and load has a large beanng on the size of operating margins employed by the ANM scheme For faster ramp rates of RNFG the higher the tngger levels are for trimming RNFG in any scenario, implying a greater energy yield by the RNFG units Smaller operating margins than those identified could be employed at the discretion of the network operator but may result in increased tripping of participating RNFG units The implications of this for network performance and the participating generators would need to be considered.

Control and measurement of the networks described above can be done using any suitable measurement devices and controllers, Figure 5 shows an example of an active network management system for implementing the invention on programmable logic controllers (PLC). In this case, zone 1 and zone 2 are nested within zone 3.

PLCs are deployed at all measurement sites and at aU RNFG units. Each RNFG PLC and measurement PLC (at each zone boundary) has a direct communications path back to a central ANM PLC. In this case, there are six RNFG units connected to the network RNFflLA PNJfl1 PNIRrr. oMCr.

margins) can be incruded to allow the margins to cater for ANIM parameter variations that are deemed to be acceptable, reasonable and regular. Variations that are out with such regular and acceptable variations may result in the individual or collective tripping of RNFG units.

ANM control zone with other zones nested as requited. The private distribution network would be monitored and controlled by the ANM scheme to facilitate micro-generation, OSM. ESS and increased energy independence from the wider grid.

A, skilled person will appreciate that variations of the disclosed arrangements are possible without departing from the invention For example, although the application of the ANM scheme to a distributionS network has been presented, it can be deployed to maintain constraints. on the transmission network. Also, forecasting techniques for wind generation, such as power production and ramp rate, and electrical demand could be used to enhance the ANM operation and could be incorporated into the setting of the tnm and reset operating margins to maximise the use of the thermal capacity of the distribution network Albo variations of the dsc1osed arrangements could be applied to energy storage systems generator control islanded electrical systems, bottlenecks and interfaces on electncal systems Accordingly the above description of the specific embodiment is made by way of example only and not for the purposes of limitation. It will be clear to the skilled person that minor modifications may be made without significant changes to the operation described.

