Can you really recognize motors ?

It is very much obvious that many of us know what is the function of motor. Many of us know better about the operating principle as well. By definition in general, An electric motor is an electrical machine that converts electrical to mechanical energy.In an electric motor the moving part is the rotor which turns the shaft to deliver the mechanical power. Mainly there are two parts of motor, they are stator and rotor. The stationary part is the stator, usually has either windings or permanent magnets. The rotor usually has conductors laid into it which carry currents that interact with the magnetic field of the stator to generate the forces that turn the shaft. However, some rotors carry permanent magnets, and the stator holds the conductors. In order to categorize any motor, its rotor plays a vital role. But, although we are very much attached to theoretical part, many of us cannot identify the type of motor by viewing its rotor.

The figures given below shows some of the rotor from which the motor type can be identified. These pictures are taken by me during one of the training program. Hope you will be benefited.

 

Fig. 1: Rotor of DC Motor

 

Fig. 2: Rotor of Phase Wound Motor

 

Fig. 3: Rotor of Squirrel Cage Motor

 

Fig. 4: Rotor of Synchronous Reluctance Motor

Fig. 5: Rotor of Synchronous Motor

 

–ANAND MANDAL

E-mail: anandkalyaneee@gmail.com

 

Nepal Energy Scenario: Future and Challenges.

MAIN THEME

The current energy crisis in Nepal clearly indicates that the future energy-demand cannot be met by traditional energy-sources. Given the present energy scenario of the country, we may conclude that the coming years will see a transition from conventional sources to renewable sources. It will be a period to give serious thought to evolving a long-term energy strategy that will include renewable, including wind, energy and providing all legal and financial support to develop the use the zero carbon emission for our sustainable future. Thus the generation of power from renewable energy resources like Biomass, Sunlight and Water resources must have to be put on high priority to meet the future energy demand. This paper aims to highlight the potentiality of energy generation for Hydro, Solar and Biogas and urgency for development of the power generation from these resources to withstand against the future energy crisis in Nepal.

INTRODUCTION

The Federal Democratic Republic of Nepal is a landlocked country, with India to the south, east and west and the People’s Republic of China to the north. It lies between 26° 22′ to 30° 27′ N latitude and 80° 04′ to 88° 12′ E longitude, with an altitudinal range from 60 m in the south to 8,848 m in the north. Nepal encloses a total area of 147,181 km² and a population of approximately 26,620,000. Nepal comprises three ecological bands or regions that straddle the country: the Mountain Region in the north that borders with China, Hill Region in the middle which contains valleys (in which the capital city Kathmandu is located), and the fertile Terai Region (flatland) to the south that borders with India. Approximately 53% of the population live in the Hill Region (including about 5% in Kathmandu valley) and 40% in the Terai. Around 83% of the total population lives in rural areas and the rest 17% resides in urban areas. The rural dominance in the country imply mass poverty as 38% of the population have disposable income of $1.25 a day and the average per capita income is $427 (WDI, 2011) Nepal’s gross domestic product (GDP) for 2008 was estimated at over $12 billion (adjusted to Nominal GDP), making it the 115th-largest economy in the world. Agriculture accounts for about 40% of Nepal’s GDP, services comprise 41% and industry 22%. Agriculture employs 76% of the workforce, services 18% and manufacturing/craft-based industry 6%.

Nepal is not rich in fossil fuel resources but it has plenty of renewable energy resources, in particular water that is running down from the vast Himalayan mountain ranges in over 6,000 rivers. With 300 sunny days a year, the sun’s freely available solar energy can also be converted into electricity. Nepal is presently facing an energy crisis of unprecedented proportions. The 706 MW total installed capacity of Nepal Electricity Authority, supplemented by net purchases from India, is inadequate to meet demand. Load shedding has thus become the rule of the day. In this context renewable energy development continues to be a high priority program of government as it provides a least cost solution to remote, sparsely populated areas unviable for grid extension, while being clean, safe and environmentally friendly. GoN’s goal for the next 20 years is to increase the share of renewable energy from less than 1% to 10% of the total energy supply, and to increase the access to electricity from alternative energy sources from 10% to 30% .By 2020, GoN has a plan to invest USD 1,076 million in renewable energy, of which USD 115 million will be allocated to mini, micro and pico hydro, USD 333 million for solar home systems and USD 135 million for biogas.

