Harmonics and Harmonics limit

Harmonics and Harmonics limit

     Harmonics stand for the unwanted AC signals or disturbances in the AC supply. In technically speaking, the fundamental AC component (e.g. 200 Hz) in the main supply comprises of 2,3,4.. times that of fundamental frequency signals (400Hz, 600Hz, 800 Hz...). The fundamental AC component is normally a pure sinusoidal signal. The Harmonic component's magnitude will be of less in amplitude compared with fundamental.

 

Fundamental and harmonic components (courtesy: online source)

Source of harmonics:

     When the non linear loads such as UPS, chargers, Computers etc. are connected with the main supply, harmonics are generated. 

Effects of harmonics:

    Due to harmonics the power losses in the line increase, poor power factor etc.

Harmonic limits:

 Voltage harmonics i.e. THD level should be < 5%

  for current harmonics the THD level should be <8%

Otherwise the Electricity board may impart penalty for the amount of harmonics generated.

What is Electrical shock? How much our body withstand with electricity? How to protect ourself from earth leakage current?

Electric shock and its prevention

We are very often or rarely sense electric shock. Then a question arises technically , What is Electrical shock? How much our body withstand with electricity?
In Practical, when we are in contact with a live electric wire or touching an electrical equipment with leakage current, a current flow in our body, then we sense the shock.

What is the safe limit of this current?
there are 5 conditions, if the current flow persist in our body and the current limits is 
1) if the current is < 2 mA(Milli Ampere), it is insensible, safe
2) if the current is 2 mA to 10 mA, it is sensible, Let go current and Harmless
3) if the current is10mA to 25 mA, Muscular Contraction occur.(Sensing the shock)
4)  if the current is 25 mA to 50 mA, Ventricular Fibrillation occur, Immediate attention is required, within 20 minutes, we have to give defibrillator to active our heart functioning.
5) > 50 mA - fatal.

How to protect ourself from earth leakage current?
1. Earthing is necessary and must for the electrical appliances used in our home.
2. Now a days ELCB ( Earth Leakage Circuit Breaker) is available in the market, which can be installed  in our house wiring along with other Switchgear. It breaks the current if the earth current is >30 mA range.ELCB will be tripped off automatically, whenever the current crosses the safe limit.

ELCB (Illustration purpose only)

Solar Net Metering

Solar Net metering

As the national electrical power demand increases, alternate energy sources play a vital role to meet out some of the energy crises. In particular, the Solar PV system’s growth is very rapid.

Net meter is a bidirectional energy meter which indicates the energy usage by a consumer and excess energy produced by the consumer and exported to the utility grid.

In a grid connected Solar PV system, the excess energy generated can be exported to the utility grid. The net meter tracks the difference of excess energy fed back to the grid and the energy consumed by the consumer.

There are two conditions,

1. If the solar energy generated units is less than the load , then the net meter runs forward, the consumer has to pay the utility company
2. If the solar energy generated units are greater than the load, then the net meter runs backward, the consumer will be credited for excess energy.

The net metering usage and its policy differ from state to state. The tariff also differs. There will be an agreement between the consumer and the utility grid company.

 Merits:

1.      As the consumer is credited for excess energy, there will be financial benefit.

2.      As the system is grid connected, no need of battery storage, its cost involved and free from maintenance.

3.      No need of two meters separately for measuring energy consumption and excess energy exported to the utility grid.

Solar MPPT Concept

Solar MPPT Concept

The usage of solar power is gaining momentum everywhere in the World in order to meet the Power Demand and also for a Pollution free World.    Though solar power is available plenty on earth, its conversion into electrical energy by using Solar panels are very common and very meager due to its low conversion in efficiency. So, it is essential to extract maximum solar power from sun by using solar panels.  

It is time for the Undergraduate / Post graduate students to undertake Solar related projects for Efficient and effective way of extracting solar power.

 

MPPT stands for Maximum Power Point Tracking. This algorithm is most predominantly used in extracting Solar power.

There are mainly two types of solar energy extraction.
1. Mechanical tracking
2. Electrical tracing using at the converter/ inverter stage.

   In Mechanical tracking, the solar panel is tilted towards the solar directions and maximum power is harvested.

  In Electrical tracking, MPPT algorithm is used in the converter / inverter stage in the solar power conversion systems by appropriately controlling the On/Off time of switching in the  converter / inverters. Compared with first method, where mechanical control has been a drawback, in the second method, maximum power can be obtained by appropriately controlling the output voltage of solar panel.