expanding the ambit of ancillary services in india ... · the feedback report also suggested the...

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Expanding the Ambit of Ancillary Services in India –Implementation and Challenges

K V N Pawan Kumar, *Anupam Kumar, S C Saxena, S S Barpanda, Goutam Chakraborty, P K Agrawal, K V S Baba Power System Operation Corporation Ltd. (POSOCO)

New Delhi, India [email protected]

Abstract — Ancillary services is one of the four essential

pillars of market design; the other three being scheduling & despatch, imbalance handling and congestion management. The regulatory framework for ancillary services was introduced for the first time in India in 2015 and implemented in April 2016. Ancillary services have gained increased importance in today’s restructured power systems to ensure reliable operation of the grid. This paper traces the experience gained in terms of improvements in the Indian power system operation since 2016. This paper also discusses the need for expanding the scope of ancillary services in India as advanced grid reliability services such as Fast Frequency Regulation, Reactive Support and Black Start. This would provide additional incentives to the deployment and operation of flexible resources.

Keywords—Ancillary Services, Indian Electricity Market, Power System Operation, Renewable Integration

I. INTRODUCTION

Grid operators need to be equipped with tools and procedures to operate the power system in a reliable and stable manner over a continuum of time that ranges from a fraction of a second to years into the future [1]. The suite of instruments collectively referred to as “ancillary services”, support balancing of the supply and demand in the real time. The ancillary services framework introduced in India, in 2016, is a form of slow tertiary control.

Generally, the system operator procures ancillary services for ensuring security, reliability, stability and quality of the power supply. Ancillary services can be provided by generators, load serving entities and transmission operators. Both conventional & renewable generators have the capability to provide ancillary services.

Internationally, in the case of United States Independent System Operator (ISOs)/Regional Transmission Operator (RTOs), generally, the procurement of ancillary services is done in the day-ahead and/or in the real-time market. On the other hand, in the case of European ISOs/Transmission System Operator (TSOs), generally, the ancillary services capacity procurement is done on monthly or annual basis.

Alongwith the advent of renewables, flexibility in transmission and distribution alongwith smart technological enhancements of the demand side resources as the potential contributors to reliability in the future are the drivers for change. These measures are supplementing the traditional reliability services provided by the conventional generation. The innovations in hardware and software, especially power

electronics side, also allow the renewable generators to contribute to ancillary services [1].

Therefore, in addition to frequency control ancillary services, expanding the ambit to other technologies and other forms of ancillary services such as network control ancillary services for voltage control and system restart ancillary services is being envisaged in the future.

II. REGULATORY MANDATE

The central regulator i.e. Central Electricity Regulatory Commission (CERC) notified the regulations for Reserve Regulation Ancillary Services (RRAS) on 13th August 2015 [2]. The relevant extracts from the regulations, which provides for replication of the framework at state level, is quoted as below:

“…2(k)…At the intra state level, the State Load Despatch Centre would be the nodal agency as and when such services are introduced by the [State Electricity Regulatory Commissions] SERCs…”

While the draft regulations were floated for public consultations by CERC, there were several stakeholders who proposed expansion of the scope of ancillary services by including other services such as primary/secondary frequency control, voltage control and black-start. While appreciating the need for introduction of other forms of ancillary services, CERC recorded the analysis and decision in the Statement of Reasons [3] as quoted below:

“…The Commission would like to move in a calibrated manner in so far as introduction of ancillary services is concerned. As such to start with, only the Inter-State Generating Stations which are regional entities are being covered in the framework. Based on the experience of implementation of the present framework, it would be scaled up to cover other forms of ancillary services and other generating stations and reserves available in the country. National Smart Grid Mission has been launched under Ministry of Power, in association with MNRE, MoUD and MoHI. The Commission is working closely with MoP on this mission. Demand response is being tested in various states by respective DISCOMs as well as the Bureau of Energy Efficiency. The Commission’s vision is to incorporate these components for Ancillary Services at the right time…”

A half yearly feedback was submitted, in November, 2016, to the central regulator based on the experience gained in RRAS implementation [4]. The report analyzed the benefits to the system and also recommended the changes required for

Proceedings of the National Power Systems Conference (NPSC) - 2018, December 14-16, NIT Tiruchirappalli, India

eliminating the operational difficulties faced by the nodal agency i.e. National Load Despatch Centre (NLDC) in coordination with Regional Load Despatch Centres (RLDCs).