 Present Energy Scenario of Nepal

The per capita primary energy consumption of Nepal (14 GJ) is one of the lowest in the world, just above Bangladesh. In comparison with neighboring countries, it is 52 GJ in China and 22 GJ in India. The Asian average is 26 GJ. In the context of electricity consumption, Nepal’s case is among the lowest, with just 69 kWh per capita. Three broad types of energy sources exist in Nepal: commercial, traditional and alternative energy. Commercial sources of energy include conventional fossil based, carbon intensive (coal and petroleum fuels) and electricity from large hydro plants. Traditional energy sources include biomass contents like fuel wood, biogas, agricultural by-products and animal waste used for direct combustion. Alternative energy sources include all non-conventional forms of energy such as photovoltaic, micro-hydro, wind, biofuels, geothermal, etc. The total energy consumption of the country remains primarily driven by traditional sources. Total energy consumption in Nepal in the year 2008/09 was about 9.4 million tons of oil equivalent (401 million GJ) of which some 87% was derived from traditional resources such as woody biomass and animal waste, 1% from small renewable energy sources, and only about 12% from commercial energy sources such as petroleum and fuel products and electricity from small to large hydropower plants. In the residential sector, biomass contributes about 96% of the total energy consumed.   The shortages of power and frequent power outages have severely constrained the growth potential of the country.  A little over half (56%) of HH in the country have access to electricity (including off-grid solutions). On the other hand, 33% of HH still depend largely on kerosene for lighting. Among five administratively defined development regions, the Western development region has the highest proportion of HH using electricity (63%), while the Mid-western development region has the lowest (34%). By ecological regions, the Mountains have the least proportion of HH that use electricity (41%). The proportion of HH using electricity in the Hills (56%) and Terai (59%) are slightly higher. As to be expected, urban areas have better access to electricity relative to rural areas (93% versus 49%).

At present, the Integrated Nepal Power System (INPS) has a total installed capacity of some 706 MW of which 652 MW (92%) is generated from hydro resources. The annual electricity generation on the grid system in 2009-2010 was about 3,690 GWh, of which about 57% was generated by power plants owned by the Nepal Electricity Authority (NEA), 26% by IPPs, and the remaining 17% was imported from the Indian grid.  The power system has about 1,854,275 customers, which is an increase of 10.6% from the previous year. Table-1 shows the composition of NEA’s installed capacity. 

Source	MW	% of Total
Major Hydro (NEA) – grid connected	472.99	67.0
Small hydro (NEA) – isolated	4.54	0.7
Total hydro (NEA)	477.53	67.7
Hydro (IPP)	174.53	24.7
Total hydro (Nepal)	652.06	92.4
Thermal (NEA)	53.41	7.6
Solar (NEA)	0.10	0.0
Total capacity including private and others	705.57	100.0

Table 1: Composition of NEA installed Capacity

 

The peak load in Nepal occurs during the winter when the run-of-river power plants generate at a lower capacity (compared to the installed capacity) due to low river flows. According to the NEA, the peak demand in 2010 was 885 MW, which was an increase of 9% over the previous year. The annual energy demand was 4,367 GWh resulting in a shortfall of some 676 GWh, resulting in load shedding of 12-14 hours per day.The peak demand met by NEA rose steadily from 603 MW in 2006 to 946 MW in 2011 (with the excess over installed capacity supplemented by purchases from India), indicating a compound annual growth rate (CAGR) of 9.4%.  Likewise, the total available energy increased from 2,781 GWh to 3,858 GWh at a CAGR of 6.8% during the same period. Electricity sales by NEA increased from 2,033 GWh in 2006 to 2,735 GWh in 2011at a CAGR of 6.1%.  In terms of composition, the domestic sector accounted for 43% of the total consumption in 2011, followed by the industrial sector at 38%.  Consumption by other sectors is very much smaller, and comprised commercial (7.5%), non-commercial (4.0%), street lighting (2.4%), water supply & irrigation (2.0%), community sales (1.7%), and bulk supply to India (1.1%), with negligible amounts consumed by transport and temples.

The energy and demand forecast for the financial years 2010-11 to 2027-28 is provided in the Table 2below.  The electricity demand is forecast to reach about 3,679 MW in the financial year 2027-28, (medium growth scenario) which is an increase of some 2,800 MW from the present peak demand. The energy forecast indicates an energy output of 17,404 GWh by fiscal year (FY) 2027-28. 

