Busbars

Strain Busbars

Busbars are electrical conductors which serve to pool up the power from different sources and distribute them to various feeders.  Busbars are generally made of copper or aluminium.  Busbars are found in substations, switchboards, distribution boards, etc. 

Busbars are sized according the current they carry.  Busbars are either flat or hollow.  This is to facilitate heat dissipation.  Busbars are supported by means of insulators.  Busbars are made flat or hollow to avoid the skin effect. 

Indoor busbars used in switchboards and distribution boards are usually flat. 

Outdoor busbars can either be hollow or strained.  Hollow busbars are rigid and are supported by means of hollow insulators.  It is easy to maintain these insulators as they are closer to the ground.  Their higher surface area minimizes the effect of corona.  They are more reliable.  However, they are expensive and require a larger area. 

Strained busbars are an overhead system of wires supported by insulators mounted usually on metallic frames.  The conductors are usually made of ACSR (Aluminium Core Steel Reinforced)

Other types of busbar include Insulated Phase busbars which consists of a rigid bar enclosed by a metallic enclosure and supported by insulator and Gas insulated busbars which consist of rigid conductors placed in a cylindrical tube filled with Sulphur hexafluoride gas)

Effect of Corona on Insulation

Corona refers to the luminous discharge when the fluid around a conductor gets ionized. 

Fractional Horse Power motors

Fractional HP Motors are motors whose power rating is less than one horse power i.e. 746 watts.  Fractional Motors range from an output of 1/20th horsepower to 1 horse power.  Motors less than 1/20th horse power are called sub-fractional horsepower motors.  

Fractional motors find wide application in automobiles for rolling up windows, windshield wipers, etc.  Induction motors, synchronous motors and dc motors can be used as Fractional HP motors.  

Fractional HP Motors also find wide application in household appliances.   Fractional Horse Power motors used in household application such as exhaust fans, blowers etc are usually single phase.  They are generally of the split phase or the capacitor run type.  

Extremely low speeds can be obtained using Fractional HP motors by means of suitable drives. 

Stepper motors and servo motors are also types of Fractional HP motors.  Fractional HP motors are also available as geared motors.

Lugs in wiring

Lugs are components which are widely used in electrical wiring.  They are used to connect cables to terminals.  Lugs enable quick disconnection of cables and reconnection.  They also protect the uninsulated ends of wires and cables.

Besides, they enable proper contact between terminals and wires.  Lugs are available in a wide range of shapes.  Some common types are the pin type lugs generally used in push type connections, fork type lugs are used in screw terminals and circular lugs. 

Lugs also serve to enable the connection of cables with large cross-sections to smaller terminals. Lugs are usually made of aluminium or copper.  They are tin plated to prevent oxidation.  The lugs are joined to the wire or cable by crimping, soldering or welding.   Some lugs are provided with PVC sheaths to protect against electric shocks.  Lugs are annealed to offer better ductility.

Circular Lug

Some lugs have inspection holes which enable full insertion of the cable into the lug .

Equipotential Bonding

A pipeline connected to the earthing grid

Equipotential bonding refers to the maintenance of all metallic objects in a vicinity in the same potential.  It is a widely followed practice in earthing.  Equipotential bonding ensures that all metallic objects are at the ground potential.  This eliminates the risk of shock occurring when someone accidentally comes in contact with objects at different potential.  An area where all the objects are kept at the ground potential is called the earthed equipotential zone. 

For instance, in a building there are many metallic fittings which are not part of the electrical distribution system such as bathroom fittings, pipes, metallic supports, steel supports used during construction etc.  Should these fittings become live due to a leak in an electric circuit, they can pose a danger of electrocution.  Hence, it is important that all metallic objects are kept at the ground potential by connecting them to the earthing grid. 

Pipes which are made of plastic or PVC need not be connected to the equipotential network.  In areas, which are likely to be wet such as bathrooms, the fittings are usually connected by an additional link to the equipotential grid.  This is known as supplementary bonding.  

Electronic devices such as computers and telecom equipment sometimes have a separate earthing pit.  This is unsafe as it permits the rise of potential between the main earthing grid and the separate electronic earthing pit in the event of lightning strike.  This can result in damage to the equipment. 

image courtesy : dehn.de

Running Three Phase motors with single Phase supply

A three phase device can be run with a single phase converter by means of a static capacitor phase converter.  The phase converter converts the single phase voltage into three voltages which can be connected to the three phases of the motor. 

The single phase supply is connected to two of the motor phase terminals.  The other terminal is connected to one of the single phase terminals through a capacitor.  The capacitor introduces a phase shift which causes the third phase to be out of phase by 120 degrees.  The produces the rotating magnetic field required for starting and running the three phase motor.    

In motors, the starting current is usually about six times the rated current.  Hence, a bigger value capacitor is usually used as a starting capacitor.  The starting capacitor is kept in line by means of a switch which is opened as the motor picks up speed. 

Phase Sequence Relay for motors

Phase sequence protection is an important safety for motors.  Reversing the phase sequence causes the motor to reverse its direction of rotation.  This can cause serious damage and injury to personnel if for instance, the motor is coupled to cutting equipment, or conveyor belts.  

The phase sequence indicator works by monitoring the phase sequence continually and preventing the motor from starting if the phase sequence has been reversed in the supply.