If you can't explain it simply, then you don't know it well enough. — Albert Einstein

Types of Electrical Loads

An electrical load is a device or an electrical component that consumes electrical energy and convert it into another form of energy. Electric lamps, air conditioners, motors, resistors etc. are some of the examples of electrical loads. They can be classified according to various different factors. Some popular classifications of electrical loads are as follows.

Resistive, Capacitive, Inductive

Electrical loads can be classified according to their nature as Resistive, Capacitive, Inductive and combinations of these.

Resistive Load

  • Two common examples of resistive loads are incandescent lamps and electric heaters.
  • Resistive loads consume electrical power in such a manner that the current wave remains in phase with the voltage wave. That means, power factor for a resistive load is unity.

Capacitive Load

  • A capacitive load causes the current wave to lead the voltage wave. Thus, power factor of a capacitive load is leading.
  • Examples of capacitive loads are: capacitor banks, buried cables, capacitors used in various circuits such as motor starters etc.

Inductive Load

  • An inductive load causes the current wave to lag the voltage wave. Thus, power factor of an inductive load is lagging.
  • Examples of inductive load include transformers, motors, coils etc.

Combination Loads

  • Most of the loads are not purely resistive or purely capacitive or purely inductive. Many practical loads make use of various combinations of resistors, capacitors and inductors. Power factor of such loads is less than unity and either lagging or leading.
  • Examples: Single phase motors often use capacitors to aid the motor during starting and running, tuning circuits or filter circuits etc.

Types of loads in power system

Domestic load / residential load

Domestic load consists of lights, fans, home electric appliances (including TV, AC, refrigerators, heaters etc.), small motors for pumping water etc. Most of the domestic loads are connected for only some hours during a day. For example, lighting load is connected for few hours during night time.

Commercial load

Commercial load consists of electrical loads that are meant to be used commercially, such as in restaurants, shops, malls etc. This type of load occurs for more hours during the day as compared to the domestic load.

Industrial load

Industrial load consists of load demand by various industries. It includes all electrical loads used in industries along with the employed machinery. Industrial loads may be connected during the whole day.

Municipal load

This type of load consists of street lighting, water supply and drainage systems etc. Street lighting is practically constant during the night hours. Water may be pumped to overhead storage tanks during the off-peak hours to improve the load factor of the system.

Irrigation load

Motors and pumps used in irrigation systems to supply the water for farming come under this category. Generally, irrigation loads are supplied during off-peak or night hours.

Traction load

Electric railways, tram cars etc. come under traction loads. This type of loads reaches its peak during morning and evening hours.

Some other classifications of electrical loads

According to load nature

  • Linear loads
  • Non-linear loads

According to phases

  • Single phase loads
  • Three phase loads

According to importance

  • Vital electrical loads (e.g. required for life safety)
  • Essential electrical loads
  • Non-essential / normal electrical loads
Electrical loads may also be classified in may different manners, such as according to their functions.
Read More...

The Future of Solar Energy in India

India, with its booming economy and humongous population of over 1 billion, has always faced shortage of energy. Even though the country is among the largest producers of electricity in the world, it is hardly ever able to meet the electricity requirements of its ever-so-rapidly increasing population. At present, almost 53% of India’s energy requirements are met with coal; going by the predictions, the coal reserves of the country will not last beyond 2050. [coal power plant]. It is common knowledge that over 72% of the population of this third world country still resides in villages, with only about half of its rural population getting access to electricity. It is high time India moved to renewable ways to feed its population its fair-share of electricity.

Solar energy has emerged as the most viable and environment-friendly option for India to cater to the energy requirements of one and all—including the 50% of its rural inhabitants who still live without electricity. A typical solar system is very easy to set up and just entails installing solar panels correctly in order for it to work. Quite a few people were already aware of its benefits and were really quick at setting their properties up with solar systems; in fact, the utilization of solar energy in India is nothing new and has existed in select locations for quite some time now. However, it has yet to pick up steady momentum.
the future of solar energy in India
The future of solar energy in India is as bright as that of the sun the solar systems derive power from. A brief overview of why India will definitely turn to solar power sooner or later is as follows:

1. Geographical Advantage
geography wise installed solar capacity in India
How long can India ignore the looming threat to its fossil fuel reserves? The geographical location of India is such that it can not only produce enough energy to meet its own requirements, but also produce enough energy for the entire world! Because it falls in the tropical region, it receives generous amounts of solar radiation all through the year amounting to nearly 3,000 long hours of sunshine. In India, there are top five states which have highest renewable energy capacity where solar modules are able to produce ample amounts of electricity even on overcast days.

