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Tuesday, 30 December 2014

Congestion Management in Day Ahead Indian Energy Market

The enactment of Electricity Act 2003 was a major reform intended to bring in competition and introduction of private players in the Indian power sector. These reforms covered nearly every aspect of electricity generation, transmission, sub-transmission and distribution. 

The Central Electricity Regulatory Commission (CERC) sets the terms for open access to grid and regulate power trading in India. 

Power Exchanges in India:

The Electricity Act sanctioned wholesale and a day-ahead electricity market and opened up two Power Exchanges (PX) in India in the year 2008.      

Power Exchange India Ltd. is India’s first institutionally promoted power exchange. Indian Energy Exchange Ltd. (IEX) is another automated power trading platforms for delivery of electricity. Today more than 1000 private generators, both commercial and renewable producers, and more than 3000 open access consumers across 29 states and 5 union Territories are using the IEX platform to manage their energy trading portfolio. 

In order to promote short-term electricity trading, the third exchange i.e. the National Power Exchange (NPEX) was also approved by CERC in the year 2008-09. Although the promoters of this third exchange, a joint venture of Power Finance Corporation (PFC), National Thermal Power Corporation (NTPC), National Hydro Power Corporation (NHPC), and Tata Consultancy Services (TCS), have decided to wind up the company. Following the company’s decision, CERC has withdrawn the permission granted to the exchange.

Ways to trade wholesale electricity in India:

There are three ways to trade wholesale electricity in India:
1.      bilateral contracts between buyers and sellers,
2.      the day-ahead market and
3.      Real-time balancing or Unscheduled Interchange (UI).

These segments differ in terms of the time when electricity is traded relative to the date of delivery, how prices are set and the regulatory limits. Most trade happens through long-term bilateral contracts set more than one year in advance of delivery. Nearly 89% of the total electricity generation is traded on long-term contracts, typically between state-owned generators and distribution companies. 

Short-term Bilateral contracts, set less than one year in advance of delivery, comprise a further 5% of generation. These contracts are mediated by power traders and most often apply to daily or monthly blocks. 

The last of the scheduled power trade is the day-ahead market, which handles 2% of generation. Rest of the generation, about 3% of generation, is not scheduled, which is demanded and supplied in real time through a mechanism called Unscheduled Interchange (UI).

Day Ahead Market:

Day Ahead Market (DAM), which gets its name for hosting electricity trading one day-ahead of when the power is to be delivered, was launched in June 2008. In this market, participants transact electricity on a 15 minute time block basis, thus total 96 blocks for a day. DAM is a physical electricity trading market for delivery of electricity for some or all the 15 minute blocks in 24 hours of the next day. The next day starts from midnight. The prices and quantum of electricity to be traded are determined through a double sided bidding process.

In the double auction pools or double sided bidding process, the distribution companies also bid for purchasing power. Once the buyer and seller bid the amount of power and the price, the power exchange forms an aggregate supply bid curve for suppliers and aggregate demand bid for the buyers or consumers. The supply bids are stacked from lowest to highest whereas the demand bids are arranged from highest to lowest. 

The Market Clearing Price (MCP) is determined on the basis of intersection point of the demand and supply curve. Clearance is obtained from the respective State Load Despatch Centre (SLDC) by buyers and sellers on the basis of availability of network.    

A day prior to the actual delivery of electricity, both buyers and sellers submit their bids. These bids are totally anonymous and submitted electronically during the bid call session which is from 10.00 am to 12.00 noon. The minimum allowable quantity for buy/sell in the standing clearance should not be less than 0.1 MW. The minimum volume step is also 0.1 MW and the minimum quotation step is Rs. 1 per MWh.


In the competitive electricity market, there is significant and frequent change of power flows due to market arrangements. Because of these flow variations overloading of transmission lines and transformers beyond transfer limit may take place. This is called congestion of transmission system.

Generally when there is no congestion in the transmission system, MCP is the same for the entire Power System. But when congestion happens, the concept of Locational Marginal Price is used.

