BSES Training Report

BSES INTERNSHIP PROJECT DISTRIBUTION & TRANSMISSION Pooran Chand (2K11/EE/080)

s

ACKNOWLEDGEMENT I would like to express my sincere thanks to Mr. S. K. GUPTA (DGM, BSES-Laxmi Nagar) for allowing me to go through the training under his surveillance. This training has provided me a great experience and knowledge about the networking and working of the company.

I am very grateful for the cooperation and interest of Mr. RAJKUMAR (BSES mentor) who took part in this and assisted me through all stages in project and provided me a great overview of the company BSES, a power distribution company.

It would not have been possible without his help. This research was supported by I would also like to express my sincere thanks to all the advisors for their cooperation and encouragement during this project.

Last, I express my thanks to Delhi Technological University for having provided me with this unique opportunity to train for four weeks.

Pooran Chand 2K11/EE/080 Delhi Technological University Delhi -110042

THE BEGINNING The Delhi Vidyut Board was formed by the Government of NCT Delhi in 1997 for the purpose of generation and distribution of power to the entire area of NCT of Delhi except the areas falling within the jurisdiction of NDMC and Delhi Cantonment Board. On July 1, 2002, The Delhi Vidyut Board (DVB) was unbundled into six successor companies: Delhi Power Supply Company Limited (DTL)-TRANSCO; Indraprastha Power Generation Company Limited (IPGCL)GENCO; BSES Rajdhani Power Limited (BRPL)-DISCOM; BSES Yamuna Power Limited (BYPL)DISCOM; North Delhi Power Limited (NDPL)-DISCOM.

BSES BSES IN DELHI Following the privatization of Delhi’s power sector and unbundling of the Delhi Vidyut Board in July 2002, the business of power distribution was transferred to BSES Yamuna Power Limited (BYPL) and BSES Rajdhani Power Limited (BRPL). These two of the three successor entities distribute electricity to 28.34 lakh customers in two thirds of Delhi. The company acquired assets, liabilities, proceedings and personnel of the Delhi Vidyut Board as per the terms and conditions contained in the Transferred Scheme.  BSES Yamuna Power Limited, Shakti Kiran Building, Opp. Karkarduma Court, Delhi 110096  BSES Rajdhani Power Limited, BSES Bhawan, Nehru Place, Delhi 11019.

BSES Yamuna Power Limited (BYPL) BYPL distribute power to an area spread over 200 sq. km with a population density of 5953 per sq. km. Its 11.9 lakh customers are spread over 14 districts across Central and East areas including Chandni Chowk, Daryaganj, Paharganj, Sankar Road, Patel Nagar, G T Road, Karkardooma, Krishna Nagar, Laxmi Nagar, Mayur Vihar, Nand Nagri and Karawal Nagar.

BSES Rajdhani Power Limited (BRPL) BRPL distribute power to an area spread over 750 sq. km with a population density of 2192 per sq km. Its 16.44 lakh customers are spead in 19 districts across South and West areas including Alakananda, Khanpur, Vasant Kunj, Saket, Nehru Place, Nizamuddin, Sarit Vihar, Hauj Khas, R K

Puram, Janakpuri, Najafgarh, Nagloi, Mundka ,Punjabi Bagh, Tagore Garden, Vikas Puri, Palam and Dwarka.

VISION To be amongst the most admired and most trusted integrated utilities companies in the world. To deliver reliable and quality products and services to all consumers at competitive costs, with international standards of customer care, thereby creating superior value for all stakeholders. To set new benchmarks in: standards of corporate performance and governance, through the pursuit of operational and financial excellence, responsible citizenship and profitable growth.

Mission            

To attain global best practices and become a world class utility. To provide: uninterrupted, affordable, quality, reliable, safety and customer care. To achieve excellence in: service, quality, reliability, safety and customer care. To earn: trust and confidence of all customers and stakeholders by exceeding their expectation and make the company a respected household name. To work: with vigor, dedication and innovation keeping total customer satisfaction as the ultimate goal. To consistently achieve: high growth with highest level of productivity. To be: a technology driven, efficient and financially sound organization. To be a responsible corporate citizen nurturing human values and concern for society, the environment and above all, people. To contribute: towards community development and nation building. To promote a work culture that fosters: individual growth, team spirit and creativity to overcome challenges and attain goals. To encourage: ideas, talent and values systems. To uphold the guiding principles of: trust, integrity and transparency in all aspects of interactions and dealing.