Fiscal Year	Energy (GWh)	System Peak Load (MW)
2010-11	4,430.70	967.10
2011-12	4,851.30	1,056.90
2012-13	5,349.60	1,163.20
2013-14	5,859.90	1,271.70
2014-15	6.403.80	1,387.20
2015-16	6,984.10	1,510.00
2016-17	7,603.70	1,640.80
2017-18	8,218.80	1,770.20
2018-19	8,870.20	1,906.90
2019-20	9,562.90	2,052.00
2020-21	10,300.10	2,206.00
2021-22	11,053.60	2,363.00
2022-23	11,929.10	2,545.40
2023-24	12,870.20	2,741.10
2024-25	13,882.40	2,951.10
2025-26	16,142.70	3,418.90
2027-28	17,403.60	3,679.10

Nepal boasts snowy mountains (Himalayan range) in the North which acts as a perennial source for many free flowing rivers establishing the country second richest in water resource in the world after Brazil (Joshi and Khadka, 2009). The nation is capable of producing 42,000 MW of technically and economically viable commercial electricity from large hydro plants (EIA, 2010). However, Nepal Electricity Authority (NEA) has just managed to develop only 652.06 MW (public sector: 477.53 MW and private sector: 174.53 MW) of generation capacity including that of the Independent Power Producers (IPPs). The country, being a net importer of electricity, imports 100-150 MW of electricity annually from India. The developments of large hydropower is rather slow than anticipated. Thus, Nepal serves as a unique case of being resource rich and policy poor in terms of hydro power generation considering its potentials. Figure below shows that the energy consumption pattern by source type in 2008/09 has marginally changed as compared to 1995/1996. While fuel-wood comprised 77% of traditional energy consumption in 2008/09; marginal increment in commercial and alternative energy usage is observed in more than a decade time period. The nation remains distinctly dependent on biomass to meet the energy demand while renewable having a negligible share in total energy consumption.   

 

 

Energy consumption of traditional sources is driven by the residential sector unlike in most developed countries where the industrial sector drives the national energy consumption. In 2008/09, the residential sector in Nepal consumed 89.1% of energy contributing to major exploitation of forests and deforestation in rural areas. The transport sector consumed 5.2% of total energy which primarily includes the fossil based petroleum products. However, the lack of any oil, gas and coal reserves in the country implies that India remains the sole supplier of commercial energy sources to Nepal (WECS, 2006). Thus, a major share of export earnings is spent to import petroleum products annually and widening the bilateral trade deficit with India. Further, the irregularity in supply coupled with the rising and volatile prices of oil and gas in the international markets increases the risks of over-dependence on the imported commercial energy sources.

 

Around 16.5 million people currently living in Nepal are devoid of electricity and the country has an overall low score of 0.107 in terms of Human Development Index (HDI). Although, the rate of electrification increased to 43.6% in 2008 as compared to 30% in 2005; the benefits of electrification are largely confined to urban areas (IEA, 2008).  Only 34% of rural population had access to electricity in 2008 as compared to 90% access for urban population during the same year. Moreover, the urban population is growing at 18% while the rural population growth rate stands at around 1.2%. Alternative energy sources based on decentralized production can play a significant role in mitigating these concerns and contribute towards sustainable development of the nation. At present, the Integrated Nepal Power System (INPS) has a total installed capacity of some 706 MW of which 652 MW (92%) is generated from hydro resources. The annual electricity generation on the grid system in 2009-2010 was about 3,690 GWh, of which about 57% was generated by power plants owned by the Nepal Electricity Authority (NEA), 26% by IPPs, and the remaining 17% was imported from the Indian grid.  The power system has about 1,854,275 customers, which is an increase of 10.6% from the previous year.. According to the NEA, the peak demand in 2010 was 885 MW, which was an increase of 9% over the previous year. The annual energy demand was 4,367 GWh resulting in a shortfall of some 676 GWh, resulting in load shedding of 12-14 hours per day. The peak demand met by NEA rose steadily from 603 MW in 2006 to 946 MW in 2011 (with the excess over installed capacity supplemented by purchases from India), indicating a compound annual growth rate (CAGR) of 9.4%.  Electricity sales by NEA increased from 2,033 GWh in 2006 to 2,735 GWh in 2011at a CAGR of 6.1%.  In terms of composition, the domestic sector accounted for 43% of the total consumption in 2011, followed by the industrial sector at 38%.  Consumption by other sectors is very much smaller, and comprised commercial (7.5%), non-commercial (4.0%), street lighting (2.4%), water supply & irrigation (2.0%), community sales (1.7%), and bulk supply to India (1.1%), with negligible   amounts consumed by transport and temples.

It is estimated that Nepal has about 42,000 MW of commercially exploitable hydro power including over 100 MW of micro hydro power; 2,100 MW of solar power for the grid; and 3,000 MW of wind power. Similarly 1.1 million domestic biogas plants can be developed in the country. These assume greater significance in the context of non-availability of fossil fuel and other forms of energy in Nepal. The subsections below discuss the current status of the existing and potential renewable technologies in Nepal.

