Failure of Distribution Transformers in India

Transformer industry in India:

Transformer industry in India has evolved over a period of time and is now a matured industry capable of manufacturing a wide range of power, distribution and special type of transformers for different applications. Recently it has manufactured a UHV 1200 kV class transformer for the test station at Bina in Madhya Pradesh. 

The power transformer market in India is well organized and their customers are large entities like Central Transmission Utility (CTU) and the State Transmission Utilities (STU) whereas the distribution transformer market is dominated by un-organized players.

The number of distribution transformers currently in service is nearly 4.3 million and the number is adding at an annual rate of approximately 10%. Distribution transformers of 11/0.4 kV class usually come with both aluminium and copper winding. 

Failure rate of Distribution Transformers in India:

"The failure rate of distribution transformers in India is as high as 25 to 30% which is the highest in the world."

Reports say that every year distribution transformers worth rupees 200 Crores fail; which is a great financial loss to the nation and which can be avoided. 

Causes of Failure of Distribution Transformers:

Substantial failure rate of distribution transformers in India is mainly due to:

i)   the design criterion, 
ii)  the material used in manufacturing, 
iii) maintenance practice, 
iv) material used in maintenance, and
v)  Un-authorized electrical loads.

The operating conditions, particularly in rural India, like weather conditions, overloading, through or passing faults, inadequate protection, public interference, poor maintenance of LT and 11 kV lines often results in distribution transformer failure.

Distribution transformers installed in rural areas form the bulk of these transformers. They are very much exposed to vulnerable weather conditions particularly lightning. These transformers feed lengthy Low Tension (LT) lines which are more prone to faults because of these atmospheric conditions. 

Majority of the transformers have poor efficiency because of improper or unbalanced loading conditions. It is common practice to connect additional electrical load on these transformers on the basis of maximum demand recorded at some point of time or on the basis of assessed maximum demand without considering the seasonal variations and the actual diversity factor. 

Un-authorized electrical connections also result in overloading. Wide variation in load and ambient temperature make undesired ingress of moisture, particularly in rural areas, which weakens the dielectric strength of transformer oil, forms sludge and deposits on the winding which on passage of time may obstruct the ducts in the winding provided for oil circulation. 

The routine maintenance of LT and 11 kV lines and protective equipments associated with these transformers are also poor. Figure 1 shows a badly maintained LT fuses on one of the distribution transformers.

Fig. 1: Badly maintained LT fuses

Prolonged operation of distribution transformer under abnormal operating condition such as faults, overloading or unbalance load deteriorate the insulating materials; ultimately leading to failure. Figure 2 below shows the damaged High Voltage (HV) winding of  a 11/0.4 kV distribution transformer.

Fig. 2:  Damaged High Voltage winding of  a 11/0.4 kV distribution transformer.

Repair rate of Distribution Transformers:

The repair rate of distribution transformers is also high in India. Each distribution transformer is repaired 2 to 3 times in its whole life span of 25 years (due to fund paucity) reducing the efficiency further with each repair. The direct economic impact of distribution transformer failure is in terms of cost of repair or replacement whereas indirect economic impact comes in the form of revenue loss due to supply interruption and increased losses.     
  

How to reduce Failure of Distribution Transformers:

This significant failure rate of distribution transformer in the country can be curbed to some extent by employing Complete Self-Protection (CSP) scheme which enables the transformer to protect itself from faults. 

In the CSP scheme, transformers are equipped with primary fuses, secondary side circuit breakers and lightning arresters. The primary side fuse is mounted inside the primary bushing and is in series with the primary winding to isolate the transformer in case of faults inside the transformer or on its LT side. Secondary circuit breakers and lightning arresters are there to protect the transformer from overloads, LT side faults and lightning strokes respectively.  

Do we need the World’s largest single location Solar Electricity Power Plant?

Ambitious target of  Solar Power:

The country is set to become a global leader in solar electric energy production and has an ambitious target of installing 22000 MW of capacity by 2022. This target has been revised to 1,00,000 MW. 

Ministry of New and Renewable Energy (MNRE) has envisaged setting up of large scale Solar Power Plants in India in the 13th Five Year Plan (FYP). These solar power plants will be known as Ultra Mega Solar Power Plants (UMSPP) and will be set up in the desert and wastelands of Sambhar (Rajasthan, 4000 MW), Kharaghoda (Gujarat, 4700 MW), and Leh/Kargil (J&K, 2400 MW).