The feedback report also suggested the expansion of the ambit of present ancillary services. It was suggested that another form of ancillary services is needed to cover reactive power support in different forms such as condenser mode operation of hydro machines. Pumped storage hydro plants may also be brought under the ambit of ancillary services. The blackstart as an ancillary service was also proposed as one of the classical ancillary services.

III. CASE-STUDIES: BENEFITS OF IMPLEMENTATION

a) Improvement in System Frequency Profile The frequency profile has improved since implementation

of ancillary services. The frequency floats around 70-75 % of time within the Indian Electricity Grid Code (IEGC) mandated operating frequency band of 49.90-50.05 Hz. Most of the days the average frequency is close to national reference frequency of 50 Hz (Figure 1). The Frequency Variation Index (FVI) has also shown improvement to around 0.03 since RRAS implementation.

Figure 1: Average Indian Grid Frequency 2012 - 2018

Figure 2: Frequency Profile on 29th April, 2018

On 29th April 2018, the frequency remained with the IEGC operating band for 88.5 % of the time (Figure 2). It was possible due to the RRAS Regulation ‘Up’ instructions issued for around 1300 MW during the peak hours of the day.

Figure 3: Frequency Profile on 24th September, 2017

On 24th September 2017, FVI of 0.019 for Indian power system was recorded (Figure 3). During the day, net RRAS ‘Up’ instructions for about 18 Million Units (MUs) and in the early morning hours, RRAS ‘down’ instruction were despatched to maintain the grid frequency within the IEGC mandated band.

Maximum RRAS ‘Up’ instruction of 3600 MW and RRAS ‘down’ instruction of 427 MW were despatched in a time-block of 15-minutes. Further, two thermal generating units in the northern region, totaling to 750 MW, were despatched up to their technical minimum, under RRAS, for maintaining hot spinning reserves.

b) Load Following

Figure 4: All India Load Curve on 28th April, 2018

On 28th April 2018, all India maximum energy of 3862 MU was met (Figure 4). In order to meet the high demand


throughout the day, about 22 MU of RRAS ‘Up’ instruction was despatched. The maximum RRAS ‘Up’ instruction of 2700 MW was implemented in a 15-minute time-block with an average of 900 MW of continuous RRAS ‘Up’ instruction applied for maintaining the grid parameters during the day.

c) Facilitating Large Scale Integration of Renewables

On 03rd April 2017, during early evening hours, the total

all-India wind generation was around 2200 MW. Within an hour, the wind generation reduced to 1700 MW. As the peak hours were approaching, this sudden decrease of around 500 MW of wind generation had to be managed to bridge the supply-demand gap.

Therefore, RRAS ‘Up’ of around 1000 MW was implemented to fulfil the gap and helped the grid to meet the demand during high ramping period of evening hours (Figure-5).

The unpredictable variations of generation from renewable source such as wind and solar are being handled by the system operators through the despatch of ancillary services in the real time operation.

Figure 5: RRAS Despatched for Handling Wind Variability

d) Handling Low Probability High Impact Events

On 13th May, 2018 at around 1355 hrs, stormy weather conditions formed in northern and eastern parts of India. A number of vital 765 kV and 400 kV transmission lines tripped and load loss of around 22 GW was recorded (Figure 6). In order to handle extreme weather conditions and sharp fall in demand, RRAS instructions were issued immediately to manage the grid conditions.

A maximum RRAS ‘down’ instruction of around 3500 MW was implemented. When the load started picking up with the restoration of transmission lines next day, the RRAS ‘down’ instruction was withdrawn.

Figure 6: Extreme Weather Condition on 13th -14th May, 2018

IV. BROADENING THE SCOPE OF ANCILLARY SERVICES

The implementation of ancillary services in Indian electricity market has been conceived through a regulated mechanism. With the help of in-house development of customized software solution, RRAS has addressed the congestion management issues and optimization at regional & pan-India level, thereby, facilitates integration of renewables too [5].

Various challenges have been experienced in the RRAS implementation such as ‘gate closure’ in the multi-lateral scheduling system, maintaining adequate reserves quantum and forecasting by the utilities for resource adequacy.

At present, conventional generating stations (coal, lignite and gas based), designated as regional entities with their tariff determination/adoption by the central regulator i.e. CERC, are mandated to participate as RRAS providers. The un-despatched surplus capacity available in these generating stations is used for RRAS Regulation ‘Up’ service. The RRAS Regulation ‘Down’ service is provided by these generating stations when they back down upto 55% of their installed capacity less auxiliary consumption. The revised schedule for reduction in generation is prepared without revising the schedule of any of the beneficiaries.