Customer Profile Category

BRPL

BYPL

Domestic

1,465,561

904,463

Non Domestic

244,071

295,890

Industrial

12,694

19,704

4,259

51

Agriculture Railway Traction

1

DMRC

6

1

Others

6,396

7,476

Total

1,733,005 st

*Customer Base as of 31 March’12

-

1,227,755

DEFINE An electrical grid is an interconnected network for delivering electricity from supplier to consumers. It consists of three main components: 1. Power stations that produce electricity from combustible fuel (coal, natural gas and biomass) or non-combustible fuels (wind, solar, nuclear, hydro power). 2. Transmission lines that carry electricity from power plant to demand centres. 3. Transformers that reduce voltage so distribution lines carry power to final delivery.

In the power industry, electrical grid is a term used for an electricity network which includes the following three distinct operations: 1. Electricity generation-Generating plants are usually located near a source of water, and away from heavily populated areas. They are usually quite large to take advantage of economies of scale. The electric power which is generated is stepped up to a higher voltage- at which it connects to the transmission network. 2. Electric power transmission –The transmission network will move (wheel) the power long distances-often across state lines, and sometimes across international boundaries, until it reaches its wholesale consumer (usually the company that owns the local distribution network). 3. Electricity distribution- Upon arrival at the substation, the power will be stepped down in voltage- from a transmission level voltage to a distribution level voltage. As it exits the substation, it enters the distribution wiring. Finally, upon arrival at the service location, the power is stepped down again from the distribution voltage to the required service voltage.

Generation stage: Electrical generation is the process of generating electric energy from other form of energy. Electrical power starts at the power plant, in almost all cases the power plant consists of a spinning electrical generator. A generator is a machine that transforms mechanical energy into electrical energy. Sometimes has to spin that generator; it might be a water wheel in a hydroelectric dam, a large diesel engine or a gas turbine. But in most areas the thing spinning the generator is a steam turbine. The steam might be created by burning coal, oil, natural gas or the fission of nuclear fuel. And some generating stations use renewable energy sources like sun and wind. Sometimes, another stages of power generation is provided in transmission and distribution stages (Embedded generation) to meet additional power requirements in some load areas.

TRANSMISSION Electrical power transmission is defined as the process of transferring electrical energy from one point to another. Electrical power transmission or “high voltage electrical transmission” is the bulk transfer of electrical energy, from generating plants (historically hydroelectric power-plants). Electrical transmission lines can vary a few kilometers long in urban surroundings to thousands of kilometers for lines carrying power from remote power plants.

The transmission lines are interconnected with every completely different to make higher networks, so that if one line ought to fail, another can take over the electrical load. Transmission lines can be overhead or underground. Transmission stages: Electric-power transmission is the bulk transfer of electrical energy; from generating power plants to substations located near population centers. The 3-phase power leaves the generator and enters a transmission substation at the power plant. This substation uses large transformers to convert the generator’s voltage (which is at the thousands of volts level) up to extremely high voltages for long-distance transmission on the transmission grid. Typical voltages for long distance transmission are in the 155,00 to 765,000 volt range in order to reduce line losses. Transmission stage may include sub-station stages (secondary transmission) to supply intermediate voltage levels. Sub-transmission stages are used to enable a more practical or economical transition between transmission and distribution systems.

Overhead transmission

High-voltage overhead transmission conductors are not covered by insulation. The conductor material is nearly always an aluminum alloy, made into several strands and possibly reinforced with steel strands. Conductors sizes ranges from 12 mm2 to 750 mm2 ( 1,590,000 circular miles area), with varying resistance and current-carrying capacity. Thicker wires would lead to a relatively small increase in capacity due to skin effect, that causes most of the current to flow close to the surface of the wire. Because of this current limitation, multiple parallel cables (called bundle conductors) are used when higher capacity is needed. Bundle conductors are also used at high voltages to reduces energy loss caused by corona discharge. Today, transmission-level voltages are usually considered to be 110 kV and above. Lower voltages such as 66 kV and 33 kV are usually considered sub transmission voltages but are occasionally used on long with light loads. Voltages less than 33 kV are usually used for distribution. Voltages above 230 kV are considered extra high voltages and require different designs compared to equipment used at lower voltages.