Sambhar Ultra Mega Solar Power Plant:

The solar plant at Sambhar Lake, is the first of the four UMSPP projects conceived by MNRE and Ministry of Power (MoP) in the year 2013. MoU has been signed for setting up the Solar Power Plant, with a total installed capacity of 4000 MW, near Sambhar Lake, in Rajasthan (India). The plant is proposed to be set up in a time span of 7 years. When fully commissioned, this would become the largest single location solar electricity generation in the world. The plant is expected to generate 6,000 million kWh of electricity each year and with a life span of 25 years, it is set to offset nearly 4 million tonnes of Carbon Dioxide annually. 

The proposed site has plain surface and the required basic infrastructural facilities such as road approach etc. Also the transmission and distribution system is very much there as claimed by the Solar Energy Corp. of India (SECI).

This solar Photovoltaic (PV) power plant is a joint venture of 6 companies and requires about 9000 hectares of land which is to be provided by Sambhar Salts Ltd. (SSL) whereas the equipments are to be provided by Bharat Heavy Electricals Ltd.(BHEL). The arrangement for evacuation of electrical energy, to be produced from this UMSPP, is the responsibility of POWERGRID whereas sale of energy is proposed through SECI. The project manager is Satluj Jal Vidyut Nigam Ltd. (SJVNL) and the operation and maintenance is to be done by Rajasthan Electronics and Instrumentation Ltd. (REIL). The first phase of 1000 MW was to be set up by 2016.

Ecology around the Sambhar Salt Lake: 

Sambhar Salt Lake is declared as a protected site of international importance. Experts say that the wetlands support large biological diversity, provide groundwater recharge, and help to control erosion and flood. The proposed Solar Power Plant is expected to cover nearly 40% of the Sambhar Salt Lake, the lake which attracts 70 species of migrant birds and is the second largest breeding ground of Flamingo birds in India. In the year 1982-83 nearly 5,00,000 flamingo birds visited the lake. Flamingo are tall birds, come in flocks and require large area for feeding and breeding. 

This proposed project could be seen as a step ahead in this direction and can be seen as a great success if it is completed without disturbing the fragile ecology around. Promoters of the project believe that the solar power plant can coexist with wetland ecology. 

Several experts are against the decision. If the growth in solar energy capacity addition is at the cost of polluting and damaging this wonderful ecology around, then, do we need such projects?  

TRANSMISSION EXPANSION PLANNING

A transmission system connects the various generating power plants to major electrical load centres and thus forms a vital link to the economic and technical development of any country. 

What is Transmission Expansion Planning?

Transmission planning or transmission expansion planning is the process of designing future transmission network configuration that meets the predicted future needs of loads and generation. 

Fundamental objective of transmission planning:

The fundamental objective of transmission planning is to develop the system as economically as possible and to maintain an acceptable reliability level. 

Transmission planning may include:

·         Construction of new lines,

·         Determination of voltage level,

·         Network enhancement,

·         Substation configuration,

·         Selection of new technologies such as FACTS, EHV-DC etc

A transmission or network expansion may be concerned with one or more of the above mentioned tasks and each task require technical, economical, environmental and social assessments. 

The technical assessment includes load forecast, power flow calculations, contingency analysis, voltage and transient stability analysis, short circuit analysis and reliability evaluation.

Factors that call for the development of a Transmission system:

There are many factors that call for the development of a transmission system and these are:

·         Load growth,

·         New power plants,

·         Aging of equipment or Technology,

·         Commercial opportunities,

·         Reliability requirements, etc.

The first three factors account for most of the transmission expansion.

Classification of Transmission Planning:

Transmission planning can be divided into:
i)    long term, 
ii)   medium term, and 
iii) short term planning based on the duration involved. 

Long term planning involves a long planning period usually of 20 to 30 years; whereas medium term planning can be of 10 to 20 years. 

The problems and issues considered in long term planning are preliminary and often requires significant and repeated changes because of uncertain input data and information, change in technology etc. Considerations of long term planning are modified and corrected in the medium term planning according to the actual information obtained in later stages. Short term planning deals with the issues that have to be resolved within 10 years.

Regulated and Vertically  Integrated Utilities:

The electric power industry, over the years, has been dominated by large utilities that had an overall authority over all activities in generation, transmission and distribution of power. Such utilities are called as Vertical Integrated Utilities (VIU). 

They serve as the only service provider in the area and are obliged to provide electricity to everyone in the area. Transmission expansion in a regulated power industry is a centralized affair well coordinated with generation expansion planning. All the necessary information is available to the network planner. 

The main aim of transmission expansion planning in this regulated environment is to minimize the expansion cost while satisfying certain technical and economical constraints.