Figure 7: Depletion of Generation Reserve Quantum


It is observed that during the high demand period, the generation reserve quantum available for RRAS Regulation ‘Up’ service is very less (Figure 7).

Out of more than 340 GW of installed generation capacity in the country, about 56 GW of thermal and about 12 GW of hydro capacity has been brought under the RRAS mechanism. However, the hydro generation capacity has no un-despatched surplus and therefore, not despatched under the current framework.

Therefore, there is ample scope in the regional entity generators, Independent Power Producers (IPPs) and intra-state generators to increase the ambit for provision of ancillary services. Further, 70 GW of renewables also have the potential to provide the support services to the grid. The various types of additional ancillary services, which may aid in secure and reliable system operation, are proposed as below:

a) Fast Tertiary Control through Hydro

The grid conditions are dynamic in nature. The present RRAS instructions can be implemented at a minimum time gap of around 16 minutes and hence, act as slow tertiary control. The majority of the generation capacity despatched in the present RRAS mechanism is coal based and hence, have the ramp limitations. Generally, it is observed that during hourly boundary, there are sharp fluctuations in frequency for very short periods of time (Figure 8).

Figure 8: Frequency Fluctuations over a Day

In contrast to coal based generating stations, hydro generators demonstrate better regulation behaviour. The hydro generators, especially reservoir/storage based, are better placed to contribute their fast response capabilities through the ancillary services mechanism.

The relevant extracts from the Technical Standards for Connectivity to the Grid [6] notified by CEA are quoted as below:

“All generating machines irrespective of capacity shall have electronically controlled governing system with appropriate

speed/load characteristics to regulate frequency. The governors of thermal generating units shall have a droop of 3 to 6% and those of hydro generating units 0 to 10%.”

The total generation capacity of hydro station in India is

around 45 GW, which consist of 14,882 MW in central sector, 26,928 MW in state sector and rest 3,394 MW in private sector. The hydro station can be further classified based on their storage type. There are about 3.7 GW storage type, 5.6 GW pondage type and 6.2 GW run-of-the-river type hydro power station as regional entities. Since hydro generation can offer more operational flexibility, hence, there is a need for regulatory approaches to acknowledge that:

• Hydro generating plants are “energy limited resources”

but the conventional fuel based plants are “ramp limited resources”

• The utilization of water by the hydro power station for generation has other limiting factors such as irrigation, flood control etc.

• The marginal cost of hydro station is almost negligible. The hydro tariff design in India differentiates the variable charges and fixed charges on ‘notional’ basis only. Thus, the present settlement mechanism of RRAS needs a fundamental change to hydro potential for ancillary services.

The Forum of Load Despatchers (FOLD) [7] “Report on Operational Analysis for Optimization of Hydro Resources & facilitating Renewable Integration in India” has also recommended utilization of the hydro generation for provision of Ancillary Service.

As the hydro generating stations have fast ramp

capability compared to the conventional power station (thermal), the hydro generating unit capabilities are more suitable for handling sharp fluctuations in the frequency for very short durations (say 5-10 minutes at a time) such as those observed at the hour boundaries and any other exigency. The hydro units which are synchronized to the grid can ramp up or ramp down fast as per the grid requirement.

There is a need to encourage the hydro generators to

participate through fast tertiary frequency control through a suitable compensation mechanism. It would have to be ensured that the despatch of hydro stations in ancillary services shall not hamper the existing scheduling framework. The current 15-minute time block based system may be evolved to faster 5-minute time block scheduling and settlement for precise control of fast responding resources in the ancillary services.

b) Secondary Frequency Control Secondary frequency control in the form of Automatic

Generation Control (AGC) from all the generating stations has


been mandated as per the CERC Roadmap on Operationalization of Reserves in the country. A pilot project on AGC has been operationalized in the northern region in January, 2018. It paves the way forward for secondary regulation services through AGC to be introduced pan-India. CERC also observed that a settlement system based on 5-minute time block is likely to bring in better granularity in grid management and ramp monitoring. CERC, therefore, directed that 5-minute accounting should be implemented for improved record of AGC signal and the up/down response of the plant [8]. A detailed plan was submitted to CERC by POSOCO in July’17 in which secondary control was recommended to be added as an Ancillary Service [9]. Similar initiatives may be considered for implementation of AGC in other regions for different types of generating stations viz. gas, hydro, renewable etc.

c) Voltage Control The power stations in the country have significantly

contributed to the voltage stability of the grid by absorbing reactive power from the grid by running as synchronous condenser during off-peak hours. Presently, the synchronous condenser operation of hydro power stations is being done as per instructions of system operators (RLDCs/SLDCs) under the regulatory framework of grid code.