Method of managing the transmission congestion:

Congestion of transmission system should be alleviated for the secure operation of the system. It can be mitigated by rescheduling the generators, and simultaneously curtailing the electrical load. In different types of electricity market, the method of managing the transmission congestion differs. 

The following three methods:
1.      Price Area Congestion Management,
2.      ATC based Congestion Management, and
3.      OPF based Congestion Management.

Apart from the above methods, application of FACTS devices also relieves congestion. Suitable placement of various shunt and series FACTS devices are helpful in increasing the load-ability of the transmission network resulting in reduction in congestion.

In the Indian Day Ahead Market, Price Area or Market Splitting technique is adopted for congestion management. In this method, the calculated contractual power flow is compared with the available transmission capacity for spot trading. If the power flow exceeds the transmission capacity, the prices on both sides of the transmission bottleneck are adjusted so that the calculated power flow equals the transmission capacity. When the flow exceeds the capacity, the whole market area is split into surplus area and deficit area. The price of energy is lowered in the electricity surplus area and increased in the deficit area. This in turn, reduces the sale and increases the purchase in the electricity surplus area. Similarly, in the deficit area the sale is increased and the purchase is reduced.

This reduces the power flow on the congested line and the contracted flow becomes equal to the transmission capacity. The country has 5 electrical regions, the Northern region, North-Eastern region, Eastern region, Western region, and the Southern region. Each region has been divided into 2 bid-areas so as to accommodate any emergency of congestion in the intra-regional transmission system.

Sunday, 28 December 2014

Some Definitions as per the Central Electricity Regulatory Commission Regulations, 2010.

The Indian Electricity Grid Code (IEGC) 2006 is a regulation made by the Central Electricity Regulatory Commission (CERC) in exercise of powers conferred under The Electricity Act 2003. IEGC lays down the rules, guidelines and standards to be followed by the persons and participants in the system engaged in planning, developing and operating the Power system.

Further regulations were made by the CERC, called Central Electricity Regulatory Commission (IEGC) Regulations 2010, have superseded the IEGC and have come into force from May 2010.

Some of the definitions as mentioned in these regulations are:

1.      Ancillary services: Ancillary services are those services necessary to support the power system operation in maintaining power quality, reliability and security of the system or the grid. Examples are active power support for real time load following, reactive power support, black start etc.

2.    Black Start:  Black Start means the starting of a power plant or system after a partial or total blackout in the region.

3.   Available Transfer Capability (ATC): Available Transfer Capability is the Total Transfer Capability (TTC) minus Transmission Reliability Margin (TRM). ATC is the transfer capability of the transmission system, of the inter-control area, available for commercial transactions. These transactions may be through long term access, medium term open access, and short term open access in a specific direction considering the security aspects of the network.

4.      Total Transfer Capability (TTC): Total Transfer Capability is the quantity of electric power that can be transmitted reliably over the transmission system of the inter-control area under a given set of operating conditions considering the occurrence of the worst credible contingency.

5.       Transmission Reliability Margin (TRM): Transmission Reliability Margin is the margin in terms of MW kept in the Total Transfer Capability (TTC) required to ensure the security of the interconnected transmission system under a reasonable range of uncertainties.

6.      Bilateral Transactions:  Bilateral Transaction means a transaction for exchange of electrical energy in MWh between a given buyer and a seller from a given point of injection to a mentioned point of drawal for a fixed or changing quantity of power (MW) for any time period during a month. This transaction of electrical energy may be a direct transaction or through a trading licensee or power exchange.

7.      Unscheduled Interchange: For a generating station or a seller, Unscheduled Interchange means the total actual generation minus its total scheduled generation in a given time block, whereas for a buyer or a beneficiary, it is total actual drawal minus its total scheduled drawal in the given time block.

8.      Long Term Access: Long Term Access means the authority to use the Inter State Transmission System (ISTS) for a period more than 12 years, but not exceeding 25 years.

9.      Medium Term Open Access: Medium Term Open Access means the authority to use the Inter State Transmission System (ISTS) for a period more than 3 months, but not exceeding 3 years.

10.  Short Term Open Access: Short Term Open Access means the authority to use the Inter State Transmission System (ISTS) for a period upto 1 month at one time.

