Importance of Reactive Power for Distributed Generation

"Sharpening Skills..... Serving Nation" International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459...
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"Sharpening Skills..... Serving Nation"

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 4, Special Issue 1, February 2014) International Conference on Advanced Developments in Engineering and Technology (ICADET-14), INDIA.

Importance of Reactive Power for Distributed Generation Akash, Gaurav Shah1, Himnay Pratap Singh2, Avinas Kumar Chauhan3 Moradabad Institute of Technology, Moradabad Abstract-- Reactive power, measured in volt-amperes reactive or VARs, is one of a class of power system reliability services collectively known as ancillary services. Ancillary services are essential for the reliable operation of the bulk power system. Reactive power flows when current leads or lags behind the voltage; typically, the current lags because of inductive loads like motors. Reactive power flow wastes energy and transmission capacity, and causes voltage drop. The role of reactive power in maintaining system reliability, especially during unforeseen system contingencies, is the reason for the growing interest by regulators and system operators alike in alternative reactive power supplies. Distributed Generation is an attractive option for solving reactive power and distribution system voltage problems because of its proximity to load. Distributed Generation is very useful for the supply of MW in remote areas but since DGs are not able to produce VAR. So we have to compensate VAR through compensating devices to fulfill the demand of MW in remote areas.

I. INTRODUCTION Reactive power, measured in volt-amperes reactive or VARs, is one of a class of power system reliability services collectively known as ancillary services. Ancillary services are essential for the reliable operation of the bulk power system. Reactive power flows when current leads or lags behind the voltage; typically, the current lags because of inductive loads like motors. Reactive power flow wastes energy and transmission capacity, and causes voltage droop.

Fig. 1: A simple block diagram of supplying reactive power for DG

To correct power flow, leading reactive power (current leading voltage) is supplied to bring the current in phase with voltage. Reactive power can be supplied from either static or dynamic VAR sources. Static sources are typically transmission and distribution equipment, such as static VAR compensators or capacitors at substations, and their cost has historically been included in the revenue requirement of the transmission owner (TO), and recovered through cost-of-service rates.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 4, Special Issue 1, February 2014) International Conference on Advanced Developments in Engineering and Technology (ICADET-14), INDIA. By contrast, dynamic sources are typically energy producers, including generators capable of producing both real and reactive power, and synchronous condensers, which produce only reactive power. Thee equipment may be owned either by tos or independent entities. For dg to supply reactive power, the cost of modifying these devices to provide reactive power needs to be reduced and system operators must develop a compensation plan for a local voltage regulation service. Fig. 1 shows a simple block diagram which shows the introduction and idea behind this topic that is supplying reactive power for distributed generation. As we know that many of the distributed generation sources like Solar Energy, Wind Energy, Photovoltaic can only able to produce real power that is KW. They are not able to produce reactive power. As we all know that reactive power is too necessary for our system operation. It is the imaginary part of the total power that is VA. Also we are familiar to the situation that the condition of the villages in terms of electricity is very bad. As India is a developing country and the majority of this country is villages. So the condition of the electricity in the villages are need to be improved. As we all know that the government of the India and many other companies which provide electricity are only able to provide approx. 6 to 8 hours electricity in a whole day. So supplying reactive power is a very good concept to provide electricity in the villages, in many of the remote areas in India so that India can become a developed country. Also in remote areas, if we use the concept of distributed generation, then there will no need to install transmission and distribution system (T & D). II. REACTIVE P OWER Reactive power is a concept used by engineers to describe the background energy movement in an Alternating Current (AC) system arising from the production of electric and magnetic fields. These fields store energy which changes through each AC cycle. Devices which store energy by virtue of a magnetic field produced by a flow of current are said to absorb reactive power; those which store energy by virtue of electric fields are said to generate reactive power. Power flows, both actual and potential, must be carefully controlled for a power system to operate within acceptable voltage limits.