2. Upcoming Solar Projects in India
The states of Andhra Pradesh, Gujarat, Madhya Pradesh, Rajasthan, Punjab, Haryana and Maharashtra have incredulous amounts of potential to tap solar energy, owing to their strategic location. At present, the Thar region in Rajasthan is home to some of the best solar projects of the country, generating close to 2,100 GW power. Gujarat houses one of the largest solar power plants in India. Last year saw Indian government has been approved of a master plan envisaging the upgradation of 50 of India’s cities to blossoming solar cities.

3. How to Use Solar Energy in Multiple Applications Around You?
One more reason as to why the future of India’s electricity lies inevitably in harnessing solar energy is because of the number of ways in which the radiation of the sun can be put to use—from solar panels that are the backbone of any solar system, solar inverters, solar street lights, solar UPSs, solar fans, solar lanterns, solar cables, solar mobile chargers, solar power conditioning units, solar home systems, solar road safety equipment and solar fencing to even solar CCTV cameras!
solar energy powered appliances around you
4. Highly Advantageous at Cheap Cost
It is true that solar panels and solar systems are slightly expensive to purchase, to begin with. It is, however, also true that solar systems once set up help save money, from the moment on! Solar panels usually have a lifespan of around 25 years and are definitely worth the investment in every respect. The use of solar energy to power electrical appliances eliminates any dependency whatsoever on the constant supply of electricity to any place. Solar power is also good riddance of hefty monthly electricity bills for the common man.

5. Employment Prospects
The transition to the utilization of solar energy is an imminent and long-impending one. It is only a matter of time before we see an entire solar sector come up. The persistent problem of unemployment in India will definitely also get better and the unemployed youth will be able to see the light of day with the creation of more and more jobs.
number and type of jobs created in India's solar sector
Even though many people have already taken to installing solar panels in their homes and offices for meeting their energy requirements on a daily basis, there is still a long way to go before India becomes a complete solar nation.
Read More...

Economic choice of conductor size - Kelvin's law

As economy is one of the most important factors while designing any transmission line, the cost of required conductor material is a considerable part. Thus, it becomes vital to select a proper size of the conductor. The most economic design of a transmission line is for which the total annual cost is minimum. Total annual cost can be divided into two parts, viz. annual charges on capital outlay and running charges. Annual charges on capital outlay include depreciation, interest on the capital cost, maintenance cost etc.. The cost of energy lost during the operation is counted in running charges. Regarding this, there are two important points that must be noted -
  • if the cross-sectional area of the conductor is decreased, the total capital cost of the conductor decreases but the line losses increase (resistance increases with the decrease in the conductor size, hence, I2R loss increases)
  • whereas, if the cross-sectional area of the conductor is increased, the line losses decrease but the total capital cost increases.
Therefore, it is important to find the most economical size of the conductor. Kelvin's law helps in finding this.
[Also read: Economic choice of transmission voltage]

Kelvin's law for finding economic size of a conductor

Let, area of cross-section of conductor = a
annual interest and depreciation on capital cost of the conductor = C1
annual running charges = C2
Now, annual interest and depreciation cost is directly proportional to the area of conductor.
i.e., C1 = K1a
And, annual running charges are inversely proportional to the area of conductor.
C2 = K2/a
Where, K1 and K2 are constants.
Now, Total annual cost = C = C1 + C2
                 C = K1a + K2/a
For C to be minimum, the differentiation of C w.r.t a must be zero. i.e. dC/da = 0.
Therefore,
Kelvin's law for economic choice of conductor size

"The Kelvin's law states that the most economical size of a conductor is that for which annual interest and depreciation on the capital cost of the conductor is equal to the annual cost of energy loss."
From the above derivation, the economical cross-sectional area of a conductor can be calculated as,
a = √(K2/K1)

Graphical illustration of Kelvin's law

As the annual cost of conductor is directly proportional to size of the conductor, it is shown by the straight line C1 in the figure. Annual cost of energy loss is shown by the curve C2. The total annual cost curve is obtained by adding the curve C1 and C2. The lowermost point on total annual cost curve gives the most economical size of the conductor which corresponds to the intersection point of curve C1 and C2. So, here, the most economical area of cross-section of the conductor is represented by ox and the corresponding minimum cost is represented by xy.