11.  Inter State Transmission System (ISTS): Inter State Transmission System means any transmission system for the conveyance of electricity from one state to another, across the territory of an intervening state as well as within the state, built, owned, operated and controlled by Central Transmission Utility (CTU), i.e. Power Grid Corporation of India.

12.  Control Area: Control area is an electrical system bounded by interconnecting Tie lines, metering and telemetry system which controls its generation and or load to maintain its scheduled interchange with other area and helps to regulate the frequency of a synchronously operating power system. 

13.  Congestion: Congestion is a case where the demand for transmission capacity exceeds the Available Transfer Capability.

14.  Demand: Demand means the demand for active power in MW and reactive power in MVAr.

15.  Load: Load is the MW/MWh/MVA/MVAh consumed by a utility or installation.

16.  Ex-power plant: Ex-power plant means the net active power output in MW and energy output in MWh of a generating station after deducting the auxiliary consumption of the power plant and the transformation losses.

17.  Despatch Schedule: Despatch Schedule   is the net MW and MWh output of a generating station or power plant (ex-power plant) scheduled to be injected to the grid from time to time.

18.  Spinning Reserve: Spinning Reserve means partly loaded generating capacity with some reserve margin that is synchronized to the rest of the system and is ready to provide increased generation at short notice pursuant to despatch instructions by the system operator or instantly in case of frequency collapse.

19.  Independent Power Producer (IPP): Independent Power Producer is a generating company not owned or controlled by the Government (Central or State Government).

20.  Forced Outage: Forced Outage means an outage of a generating unit or a transmission facility due to a fault or any other reasons apart from planned shutdown.

21.   Connection Point: Connection Point is a point where a plant and or electrical apparatus connect to a transmission or distribution system.

Monday, 22 December 2014

Rising Demand for Energy Auditors and Energy Managers

"There is a huge potential for energy saving in India."
Government of India enacted the Energy Conservation Act (ECA) 2001, which provides the necessary legal framework, institutional arrangements and a regulatory mechanism for the much needed energy conservation and energy efficiency drives in the country. 

Energy efficiency is very important to all organizations particularly to energy intensive units. Institutions and organizations looking for more financial return opt for superior energy management. A sound and effective energy management system is a pre-requisite for identifying and implementing energy conservation measures, and sustaining the momentum. 

Support of top management, good strategy, effective monitoring system, and adequate technical ability are the four essential requirements for a successful energy management.

What is Energy Audit?
"Energy audit is an in-depth and detailed study of a facility or organization to find out how and where energy is being used, to identify opportunities to eliminate energy wastage, and to evaluate the economics and technical possibilities of implementing the suggestions."
It is also defined as the verification, monitoring and analysis of use of energy. Energy audit also includes the submission of technical report containing recommendations for improving energy efficiency with cost benefit analysis and an action plan to increase energy efficiency.   

Provisions in Energy Conservation Act 2001

The EC Act 2001 mandates designated consumers of energy to get regular energy audits carried out. Certain minimum specific energy consumption limits are being set up under the mandate of this Act. Establishments and organization, having a connected electrical load of 500 kVA and more, come under the category of designated consumer. 

Several states in India, for example Tamil Nadu, Kerala, West Bengal, Delhi etc. have made energy audit compulsory for all industrial consumers whose connected load exceeds 500 kVA. The energy audit of these establishments is to be carried out once every year by certified energy auditors and managers. 

The report of the audit is to be submitted to the power department of the state government. All other states in the country are in the process of implementing the same. This means that there will be a huge demand for Energy Auditors and Energy Managers in the country in the coming years, as one can predict.

National level certification examination for Energy Auditors and Energy Managers

In India, Bureau of Energy Efficiency (BEE) is conducting a national certification examination for Energy Auditors and Energy Managers each year since 2004. Passing of these examinations is the qualification needed for an engineer to be designated as Certified Energy Auditors and Energy Managers

The eligibility for the examination is a graduate engineer (BE/B-Tech or equivalent) with 3 years experience in an organization where energy is used for its operation, maintenance etc. The work experience in case of post graduate engineers is relaxed by one year. 

