Discussion on Algorithm of Spinning Reserve Ancillary Services Compensation Capacity in the

Regional Power GridPengzan Jiang

North China Electric Power University & Yunnan Power Grid

Company Postgraduate Workstation Kunming, China

E-mail: jpzmail@163.com

Yanhui Xu School of Electrical and Electronic Engineering North China Electric

Power University Beijing, China

Dada Wang Electric Power Research Institute

Yunnan Electric Power Test Research Institute (Group) Ltd.

Kunming, China

Abstract-According to the management rules about spinning reserve ancillary services in CSG(China Southern Power Grid Co., Ltd.), the date of spinning reserve ancillary services in Yunnan power grid is counted, it’s found that the current compensation capacity algorithm is not well reflect the spinning reserve demand of the grid side. This paper proposes the concept of the validity coefficient of spinning reserve to improve the compensation algorithm, which have been tested and verified by the actual operation date. It can be used for reference on the better use of Yunnan power grid spinning reserve resources and the development of the spinning reserve ancillary service market.

Keywords-spinning reserve; compensation capacity; validity coefficient

I. INTRODUCTION The ancillary service is an important part of the

electricity market. In order to ensure the market develop healthy and orderly, it’s needed to establish appropriate mechanisms to stimulate the market participants to actively involved in ancillary service market transactions. The participants should reduce service costs in effectively and improve service quality, at the same time, they should provide adequate ancillary services. Then, it requires the market mechanism to ensure participants receive appropriate benefits. Quantitative indicators of ancillary service, cost analysis and pricing urgent need to be resolved. Both domestic and international researchers and engineering have conducted extensive study.

“Power Plants of Southern Regions Operation Management Implementation Regulations” and “Power Plants of Southern Regions Ancillary Services Management Implementation Regulations” (“the Two Regulations” in short) have began to implement in the Yunnan Power Grid in February, 2010. “China Southern Power Grid ‘1+5’ Plant Ancillary Service Assessment Technical Support System” (“the Support System” in short) is also put into operation, which bases on “the Two Regulations”. Now, the ancillary service management regulations of CSG are in its infancy, and various power companies is actively improving the regulations.

Spinning reserve is an important part of the ancillary services, and its research is significance to the power plant

and the power grid. Most of the spinning reserve studies[1-6] base on the improved electricity market, so their practicality are limited greatly at the environment of the domestic electricity market. This paper will research the compensation algorithm of the spinning reserve capacity, based on the operating data from “the Support System” and the actual operation

II. ANALYSIS OF CURRENT MANAGEMENT IMPLEMENTATION DETAILS

To ensure power supply reliable, the power dispatch center designates the power generators to reserve generating capacity, and the reserved generating capacity is the spinning reserve[7]. Then, power generation companies as an independent economic entity has passive participation spinning reserve ancillary services, and reasonable compensation mechanism can increase the initiative of their participation.

Generation spinning reserve capacity is the generating capacity no loaded part of the online operation generator. Assumed that all generations can reach the rated capacity, single generator spinning reserve capacity Pxi is defined as:

Pxi=PNi-Pi (1)

Where PNi is the rated capacity and Pi is the operation capacity of the generator.

And the spinning reserve of the whole power grid is the sum of the n generators’ reserve capacity, as follows:

1

n

X Xii

P P=

= (2)

According to “the Two Regulations” , the compensation capacity of the spinning reserve service is defined as[8]: when the reserve capacity of the thermal power generator exceeds the 30% of the rated capacity, the compensation capacity is the integration of the difference between 70% of the rated capacity and the operation capacity in the reserve time; when the reserve capacity of the hydropower generator exceeds the 80% of the rated capacity, the compensation capacity is the integration of the difference between 20% of the rated capacity and the operation capacity in the reserve time.

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Except the above two situations, the power generation companies can’t receive any compensation.

According to the definition of the compensation capacity, the spinning reserve which is provided by the generator is divided into two parts: basic and compensation. When the generator’s operation capacity is low, not only the opportunity cost of power generation is lost, but also because of reduced efficiency, the electricity cost is increased. So, the spinning reserve service will cause economic losses to the power plant. And the severity of the economic losses determine the parameters of the spinning reserve basic and compensation capacity, that is, 70% ( the thermal power generator) and 20% (the hydropower generator), but these need to further discuss.

The more important question is: in accordance with this spinning reserve compensation capacity algorithm, whether the level of parameters, that generators do not meet the standard without any compensation, but they participate the spinning reserve and have economic losses at a certain extent.

Take one day’s power plant generation date form “the Support System” randomly for example, shown in Figure 1, where the solid line is the power generation load curve, and dotted line is the spinning reserve instantaneous compensation power, that is, the sum of the differences under the compensation terms, the one difference between 70% of the thermal power generator rated capacity and their operation capacity, the other difference between 20% of the hydropower generator rated capacity and their operation capacity. And the solid line’s baseline is the left value axis, the dashed line’s is the right.

Fig.1 Compensation Situation of Spinning Reserve Ancillary Services

As the Figure 1 shown, generation load power exceeds 6000 MW at 8 o’clock and the load power enters the peak period. After that time, the spinning reserve capacity is less than before that time, and the spinning reserve capacity in the load peak period is more important than the load low period, so the former should increase their compensation intensity. However, the current compensation algorithm is not fully reflecting this from the spinning reserve compensation power.

