Estructura del comercio exterior de prendas de vestir de Estados Unidos El abastecimiento de Estados Unidos en otros países es determinado y apoyado por una

To demonstrate the practicability of this LRIC-voltage network charging principle, a practical network is opted as the test network. The reason for this choice being that this particular network should in absolute terms reflect the configuration of a practical distribute network. In this regard, the practical system to be employed shall be the Pembroke network in Wales under the ownership of Western Power Distribution (WPD).

The geographic map of this system is shown below in figure 4.6.

Figure 4.6: Pembroke network (Wales) [66]

This network is apportioned into two zones: zone 1 and zone 2. Zone 1 is a rural area comprising of 23 lines and 29 transformers. On the other hand, zone 2 is a central area comprising of 33 lines, 25 transformers.

The SVCs have the investment costs of £696,960.00, £174,240.00, £116,100.00,

£58,058.00 and £696.00 at the 132-kV, 33-kV, 22-kV, 11-kV and 0.415-kV voltage levels, respectively. Bus 5140 is the slack bus. The voltage limits are assumed to be 16% pu on the 11-kV, 22-kV and 33-kV levels. While the voltage limits are (1-6% & 1+10%) pu on the 0.415-kV level and 110% pu on the 132-kV level as detailed by [122]. The use of power flow was employed to capture the nodal voltage charges while performing nodal withdrawals/injections on the system. Also, the annual load growth for this test network is assumed to be 1.6% while the discount rate is assumed to be 6.9%.

Table 4.5: LRIC-voltage network charges due to 1 MVAr withdrawal at each node on the Pembroke practical test system.

Bus

Initial Voltage LRIC-V Distance

Bus

Initial Voltage LRIC-V Distance

Bus

Initial Voltage LRIC-V Distance Voltage Difference Charges

from slack

Bus Voltage Difference Charges from slack Bus Voltage Difference Charges from slack Bus

(pu) (pu) (£/MVAr/yr) (km) (pu) (pu) (£/MVAr/yr) (km) (pu) (pu) (£/MVAr/yr) (km)

Figure 4.7: Circuit diagram of the Pembroke network

Table 4.5 shows the LRIC-v network charges owing to 1 MVAr nodal withdrawals.

Specifically, columns 1-5, show bus name, voltage before withdrawal, voltage difference (voltage after nodal perturbation – voltage before nodal perturbation), LRIC-v charges and bus distance from the slack bus, respectively. While figure 4.7 shows the circuit diagram of the Pembroke network. All the red circled busbars have their voltages before withdrawals above 1 pu (that is, upper bus voltage limits critical) and while the rest have their voltages below 1 pu (that is, lower bus voltage limits critical).

For the buses with critical upper voltage limits, during MVAr withdrawals, their voltage upper margins would be increased as the voltage would be reduced on these particular buses.

As a result, these buses would earn credits while on the other hand, the buses with critical lower voltage limits would be penalised as these would earn a costs for degrading their already critical bus lower margins. Since there are 42 critical upper bus limits, therefore, the

5140 - BSP

critical lower bus limits dominate hence during withdrawals the results are nodal costs as can be seen in table 4.5.

Generally, the costs increase as bus distance increases from the slack bus. However, bus 3081 attracts the most cost even though bus 3048 is the furthest from the slack bus. This is due to the fact that, bus 3048 has its upper voltage limit critical and as such during withdrawal at this bus, it attracts credit since this upper limit margin would be increased, therefore, delaying VAr device investment at this bus. This, in turn, result in the overall LRIC-voltage cost reduced due to this perturbation, at this bus. Since bus 3051 is the same distance from the slack bus as bus 3048, its overall costs are reduced, as well, since even though it itself attracts a cost but since it is closest to bus 3048 which attracts a significant credit during withdrawal at bus 3048. It should be noted, as well, that bus 3051 attracts more cost than bus 3048, consequent to the latter reason. Buses 3081 and 3084 attract the largest costs, respectively. The cost for bus 3081 is more than that of bus 3084 as the latter supplies the former, through a transformer, with power requirement and as a result there is a voltage drop across the transformer. It should be noted that voltage is 1 pu at bus 3081, before withdrawal, such that, during withdrawal it attracts a cost since this action would degrade its lower voltage limit margin, therefore, advancing the VAr asset investment horizon at this bus to a closer date. It should be noted that the resulting distances for these respective buses from the slack bus are quoted to be the same but their costs are different. The earlier stated reasoning applies to other buses with the same distances from the slack bus but with different costs. The slack bus, buses 5151 and 5152 attract no costs as their respective voltages for the slack bus did not change while those for buses 5151 and 5152 slightly change since they are close to the slack bus.