Saturday, 20 December 2014

Bhopal: City of biggest artificial lake in Asia

Bhopal, the capital of Madhya Pradesh (India), is a fascinating blend of old historic monuments, modern urban planning and scenic beauty. The city today presents a multi-faceted profile; the old Bhopal with it's markets, mosques and palaces, equally impressive is the new city with it's garden, parks and buildings. 

Bhopal is well connected to other cities in the country by air, rail and road. It is 740 km from Delhi and 790 km from Mumbai. Major tourist attraction around Bhopal is Sanchi and Pachmarhi.

The two lakes, 'Bada Talab' and 'Chotta Talab', still is the lifeline and the nucleus of the city. Bada Taalab” or “Upper Lake” which is one of the prides of Bhopal is said to have been built in the 11th century by the Parmar King, Raja Bhoj. Hence the lake is also known as “Bhojtaal”. This lake, with an area of 31 km2, was created by constructing an earthen dam across the river Kolans and is the biggest artificial lake in Asia. 

Later on in 1965 another dam with eleven gates was constructed at Bhadbhada, hence called the Bhadbhada dam, to control the outflow of the lake. Bada Taalab is a major source of drinking water in the city. Its water is also used for irrigation purpose. There are 87 villages of Bhopal and Sehore district in its catchment area.   

Bhojtaal or Bada Taalab is also a popular tourist and picnic place for the locals and the nearby residents because of its scenic and panoramic beauty, particularly during the monsoon. India’s first National Sailing club has been established at the Boat Club located at this very lake. The club offers various sporting events such as kayaking, canoeing, rafting, water skiing, and parasailing. A number of boat operators provide facilities for exciting boating trips on sail, paddle and motor boats, but prefer to the facilities provided by M.P. Tourism. An island, called Takia island, at the centre of this lake has a tomb of Shah Ali Shah Rahamatullah Alla and hence a place of religious and archaeological significance.

Fig.1: Banks of Bhojtal

An old meter gauge steam engine, “Hill Stallion” manufactured by Tata Locomotive in 1963 used and retired by Indian Railways, is also at display at the banks of the lake.

A national park called “Van Vihar” and a museum called “Manav Sangrahalaya” is located nearby to the lake. At Van Vihar one can see tigers, bears, leopards, variety of deer, alligators, and other reptiles in captivity.  “Manav Sangrahalaya” depicts the ancient and tribal history of India.

Wednesday, 17 December 2014

MATLAB Coding for DC Power Flow

Let us consider that the conductance ‘G’ of a transmission line is very low as compared to the susceptance ‘B’. Also under normal operating conditions of the transmission line, the difference in the angles of the voltage at the two buses, which are connected by the given transmission line, is usually very less (less than 15o). Similarly, the numerical values of the voltage at the two buses are very close to 1.0 p.u. With these approximations, the real power flow in a transmission line is proportional to the circuit susceptance ‘B’ and the difference in voltage phasor angles.
The DC power flow equations (in matrix form) based on the above fact is given as:
[P] = [B’][theta]
where [P] is the vector of nodal active power injection for all the buses except the reference bus,
[theta] is the vector of nodal phase angles for all the buses except the reference bus,
[B’] is the B-prime matrix
Now [B’]= [D] *[ S]
where [D] is a matrix having non-diagonal elements of zeros and the diagonal elements in position row m, column m contains the negative of the susceptance of the mth branch.
S is branch-node incidence matrix also called the adjacency matrix or the connection matrix after eliminating a column corresponding to reference bus.
The MATLAB Coding for the DC power flow is as given below:
The inputs required for the coding are the branch data and the bus data. Branch data should have the numbering of the total branches in the network, from bus number, to bus number, and branch susceptance. The bus data should have the numbering of each buses in the network, and load and generation data at each bus.
% “br_data” is the branch data; “bus” is the bus data.
% Col.1 of “br_data” is the numbering of branches.
% Col.2 of “br_data” is the ‘from-bus’ number.
% Col.3 of “br_data” is the ‘to-bus’ number.
% Col.4 of “br_data” is the susceptance of branches.
% Col.1 of “bus” is the numbering of buses.
% Col.2 of “bus” is the active load at respective buses.
% Col.3 of “bus” is the active generation at respective buses.
% mention the reference bus number
>> ref_bus=6; % here bus number 6 is considered the reference bus
% Y-BUS formation
>>  YBUS=Y_bus(br_data);
% function file ‘Y_bus’is called upon; please refer to previous blogs on related topic
>> B= imag(YBUS);
% Eliminating the corresponding row & col. i.e. row & col. of reference bus
>> B(ref_bus, :)=[];
>> B(:, ref_bus,)=[];
>> BB= -B;
% Calculate the active power injected, i.e. the difference in generation and the demand at each bus
>> Pbus=(bus(:, 3) - bus(:, 2));
% Calculate the voltage angle
>> theta=(BB)^ -1* Pbus;
>> y = imag(br_data(:, 4));
>> D = -diag(y);
% formation of “bus-incidence” matrix
>> elements = max(br_data(:, 1));
>> for i =1:elements,
>> if br_data(i,2) ~= 0,
>> S(i, br_data(i,2)) = 1;
>> end
>> if br_data(i,3) ~= 0,
>> S(i, br_data(i,3)) = -1;
>> end
>> end
% Calculation for line flows (active power flows)
>> P = D*S*theta

