Power Factor #1

What exactly is Power Factor?
Power Factor (i.e. Cosɸ) of a circuit can be defined as:
Cosɸ = the cosine of an angle between Voltage (V) and Current (I).
R/Z = Resistance/Impedance
VICosɸ/VI = True Power/Apparent Power



The value of power factor can never be greater than 1(Unity)
It is usual practice to attach the word ‘lagging’ or ‘leading’ with the numerical value of power factor to signify whether the current lags or leads the voltage. Thus if a circuit has p.f. of 0.6 and the current lags the voltage, we generally write p.f. as 0.6 lagging.
Power factor can also be expressed as a percentage i.e. 60% lagging.

G.I.S - Gas Insulated Substations #1

A gas-insulated substation (GIS) uses a superior dielectric gas, sulfur hexafluoride (SF6), at a moderate pressure for phase to phase and phase to ground insulation. The high-voltage conductors, circuit breaker, interrupters, switches, current transformers, and voltage transformers are encapsulated in SF6 gas inside grounded metal enclosures. The atmospheric air insulation used in a conventional, air-insulated substation (AIS) requires meters of air insulation to do what SF6 can do in centimeters. GIS can therefore be smaller than AIS by up to a factor of ten. A GIS is mostly used where space is expensive or not available. In a GIS, the active parts are protected from deterioration from exposure to atmospheric air, moisture, contamination, etc. As a result, GIS is more reliable, requires less maintenance, and will have a longer service life (more than 50 years) than AIS. GIS was first developed in various countries between 1968 and 1972. After about 5 years of experience, the user rate increased to about 20% of new substations in countries where space was limited. In other countries with space easily available, the higher cost of GIS relative to AIS has limited its use to special cases. The IEEE [4, 5] and the IEC [6] have standards covering all aspects of the design, testing, and use of GIS. For the new user, there is a CIGRE application guide. IEEE has a guide for specifications for GIS.

The Stockbridge Damper

A Stockbridge damper is a tuned mass damper used to suppress wind-induced vibrations on taut cables, such as overhead power lines. The dumbbell-shaped device consists of two masses at the ends of a short length of cable or flexible rod, which is clamped at its middle to the main cable.It is placed about midway between the nodes of the vibrations i.e. where amplitude of the vibrations would be more. The vibration causes movement of the damper and energy is absorbed by the inter stand friction in the steel cable. The vibrations have low amplitude up to 5mm and high frequency of 50Hz-100Hz. A typical damper for use on a 132kV line is about 60cm long and weighs about 5kg.

THe 3Phase Syncronous Motors

The 3phase synchronous motor is widely used in industries because it can be easily converted into Single phase and 2phase.They are widely used in all Engineering field because their construction allows them to be used for various purposes.

Characteristic Features of Synchronous Motors.
1.    They run at synchronous speed. This machine will run at a constant speed which can be changed by     varying the supply frequency.
2.    They are not self starting.-The rotor and stator fields have to be excited by a separate D.C excitation voltage.
3.    They can be operated under a wide range of power factors (whether lagging or leading).This is why they are used for power-factor correction in power systems that have loads containing lagging power factors.

What Is 3-Phase Power?

When a conductor is rotated to cut magnetic fields, some electromotive force is induced according to Faradays Law. This voltage/emf is always in opposition to the main field according Lenz’s Law

E = -Ndø/dt

The voltage induced by a single winding is known as single phase winding, when rotated in a uniform magnetic field is known as single phase voltage.

A 3-Phase generator has 3 separate but identical conductors that are 120 Electrical degrees from one another. When the conductors are rotated in a uniform magnetic field, the result is 3 independent supplies of equal voltages which are displaced from each other.

A 3-Phase supply is carried by 3 conductors known as lines which are colored Red, Yellow & Blue. The currents in these cables are known as Line Currents and the Voltages are known as Line Voltages. The 4th conductor, known as Neutral is often used with the 3phase supply when the load is unbalanced.