Reactive power flows can give rise to substantial voltage changes across the system, which means that it is necessary to maintain reactive power balances between sources of generation and points of demand on a 'zonal basis'. Unlike system frequency, which is consistent throughout an interconnected system, voltages experienced at points across the system form a "voltage profile" which is uniquely related to local generation and demand at that instant, and is also affected by the prevailing system network arrangements. National Grid is obliged to secure the transmission network to closely defined voltage and stability criteria. This is predominantly achieved through circuit arrangements, transformers and shunt or static compensation. III. SOURCES OF REACTIVE P OWER Most equipment connected to the electricity system will generate or absorb reactive power, but not all can be used economically to control voltage. Principally synchronous generators and specialized compensation equipment are used to set the voltage at particular points in the system, which elsewhere is determined by the reactive power flows. Synchronous Generators- Synchronous machines can be made to generate or absorb reactive power depending upon the excitation (a form of generator control) applied. The output of synchronous machines is continuously variable over the operating range and automatic voltage regulators can be used to control the output so as to maintain a constant system voltage. Synchronous Compensators-Certain smaller generators once run up to speed and synchronized to the system, can be declutched from their turbine and provide reactive power without producing real power. This mode of operation is called Synchronous Compensation. Capacitive and Inductive Compensators - These are devices that can be connected to the system to adjust voltage levels. A capacitive compensator produces an electric field thereby generating reactive power whilst an inductive compensator produces a magnetic field to absorb reactive power. Compensation devices are available as either capacitive or inductive alone or as a hybrid to provide both generation and absorption of reactive power. Overhead Lines and Underground Cables - Overhead lines and underground cables, when operating at the normal system voltage, both produce strong electric fields and so generate reactive power.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 4, Special Issue 1, February 2014) International Conference on Advanced Developments in Engineering and Technology (ICADET-14), INDIA. When current flows through a line or cable it produces a magnetic field which absorbs reactive power. A lightly loaded overhead line is a net generator of reactive power whilst a heavily loaded line is a net absorber of reactive power. In the case of cables designed for use at 275 or 400kV the reactive power generated by the electric field is always greater than the reactive power absorbed by the magnetic field and so cables are always net generators of reactive power. Transformers - Transformers produce magnetic fields and therefore absorb reactive power. The heavier the current loading the higher the absorption. Consumer Loads - Some loads such as motors produce a magnetic field and therefore absorb reactive power but other customer loads, such as fluorescent lighting, generate reactive power. In addition reactive power may be generated or absorbed by the lines and cables of distribution systems. IV. D ISTRIBUTED GENERATION DG is a fairly new trend in the electricity industry, market, and deregulated systems. Till now, there are no consistent definitions that can describe DG terminologies. However, there are some definitions that can be considered common for most literatures. Some of these definitions are discussed below. DG names There are several terms used to refer to distributed generation, for example: • ―Dispersed generation‖ used in North America. • ―Embedded generation‖ used in South American countries. • ―Decentralized generation‖ used in Europe and some Asian countries. However, literature survey recommended the name of ―distributed generation‖ to be used all over the world. DG purpose Basically, it is used to provide part or all of a customer’s real power demand and/or as a standby supply. Therefore, according to this definition, there is no need to supply reactive power from DG as in the case of FC for example.

DG location A definition: ―The location of distributed generation is defined as the installation and operation of electric power generation modulars connected directly to the distribution network or connected to the network on the customer site of the meter‖. This definition under the deregulation trend encourages us suggest addition to the transmission and distribution systems definition. A transmission system can be defined as: ―The system, which is operated by an independent company and not providing power generation or involved in distribution or retail service‖. A distribution system can be defined as: ―The system, which is operated by a distribution company, can provide power generation through an electric utility or customers and involved in distribution or retail service‖. The proposed addition to the transmission system, distribution system and DG location definitions are helpful for exceptional cases as follows: • If a large industrial customer site is connected directly on the transmission network and has a CHP system. In this situation CHP can be considered as a DG because it is connected directly on the customer side of the meter. • If a distribution network capacity is limited, a medium size wind farm can be connected directly to a transmission system. In this case the wind farm cannot be considered as a DG. DG rating There are different definitions for generation size range according to some institutes and literatures as However, these definitions are dependent on the government regulations as discussed below: In the Swedish market The DG capacity is up to 1.5MW. This value is not enough for deciding that this generation rating is for DGs or not, due to the cases below: • In case of wind energy, Sweden plans offshore wind farms having a maximum capacity of 1000MW. Each wind turbine rating is 1.5MW, which can be considered as a DG based on the modular rating not the total wind farm capacity.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 4, Special Issue 1, February 2014) International Conference on Advanced Developments in Engineering and Technology (ICADET-14), INDIA. • In the case of hydro modulars the capacity is calculated as the total rating of the power station not for each individual modular. So in most cases they are not considered to be as a DG. In Germany (Berlin) The local utility BEWAG built a power generation station in the city Centre. This power station, which feeds into 110, 33 kV distribution lines, provides electricity and heat (300MW each, respectively). The generated electricity and heat are consumed locally so that this power station can be considered as a DG. According to the above discussion there is no common DG rating definition because the maximum capacity of a DG connected to the distribution network depends on the distribution system’s capacity and its voltage level. However, most literatures use small and medium DG sizes. DG power delivery area There is no specific definition for DG power delivery area, but usually the DG produced energy is supposed to be consumed within the distribution network. However, DGs can feed back some of their generated electric power to the transmission if it exceeds the distribution network load demand where DGs are installed. V. REACTIVE P OWER FOR D ISTRIBUTED GENERATION To help the reader understand these benefits, a simple two-bus system shown in Fig. 2 is used to illustrate the benefits. In the figure there is a generation bus, a load bus, and a line connecting the two buses. The generation bus represents a generation center, the load bus represents a load center, and the line represents an inter-tie or an interface between the two areas. The generation centre is a distributed generation centre which is able to provide VA (the combination of real and reactive power that is KW and KVAR respectively).Now we assume that the power transfer is in the form of (Pm + jQm). The tie line is congested due to the maximum transfer capability between two areas. We assume the generation center has a cheap unit with a cost of $20/MWh. The load center has a large amount of load, served by a utility as a load serving entity (LSE), and an expensive unit, owned by an independent power producer(IPP), with a cost of $25/MWh. The original import into the load center is (Pm + jQm). If there is a local VAR injection (Qc in the figure), the flow at the receiving end will be reduced to (Pm + j(Qm-Qc)).