Since overhead transmission wires depend on the air for insulation, design of these lines requires minimum clearances to be observed to maintain safety. Adverse weather conditions of high wind and low temperature can lead to power outages. Wind speeds as low as 23 knots (43 km/h) can permit conductors to encroach operating clearances, resulting in a flashover and loss of supply.

UNDERGROUNDED TRANSMISSION Electric power can also be transmitted by undergrounded power cables instead of overhead power lines. Underground cables take up less right-of-way than overhead lines, have lower visibility, and are less affected by bad weather. However, cost of insulated cable and excavation are much higher than overhead construction. Faults in buried transmission lines take longer to locate and repair. Underground lines are limited by their thermal capacity, which permits fewer overloads or re-rating than overhead lines. Long underground cables have significant capacitance, which may reduce their ability to provide useful power to loads.

DISTRIBUTION Electricity distribution is the final stage in the delivery of electricity to end users. A distribution system’s network carries electricity from the transmission system and delivers it to consumers. Typically, the network would include medium –voltage (less than 1 kV) distribution wiring and sometimes meters. The modern distribution system begins as the primary circuit leaves the substation and ends as the secondary service enters the consumer’s meter socket. Distribution circuits serve many customers. The voltage used is used is appropriate for the shorter distance and varies from 2,300 to about 35,000 volts depending on utility standard practice, distance, and load to be served. Distribution circuits are fed from a transformer located in an electrical substation, where the voltage is reduced from the high values used for power transmission. Conductors for distribution may be carried o overhead pole lines, or in densely populated areas where they are buried underground. Urban and suburban distribution is done with three phase systems to serve residential, commercial, and industrial loads. Distibution in rural areas may be only single phase if it is not economical to install three phase power for relatively few and small customers. Only large consumers are fed directly from distribution voltage, most utility customers are connected to a transformer, which reduces the distribution voltage to the relatively low voltage used by lighting and interior wiring systems. The transformer may be pole-mounted or set on the ground in a protective enclosure. In rural areas a pole-mounted transformer may serve only one customer, but in more built-up areas multiple customers may be connected. In very dense city areas, a secondary network may be formed with many transformers feeding into a common bus at the utilization voltage. Each customer has an “electrical service” or “service drop” connection and a meter for billing. (Some very small loads, such as yard lights, may be too small to meter and so are charged only a monthly rate.) A ground connection to local earth is normally provided for the customer’s system as well as for the equipment owned by the utility. The purpose of connecting the customer’s system to the ground is to limit the voltage that may develop if high voltage conductors fall on lower voltage conductors, if a failure occurs within a distribution transformer. If all conductive objects are bonded to the same earth grounding system, the risk of electric shock is minimized. However, multiple connections between the utility ground and customer ground can lead to stray voltage problems; customer piping, swimming pools or other equipment may

develop objectionable voltage. These problems may be difficult to resolve since they often originate from places other than customer’s premises.

Distribution network configuration Distribution network are typically of two types, radial and interconnected. A radial network leaves the station and passes through the network area with no normal connection to any other supply. This is typical of long rural lines with isolated load areas. An interconnected network is generally found in more urban areas and will have multiple connections to other points of supply. These points of connections are normally open but allow various configuration by the operating utility by closing and opening switches. Operation of these switches may be by remote control from a control centre or by a lineman. The benefit of the interconnected model is that in the event of a fault or required maintenance a small area of network can be isolated and the remainder kept on supply. Within these networks there may be a mix of overhead line construction utilizing traditional utility poles and wires and, increasingly, underground construction with cables and indoor or cabinet substations. However, underground distribution is significantly more expensive than over head construction. In part to reduce this cost, underground power lines are sometimes co-located with other utility lines in what are called common utility ducts. Distribution feeders emanating from a substation are generally controlled by a circuit breaker which will open when a fault is detected. Automatic circuit re-closers may be installed to further segregate the feeder thus minimizing the impact of faults. Long feeders experience voltage drop requiring capacitors or voltage regulators to be installed. Characteristics of the supply given to customers are generally mandated by contract between supplier and customer. Variables of the supply include:  AC or DC – Virtually all public electricity are AC today.Users of large amounts of DC power such as some electric railways, telephone exchanges and industrial processes such as aluminum smelting usually either operate their own or have adjacent dedicated generating equipment, or us rectifiers to derive DC from the public AC supply.  Voltage, including tolerance (usually +10 or -15 percent).

