EDUCATION

                              ELECTRICAL TRACTION : ELECTRIC TRACTION :            Electric traction means a locomotion in which the driving force is derived from electric motors.  There are many advantages of electric traction over other forms of jocomotion in the current days of traction in any country of development.  In fact, it is a fast-paced, safest and economical way of transporting and transporting goods to the modern day. In this type of drive the locomotive is equiped with a d.c series motor or ac series motor or three phase induction motor. The electric energy is directly fed into the motor and torque developed by the propelling the train.                             TRACTION SYSTEMS : The most commonly used traction methods are as follows. 1.  Steam engine drive  2. Internal combustion engine drive  3. Battery electric drive  4. Internal combustion engine electric drive  5. Electric drive               IDEAL TRACTION SYSTEM OF REQUIREMENTS : 1.The u

CLASS(E) FIRE EXTINGUISHER :   The following fire extinguisher is commonly used in electrical companies to extinguish fires.                         1. Soda acid type fire extinguisher            2. Chemical foam type fire extinguisher             3. Carbon - tetra - Chloride type fire extinguisher  1 . SODA ACID TYPE FIRE EXTINGUISHER:                                                     These types of fire extingushers are commonly used.  The cost is very low.  The concentrated sulfuric acid is sealed in a glass tube and the soda bicarbonate solution is kept both soluction are placed in a container and the handle on the top of the tool is used to extinguish the fire.  This will cause the glass bottle to dissolve and the acid to form carbonated oxide gas together with the soda bicarbonato solution.  The gas of this gas is sure to spray rapidly out of the liquid.  You have to spray this on it.  This can cause a fire to extinguish rapidly.  The solutions within this tool should

                        PROCEDURE FOR SHUTDOWN                                               Step 1 : Before shutting down, thoroughly study the circuits and identify which circuit breakers or control switches wants to open.  An alternative to the Consumer is to carefully study the supply mains, parallel feeders, duplicate busbar, etc.                                           Step 2 :  Keep the circuit breaker open and locked If you cannot lock the switch, remove the fuse and lock it and it should be kept secure.  Locking the circuit breaker and keeping the fuses secure will eliminate the possibility that the supplier may return the wrong supply unknowingly while working on the line.  Neutral links need to be disconnected.  In the event of some fault, the potential of the neutral is increased, so the neutral link must be split.                                             Step 3 : Hang the "Man - at - work" notice board on the circuit breaker or switch handle, This causes the

                              DYNAMIC BRAKING   DYNAMIC BRAKING (OR) RHEOSTATIC BRAKING :                         Dynamic braking is also called rheostatic braking. In this method of braking, a motor is disconnected from the supply and operated as a generator driven by the kinetic energy of the rotor. The kinetic energy of rotation is converted into electric energy, which is dissipated in the external resistance connected across the motor at the braking instant. The advantage of this type of braking is that no energy is required from the supply to brake the motor. This method of braking can be applied to brake the D.C motors, synchronous motors and induction motors. DYNAMIC BRAKING TO INDUCTION MOTOR :                                                                  fig 1.1                In 3 phase squirrel cage induction motor, the stator is disconnected from the A.C supply mains and D.C supply is given to the stator winding as shown in fig. 1.1(b). A st

                          REGENERATIVE BRAKING : REGENERATIVE BRAKING :                       In this type of braking the motor is not disconnected from the supply but remains connected to it . The machine is made to work in such a way that it generates energy and fed it back to the supply . This type of braking is better than the above two types because no energy is wasted .  REGENERATIVE BRAKING APPLIED TO D . C SHUNT MOTOR:                                                              (a) NORMAL OPERATION                             (b) BRAKING OPERATION                                            FIG 1.1     If the emf induced in the motor is greater than the supply voltage power will be fed back into the supply . The emt induced in the motor depends upon the speed and excitation of the motor . If the field is disconnected from the supply and the field current is increased by exciting it by another source as shown in fig. 1.1( b ) , the i

                                         PLUGGING : PLUGGING :                        Plugging means phase reversal. It is a simple method of electric braking. During the braking period reverse torgue produce on the motor. A special device is required to cut of the supply as soon as the motor comes to rest. This methed of braking can be applied to both A.C and D.C motors,  Plugging applied to D.C motor :                          In D.C motor the direction of torque depends on the direction of rotation of the armature. Therefore the torque developed in D.C machine is reversed either by inter changing the field terminals or the armature terminals. But usually the connections of the armature are interchanged.  Plugging applied to D.C shunt motor                                             (a) NORMAL OPERATION                                 (b) BRAKING OPERATION                                                fig 1.1