Table 4.6: LRIC-voltage network charges due to 1 MW withdrawal at each node on the Pembroke practical test system.

Bus

Initial Voltage LRIC-V Distance

Bus

Initial Voltage LRIC-V Distance

Bus

Initial Voltage LRIC-V Distance Voltage Difference Charges

from slack

Bus Voltage Difference Charges

from slack

Bus Voltage Difference Charges

from slack

Table 4.6 shows the LRIC-v charges given 1 MW nodal withdrawals. The columns 1-5 show the same parameters as in the previous table 4.5. It can be observed that the charges takes the same pattern as 1 MVAr nodal withdrawals but are reduced since the resulting network circuit X is more than the corresponding R. In that regard, bus 3081 attracts most cost. The same issue holds, since, during MW withdrawals the critical upper bus voltage margins are increased while the lower bus voltage margins are reduced, thereby, these earning credits and costs, respectively. The increase and degradation of the respective margins occur in a small way as reflected by the bus voltage changes in tables 4.6 as compared to table 4.5.

Table 4.7: LRIC-voltage network charges due to 1 MVAr injection at each node on the Pembroke practical test system

Bus

Initial Voltage LRIC-V Distance

Bus

Initial Voltage LRIC-V Distance

Bus

Initial Voltage LRIC-V Distance Voltage Difference Charges

from slack

Bus Voltage Difference Charges

from slack

Bus Voltage Difference Charges

from slack

Table 4.7 shows LRIC-V charges consequent to 1 MVAr nodal injections. Columns 1-5 show all the parameters shown in the previous tables, 4.5 and 4.6.

During nodal injections, the reverse is true, in the context of what transpires during nodal withdrawals. That is, the buses with critical lower limits attract credits during nodal injections since the respective margins of these buses are increased, therefore, users who cause this effect have to be incentivized since this benefit the network. On the other hand, the buses with critical upper limits attract costs during nodal injections since the respective margins of these buses are degraded further and in that regard the investment horizons of the VAr compensation assets are advanced forward, therefore, users who cause this effect have to be penalized.

From table 4.7, it can be observed that the results follow a similar pattern to the ones for MVAr withdrawals but they are in a negative sense since the MVAr injections attract credits for a system with dominating critical lower bus limits. However, in this case, bus 3084 attracts the most credit, because during injection at node 3081, this bus attracts cost as its upper limit margin is degraded resulting in overall reduced credit at bus 3081. On the other hand, an injection at bus 3084 attracts a credit at this bus with less significant perturbation propagated at bus 3081 thus less cost at this bus and finally contributing to more overall credit at bus 3084 to bus 3081. Slack bus, buses 5151 and 5152 attract no credits for the same aforementioned reasons.

Table 4.8: LRIC-Voltage Network Charges Due To 1 MW Injection At Each Node

Bus

Initial Voltage LRIC-V Distance

Bus

Initial Voltage LRIC-V Distance

Bus

Initial Voltage LRIC-V Distance Voltage Difference Charges from slack Bus Voltage Difference Charges from slack Bus Voltage Difference Charges From slack Bus

(pu) (pu) (£/MW/yr) (km) (pu) (pu) (£/MW/yr) (km) (pu) (pu) (£/MW/yr) (km)

Table 4.8 shows LRIC-V charges consequent to 1 MW nodal injections. Columns 1-5 show all the parameters shown in the previous tables, 4.5, 4.6 and 4.7.

The results are similar to the case involving MVAr nodal injections but they are smaller.

This is consequent to the fact that the resulting network circuit X is more that the corresponding resulting network circuit R. Here, again, bus 3081 attracts most credit while the slack bus and buses 5151 and 5152 attract no credits.