If the same MVA transfer limit is maintained, then we can send more real power over the tie-line since the reactive power flow has been reduced. Therefore, more MW can be dispatched from the cheap generation center. Hence, the output from the expensive IPP generator may be reduced. Thus, the total system cost will be reduced and the LSE utility will pay less to serve the same load.

Fig. 2: A Two-Bus System

Advantages    

The total system cost will be reduced. Power can be transferred to remote area. Power Factor will also be improved. It is the first step for the development of any country.

Disadvantages  

Most of the DG system is only able to provide active power. So, reactive power should be provided by compensation technique. It can provide energy at a very small scale. VI. CONCLUSION

Distributed generation or DG is an attractive option for solving reactive power and distribution system voltage problems because of its proximity to load. Providing dynamic reactive power near the load provides significant economic benefits such as reduced losses, increasing availability of local generation, and improved local voltage control, supply electricity in remote areas, improving the power factor, reducing total system cost. Several technology options are available to supply reactive power for DG; these include small generators, synchronous condensers, fuel cells, and microturbines.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 4, Special Issue 1, February 2014) International Conference on Advanced Developments in Engineering and Technology (ICADET-14), INDIA. They can provide continuous variable dynamic reactive power which can respond quickly to reactive power demand. Criteria need to be met for DG to become widely integrated as a source of electricity in rural areas.  The overall costs of retrofitting devices to absorb or produce reactive power need to be reduced.  There needs to be a market mechanism in place for ISOs/RTOs/TOs to procure reactive power from the customer side of the meter where DG resides.  Novel compensation methods need to be introduced to encourage the dispatch of dynamic resources close to areas with critical voltage issues. REFERENCES [1 ] ―Principles for Efficient and Reliable Reactive Power Supply and Compensation‖, FERC Staff Report, Docket No. AD 05-01-1000, Feb. 4, 2005, available at http://www.ferc.gov/EventCalendar/Files/20050310144430-02-0405 reactivepower.pdf. [2 ] J.L. Del Monaco,‖ The role of distributed generation in the critical electric power infrastructure‖, in: Proceedings of the Power Engineering Society Winter Meeting IEEE, vol. 1, 2001, 144–145.

[3 ] A. Thomas, A. Göran, S. Lennart, ―Distributed generation: a definition, Electric Power Syst. Res.‖ 57 (3) (2001) 195–204. [4 ] B. Lasseter, Microgrids ―distributed power generation‖ in: Proceedings of the Power Engineering Society Winter Meeting IEEE, vol.1, 2001, pp. 146–149 [5 ] Willam, E. Liss, ―Natural gas power systems for the distributed generation market‖, in: Proceedings of the Power-Gen International’99 Conference, New Orleans, LA, 1999. [6 ] M. Farooque, H.C. Maru,‖ Fuel cells—the clean and efficient power generators‖, in: Proceedings of the IEEE, vol. 89, issue 12, 2001, pp. 1819–1829. [7 ] F.L. Alvarado, ―Locational aspects of distributed generation‖, in: Proceedings of the Power Engineering Society Winter Meeting IEEE, vol. 1, 2001, p. 140. [8 ] N. Hadjsaid, J.-F. Canard, F. Dumas,‖ Dispersed generation impact on distribution networks‖, IEEE Computer Applications in Power, 12 (2) (1999). [9 ] Causes and Recommendations, Joint US-Canada Power System Outage Task Force, April 2004, at 17, available at ftp://www.nerc.com/pub/sys/all_updl/docs/blackout/ch1-3.pdf. [10 ] Available at ―http:// www.amsuper.com/products/ motorsGenerators/quickVAR.cfm.‖ [11 ] Available at ―http:// www.amsuper.com/ products/ motorsGenerators/documents/ IEEESuperVAR-030910-Paper.pdf.‖

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