Friday, February 19, 2010

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.

Monday, February 15, 2010


In response to a question by an anonymous user.A power surge is a sudden rise in voltage for a very short duration on the power station. They occur for a very short period of time (micro-seconds) but they cause over voltages on the power station. I will mention a few causes of power surges...

Sunday, February 14, 2010

Nigeria - Powerline falls on bus killing 20

At least 20 people have been killed in southern Nigeria after a 33kV power cable fell on their bus, police have said.Another ten people have been injured and taken to Hospital in the southern provincial capital of Port Harcourt in the Niger Delta region on Saturday.The victims died of severe burns and electrocution after heavy rains loosened the power lines around the area.The fatalities are expected to rise, police said Sunday. They also say that some of the casualties were passersby...

Friday, February 12, 2010

Hydroelectric Power Station

This is a generating station which utilizes the potential energy of water at a high level for the generation of electrical energy. It uses the gravitational force of falling or flowing water. They are located in hilly areas where dams can be built and large water reservoirs can be obtained. Hydroelectricity is the most widely used form of renewable energy. Worldwide an installed capacity of 77GWe supplied a total of 2998TWe of hydroelectricity in 2006. This was approximately 20% of the world's electricity and accounted for about 88% of electricity from renewable sources...

Monday, February 8, 2010

Why are birds able to perch on power lines without being electrocuted?

Well this question has been asked for ages by people who can't understand how on earth a bird can comfortably perch on an 11kV line and not get seriously electrocuted.Many have argued that a bird's feet has no blood flowing or that the cables are well insulated, but thats false and misleading information.In-fact transmission lines carrying high voltage (HVAC) are insulated by air not any physical material unless their is need to.Insulating these cables is costly and uneconomical because of their long distance and heavy current.
The reason is because...

Thursday, February 4, 2010


A Switchgear is an apparatus that is used to switch, control and protect electrical circuits and equipment. It is essentially used with switching and interrupting currents either under normal and abnormal conditions. Switchgear is a term used to refer to combinations of switching devices and their interaction with associated control, protective and measurement systems.
They are designed to be able to clear safely any fault which may occur in the power system. They can range from domestic 240V to industrial supply of 11kV and 132kV.In industries they are used to supply current to motors, heating equipments and capacitors. There are normally two types of switchgear assemblies namely Outdoor and Indoor Switchgear assemblies. Outdoor assemblies are mounted in fenced areas and interconnected using air insulated bus-bars. Indoor assemblies are coupled together by the switchgear manufacturer within a metal enclosure...

Domestic Appliance Series – Electric Iron

This is one of the most common types of domestic appliance that is used to straighten garments.Have you ever wondered what goes inside there, well this what happens...

Monday, February 1, 2010

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.