Monday, 15 December 2014

What are Power Transformers?

What are Power Transformers?

Power transformers are those transformers having capacity above 500 kVA and used between the generation and the distribution circuit. A typical power system consists of a variety of transmission and sub-transmission voltages and power transformers are employed at each of these stages where the voltage is to be transformed.

Power transformers are available for step up operation and are mainly used at power plants. These power transformers used at generating stations for the stepping up of voltage level are called Generator Transformer (GT). Power transformers for stepping down the voltage level can be found at all the major and intermediate sub-stations which are the transmission and the sub-transmission part of the power system.

Normal life span of a Power Transformer:

Normal life span of a power transformer is expected to be 30 years when operated under rated conditions of load, temperature etc. Transformers are rated based on the power output they are capable of delivering continuously at a specified voltage and frequency under usual operating conditions without exceeding the internal temperature limitations. Since the ambient temperature is supposed to vary according to the location, , therefore the temperature within a power transformer is usually expressed in terms of the temperature rise above the ambient temperature. Under certain conditions the power transformer may be overloaded and operated beyond its rated capacity with a predictable “loss of life”.

Classification of Power Transformer:

Power transformer may be broadly classified as:
1.  Small power transformers with capacity 500 kVA to 7500 kVA,
2.  Medium power transformers with capacity 7.5 MVA to 100 MVA,
3.  Large power transformers with capacity 100 MVA and above.

The upper range of smaller power transformer may vary throughout the sector.

Dielectric Medium in Power Transformer:

Over the years mineral or silicone oil has been used as insulating and cooling medium in transformers. Recently in 2014, Siemens has successfully produced and commissioned world's first EHV class Power Transformer that uses vegetable oil as dielectric medium.

Power transformers are normally equipped with auxiliary equipment such as fans and pumps. These forced circulation of air or oil increases the cooling and thereby increasing the rating of the transformer. 

Cooling of Power Transformer:

Usually, a power transformer will have multiple ratings corresponding to multiple stages of cooling. An example of multiple ratings would be ONAN/ONAF (i.e. Oil Natural Air Natural/ Oil Natural Air Forced) where the transformer has a base rating where it is cooled by natural convection and an additional rating because of the use of fans to provide additional cooling. A power transformer with a base rating of 16 MVA can have an additional 4 MVA capacity when the fans are ‘ON’, i.e. with ONAF cooling the MVA rating of the power transformer is 20 MVA.

Figure shows a power transformer with fans for additional cooling.