4.5 Chapter Conclusions

In this chapter, the principle of LRIC-voltage network charges is presented and demonstrated on the IEEE 14 bus test system and the 87-bus practical distribution test system. The LRIC-voltage network charging principle is to reflect the additional investment cost in network reactive power (VAr) compensation assets when accommodating new generation/demand, reflecting the cost to the network in ensuring that nodal voltages are within statutory limits. This approach makes use of spare capacity or headroom of nodal voltage of an existing network (distribution and transmission systems) to provide the time to invest in reactive power compensation devices. A nodal power withdrawal or injection will impact on system voltages, which as a result will defer or advance the future investment costs of VAr compensation devices. The LRIC-voltage network charge aims to reflect the impact on network voltage profiles consequent upon nodal power perturbation. This approach provides forward-looking economic signals that reflect both the voltage profiles of an existing network and the associated indicative future network cost of VAr compensation assets. The forward-looking LRIC-voltage network charges can be used to influence the location of future generation/demand for bettering network security and, consequently, minimize the cost of future investment in VAr compensation. Moreover, the real power and reactive power withdrawals/injections have being taken into account to derive the LRIC-V network charges in this study since both play a major role in impacting on the network nodal voltages.

Given this novel charging approach, true burden on the system, in terms of future network VAr compensation asset costs and network nodal voltages can be known to both network operators and the users. Finally, the users can exercise some economic choices whether their reactive power is to be supplied by the network reactive power or to install VAr compensation devices. This, in turn, can benefit the network by working towards the improvement of the network voltage profile. This LRIC-v network charging approach provide correct price signals as opposed to the currently used power factor penalty approach which many researchers view as inconsistent and inadequate as it would be apparently outlined below.

Comparing the proposed approach with the currently used power factor (pf) penalty, it is found that the proposed approach outweighs the currently used approach. The proposed charging approach is able to penalise the users who advance closer the network investment horizons and reward those that defer the network investment horizons in the context of the network nodal future VAr compensation assets. The currently used power factor penalty approach can only penalise the defaulters who operate below the set power factor threshold but fails to reward those users who otherwise operate above this set pf. Practically, every

network users has an impact on the network whether positive or negative as depicted by the proposed novel approach. This aforementioned impact by the user should be evaluated and, therefore, be accounted for in any associated charging approach. Further, it should be noted that WPD [68] has its power factor threshold set at 0.9. While Central Networks, the distribution company covering central England, has set a power factor threshold at 0.95 [69] and Scottish Hydro Electric Power Distribution, the distribution company covering Northern Scotland, has a power factor threshold set at 0.8 [70]. Based on the above various preset pf penalty thresholds, it is evident that there is no solid basis as to why these are chosen and, therefore, it is not cost reflective but a compromise reflecting costs and material constraints, as outlined by [71]. In addition, the pf penalty approach was proposed several years ago and, therefore, it is outdated as described by [71]. For example, if we consider two loads 200 MW + j50.1 MVAr (pf = 0.97) and 20 MW + j19 MVAr (pf = 0.72). If these two loads are connected to the above distribution networks, the larger load would not be penalised by any of the distribution networks since its pf is above the trigger pf threshold of all of them while the smaller load would be penalised since its pf is below the trigger pf threshold of all the distribution companies. This would be unfair as the larger load draws some considerable real and reactive powers from the network. Regarding the proposed novel LRIC-voltage network charging principle, both the loads would be charged in accordance to the exact proportion as the amounts of real and reactive powers consumed by each, which results in an equitable sharing of cost burden. Moreover, the proposed approach shows the nodal charges owing to the nodal perturbations as every network user impact on the network but not only the users having pf less than the chosen threshold as it is suggested by the currently used approach. The charges by this proposed novel approach obviously provide forward-looking cost-reflective correct price signals to both the loads and, moreover, this principle can easily be understood by the network users than the pf penalty approach. In this regard, the considered loads (network users) would exercise an economic choice whether to source network VAr or provide their own VAr. This, in turn, would benefit the network as the overall result being the improved network voltage profile.

Furthermost, unlike the pf penalty approach, this approach directly utilizes the actual parameter (nodal voltage) which is being monitored to ensure that the network nodal voltages are within the lower and upper limits. Also, the pf penalty approach was designed specifically to recover charges for generator operating costs.

Chapter 5

LRIC-Voltage Network Pricing To Support