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Surge Protection Device for Solar PV installation

Effects of Lightning Strike on Solar PV system: A solar PV installation is vulnerable to the effects of lightning stroke. The potenti...

Monday, 30 March 2015

Ample Job Opportunities in Wind Energy sector in India

What is the Renewable Energy scenario in the Country?

India has large Renewable Energy (RE) potential in the form of wind, solar, small hydro, bio-mass, etc. The country today has one of the most active Renewable Energy addition programmes in the world and its Renewable Energy achievements have brought in significant changes in the national energy sector. 

Since 2006, the installed wind capacity in India has grown remarkably. As on 31st July 2016, the installed Renewable Energy generation capacity in the country was 44.8 GW comprising of 27.44 GW of wind power and 8.06 GW of Solar. India has the 5th largest generation portfolio in the world. Percentage share of  RE is 14.7% of the total installed capacity.

Large scale generation capacity addition, nearly 30 GW, by Renewable Energy is envisaged in the 12th Five Year Plan of the country.  Similarly it is proposed to add 40 to 55 GW of Renewable Energy in the 13th Five Year Plan.

What are the employment opportunities in the Wind Energy sector in the Country?

The economic and social benefits of employment generated by the wind energy sector remain unknown to our young individuals, particularly the engineers. To capture the existing and future scenario of employment in wind energy sector in India, organizations like NRDC and CEEW have carried out a survey of various companies in the field of wind energy. 

Interactions with the company representative reveal that maximum employment opportunities exist in the construction, commissioning and operation and maintenance phase.  Employment opportunities increase as the project capacity increases. Manufacturing of wind mill/turbine component also enable skilled workers to be engaged as engineers, managers, executives and technicians. 

Growth in wind energy sector presents a significant and pleasant opportunity for sizable deployment of civil and electrical engineers in India.

Which are the Companies active in wind sector in India?

There are several wind turbine manufacturers, who in technical collaboration with foreign manufacturers, are having their manufacturing unit here in India and are providing turnkey solutions in this sector and thus already providing good job opportunities for our young as well as experienced individuals. The various wind turbine manufacturers are:

Sr. No
Name of the manufacturer
Collaboration/Technical assistance
Enercon India Ltd., Mumbai
Enercon, Germany
Elecon Engineering, Gujarat
Turbowind, Belgium
Global Wind power Ltd, Mumbai
Norwin, Denmark
Leitner Shriram manufacturing, Chennai
Leitwind BV, Netherland
India Wind power Ltd. , Ahmedabad
Kenersys India Pvt. Ltd, Pune
Kenersys, Germany
Pioneer Wincon Pvt. Ltd, Chennai
Regen Powertech Pvt.Ltd, Chennai
Vensys Energy, AG
RRB Energy, Chennai
Vestas Wind System, Denmark
Siva Wind turbine India Pvt.Ltd, Erode
Wind Technick Nord, Germany
Suzlon Energy Ltd., Pune
Suzlon Energy, GmBH
Winwind Power Energy Pvt.Ltd, Chennai
Winwind, Finland
Inox Wind Ltd., Noida
AMSC Windtec GmBH Austria
GE India Pvt.Ltd., Bangalore
Gamesa Wind Turbine Pvt.Ltd., Chennai
Gamesa Innovation, Spain
Essar Wind Power Pvt. Ltd., Munbai
REpower, Germany

What are the Recruitment and Selection procedures?

Vacancies and opportunities in this sector can be known by going through the website of these companies. For example, Enercon is the market leader in wind energy in Germany. It offers a wide range of challenging career opportunities in R&D, production, administration, project management, sales, maintenance and service etc. They offer job to ambitious fresher as well as experienced applicants. 

To streamline the recruitment and selection procedures the company uses electronic management system i.e. E-recruiting. Various positions available can be accessed through this system. To facilitate the applicant in on-line form submission and tracking, help is also available. Apart from the online procedure one can also approach through their known references to have a decent breakthrough.

Friday, 20 March 2015

Induction type over-current relays used in power system protection

Electromagnetic induction relays are the most widely used relays for the protection of primary distribution in the country. These relays operate on the principle of electromagnetic induction and therefore can be used on AC circuit only. Torque or the actuating force is produced in these relays when one alternating magnetic flux reacts with the current (eddy currents) induced in the rotor by another alternating flux displaced in time and space but having the same frequency.

Construction of Induction Relay:

Depending on the type of rotor whether a disc or a cup, the relay is known as an induction disc or an induction cup relay. 

In induction disc type of relays, disc is the moving element on which the moving contact of relay is fixed whereas in the case of induction cup the contact is fixed on the cup. 

There are two structures of the induction disc type of relay:

1.      Shaded pole structure, and
2.      Watt-hour meter structure.

Most of the induction relays are of watt-hour meter structure. The construction of this relay is similar to the watt-hour or the AC energy meter. It consists of two electromagnets. The upper electromagnet carries two windings; primary winding and the secondary winding. 

The advantage of this type of construction is that it can provide a larger phase angle between the two fluxes and hence a higher torque. An important feature of this type of relay is that its operation can be controlled by opening or closing the secondary winding. If the circuit is opened, no torque will be produced and thus the relay is made inoperative.