Large power transformers are large in size and cost millions of dollars. They pose unique challenges during their transportation. To know about transportation of power transformers read special arrangements for transportation of Large power Transformers

Thursday, 11 December 2014

DC Power Flow

The resistance of a transmission line is significantly less than its reactance. If the resistance of the transmission line is very low, its conductance ‘G’ is also very low as compared to the susceptance ‘B’. Also under normal operating conditions of the transmission line, the difference in the angles of the voltage at the two buses ‘i’ and ‘j’ (which is connected by the given transmission line) is usually less than 15o. Now the sine of a very small angle is the angle itself.  
Similarly, the numerical values of the voltage at the two buses are very close to 1.0 p.u. The normal range is between 0.95 to 1.05 p.u. and the product of these two values is nearly equal to 1.0 p.u. Hence, the real power flow in a transmission line is proportional to the circuit susceptance ‘B’ and the difference in voltage phasor angles.
The two variables of a DC load flow (DCLF) are the voltage angles and the active power injections. DCLF gives the estimation of active power flows on AC power system. It does not consider the reactive power flows. The DCLF is less accurate than AC load flows. They are used where repetitive and fast load flow estimations are needed such as the transmission expansion planning.

For MATLAB coding for DCLF wait for my next blog. 

Friday, 5 December 2014

Moves to Strengthen the Indian Power sector

The Indian power sector offers tremendous potential for investing companies. The power market in the country is the fifth largest in the world. The targeted generation capacity in the 12th Five Year Plan (FYP) is 88,537 MW and for the 13th FYP the envisaged generation capacity addition is 94,000 MW (by 2022). Such a boost in generation capacity needs matching transmission and distribution infrastructure. Growing environmental concerns have shifted the interest towards renewable sources of energy which mainly includes wind power, and solar PV plants. In the recent past there has been considerable growth in power plants based on non-conventional and renewable sources of energy.
The sheer size of the power market in the country along with the attractive returns available is significant to bring in many Indian and international players. The Government of India has also initiated several policies to promote and acquire investments in the power sector. The Electricity Act 2003 has given a liberal framework for generation by de-licensing the generation sector. All controls on Captive Power Plants have also been lifted. The liberal provisions in the Electricity Act 2003 have paved the way for a more reliable and cost effective power in the country. Prominent policies such as the National Electricity Policy, Ultra Mega Power Project Policy, Tariff Policy etc. have contributed a lot to boost the confidence of the participants in the power sector.

Foreign Direct Investment (FDI) up to 100 percent is permitted for generation and transmission of electrical energy produced by thermal and hydel power plants. Route to FDI is also open for renewable energy generation and distribution, distribution of electric energy and power trading. Several schemes are also there to attract new and young entrepreneurs entering the renewable energy sector. Fast and efficient growth of the power sector in the country will also facilitate the creation of enormous job opportunities.

Friday, 28 November 2014

Jamgodrani Wind Farms still with 98% machine availability

India is currently ranked at number five in Wind power production. The total installed wind power capacity at the end of January 2014 was 21,264 MW. At the top of the table is China, followed by US, Germany and Spain.
Although the state of Madhya Pradesh has not done much in the field of wind power production, but it has some successful wind farm projects to its credit. The wind power project (wind farm) at Jamgodrani Hills, near Dewas on Bhopal-Indore highway is one of the prominent wind power projects in Madhya Pradesh.
This 13 MW project was commissioned during 1995-1999 by MP Windfarms Ltd (MPWL) which is a joint sector company. The parties having stake in MP Windfarms Ltd are Consolidated Energy Consultants Ltd. (CECL), MP Urja Vikas Nigam (MPUVN) and Indian Renewable Energy Development Agency (IREDA). The project has total 58 numbers of Wind Electric Generators (WEG), each of 225 kW capacity. These wind turbines are in operation since 15-19 years and still performing nicely with 98% machine availability. The yearly operation and maintenance cost is only about 3% of the total project cost which is quiet remarkable considering that the wind farm is near the end of its life span. The life span of the project is assessed as 20 years.
These large numbers of turbines are connected to a metering point and the whole electrical energy produced is fed to the grid of the Western region Distribution Company of M.P. Figure shows the Wind turbines of Jamgodrani Wind farm, Dewas and was taken in 2010.

