Electrical Circuits

Electrical Circuits



AN ELECTRICAL CIRCUIT
The circuit shown below has a power source, fuse, switch, two lamps and wires connecting each into a loop or circle. When the connection is complete, current flows from the positive terminal of the battery through the wire, the fuse, the switch, another wire, the lamps, a wire and to the negative terminal of the battery. The route along which the electricity flows is called an electrical circuit.

Shielded Wires

Shielded Wires


A shielded wire is a type of electrical wire made of several layers of covering and conductors. It is useful for different types of applications where protecting covering of conductor is needed. Due to the specific characteristics it has found varieties of applications in different fields. It show preferable electric attributes. Each of the its cores is protected and the ground wire is closely contacted with the shield layer.

Shielded Wire

Construction of Shielded Wires
A shielded wire must have a protecting coat of layer outside it. It has a central core and an insulation layer provided. Then there is a shield layer which separates the insulation layer from a ground wire. This layer is made by a composite tape having a metal surface along with an adhesive surface. The metallic surface of the wire is longitudinally folded so that it can cover a portion of the adhesive surface. Then this tape is helically binded with the folded layer on the outer cover so that to form alternate helical patterns of the metal and adhesive layers. A sheath is used to wrap the shielded layer and the ground wire. After it the sheath layer is attached to the adhesive layer while the ground wire remains in touch with the outer metallic layer. The metal surface used inside makes the shield.

Typical Types of The conventional shielded Wires Are:

* A single core type shielded wire
* Double core type shielded wires

Composition of Shielded Wires
The shielded wire is composed of a coaxial core and many outer layers:

* A central conductor
* A plastic insulation layer ( which is made of polyethylene - a ethylene copolymer, or foamed materials)
* A shield layer which is made of soft-copper wires or tin plated soft copper wires. Each wire is longitudinally placed along the plastic insulation layer.
* A ground wire which is made of bare soft copper wire or soft copper wire covered with tin (Sn). It is laid along the length of the coaxial core or is spirally wound thereabout with a relatively large pitch.
* A plastic sheath which is made of polyethylene or polyvinyl chloride. This layer covers the coaxial core and the grounded wire.

Applications of Shielded Wires
Shielded wires are used and applied in a large number of fields and industries. Some of the most important of them are:

* Hydro power stations
* Automation Industry
* Tool Making Machinery
* Conveyor Systems
* Steel Industry
* Chemical Industry
* Cement Industry

Electric Meters

Electric Meters



An electric meter or electricity meter is a device used for measuring the amount of electrical energy supplied to a residence or company.

There are different types of electric meters available in the market, the most common of them being the (kilo) watt-hour meter or a joule meter. These meters generate invoice of the electricity after recording the measured values. The meter also records the time period for which the electricity was used.

Electric Meter

Unit of Measurement
These meters measure electricity in kilowatt-hour. A kilo watt hour can be explained as the amount of energy used by a load of one kilowatt over a period of one hour, or in other words 3,600,000 joules.

Types of Electric Meters
There are two types of prevalent electric meters being used all over the world. These meters operate by continuously measuring the instantaneous voltage (volts) and current (amperes) and multiplying the two for giving instantaneous electrical power (watts). The two types of electric meters are:

Solid State Meters
Solid state meters are modern electricity meters that display the power used on an LCD, and can be read automatically. These meters are gaining popularity the world over. These meters record useful information like:

* Maximum demand
* Power factor
* Reactive power used etc.

They meters can also have an electronic clock mechanism for computing a value, rather than an amount of electricity consumed. The pricing also varies according to the time of day, day of week, and seasonally.

Most of these meters use a current transformer for measuring current. This essentially means that the main current-carrying conductors need not pass through the meter itself. It can thus be located remotely from the main current-carrying conductors.


Electromechanical Meters
The most commonly used electricity meter is the electromechanical induction meter. This meter operates by counting the number of revolutions of an aluminium disc. This disc rotates at a speed proportional to the power. Thus the number of revolutions is proportional to the energy usage. The meter consumes a small amount of power, around 2 watts. An electromechanical induction meter's performance and accuracy can be affected by creep phenomenon. This occurs when the meter disc rotates continuously with potential applied and the load terminals open circuited.