The primary winding has tapings at fixed intervals and these tapings are connected to a plug setting bridge. With the help of plug setting bridge, the number of turns can be adjusted and hence the desired current setting can be achieved.

The plug setting bridge usually provides 7 sections of tapings to give over-current range from 50% to 200% in steps of 25%. If the relay is required to respond to earth faults, the tapings are arranged to give a range from 10% to 70% in steps of 10%. It is so because the magnitude of earth fault current is usually low compared to the phase fault currents and the earth fault relay is set independent of load current. 

The values of each tap are expressed in terms of percentage of full load rating of C.T. It gives the value above which the disc commences to rotate and finally closes the trip circuit. Adjustment of current setting is made by inserting a pin between the spring loaded jaws of the bridge socket at the required tap. When the pin is withdrawn for changing the setting while the relay is in service, the relay automatically adopts higher settings, thus avoiding the open circuit condition in C.T. secondary. Figure 1 shows an Induction type Over-current relay.

Fig.1: Induction type Over-current relay.

The secondary winding of the upper electromagnet is energized by induction from the primary winding. It is connected in series with the winding on the lower magnet. An aluminum disc is placed between the poles of the two electromagnets. The spindle of the disc carries a moving contact. The disc rotates through an angle which is adjustable between 0 degree to 360 degrees. By adjusting this angle, the travel of the moving contact can be adjusted so that the relay can be given any desired time setting.

The time required to rotate the disc through a preset angle depends upon the torque. More the torque lesser will be the time required. So the relay has inverse time characteristics. The IDMT characteristics can be obtained by saturating the magnetic circuit of the upper electromagnet. Thus, there is practically no increase in the flux after the current reached a certain value and any further increase in current will not affect the relay operation.       

Friday, 13 March 2015

Over current relays used in a power system

Over current relay is that relay which picks up when the current in the circuit exceeds the pick up value. Over current protection includes the protection from overloads as well as from short circuits. 

Depending upon the time of operation, over current relays are classified as:

i) Instantaneous over-current relay:

The over-current relay in which no intentional time delay is provided to pick up is known as instantaneous over-current relay. In these relays, the relay contacts close immediately after the current in the relay coil exceeds that for which it is set. Although, there will be a short time interval between the instant of pick up and the closing of relay contacts. The point to note is that this time delay is not intentionally provided.

Such relays have the advantage of reduced time of operation and are useful in case of faults very close to the source. The time of operation of such relays is approximately 0.01 sec. The instantaneous relay is more effective where the impedance between the relay and the source is small compared to the impedance of the section to be protected.

ii) Inverse-time over-current relay:
In inverse time over-current relay the operating time of the relay reduces as the actuating quantity increases in magnitude. These relays are normally more inverse near the pick up value of the actuating quantity and becomes less inverse as the actuating quantity is increased as shown in figure 1. 

Fig.1: Relationship between Actuating Quantity & Operating Time

The operating time of all over-current relays tend to become asymptotic to a definite minimum value with the increase in the value of current. This is an inherent quality of electromagnetic relays and is due to saturation of the magnetic circuit. So by varying the point of saturation different characteristics such as definite time, inverse definite minimum time, very inverse, and extremely inverse, are obtained. These time-current characteristics are shown in the figure below.

If the core is made to saturate at a very early stage, the time of operation remains same over the working range i.e. is independent of the actuating quantity or current as shown in the figure.; and is called definite time characteristics. In the inverse definite minimum time relays, the operating time is approximately inversely proportional to the operating current near the pick up value and becomes substantially constant slightly above the pick up value (as shown by the moderately inverse and inverse curve of the figure). This characteristic can be obtained by using a magnetic circuit which gets saturated for currents slightly greater than the pick up current. 
For the very inverse and the extremely inverse relays, the saturation of core occurs at a still later stage, and the characteristics is known as very inverse and extremely inverse characteristics as shown in the figure above.
In the next post you will see Induction type Non-directional Over-current relay. 

Saturday, 7 March 2015

Let’s design a roof top solar PV system

Levelised cost of Solar power:

When solar photovoltaic (PV) modules are installed on a building's roof top to generate electricity, it is called roof top solar PV system/ plant. Although, still in the evolving stage, but the feeling in the air is that roof top solar PV system can be a vibrant green technology in India.

Roof top solar PV cost about is about 8-9 INR/kWh and is cost effective where the grid tariff is higher than the levelised cost of solar power such as in the case of commercial and industrial consumers. Levelised cost is the cost per unit of power generated by the solar PV system taking into account all the cost incurred over the life span of the PV plant considering the time value of money.

For example the tariff for commercial consumers is around 12-13 INR/kWh in most of the Indian states. 

Roof top solar PV system is also beneficial for residential consumers in areas where power failures are frequent. Similarly residential consumers having higher energy consumption may also opt for roof top solar PV system. It is estimated that by 2016-17, the roof top solar power cost will reach the grid parity; which is a more encouraging factor in favour of roof top solar PV system in India. Currently the cost of per unit of electricity produced by diesel generators comes to about 16 INR as 1 ltr. of diesel produces about 3 to 4 kWh.      