Jamgodrani Wind Farm, near Dewas on Bhopal-Indore highway

MP Windfarms Ltd is providing the engineering services and project coordination required for a wind farm project. It is actively engaged in the design and commissioning of wind farm projects which include preparation of detailed project report, detailed construction drawing, execution of civil and electrical works, supervision of erection and commissioning etc. They are also involved in operation and maintenance business of wind turbines.
Similarly, CECL which has 51% equity in MP Windfarms Ltd has handled many wind farm related assignment, ranging from conceptualization to commissioning of wind power projects, both in the country and abroad.  

Ref: www.cecl.in

Wednesday, 26 November 2014

Matlab Coding for the demonstration of Ferranti Effect in Transmission lines

"When a long transmission line is without electrical load or very lightly loaded, the voltage at the receiving end (Vr) is greater than the voltage at the sending end (Vs). This effect seen in transmission lines is called Ferranti effect."

"Ferranti effect" is because of the substantial amount of charging current drawn by the distributed shunt capacitance of the transmission line. This charging current is greater than the current drawn by the load at the receiving end (in case of light loads). This over-voltage at the receiving end can be nicely demonstrated with the help of MATLAB. The "Ferranti effect" can be well shown in a Lab using tube-light chokes and fan capacitors.

The typical values of series inductance and shunt capacitance of a 400 kV transmission line are:

Inductance, L = 1.044 mH per km of line length, and
Shunt capacitance, C = 12 nF per km of line length.   
Assuming a system frequency of 50 Hz and a line length of 800 km, the coding is as given below.

>> C = 12*10^-9;
% Length of the line (len) is taken as 800 km with an equal spacing of 25 km.
>> len = 0:25:800;
% Total capacitance of the 800 km long line,
>> C_tot = len*C;
% Series inductance, L = 1.044 mH per km of line length
>> L = 1.044*10^-3;  
>> L_tot = len*L;
>> f = 50;
% For a sending end voltage of 400 kV,
>> Vs = 400;
% phase shift,
>> beta = len.*(2*pi*f*sqrt(L*C));
% Characteristic Impedance is Zc,
>> Zc = sqrt(L/C);
% Sending end Voltage is Vr,
>> Vr = Vs./cos(beta);
>> plot(len, Vr);
>> axis([0 800 0 700]);
>> xlabel(‘line length in km’);
>> ylabel(‘Receiving end Voltage in kV’);

>> grid;

As can be seen from the MATLAB results and plot, the receiving end voltage of a 400 kV line of length 800 km at no-load may reach 635 kV which is quite harmful. 

This dangerously high over-voltage at the receiving end can be controlled by using shunt reactor. The lagging reactive current drawn by the shunt reactor compensates for the charging current of the line and hence the increase in voltage at the receiving end is controlled.

Sunday, 23 November 2014

Indian Power System Marching ahead with One Synchronized National Grid

Nearly 70 years ago, the power system in India consisted of small isolated generating plants catering the local electrical needs. The post independence era witnessed a significant growth in the power sector. To enhance the reliability of power supply and for achieving economical operation, interconnection of individual systems was planned which led to the formation of state electricity grid in 1950s.
By the sixties, the management of power grid started on regional basis. The state owned power grids were interconnected to form regional grid. With the goal to rapidly develop India at the power sector front, the country was divided into 5 power regions viz. Northern, Western, Southern, Eastern and the North-Eastern power region. Also by mid 60s, Regional Electricity Boards came into existence in the above mentioned five power regions. The move has facilitated interconnected operation of the power system within the regions. The basic role of these regional electricity grids was planning and operation of electric power system within their region.
Now the job was to integrate these regional grids. The basic theme was the formation of a synchronously connected national grid. Things started in 1990 with the asynchronous interconnection between regional power grids made with the help of back-to-back High Voltage Direct Current (HVDC) links such as the Vindhyachal link. Later on other HVDC links also came up such as the Chandrapur and Vishakapatnam-Gazuwaka HVDC links. These HVDC links had limited capacity for exchange of power. 
The first move towards achieving the “one nation, one grid, one frequency” status, was the interconnection of North-Eastern and the Eastern grid in 1991. Next was the interconnection of Western grid with the Eastern and North-Eastern grid in 2003. Similarly in 2006 the Northern grid was interconnected with the above three grids. The four regional grids i.e. Eastern, North-Eastern, Western and Northern collectively formed the Central Grid operating synchronously at one frequency. Initially these inter-regional transmission links carried the operational surplus energy from the energy sufficient region to the energy deficient region. Later on the inter-regional transmission links were planned considering the generation plants having beneficiaries spread over the nation.
On December 2013, months ahead of the schedule, the Southern grid too was synchronously connected to the rest or the Central grid through the 765 kV Raichur-Solapur transmission network. With this the mission “one nation, one grid and one frequency” was accomplished.
Interconnected power system and formation of one national grid will reduce the investments in generation reserves, and helps to utilize the benefits of generation mixes and load pattern to a greater extent. This will also facilitate the smooth and efficient operation of the Indian electricity market. For example, till now there was a large inconsistency in the short-term electricity prices in the southern region and the other region because of the inadequate transmission capacity. 

