Book of the Week

Electric Motors and Drives: Fundamentals, Types and Applications (3rd Edition)
by Austin Hughes
ISBN-10: 0750647183 | ISBN-13: 978-0750647182

This is a useful and interesting book which covers fairly all the topics in the field of motors and drives. The concepts are explained clearly and the mathematics is kept to a minimum. Topics start from the basics and and cover almost all aspects of the topic. The topics covered include dc motors, induction motors theory and types as well as stepper motors. Starting methods for various motors are also adequately addressed. The book also covers drives for dc and ac motors. It also includes a selection guide for drives. Though there pictures and diagrams, more pictures could have been added. 

In all, a comprehensive book which covers all the important topics at a relatively low price. This book would be ideal for industry professionals as well as students of electrical engineering.

Permanent Magnet Synchronous Generators

Permanent Magnet Synchronous Generators are becoming the generators of choice in the wind turbine industry.  They are being increasingly used in place of induction generators (induction machines which run above the synchronous speed).  They are advantageous over induction generators as they have a higher efficiency.   Besides, they do not need a magnetizing current which needs to be fed from the grid.

The normal synchronous generator has a wound rotor with poles.  These poles in the rotor are excited by means of a dc current.  In a permanent magnetic Synchronous generator, the wound rotor poles are replaced with permanent magnets.  

The machine is often directly coupled to the wind turbine or through gears.  The AC output of the synchronous generator which has a variable frequency depending on the turbine speed is converted into DC.  This DC is converted into a sinusoidal AC voltage at the system frequency.  This voltage is then fed to the grid.

Permanent Magnet Synchronous Generators (PMSG) are costlier as the permanent magnets are made of rare earth metals.  NeFeB, an alloy of Neodymium, Iron and Boron is used to make these magnets.  The use of permanent magnets in the rotors minimizes the losses in the rotor and improve efficiency.

Lockout /Tagout

Lockout Hasp

Lockout/Tagout system is a set or procedures which prevent the accidental energization of electric equipment during maintenance.  Lockout Kits contain many types of locking systems such as 2 - Hinged Single-Pole Breaker Lockouts Breaker Lockouts which can be used to lock a breaker against operation. 

Wall Switch Lockouts prevent the operation of wall mounted switches.  Plug Lockouts prevent plugs from being connected to power sockets.  Lockout Hasps have multiple locking facility.  When more than one person is working on a machine, say, a transformer.  Each individual needs to place a lock on the Hasp.  This prevents the machinery from being energized until all people have finished their work.

Lockout Padlock with unique key

 The Lockout kit also contains a set of padlocks.  Each padlock has its own unique key.

Lockout for Plugs

When it is not possible to lock out an equipment, Tag out procedures should be followed.  Conspicuous tags should be placed.  The Tag or the lock should only be removed by the person placing it

Lockout for MCB

         All installations should have clear Lockout/Tagout policies. Employees should be trained on proper implementation of these systems

Lockout Tag

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 .