About 60% of the generation capacity is the hydropower in Yunnan Power Grid. The main characteristics of the hydropower generator is the start-stop speed high, this can affect the operation mode of the whole grid, of course, including the spinning reserve ancillary services operation. This maybe the reason for the differences between the

theoretical analysis and the practical operation. This paper will research this as follow.

Fig.2 Operation Situation of Spinning Reserve Ancillary Services

The date of Figure 2 and Figure 1 is in the same day. In Figure 2, the solid line is the power generation load curve, the dotted line is the operation generators rated capacity of the whole grid, and the dashed line is the spinning reserve instantaneous power, that is, the difference between the dotted line and the solid line.

Figure 2 shows the spinning reserve instantaneous power has a little change. When the load reaches its peak period, many hydropower generators will be involved in peak regulation and put into operation again. So, the operation generators rated capacity will also increase, its trends the same with the power generation load curve, then, the spinning reserve instantaneous power is maintained at around 2000 MW.

In terms of losses caused by the power accident at the different time, Figure 1 shows the spinning reserve capacity in the load peak period is less than the load low period is unreasonable.

III. IMPROVEMENT OF THE SPINNING RESERVE COMPENSATION CAPACITY ALGORITHM

Through the analysis above, the current spinning reserve compensation capacity algorithm compensates some losses of the power plant to some extent, but it doesn’t combine the spinning reserve demand situation. There are two ways to solve this problem at present. One approach is using time-compensated power price on current methods, this is more intuitive; another approach is to improve the spinning reserve compensation capacity algorithm. And this section focuses on the latter approach.

It’s generally believed that the spinning reserve capacity which the system needs is the 2% to 5% of the largest power load capacity, or the maximum rated capacity of the generators in the grid[9]. Compared to the Figure 2 show, the spinning reserve capacity which the system needs is a part of that which the system provides. And the importance of the spinning reserve capacity is different between the peak load period and the load low period. Combined with these two points, this paper suggests the validity coefficient of the spinning reserve KX , the specific expression as follows:

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max

maxX

X X

KP P KPKP P P

= ⋅ = (3)

Where K is the coefficient of the system spinning reserve and between 2% and 5%, the coefficient value can be determined according to the actual situation; Pmax is the maximum value of the day’s power generators’ operation capacity (either forecast or actual value); P is the power operation capacity at a moment. KPmax/PX is the ratio of the spinning reserve capacity which the system needs takes up that which the system provides. P/Pmax contains the different importance of the spinning reserve capacity between the peak load period and the load low period.

If the spinning reserve capacity PS which the system needs is determined according to system stability and economic principles, then the validity coefficient of the spinning reserve KX expression is changed as follows:

max

sX

X

P PKP P

= ⋅ (4)

The generator spinning reserve compensation power is the time integral of the product between the reserve capacity Pxi from Formula 1 and the validity coefficient of the spinning reserve KX , which is calculated as follows:

i X XiW K P dt= (5)

In accordance with the formulas above, the spinning reserve compensation power of the plant in a sampling time can be calculated, and then the value of this throughout the mouth is cumulated. And the cumulative value is the spinning reserve compensation power which considers the spinning reserve supply and demand situation.

IV. ANALYSIS OF CASE The case is still based on the date which is extracted from

“the Support System” in section II. If the coefficient of the system spinning reserve K is 5%, then the validity coefficient of the spinning reserve KX is calculated in accordance with Formula 3 and the result is shown in Figure 3.

Fig.3 Validity Coefficient of Spinning Reserve

The solid line is the power generation load curve, and the dotted line is the validity coefficient curve. And the solid line’s baseline is the left value axis; the dashed line’s is the right. The tends of the two curve are basically the same. The load power enters the peak period after 8 o’clock, then the

validity coefficient KX is increased higher than that in load low period, and maintains at 12.5% above. The spinning reserve compensation capacity will be a corresponding increase in load peak period.

The revised spinning reserve compensation capacity PB is calculated as follows:

1 1

n n

B X Xi X Xi X Xi i

P K P K P K P KP= =

= = = = (6)

Fig.4 Revised Compensation Situation of Spinning Reserve Ancillary

Services

The result of PB is shown in Figure 4. The solid line is the power generation load curve, and the dotted line is the validity coefficient curve. And the solid line’s baseline is the left value axis; the dashed line’s is the right.

PB and the power generation load are proportional to change, that is, the spinning reserve compensation capacity is determined by the power generation load. As Figure 4 shown, the revised compensation capacity of the spinning reserve about 300 MW, and the total amount of compensation power is the same to that which has shown in Figure 1. So the new algorithm has re-allocated existing total compensation according to the spinning reserve capacity which the system needs, and solved the problem in section II successfully.

V. CONCLUSION “The Two Regulations” have been implemented and

guided the operation of ancillary service in the Yunnan Power Grid more than one year. This paper has analyzed the current operation situation of “The Two Regulations”, sum up experience, and made recommendations for improvement. It has a strong practical significance for further development of related work.

The spinning reserve capacity which the system needs is different between the peak load period and the load low period. So, the current algorithm of spinning reserve ancillary services compensation capacity has deficiencies, and needs to continue to improve. In this paper, the concept of the validity coefficient of the spinning reserve has been proposed, and then the compensation capacity algorithm has been improved. The improved algorithm has solved the problem though the case analysis in section III.

But there are still many places need to refine and improve in Yunnan Power Grid ancillary services, such as: the maximum operation capacity of generator, the seasonal variations in hydropower generator, generation costs, etc.

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