Factors to be considered before installing a solar PV plant on your rooftop:

The factors to be considered before installing a solar power plant on your building’s rooftop include:

 i)   electrical load, 
ii)  working hours, 
iii) roof size, and 
iv) geographic location of the building. 

The subsidy given by the central and state governments, local utilities, and local community regulations and incentives are also some key determinants in the evaluation.
Roof-top solar arrays are best installed on a large and flat-roof where direct sunlight without shadow is available. Currently, commercially available silicon-based solar PV panels are made from solar cells encased in a special type of toughened glass. These are guaranteed for 25 years of field life but the power yield drops about 0.6 per cent a year. 

One can use mono-crystalline or polycrystalline panels. Mono-crystalline panels are a bit more efficient. The electrical energy (DC) generated by the solar PV modules during the sunshine hours is stored in the batteries. The energy stored in the batteries is converted into 230V AC mains using an inverter for further use. This solar energy can be used for captive consumption or exported to the grid. 

Here in this discussion we are calculating or designing for battery less solar PV system.

Steps in designing your roof top solar PV system

These are few of the steps that have to be taken before finalizing your roof top solar PV system:
1.   Estimate the energy required from roof top solar PV system,
2.   Calculate the shade-free roof top available for installation of roof top solar PV system,
3.   Estimate the capacity of the roof top solar PV system that can be installed,
4.  Approach some of the known vendors of  solar PV system and obtain the quotations as per your requirement,
5. Evaluate the quotations received from the price, warranty viewpoint, and
6.   Finalize the vendor and the deal.

Estimating the required capacity of solar PV system

The amount of energy needed is determined based on the load that needs to be fed from the roof top solar PV system. For this one has to collect the exact electrical load of each appliance that has to be connected to the PV system and it’s working hours/day. The table shows how this work is to be executed.
Table 1
Sr. No
Name of the appliance
Electrical load
Working hours per day
Total number
Energy/day (kWh/day)
0.06 x 4 x 1 = 0.24
Ceiling Fan
0.08 x 10 x 2= 1.6
1.84 kWh/day

So whatever energy requirement you have calculated is to be divided by the insolation level to get the size of solar PV system. Suppose that the energy requirement of particular premise is 2 kWh/day, then the solar PV system size should be
= Energy requirement/ insolation level
The insolation level in India is pretty good; for example in Bhopal (India) it is about 5.6 kWh/m2

So the capacity of solar PV system required in Bhopal for an energy consumption of 2 kWh/ day
= 2/5.5 = .36 kW or 360 W   
An extra 30% is added as technical margin. Hence finally the solar PV system capacity required is
= (2 x 1.3)/5.5 = 470 W
In this way you can calculate the capacity of the solar PV system. If one has to keep the investment low, he/she has to keep some of the large loads off the solar PV system; either by switching “off” that load/ loads or by feeding it from some other energy source.

Panel Size

A roof top solar PV system using lower efficiency PV panels will require more roof top area and vice-versa. Suppose that a 1 kW solar PV system with 12% efficiency requires 125 sq. feet of roof top area, then a same capacity plant with 14% efficiency will need only 107 sq.feet area. Normally a roof top solar PV system requires about 100 to 130 sq. feet of shade free roof top area per kW of installed capacity.
Now coming back to our calculations for the PV system with proposed capacity of 470 W, in all 4 panels of 130 Wp capacity each is required. Here we have assumed that we are using 130 Wp, 12 V capacity panels. The calculation is 470/130 = 3.6, thus 4 number PV panels are required for PV system of 470 W (In fact 4 panels of 130 Wp capacity means 520 W).
The standard warranty in case of PV panels is 5 years as given by reputed manufacturers. Additionally the panel must be able to produce at-least 90% of its rated power output (at the given solar irradiation) during the first 10 years. Similarly it must produce at-least 80% of its rated power output (at the given solar irradiation) during rest of its lifespan.

Inverter Size

The electricity generated by solar PV panels are DC in nature and needs to be converted into AC using an inverter to run your normal domestic, commercial or industrial appliances. Inverters determine the quality of the AC power delivered by the solar PV system. Different inverter technologies are available in the market which support different levels of starting current requirement and hence affects the kind of equipments that can operate on the solar PV system. 

Now a day’s hybrid inverters are in the scene that automatically switches between 2 or more sources of power. These inverters have in-built automatic data logger, charge controllers, MPPT controller, islanding prevention, and various other kinds of protections much needed to keep your solar installation, equipments and the premise safe.      
The size of the inverter is kept normally 1.5 times the size of the solar PV system i.e. if the panel size is of 520 W then the inverter should be of 780 W. The inverter’s size is kept higher to prevent throttling of power output of the PV panel.

Solar installation companies, often called integrators, can complete a small roof-top project within a few weeks. Of all the components of a solar PV plant, solar module accounts for nearly 55 per cent of the total project cost. The investment primarily depends upon the size of the power plant. 
So, are you ready for the order?