Limitations of Kelvin's law

Although Kelvin's law holds good theoretically, there is often considerable difficulty while applying it in practice. The limitations of this law are:
  1. It is quite difficult to estimate the energy loss in the line without actual load curves which are not available at the time of estimation.
  2. Interest and depreciation on the capital cost cannot be determined accurately.
  3. The conductor size determined using this law may not always be practicable one because it may not have sufficient mechanical strength.
  4. This law does not take into account several factors like safe current carrying capacity, corona loss etc.
  5. The economical size of a conductor may cause the voltage drop beyond the acceptable limits.

Modified Kelvin's law

The actual Kelvin's law does not count the cost of supporting structures, erection, insulators etc.. It only accounts for the capital cost of conductor and corresponding interest and depreciation. Also, for underground cables, the cost of insulation and laying is not considered in the actual Kelvin's law. To account for these costs and to get practically fair results, the initial investment needs to be divided into two parts, viz (i) one part which is independent of conductor size and (ii) other part which is directly proportional to the conductor size. For an overhead line, insulator cost is almost constant and the cost of supporting structure and their erection is partly constant and partly proportional to the conductor size. So, according to the modified Kelvin's law, the annual charge on capital outlay is given as, C1 = K0 + K1a. where, K0 is an another constant. The differentiation of total cost C w.r.t. to the area of conductor (a) comes to be same as derived above under the heading Kelvin's law.
The modified statement of Kelvin's law suggests that the most economical conductor size is that for which the annual cost of energy loss is equal to the annual interest and depreciation for that part of capital cost which is proportional to the conductor size.
[Also read: Economics of power generation]
Read More...

Economic choice of transmission voltage

While designing any transmission line, economy is one of the most important factors the engineer must consider. An electrical power transmission line must be designed in such a way that the maximum economy is achieved. Economics of electric power transmission is influenced by various factors such as the right of way, supporting structures, conductor size, transmission voltage etc. Transmission voltage closely influences the economics of power transmission. Generally, electric power is transmitted using 3-phase AC system at high voltages. Before studying how to choose economic transmission voltages, one should know the advantages and limitations of high voltage transmission.

Advantages of high voltage transmission

  • Efficient transmission of larger amounts of power:
    In a 3 phase AC system, power is calculated as P=√3*VIcosɸ. It is clear that, for a large amount of power to be transmitted at a lower voltage, the amount of current will be very large. Let's take an example, 200 MW of power is to be transmitted at 11kV and consider cosɸ = 0.8 lagging. In this case, the amount of current that will flow through the line would be 200,000,000 / (√3 * 11,000 * 0.8) ≈ 13,122 A. For safely carrying this much large current, a conductor with very large diameter or much more number of conductors in bundled form may be required. And if the same power is transmitted at 220kV, the current would be 200,000,000 / (√3 * 220,000 * 0.8 ) ≈ 656 A. As the power lost in a conductor is given as I2R, you can see large saving in losses can be achieved by transmitting electricity at higher voltages. From this example, it is clearly not feasible and practical to transmit larger power at lower voltages. Also, transmission of electricity at higher voltages is more efficient.
  • Saving in conductor material: As shown above, for the same amount of power transmitted at a higher voltage the current will be relatively lower. Current carrying capacity of a conductor depends on the diameter of the conductor (conductor size) along with few other factors. That means, for larger currents to be transmitted, the conductor size must be larger. Hence, transmitting power at higher voltages will reduce the amount of current to be carried and consequently the required conductor size would also be lesser.
  • Improved voltage regulation:
    Decreased current will also result in decreased voltage drop across the line. Voltage regulation is defined as (VS  - VR)/VS. As voltage drop is decreased, the difference between sending end voltage and receiving end voltage is also decreased. Thus, voltage regulation is improved.

Limitations of high transmission voltage

With increase in the transmission voltage
  • cost of insulators increases
  • cost of transformers increases
  • cost of switchgear increases
  • cost of lightning arrestor increases
  • cost of support towers increases (as taller towers with longer cross arms are required)