 

–ANAND MANDAL

E-mail: anandkalyaneee@gmail.com

 

References:

1) NEA Annual Reports.

2) Drafts prepared by GoN.

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FACTS and HVDC

SIMILARITY BETWEEN FACTS AND HVDC

While some of the relevant technology i.e., Static VAR Compensation is already in wide use, the FACTS concept has brought to the table a tremendous potential for thyristor based controllers which will surely revolutionize the power system. The technology offers the utilities the ability to:

1. Control power flows on their transmission routes;
2. Allow secure loading of transmission lines to their full thermal capacity.

FACTS technology, while allowing use of transmission to its thermal capacity, does not do away with the need for additional transmission lines or the upgrading of existing lines where thermal limits have been reached or when evaluation of losses added to the cost of FACTS technology shows that new lines or upgrading of existing lines is the most optimum answer.

Often, ac transmission systems are thought of as being “inflexible”. Power flow in ac networks simply follows Ohm’s law and ordinarily cannot be made to flow along specific desired paths. As a result, ac networks suffer from parallel-path, or “loop” flows. The power flows from source to load in inverse proportion to the relative impedances of the transmission paths. Low  impedance paths take the largest fraction of flow, but all lines in the interconnection are a part of the flow path. Thus, utilities not involved in an interchange power transaction can be affected.

A fundamental notion behind FACTS is that it is possible to continuously vary the apparent impedance of specific transmission lines so as to force power to flow along a “contract path”. This is a brand-new concept for many system planners. As illustrated in Figure 1, with precise control of the impedance of transmission lines using FACTS devices, it is possible to maintain constant power flow along a desired path in the presence of continuous changes of load levels in the external ac network, and to react in a planned way to contingencies. Just as in HVDC applications, FACTS controls could be designed to enhance the behavior of the uncontrolled systems.

Fig. 1: FACTS can direct flow along a desired path

The flexible system owes its tighter transmission control to its ability to manage the interrelated parameters that constrain today’s systems ,including series impedance, shunt impedance, phase angle, and the occurrence of oscillations at various frequencies below the rated frequency. By adding to in this way, the controllers enable a transmission line to function nearer its thermal rating. For example, a 500-kV line may have a loading limit of 1000-2000 MW for safe operation, but a thermal limit of 3000 MW.

It is often not possible both to overcome these constraints and maintain the required system reliability by conventional mechanical means alone, such as tap changers, phase shifters, and switched capacitors and reactors (inductors). Granted, mechanical controllers are on the whole  less expensive, but they increasingly need to be supplemented by rapidly responding power electronics controllers.

The new technology is not a single, high-power electronic controller, but rather a collection of controllers, which can be applied individually or collectively in a specific power system to control the five interrelated functions already mentioned. The thyristor is their basic element, just as the transistor is the basic element for a whole variety of microelectronic circuit. Because all controllers for the flexible transmission system are applications of similar technology, their use will eventually benefit from volume production and further development of high-power electronics.

Electric power networks integrate generation and load centers within each utility system and through interconnections among neighboring systems, share power with vast regional grids. The purpose of this is to take advantage of the diversity of loads, changes in peak demand due to weather and time differences, the availability of different generation reserves in various geographic regions, power sharing arrangements among utilities , shifts in fuel prices, regulatory changes, and other discrepancies.

 

Applying Flexibility to the Electric Power System

The power industry term FACTS (Flexible AC Transmission Systems) covers a number of technologies that enhance the security, capacity and flexibility of power transmission systems. FACTS solutions enable power grid owners to increase existing transmission network capacity while maintaining or improving the operating margins necessary for grid stability. As a result, more power can reach consumers with a minimum impact on the environment, after substantially shorter project implementation times, and at lower investment costs – all compared to the alternative of building new transmission lines or power generation facilities.

The two main reasons for incorporating FACTS devices in electric power systems are:
· Raising dynamic stability limits

· Provide better power flow control

Benefits of FACTS

Rapidly Implemented Installations: FACTS projects are installed at existing substations and avoid the taking of public or private lands. They can be completed in less than 12 to 18 months—a substantially shorter timeframe than the process required for constructing new transmission lines.

Increased System Capacity: FACTS provide increased capacity on the existing electrical transmission system infrastructure by allowing maximum operational efficiency of existing transmission lines and other equipment.

Enhanced System Reliability: FACTS strengthen the operational integrity of transmission networks, allowing greater voltage stability and power flow control, which leads to enhanced system reliability and security.