The static reactive power (VAR) exchange by a load

serving entity with the Extra High Voltage (EHV) grid (at a voltage level > 33 kV) is priced at ₹ 14 paise/ KVArh under the grid code (IEGC) for keeping voltage within 97% to 103% of nominal value. This provision excludes the generating stations. Thus, an incentive scheme linked to the dynamic reactive support from power stations running as synchronous condensers may be considered by the appropriate commission to promote this essential ancillary service for the EHV grid.

d) Black-start service

The black-start service is an essential and unique service available from a limited number of power stations in the country. At present, most of the black-start capable power stations in the country are hydro power stations. However, the success rate of black start from a hydro power station depends largely on healthiness of the black-start diesel generator sets available at the power station with redundancy. Also, the black start capable hydro stations are strategic assets for ensuring grid resilience and hence, reliable & uninterrupted supply of survival power is a must.

As per the provisions in the IEGC, the black start capable

power stations are mandated to demonstrate black start capability once in every six months through conduction of mock drills, under intimation to respective Regional /State Load Despatch Centres (RLDCs/SLDCs).

However, there is no scheme for incentivizing black start service rendered by the power stations. In the absence of any

compensation, the upcoming power stations may give black-start facility least priority and in the worst case, it may not be commissioned for cost optimization. Thus, the appropriate regulatory commission may facilitate financial incentive as compensation through provision of black-start ancillary services which may be linked to compliance mandated in the IEGC.

V. CONCLUSION

Ancillary Services have proved to be a valuable mechanism to grid managers for maintaining the system parameters, especially, during extreme weather conditions, generating unit outages, transmission line trippings and high demand position.

With the increase in challenges and complexities for

smooth operation of grid, it is required to provide some more options/products under ancillary services. Further implementation of ‘gate closure’ in the multi-lateral scheduling system shall help in accessing the reserve requirement. Additional ancillary services have been proposed such as Fast Tertiary Control through Hydro, Secondary Frequency Control, Voltage Control and Black-start service. After gaining the experience from the current regulated version, a market based model for providing ancillary services may be considered in future.

ACKNOWLEDGMENT

The authors are thankful to the power system professionals and POSOCO management for the support and guidance. The perspectives expressed in this paper are those of the authors and not necessarily of the institution they belong to.

REFERENCES

[1] NESCOE (2017). Ancillary Services Primer [online] Available at: http://nescoe.com/resource-center/ancillary-services-primer-sep2017/

[2] CERC (2015). Ancillary Services Operations Regulations [online] Available at: http://cercind.gov.in/2015/regulation/Noti13.pdf

[3] CERC (2015). Statement of Reasons - Ancillary Services Operations [online] Available at: http://cercind.gov.in/2015/regulation/AncillarySOR-11092015.pdf

[4] POSOCO (2016). Report on RRAS implementation in Indian Grid Half Year Analysis and Feedback [online] Available at: https://posoco.in/download/half-year-feedback-to-cerc/?wpdmdl=8916

[5] S. K. Soonee et al., "Ancillary services in India — Evolution, implementation and benefits," 2016 National Power Systems Conference (NPSC), Bhubaneswar, 2016, pp. 1-6.

[6] CEA (2012). Technical Standards for Connectivity to the Grid, (Amendment) Regulations [online] Available at:


http://cea.nic.in/reports/regulation/grid_connectivity_12112013.pdf

[7] POSOCO (2017). FOLD-POSOCO Report on Operational Analysis for Optimization of Hydro Resources & facilitating Renewable Integration in India [online] Available at: https://posoco.in/download/fold-posoco-report-on-operational-analysis-for-optimization-of-hydro-resources/?wpdmdl=14168

[8] POSOCO (2017) Detailed Modus Operandi on operationalization of Spinning Reserves [online] Available at: https://posoco.in/download/detailed-modus-operandi-on-operationalization-of-spinning-reserves/?wpdmdl=13461


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