Restructuring and Deregulation of Power Sector:

Different countries have restructured and deregulated its power industry and many more are in the process. India too have restructured and deregulated its power sector. 

The introduction of deregulation has brought several new entities. One of the first steps in the restructuring process of power sector has been the separation of the transmission activities from the generation activities. It has redefined the scope and role of many of the existing players in the power sector and envisaged to some form of electricity market inducing competition at various levels of electricity related transactions.    

Transmission Expansion Planning in Restructured era:

The restructuring and deregulation have introduced new complexities to the transmission expansion planning. Stakeholders have different desires and expectations from the performance and expansion of the transmission system. 

Providing non-discriminatory access, facilitating competition, minimizing the cost of installation and operation, minimizing the environmental impacts are the desires of different stake holders of the power system. These participants of the electricity market take their decisions independently and also change their strategies frequently to maximize their benefits. 

Consumers of electricity change their load and hence consumption according to the price signals. Availability of independent power producers (IPP) is uncertain because of the changing scenario. Wheeling power are time varying and affect the nodal prices. Therefore, there is no specific pattern of load and the dispatched power in the deregulated electric sector.

Thus, restructuring and deregulation of power industry have changed the objectives of transmission expansion planning and increased the uncertainties.    

Electrical Engineering: One of the fastest growing fields in India

The demand for electrical energy in India has increased many folds during the recent time because of:

1. growth in population, 
2. enhanced lifestyle, 
3. increased automation in industrial sector etc. 

Recent studies by the US Department of Energy indicate that China, India and Brazil will be the most rapidly growing countries in terms of electrical demand. Total 1102.9 TWh of electricity was produced in the country during 2013-14 making it the 3^rd largest producer of electrical energy in the world in the year 2013. 

International Energy Agency estimates that India will add another 600 to 1200 GW of installed capacity before the year 2050. This is clearly echoed in the report of Ministry of Power, Government of India, 2012, in which additional generation capacity to be added in the 12^th Five Year Plan is stated as 76 GW. It needs to add another 170 GW of installed generation capacity in the next decade to get the desired 9% growth in GDP and this can be achieved through large capacity power projects such as the Ultra Mega Power Projects based on super-critical technology.  

As on July 2014, the installed generation capacity in India is 250.5 GW. Indian electricity sector is certainly amongst the most active players in Renewable Energy (RE) utilization especially the wind energy. The grid interactive wind and solar generation is 21.69 GW and 2.75 GW respectively; with still more projects to materialize in the coming decades. 

The objective of Jawaharlal Nehru National Solar Mission (JNNSM) is to establish India as a global leader in solar energy by creating conducive atmosphere in the country. The mission under the brand name “Solar India” set an ambitious target of adding 20 GW of grid connected and 2 GW of off-grid capacity by year 2022.

Private sector has a great role to play in Indian power sector and there are many prominent names that have registered their strong presence. At present private sector accounts for nearly 40 % in the total installed generation capacity of the country and is set to increase. Moreover, private players are extending technical assistance to government in erecting power plants and other facilities, involved in power trading, evolving clean energy development mechanism, supplying the power etc. as on March 2014, India had 13.9 GW of installed generation capacity based on super-critical technology; of which Adani Power (one of the leading private players in the Indian power sector) has commissioned the maximum of 6.6 GW. Other big private companies in the generation sector are Tata Power, Reliance Power, Essar Power etc. Government of India has issued certain guidelines for private sector participation in transmission sector also.        

In the light of above facts, various job opportunities are available to electrical engineers in Indian power sector. They can work in both public and private sector industries involved in power generation, transmission, distribution industry as well as in their ancillary units. These companies employ them as engineers or managers, and make them responsible for design and development, installation, commissioning, operation and maintenance of power handling equipment and systems. The service sector which provides the required maintenance also forms a sizable segment.  

The various governmental organizations involved in the Indian power sector are National Thermal Power Corporation (NTPC), National Hydro Power Corporations (NHPC), Damodar Valley Corporation (DVC), Power Finance Corporation (PFC), Power Grid Corporation of India Limited (POWERGRID), and various state level power generation companies and power suppliers. These agencies are providing ample job opportunities to graduate electrical engineers. The companies are advertising the vacancies in leading national/ local newspapers and posting the same on their websites. These companies usually ask for 60 percent or above in graduation level. The recruitment process consists of mainly written test, group discussion and personal interview. Sometimes, a technical interview may also be conducted. 

The final selection is based on the overall performance of the candidate. Reservation to various categories is given as per the prevailing government rules. Initially, selected candidates have to work on probation as graduate engineer trainee for one or two years and on the successful completion of probation period they are absorbed as regular engineers.