 Frequency, commonly 50 or 60 Hz, 16.6 Hz and 25 Hz for some railways and, in a few older industrial and mining locations, 25 Hz.  Phase configuration (single-phase, poly phase including two phase and three phase).  Maximum demand (usually measured as the largest amount of power delivered within a 15 or 30 minute period during a billing period).  Load factor, expressed as a ratio of average load to peak load over a period of time. Load factor indicates the degree of effective utilization of equipment (and capital investment) of distribution line or system.  Power factor of connected load.  Earthing systems.  Prospective short circuit current  Maximum level and frequency of occurrence of transients.

(RING DISRIBUTION SYSTEM)

The Distribution stage: Electricity distribution is the final stage in the final stage in the delivery of electricity to end users. A distribution system’s network carries electricity from the transmission system and delivers it to consumers. For power to be useful in a home or business it comes off the transmission grid and is stepped down to the distribution grid in a power distribution substation, and this may happen in several phases as follows: Primary distribution system (HV distribution) It is that portion of network between the sub-transmission substation and secondary distribution system. The primary system consists of step- down transformer and sometimes embedded generation can be used at voltage levels which range from 33 kV to 6.6 kV. The secondary distribution system (LV distribution): It is that portion of the network between the primary feeders and utilization equipment. The secondary system consists of step-down transformers and secondary circuit at utilization voltage levels which range from 480 V to 120 V. Note: Residential secondary systems are predominantly single phase, but commercial and industrial systems generally use three-phase power.

(LT AERIAL BUNCH CONDUCTOR)

AUTOMATION IN POWER DISTRIBUTION The demand for electrical energy is ever increasing. Today over 21 %( theft apart!!) of the total electrical energy generated in India is lost in transmission ( 4-6%) and distribution ( 15-18%). The electrical power deficit in the country is currently about 18%. Clearly, reduction in distribution losses to a 6-8% level in India with the help of newer technological options (including information technology) in the electrical power distribution sector which will enable better monitoring and control.

How does Power reach us? Electrical power is normally generated at 11-25 kV in a power station. To transmit over long distances, it is then stepped-up to 400 kV, 220 kV or 132 kV as necessary. Power is carried through a transmission network of high voltage lines. Usually, these lines run into hundreds o9f kilometers and deliver the power into a common power pool called grid. The grid is connected to load centers (cities) through a sub-transmission network of normally 33kV (or 66 kV) substation, where the voltage is stepped-down to 11 kV and lower. The power network, which generally concerns the common man, is the distribution network of 11 kV lines or feeders downstream of the 33 kV substation. Each 11 kV feeder which emanates from the 33 kV substation branches further into several subsidiary 11 kV feeders to carry power close to the load points (localities, industrial areas, villages etc.). At these load points, a transformer further reduces the voltage from 11 kV to 415 V to provide the last mile connection through 415V feeders (also called as Low Tension (LT) feeders) to individual customers, either at 240 V (as single-phase supply) or at 415 V (as three-phase supply). A feeder could be either an overhead line or an underground cable. In urban areas, owing to the density of customers, the length of an 11 kV feeder is generally up to 3 km. On the other hand, in rural areas, the feeder length is much larger (up to 20 km). A 415 V feeder should normally be restricted to about 0.5-1.0 km. Unduly long feeders lead to low voltage at the consumer end.