Claims

Claims 1. A method for controlling a regulated group of energy producing/consuming devices in an electricity network, the method comprising: applying one or more fixed or variable sequential trigger levels to disconnect individual regulated energy producing /consuming devices in the event that the trigger point is exceeded, wherein the regulated energy producing/consuming devices are individually and sequentially disconnected from the network.
2 A method as claimed in claim I compnsing applying one or more reset trigger levels which when breached reset the regulated energy producing/consuming devices to re-start producing /consuming power the reset level being lower than the sequential trigger level.
3. A method as claimed in claim 1 or claim 2: comprising applying one or more trim trigger levels, which when breached causes the regulated energy producing / consuming devices to reduce their producing / consuming power.
4. A method as claimed in claim 3 wherein the trim level is between the sequential trigger level and the reset level.A method as claimed in any of the preceding claims comprising applying a tnp operating margin which when breached causes all of the regulated energy producing / consuming devices to stop producing / consuming power 6 A method as claimed in any of the preceding claims comprising calculating the one or more trigger levels in real time as a function of one or more conditions.7 A method as claimed in any of the preceding claims comprising varying one or more of the trigger levels.8. A method as claimed in claim 7 wherein the one or more trigger levels are varied by an amount dependent on a gradient of power export.9. A method as claimed in claimS 8 wherein the gradient of power export is influenced by ramp rates of one or more of: the regulated energy producing / consuming devices; energy producing/consuming devices that have unconstrained access to the network during the N and N-i condition (firm generation devices); energy producing/consuming devices that are required to curtail output to meet network constraints during the N-i condition (non-firm generation); and the electrical load.10. A method as claimed in claim 9 comprising assessing a probability of certain pre-determined ramp rates of energy producing/consuming devices occurring and using this to determine the one or more trigger levels.11. A method as claimed in any of claims 7 to 10 wherein the one or more trigger levels are varied by an amount dependent on a time taken to respond to a breach of a trigger level.12. A method as claimed in any of the preceding claims wherein one or more zones that have to be actively managed are defined in the network and the fixed or variable trigger levels are defined within those zones.13. A method as claimed in any of the preceding claims comprising monitoring one or more power system parameters such as voltage and/or current, to determine whether the one or more trigger levels are breached.14, A system for controlling energy producing/consuming devices in an electricity network, the system being adapted to sequentially and individually trip or disconnect the energy producing/consuming devices in the event that one or more fixed or variable sequential trigger levels is exceeded.15. A system as claimed in claim 14 adapted to apply one or more reset trigger levels which when breached cause the regulated energy producing/consuming devices to re-start producing /consuming power, the reset level being lower than the sequential trigger level, 16.A system as claimed in claim 14 or claim 15 adapted to apply one or more trim trigger levels, which when breached causes the regulated energy producing / consuming devices to reduce their producing / consuming power.17 A system as cLaimed in claim 16 wherein the trim level is between the sequential trigger level and the reset level.18. A system as claimed in any of claims 14 to 17 adapted to apply a trip operating margin which when, breached causes all of the regulated energy producing / consuming devices to stop producing / consuming power.19 A system as claimed in any of claims 14 to 18 compnsing varying one or more of the bigger levels.A system as claimed in claim 19 wherein the one or more tngger levels are varied by an amount dependent on a gradient of power export 21 A system as claimed in claim 20 wherein the gradient of power export is influenced by ramp rates of one or more of the regulated energy producing / consuming devices, energy producing/consuming devices that have unconstrained access to the network during the N and N-i condition (firm generation devices); energy producing/consuming devices that are required to curtail output to meet network constraints during the N-i condition (non-firm generation), and the electrical load 22 A system as claimed in claim 21 operable to assess a probability of certain predetermined ramp rates of energy producing/consuming devices occurring and using this to determine the one or more trigger levels, 23. A system. as claimed in any of claims 14 to 22 wherein one or more zones that have to be actively managed are defined in the network and the fixed or variable trigger levels are defined within'th ose zones.24 A method for controlling energy producing/consuming devices on an electricity network, the method comprising:, applying one or more trigger levels which when breached cause energy producing/consuming devices to stop producing/consuming power, and one or more reset trigger levels which when breached cause the energy producing/consuming devices to re-start producing /consumin.g power.25. A method as claimed in claim 24 comprising applying one or more fixed or variable sequential trigger revels to disconnect individual regulated energy producing /consuming devices in the event that the trigger point is exceeded, wherein the regulated energy producing/consuming devices are individually and sequentially S disconnected from the electricity network, the sequential trigger level being higher than the reset trigger level.25, A method as claimed in claim 24 or claim 25 wherein one or more zones to be act'vely managed are defined in the electricity network and the fixed or variable trigger levels are defined within those zones.27 A method for controlling energy producing/consuming devices on an electricity network comprising: monitoring one or more power system parameters such as voltage and/or current, and depending on the monitored parameters applying one or IS more trigger levels which when breached cause energy producing/consuming devices to stop or start or reduce or increase producing/consuming power.28. A system for controlling energy producing/consuming devices that have to be regulated on an electricity network, the system adapted to receive information on one or more measured power system parameters, such as voltage and/or current within one or more zones that have to be actively managed; apply one or more trigger levels to each zone; and cause the energy producing/consuming devices in a zone to stop or start or reduce or increase producing/consuming power when the one or more trigger levels are breached in that zone.29 A system as claimed in claim 28 including at least one sensor or monitonng device for sensing or monitoring the power system parameters 3Q.A system as claimed in claim 28 or claim 29 wherein the system comprises one or more controllers or processors for receiving the information, applying the parameters and controlling the regulated energy producing/consuming devices.31. A system as claimed in any of claims 28 to 30 wherein communication means are provided for communicating the sensed parameters to the controller.32. A system as claimed in any of claims 28 to 31 wherein means are provided for communicating control instructions from the controller to the energy producing / consuming devices..33. A system as claimed in any of claims 28 to 31 wherein the one Or more trigger levels include one or more of a trip operating level at which all the regulated energy producing/consuming devices are disconnected, a sequential trip operating level at which regulated energy producing/consuming devices are sequentially disconnected, a tnm operating level, at which the output of regulated energy producing/consuming devices is reduced, and a reset trigger level at which any disconnected regulated energy producinglconsuming devices are re-connected to the network 34 A computer program having code or instructions on a data carrier or computer readable medium for controlling a computer to implement the method of claims 1 to 13.35. A computer program having code or instructions on a data carrier or computer readable medium for controlling a computerto implement the method of claim 24 to 27.