Economic choice of transmission voltage

From the above advantages and limitations of high voltage transmission, we can say that with increase in transmission voltage the cost of conductor material can be reduced and the efficiency can be increased. But the cost of transformers, insulators, switchgear etc. is increased at the same time. Thus, for overall economy, there is an optimum transmission voltage. The limit to use of higher transmission voltage is reached when the saving in cost of conductor material is offset by the increased cost of transformers, switchgear, insulators etc. The economical transmission voltage is one for which the sum of cost of conductor material, transformers, switchgear, insulators and other equipment is minimum.
economic choice of transmission voltage
If the power to be transmitted and the length of transmission are known, calculations are made for various transmission voltages. Initially, some standard transmission voltage is selected and the relative total cost of equipment is determined. A graph is drawn for the total cost of transmission with respect to various transmission voltages as shown in the figure at right. The lowest point on the curve gives the optimum transmission voltage. As here in the graph, point P is the lowest and the corresponding voltage OA is the optimum transmission voltage.
The above method of finding economical transmission voltage very rarely used as it is hard to pre-determine the costs of various equipment. Instead, an empirical formula, according to the American practice, is used. According to this formula, an economical transmission voltage for a 3 phase AC system is given as,
formula for economic choice of transmission voltage
Where, V = line voltage in kV
       P = maximum power per phase (in kW) to be delivered over single circuit
       L = distance of transmission in km
Economical transmission voltage depends on the power to be transmitted and the length of transmission. If the power to be transmitted is large, cost per kW of terminal equipment reduces. This results in increased economic transmission voltage. If the distance of transmission is increased, saving in the cost of conductor material can be significantly increased by increasing the transmission voltage. 

[Also read: Power generating stations]
Read More...

Basics of Electrical Power Transmission System

Electrical energy, after being produced at generating stations (TPS, HPS, NPS, etc.) is transmitted to the consumers for utilization. This is due to the fact that generating stations are usually situated away from the load centers. The network that transmits and delivers power from the producers to the consumers is called the transmission system. This energy can be transmitted in AC or DC form. Traditionally, AC has been used for years now, but HVDC (High Voltage DC) is rapidly gaining popularity.

Single line diagram of AC power transmission system

A typical single line diagram that represents the flow of energy in a given power system is shown below:
single line diagram of electric power transmission system

Electrical power is normally generated at 11kV in a power station. While in some cases, power may be generated at 33 kV. This generating voltage is then stepped up to 132kV, 220kV, 400kV or 765kV etc. Stepping up the voltage level depends upon the distance at which power is to be transmitted. Longer the distance, higher will be the voltage level. Stepping up of voltage is to reduce the I2R losses in transmitting the power (when voltage is stepped up, the current reduces by a relative amount so that the power remains constant, and hence I2R loss also reduces). This stage is called as primary transmission.
The voltage is the stepped down at a receiving station to 33kV or 66kV. Secondary transmission lines emerge from this receiving station to connect substations located near load centers (cities etc.).
The voltage is stepped down again to 11kV at a substation. Large industrial consumers can be supplied at 11kV directly from these substations. Also, feeders emerge from these substations. This stage is called as primary distribution.
Feeders are either overhead lines or underground cables which carry power close to the load points (end consumers) up to a couple of kilometers. Finally, the voltage is stepped down to 415 volts by a pole-mounted distribution transformer and delivered to the distributors. End consumers are supplied through a service mains line from distributors. The secondary distribution system consists of feeders, distributors and service mains.

Different types of transmission systems

  1. Single phase AC system
    • single phase, two wires
    • single phase, two wires with midpoint earthed
    • single phase, three wires
  2. Two phase AC system
    • two-phase, three wires
    • two-phase, four wires
  3. Three phase AC system
    • three-phase, three wires
    • three-phase, four wires
  4. DC system
    • DC two wires
    • DC two wires with midpoint earthed
    • DC three wires
Electric power transmission can also be carried out using underground cables. But, construction of an underground transmission line generally costs 4 to 10 times than an equivalent distance overhead line. However, it is to be noted that, the cost of constructing underground transmission lines highly depends upon the local environment. Also, the cost of conductor material required is one of the most considerable charges in a transmission system. Since conductor cost is a major part of the total cost, it has to be taken into consideration while designing. The choice of transmission system is made by keeping in mind various factors such as reliability, efficiency and economy. Usually, overhead transmission system is used.

Main elements of a transmission line

Due to the economic considerations, three-phase three-wire overhead system is widely used for electric power transmission. Following are the main elements of a typical power system.
  • Conductors: three for a single circuit line and six for a double circuit line. Conductors must be of proper size (i.e. cross-sectional area). This depends upon its current capacity. Usually, ACSR (Aluminium-core Steel-reinforced) conductors are used.
  • Transformers: Step-up transformers are used for stepping up the voltage level and step-down transformers are used for stepping it down. Transformers permit power to be transmitted at higher efficiency.
  • Line insulators: to mechanically support the line conductors while electrically isolating them from the support towers.
  • Support towers: to support the line conductors suspending in the air overhead.
  • Protective devices: to protect the transmission system and to ensure reliable operation. These include ground wires, lightening arrestors, circuit breakers, relays etc.
  • Voltage regulators: to keep the voltage within permissible limits at the receiving end.
Read More...