Bottlenecks in Ensuring Reliable Power Lack of information at the base station (33kV sub-station) on the loading and health status of the 11kV/415V transformer and associated feeders is one primary cause of inefficient power distribution. Due to absence of monitoring, overloading occurs, which results in low voltage at the customer end and increases the risk of frequent breakdowns of transformers and feeders. In fact, the transformer breakdown rate in India is as high as around 20%, in contrast to less than 2% in some advance countries. In the absence of switches at different points in the distribution network, it is not possible to isolate certain loads for load shedding as and when required. The only option available in the present distribution network is the circuit breaker (one each for every main 11kV feeder) at the 33kV substation. However, these circuit breakers are actually provided as a means of protection to completely isolate the downstream network in the event of fault. Using this as a tool for load management is not desirable, as it disconnects the power supply to a very large segment of consumers. Clearly, there is a need to put in place a system that can achieve a finer resolution in load management.

In the event of a fault on any feeder section downstream, the circuit breaker at the 33kV substation trips (opens). As a result, there is a black out over a large section of the distribution network. If the faulty feeder segment could be precisely identified, it would be possible to substantially reduce the blackout area, by re-routing the power to the healthy feeder segments through the operation of switches (of the same type as those for load management) placed at strategic locations in various feeder segments.

Example for a complete power system grid:

 The generator produces 20,000 volts.  This, however, is raised to 138,000 volts for the long transmission journey.  This power is conducted over 138,000 volt (138 kV) transmission lines to switching stations located in the important load area served.  When the power reaches the switching stations, it is stepped down to 34,500 volts (34.5 kV) for transmission in smaller quantities to the substations in the local load areas and industrial consumers can utilize electrical power at this stage.  Then it is stepped down to 13,800 volts (13.8 kV) for direct distribution to local areas and industrial, commercial and residential consumers can utilize electrical power at this stage by using appropriate step down transformer to their grid’s voltage level.

CIRCUIT BREAKERS Medium-Voltage circuit breakers Medium-voltage circuit breakers rated between 1 and 72 kV may be assembled into metal enclosed switchgear ups for indoor use, or may be individual components installed outdoors in a substation. Air-breaker circuit breakers replaced oil-filled units for indoor applications, but are now themselves being replaced by vacuum circuit breakers (up to about 35 kV). Like the high voltage circuit breakers described below, these are also operated by current sensing protective relays operated through current transformers. The characteristics of MV breakers are given by international standards such as IEC 62271. Medium-voltage circuit breakers nearly always use separate current sensors and protective relays, instead of relying on built-in thermal or magnetic over current sensors. Medium-voltage circuit breakers can be classified by the medium used to extinguish the arc: 





Vacuum circuit breakers-with rated current up to 3000 a, these circuit breakers interrupt the current by creating and extinguishing the arc in a vacuum container. These are generally applied for voltages up to about 35,000 V, which corresponds roughly to the medium-voltage range of power systems. Vacuum circuit breakers tend to have longer life expectancies between overhaul than do air breakers. Air circuit breakers- rated current between up to 10,000 A. Trip characteristics are often fully adjustable including configurable trip thresholds and delays. Usually electronically controlled, through some models are microprocessors controlled via an integral electronic trip unit. Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance. SF circuit breakers extinguish the arc in a chamber filled with sulphur hexafluoride gas.

Medium-voltage circuit breakers may be connected into the circuit by bolted connections to bus bars or wires, especially in outdoor switchyards. Medium-voltage circuit breakers in switchgear line-ups are often built with draw-out construction, allowing breaker removal without disturbing power circuit connections, using a motor-operated or hand-cranked mechanism to separate the breaker from its enclosure.

Sulphur hexafluoride (SF) high-voltage circuit-breaker A sulphur hexafluoride circuit breaks uses contacts surrounded by sulphur hexafluoride gas to quench the arc. They are most often used for transmission-level voltages and may be

incorporated into compact gas-insulated switchgear. In cold climate, supplemental heating or de-rating of the circuit breakers may be required due to liquefaction of the SF gas.