A huge job potential also exists in rapidly growing private sector for electrical engineers. As far as their selection criterion is concerned, it varies from company to company. However, most of them are hiring on the basis of personal interview of eligible candidates. 

Some of the major private companies in power sector are Tata Power, Reliance Power, Adani Power, Torrent Power, Essar Power, Crompton Greaves, Siemens, Alstom T&D India, Suzlon Energy etc. 

Phase Shifting Transformers: A crucial component for Transmission Lines

Phase Shifting Transformers (PST), also called Phase Angle Regulator (PAR), are crucial components in the ongoing endeavor for improved transmission capacity, reliability and security. They are an effective and economical tool to ensure reliable and efficient power flow control in overloaded transmission lines.  

PST help to control the power flow in the transmission line enabling the existing line to be loaded up to the thermal limits, deferring or avoiding the investment in new transmission lines. The electrical losses in the system and hence the operating cost are also minimized by balancing the power flow in the network and optimizing the power flow. System reliability is also increased by employing PSTs which help in mitigating post-contingency overloads and undesired load flows. The impedance of two or more lines, which are in parallel, determine the load sharing between them. In case of different impedance and hence unbalanced loading, PSTs help to balance the load sharing. 

Concept of Phase Angle Regulation:

The basic concept of phase angle regulation is the addition of an appropriate quadrature voltage component to the prevailing bus voltage in order to increase or decrease its magnitude or angle to the desired value. This injected voltage will change the existing phase angle of the system voltage. For comparatively small angular modifications, the resultant angular change is nearly proportional to the injected voltage. But with large angular compensations, the magnitude of the system voltage changes significantly.

Application of Phase Shifting Transformers:

PSTs have more windings and tap changer than the traditional power transformers and hence are more complex. Two 1630 MVA, 400 kV, + 18^o PSTs are installed in Italy to increase the power transfer from France to Italy and to increase reliability. Similarly, to optimize power flow and to increase the system reliability three 1400 MVA, 400 kV, ± 25^o units are installed in Belgium. A 600 MVA phase shifting transformer was manufactured by Siemens for a Slowenian sub-station. This PST had a No-load phase angle of ± 40^o  with ± 32 steps. Thus, PSTs are crucial components in any power transmission line and are used through out the world. 

Phase Shifting Transformers by BHEL: 

India’s first PST, 315 MVA, 400/220/55/33 kV class, 3-phase, ± 15%, was developed by BHEL Bhopal for APGENCO. This PST is a quadrature type, dual core, dual tank design which consisted of two transformers, called the shunt and the series unit. The complexity of the transformer can be judged by the factor that it has 6 numbers of 220 kV bushing on the series transformer, whereas the shunt unit consisted of 15 number bushings.  

    

Modern phase angle regulators with fast power electronic control using thyristors etc can also be used to mitigate dynamic disturbances, for transient stability enhancement, damping of power oscillation and minimization of post-contingency overloads and corresponding voltage dips.

Ref:

·         S Sachdeva, R K Singh, S.K Gupta, J.S. Kuntia, and R.K.Tiwari, “Development of India’s first phase shifting transformer”, W& E International (Energy Section).

·         Hingorani & Gyugyi, “Understanding FACTS”, John Wiley India.

Better Coal Management: Derailed Generation Sector’s prime requirement

Last updated: Feb 05, 2017 

Significant Generation Capacity Addition:

India has achieved significant generation capacity addition in the last 50 years. The current installed capacity of Indian power system is 305.5 GW (as on Aug 2016) with coal based power plants having a share of nearly 61 percent. Thus, coal based thermal power plants dominate the current Indian generation scenario and in the future also.

India to be among the most rapidly growing countries:

Recent studies by the US department of energy indicate that China, India and Brazil will be the most rapidly growing countries in terms of electrical demand. This is clearly echoed in the report of the “Working Group on Power”, Government of India, Ministry of Power, 2012, in which the additional generation capacity to be added in the 12^th Five Year Plan is stated as 76 GW. It needs to add another 170 GW of installed generation capacity in the next decade to get the desired 9% growth in GDP and this can be achieved only through large capacity power projects. 

Concept of Ultra Mega Power Project:

In view of this, the Government of India has come up with the concept of Ultra Mega Power Project (UMPP). These coal powered, super-critical technology based power projects, each with a capacity of 4 GW or more is a series of ambitious power projects planned by the Government of India.

