YACIMIENTOS.'()E MINERALES VE. URANIO

Demand in the network is usually expected to grow, but there are also areas where no electric load growth or even negative load growth is expected. As for generation, power generation growth normally means new generation connection in a lump sum rather than the growth of the existing generation. Hence, nodal existing generation growth rates are assumed to be zero.

These different load growth forecast throughout the whole network will lead to differ­

ent types of circuit loading growth patterns, namely positive, negative and zero circuit loading growth. These growth patterns are results of different circuit loading growth rates, r^ℓ, and they are treated differently in LRIC pricing to give adequate economical signals for network users to act upon.

In addition to circuit loading growth patterns, the LRIC prices for demand and gener­

ation are also dependent on whether the circuit is demand- or generation-dominated.

Demand will be charged if the supporting circuits are demand-dominated and will be rewarded otherwise. This also applies to generation where generation will be charged when the supporting circuits are generation-dominated.

A circuit can be either demand- or generation-dominated seen by customers at differ­

ent locations. If a load withdrawal at a node results in a flow increase at a circuit, then the circuit is considered as demand-dominated seen by this load. However, this same circuit can be generation-dominated if a load injection at another node causes power flow decrease.

Figure 4.6. 2-bus test system

For instance, if the power is flowing from Bus 2 to Bus 1 in Figure 4.6, a load incre­

ment at Bus 1 will cause the power flow at the circuit to increase. Hence, for the pricing purpose, the circuit is demand-dominated seen by the customers – both load and gen­

eration at Bus 1. However, a load injection at Bus 2 will result in a counter flow at the circuit. Therefore, the circuit is generation-dominated seen by both the load and

Chapter 4 LRIC: Growth Rates

generation at Bus 1. Therefore, load at Bus 1 and generation at Bus 2 will be charged for using the line whilst load at Bus 2 and generation at Bus 1 will be rewarded.

4.3.1 Positive Circuit Loading Growth Pattern

A circuit with positive circuit loading growth means that the circuit loading level is increasing in the long term. These growth pattern is influence by the dynamic element D_B and its growth rate r_B. There are two possibilities where a circuit could have a

The positive growth patterns of these two positive and negative r_B cases are shown in Figure 4.7. From the graph, it is shown that the loading level of the positive r_B case grows exponentially, while the loading level of the negative r_B grows logarithmically.

Chapter 4 LRIC: Growth Rates

For instance, in the Figure 4.6 example, if power flows from Bus 2 to Bus 1 and load at Bus 1 has a positive nodal growth rate, the positive exponential circuit loading growth pattern can be obtained. On the other hand, if power flows from Bus 1 to Bus 2 (i.e. the circuit is generation-dominated seen by customers at Bus 1) and the load at Bus 1 has a negative growth rate, the positive logarithmic circuit loading growth pattern can be achieved.

For the negative r_B case the loading level will never reach the maximum allowed load­

ing level and hence no reinforcement cost will be seen. Therefore, only the positive r_B case will be considered for network pricing, and there will not be any investment cost for the negative r_B case.

4.3.2 Negative Circuit Loading Growth Pattern

Negative circuit loading growth indicates that the loading level of the circuit is de­

creasing. Similarly, there are two possibilities where a circuit could have a negative circuit loading growth:

• When D_B is positive and r_B is negative

• When D_B is negative and r_B is positive

The negative growth patterns of these two positive and negative r_B cases are shown in Figure 4.8. From the graph, it is shown that the loading level of the negative r_B case decreases exponentially. This also means that the loading level will decrease slower with time and will never reach zero. Hence, if a circuit loading level is diminishing and the r_B is negative, the LRIC price is zero as no reinforcement is required.

On the other hand, for the positive r_B case, the size of the loading level decrement grows with time. Therefore, at some point the loading level of the circuit will become zero and the flow on the circuit will ’flip’ to another direction (loading level becomes negative). The D_B flow with the positive r_ℓ will continue grow until the loading level reaches the maximum allowed capacity. Reinforcement is then required.

In the Figure 4.6 example, if power flows from Bus 2 to Bus 1 and load at Bus 1 has a negative growth rate, the exponential negative circuit loading growth pattern is reached. If power flows from Bus 1 to Bus 2 (generation-dominated) and load at Bus 1 has a positive growth rate, then the loading level of the line will diminish until it reaches zero and ’grow’ exponentially at the different direction (load-dominated).

Chapter 4 LRIC: Growth Rates

Zero circuit loading growth will occur when demand is not growing or not decreasing, i.e. r_B is zero. The loading levels of the corresponding circuits remain the same. This might happen at some remote areas where the domestic customers merely change their usage of electricity.

For zero circuit loading growth case, as there is no change in the loading level hence there is no need for investment. Therefore, there is no reinforcement cost for circuits