TRANSFORMER

1. Transformer Tank-This hold the transformer windings and its insulating medium (oilfilled). Transformer tanks must be air-tightly sealed for it to isolate its content from any atmospheric contaminants. 2. High Voltage Bushing-this is the terminals where the primary windings of the transformer terminates and serves as an insulator from the transformer tank. Its creapage distance is dependent on the voltage rating of the transformer. 3. Low Voltage Bushing-Like the high voltage bushing, this is the terminals where the secondary windings of the transformer terminates and serves as an insulator from the transformer tank. Low voltage bushing can be easily distinguished from its high voltage counterpart since low voltage bushings are usually smaller in size compared to the high voltage bushing.

4. Cooling Fins/Radiators-in order for the transformer to dissipate the heat it generated in its oil-insulation, cooling fins and radiators are usually attached to the transformer tanks. The capacity of the transformer is dependent to its temperature that is why it is imperative for it to have a cooling mechanism for better performance and higher efficiency. 5. Cooling Fans-can be usually attached to the cooling fins. Cooling fans can be either be a timer controlled or a winding/oil temperature controlled. Cooling fans helps raises the transformer capacity during times when the temperature of the transformer rises due to loading. Cooling fans used on the transformer are actuated by the help of a relaying device which when senses a relatively high temperature enables the fan to automatically run. 6. Conservator Tank-A oil preservation system in which the oil in the main tank isolated from the atmosphere, over the temperature range specified, by means of an auxiliary tank partly filled with oil and connected to the completely filled main tank. 7. System Ground Terminal-system ground terminals in a power transformer are usually present whenever the connection type of the transformer windings has wye in it. This terminal can be found in-line with the main terminals of the transformer. 8. Drain valve- can be usually found in the bottom part of the transformer tank. Drain valves are used whenever oil replacement is necessary. Through this valve, the replacement of oil in an oil-filled transformer can be easily done simply by opening this valve like that of a faucet. 9. Dehydrating Breather-are used to prevent the normal moisture in the air from coming in contact with the oil in electrical equipment as the load or temperature changes. This reduces the degeneration of the oil and helps maintain its insulation capability. When used with conservator system with a rubber air cell it reduces moisture accumulation in the cell. Some breathers are designed for sealed tank transformers and breathe only at pre-set pressure levels. 10. Oil Temperature/Pressure gauges-these are used for monitoring the internal characteristics of the transformer especially its winding. These gauges help the operator in knowing the level of the temperature inside the transformer (oil & winding). This will also serve as an alarm whenever a certain level is reached that could be harmful to the transformer winding. 11. Bushing Current Transformer-modern transformer construction today now includes current transformers. These are usually found around the transformer terminals which will be later be used for metering and relaying purpose. Its terminals are found in the control panels attached to the transformer.

12. Control Panel-this houses all of the transformer’s monitoring devices terminals and auxiliary devices including the terminals of the bushing current transformers and cooling fans. Control panels are very useful especially when a remote control house is needed to be constructed, this will serves as their connection point. 13. Surge Arresters- this type of arresters are placed right directly before and after the transformer terminals in order to minimize the exposure of the transformer. Like any other surge arresters, its purpose is to clip sudden voltage surge that can be damaging to the winding of the transformer.

COMPLAINTS Whenever there is some fault in the transmission/distribution lines, complaint centre is informed about the location and he notes down the details and further contacts the lineman to go the location and repair the faults. For every fault, a slip is detached from BSES slip book and given to lineman who is given the duty to repair fault at the provided location. These records are maintained properly. In case of LT fault, LT feeder team is informed and it takes the responsibility to repair the problem caused. In case of HT fault, HT feeder pursues the operation. For every substation a team, car and necessary equipment are provided so that they can help in solving the nearby complaints. Complaints can be lodged by three methods1. Through internet/email. 2. Through personally walking to the complaint centre. 3. Through telephone. Each of the complaint is dealt seriously and response team responds and takes the necessary action immediately, as any delay in this might cause serious consequences.

CABLE SIZES Cable use

size (mm2)

LT main

4*300

Single core cable from transformer

630

Feeder-pillar to Feeder-pillar

4*150

Feeder-pillar to Service pillar

4*95

Service cable-1

4*50

Service cable-2

4*25

BIBLOGRAPHY    

Wikipedia.com Google.com Bsesdelhi.com IITK.com