Now all the regional grids were synchronized but still the power transfer capability of the national grid was low considering the giant size of the Indian power system. At the end of the 11th Five Year Plan (FYP) the total inter-regional power transfer capacity through inter-regional transmission link was about 28 GW. This inter-regional capacity is expected to reach 65 GW by the end of 2017. So we have completed the “one nation, one grid, one frequency” challenge, but to make this unified grid of significant size having a matching transfer capability and its efficient operation is a bigger one.

Thursday, 20 November 2014

Growth of Transmission System in India

At the time of Independence, the power system in India consisted of small isolated power generating plants catering the electrical needs of major cities and towns. The total installed capacity at that time was merely 1300 MW and the highest transmission voltage was 132 kV AC. The post independence era witnessed an appreciable growth in the power sector.
With the goal to rapidly develop India at the power sector front, the country was divided into 5 power regions viz. Northern, Western, Southern, Eastern and the North-Eastern power region. Also by mid 60s, Regional Electricity Boards came into existence in the above mentioned five power regions. The move has facilitated interconnected operation of the power system within the regions. Interconnected power system reduces the investments in generation reserves, and helps to utilize the benefits of generation mixes and load pattern to a greater extent. The transmission voltage had increased to 400 kV AC by the 70s. Significant transmission networks were developed by Uttar Pradesh, Maharashtra, Madhya Pradesh, Gujarat, Orissa, Andhra Pradesh and Karnataka as these states were having the bulk of the electrical load.
In the year 1975, to enhance the generation capacity, which till the time was carried out at the state level, Central sector generation utilities i.e. National Hydroelectric Power Corporation (NHPC) and National Thermal Power Corporation (NTPC) were formed. These corporations established generating power plants of large capacity, say of 1000 MW capacity, and developed the much needed transmission systems. To speed up the transmission infrastructure development, Power Grid Corporation of India (POWERGRID) was created in 1989.
Till the time all the 5 power regions were operated independently and that too at different operating frequency. Therefore in 1990 asynchronous interconnection between regional power grids were made with the help of back-to-back HVDC links. This was the introduction of HVDC system in the country. In the year 2007, India touched the 765 kV AC transmission voltage and by 2009 we had a couple of ± 500 kV bipolar HVDC lines. 
Fig: Under construction 765 kV lines in Madhya Pradesh

Shortly (by 2015) we are going to have the first multi-terminal UHV DC system. The ±800 kV, 1728 km long Biswanath- Agra UHV DC transmission system with a  8 GW converter capacity, including a 2 GW redundancy, will transmit hydroelectric power from the country’s northeast region to Agra in Uttar Pradesh.
In the next decade 1200 kV UHV AC system is expected to emerge as the main transmission level in India along with the 800 kV UHV DC system. The power transfer capacity of 1200 kV UHV AC transmission system is expected to be between 6000 to 8000 MW. To develop 1200 kV AC transmission system in India, a joint venture for a test sub station and test line by Power Grid Corp. of India and CPRI is under progress at Bina in Madhya Pradesh.

Watch out for development of national grid in the coming blog.