Various Issues in Coal Management Activities:

The various coal management activities such as planning, contracting, procurement, logistics and delivery are managed by different agencies. Thermal power plants, other than pit-head plants, rely on ship, rail or road transportation services to deliver coal from the sources to their plant location. Coal inventory management at the thermal power plant involves accounting of received and consumed coal. 

Many thermal plants have in-adequate automation and management system, often leading to inaccurate coal requirement forecasting. Tracking of coal transportation is also not very advanced. All this lead to inefficiencies and uncertain conditions causing either power plant outage due to lack of coal or un-necessary piling up of coal inventory and blocking of resources. 

Generating companies typically stock up coal for nearly 10 days of operation. The financial loss on account of power plant shut down because of non-availability of coal can be as much as 2 million USD per day for a thermal power plant of 1000 MW.

Therefore, the performance of Indian generation sector is going to be greatly affected by the coal supply management to its coal based thermal power plants. Officials say that the coal production is the same since the last 5 years and the credit goes to improper planning, policies and prevailing corrupt practices. Adding to the wound is the recent declaration of Supreme Court of India which states that the entire allocation of coal blocks from 1993 to 2010 was illegal, arbitrary and non-transparent.

There are situations when majority of coal based power plant in India have left with less than 7 days of coal stock. Many coal based power plants of the Central, State and private sector have been shut down in the past on account of in-adequate coal supply. This also increases the spot price of electricity at the Indian Energy Exchange (IEX). Same situation has aroused in year 2012 also.

Properly Integrated and Automated Coal Management System is required:

The message is loud and clear that the country’s power sector and hence the growth is dependent largely on the coal supply to the thermal power plants. A properly integrated and automated coal management system is required to keep the coal inventory to a minimum, at the same time ensuring un-interrupted power generation.

A better and efficient coal management system has to be derived keeping in view the various Ultra Mega Power Projects coming up in the 12^th and 13^th FYP. Special attention has to be given for demand side management so that the load can be properly managed during such a crisis.

Ref:

www.cea.nic.in/reports/monthly/inst_capacity

Hindustan Times, 4^th sep. 2014

Basics of Static Synchronous Series Compensation

Power transfer over long AC transmission line is mainly limited by the series reactance of the line. The series capacitive compensation decreases the overall effective series reactance of the transmission line i.e. the series capacitive compensation cancels a portion of the line's inductive reactance and hence increases the transmittable power. 

Thus, controllable series line compensation can be applied to control the flow of power in transmission lines. Along with the application of fast controls we can minimize the effect of system disturbances, thereby reducing the required stability margin.

Degree of Compensation:

The ratio of the capacitive reactance of the compensator to that of the inductive reactance of the line is called degree of compensation. The transmittable power over a transmission line rapidly increases with the degree of series compensation.

Another explanation of the series compensation which is helpful in understanding the concept of converter based power flow controller is as given below:

“In order to increase the power flow over a transmission line and hence the current through the line, the voltage across the series reactance must be increased. This can be done by an appropriate series connected compensator, which produces a voltage Vc opposite to the existing voltage across the series reactance, thereby causing the voltage across reactance to increase.”

Thus the series capacitive compensation works by increasing the voltage across the inductive reactance of the transmission line, which results in corresponding increase in the transmission line current and hence the transmitted power. 

Concept of Static Synchronous Series Compensator:

The Static Synchronous Series Compensator (SSSC) was proposed by Dr L. Gyugyi in 1989. Similar to STATCOM, the SSSC uses a Voltage Sourced Converter (VSC) and is connected in series with the transmission line through a coupling transformer. It is also called series STATCOM. Figure 1 shows a SSSC connected in a transmission line through a coupling transformer.

 Fig.1:  SSSC connected in a transmission line through a coupling transformer.

The VSC generates an AC voltage that is applied to the coupling transformer. With suitable internal control, the magnitude and phase angle of the three alternating voltages produced by the controller i.e. VSC can be controlled. 

The SSSC can generate or absorb reactive power and can also exchange active power with the Power System when the DC terminal of the VSC is connected to a suitable storage battery or other adequate energy source.

Comparison with series capacitor:

In comparison to series capacitor, the SSSC can control the magnitude of injected voltage Vq independent of the transmission line current. The SSSC’s output voltage can be reversed by simple controlling to make it lag or lead the line current by 90^o. SSSC can increase the transmitted power by a fixed fraction of the maximum power transmittable by the uncompensated line, independent of the angle power angle δ. It can decrease, as well as increase the power flow to the same degree by just reversing the polarity of the compensating voltage.

SSSC is more capable of controlling the transmittable power when compared to controlled shunt compensation. Hence, SSSC can be more effective in increasing the transient stability limit and in damping power oscillations.