Improved System Controllability: FACTS allow improved system controllability by building “intelligence” into the transmission network via the ability to instantaneously respond to system disturbances and gridlock constraints and to enable redirection of power flows.

Seamless System Interconnections: FACTS, in the form of BTB dc-link configurations, can establish “seamless” interconnections within and between regional and local networks, allowing controlled power transfer and an increase in grid stability.

 

–ANAND MANDAL

E-mail: anandkalyaneee@gmail.com

 

Flexible AC Transmission System (FACTS)

Flexible Alternating Current Transmission System (FACTS) is a static equipment used for the AC transmission of electrical energy. It is meant to enhance control ability and increase power transfer capability of the network. It is generally a power electronics based device.

FACTS is defines by IEEE as “a power electronic based system and other static equipment that provide control of one or more AC transmission system parameters to enhance controllability and increase power transfer capability.

FACTS technology

FACTS could be connected:
· in series with the power system (series compensation)
· in shunt with the power system (shunt compensation)
· both in series and in shunt with the power system.

Series compensation

In series compensation, the FACTS is connected in series with the power system. It works as a controllable voltage source. Series inductance exists in all AC transmission lines. On long lines, when a large current flows, this causes a large voltage drop. To compensate, series capacitors are connected, decreasing the effect of the inductance.

 

Fig. 1:FACTS for series compensation- vector diagram 

Series compensation is a well established technology that is primarily used to reduce transfer reactances, most notably in bulk transmission corridors. The result is a significant increase in the transient and voltage stability in transmission systems. Series compensation is self-regulating in the sense that its reactive power output follows the variations in transmission line current, a fact that makes the series compensation concept extremely straightforward and cost effective. Series compensation is defined as insertion of reactive power elements into transmission lines and provides the following benefits:

• Reduces line voltage drops
• Limits load-dependent voltage drops
• Influences load flow in parallel transmission lines
• Increases transfer capability
• Reduces transmission angle
• Increases system stability

Thyristor controlled series capacitors add another controllability dimension, as thyristors are used to dynamically modulate the ohms provided by the inserted capacitor. This is primarily used to provide inter-area damping of low frequency electromechanical oscillations, but it also makes the whole series compensation scheme immune to subsynchronous resonance (SSR).

 

 

Fig 2. Series Compensation (Photo Coutesy: ABB)

Shunt compensation

In shunt compensation, power system is connected in shunt with the FACTS. It works as a controllable source. Shunt compensation is of two types:

1) Shunt capacitive compensation:

This method is used improve the power factor. Whenever an inductive load is connected to the transmission line, power factor lags because of lagging load current. To compensate, a shunt capacitor is connected which draws current leading the source voltage. The net result is improvement in power factor.

2) Shunt inductive compensation

This method is used either when charging the transmission line, or, when there is very low load at the receiving end. Due to very low, or no load — very low current flows through the transmission line. Shunt capacitance in the transmission line causes voltage amplification (Ferranti Effect). The receiving end voltage may become double the sending end voltage.To compensate, shunt inductors are connected across the transmission line.

 

Fig. 3: FACTS for shunt compensation- vector diagram 

Static VAR Compensator

. It helps in keeping steady state and dynamic voltages within their limits, but it does not provide any control of active power. The var output can be varied continuously between the capacitive and inductive ratings of the equipment. The necessary reactive power required for the compensation is generated or absorbed by capacitor or reactor banks. Thyristor switches are only used to control the combined reactive impedance the banks present to the system. An advanced static compensator has been recently presented . This device provide control for real and reactive power.

In general,

Benefits of Reactive Power Compensation

Reactive Power Compensation projects assist customers improve the technical reliability and economics of their transmission and distribution system

• Voltage support and improved regulation
• Increased transmission capacity
• Reduced system expansion costs
• Reduced kW and KVAr system losses
• Improved system power factor
• Improved economics of electricity supply
• Reduction of harmful harmonics
• Improved system stability.

What are FACTS devices?

FACTS stand for Flexible AC Transmission Systems. The term “FACTS” covers several power electronics based systems used for AC power transmission. FACTS solutions are particularly suitable in applications, which require one or more of the following qualities:

· Rapid dynamic response
· Ability for frequent variations in output
· Smoothly adjustable output
· Fast implementation to achieve considerable increase in transmission capacity.

FACTS involve devices such as:

· Static Var Compensators (SVC) which are a well know workhorses that have been around for the last 20 years and well utilized within Australia.
· STATCOM are new innovative devices based on utilization of high tech power electronic components, which result in a small installation footprint and very fast response times.
· Thyristor Controlled Series Compensation is a very cost-effective way to improve power transfer and counter power swings and SSR.