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Showing posts from February, 2018

What is the capacitor?

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 The Capacitor.         A capacitor is formed when two conductors, usually of aluminium, are separated by an insulator sus as paper ect. For use in motors the strips are rolled together into a compact unit and placed into a sealed metal or plastic container. This may be either cylinderical or rectangular in shape and may be mounted on, in, or away from the motor. Two terminals or leads are provied for connection. The name capacitor is descriptive of the operation of the device. The capacitor acts essentially as a storage units that is,has capacity to store electricity and provides a leading current to the auxiliary or starting winding. All capacitors have this quality and all are electrically the same;they differ only in mechanical construction.     THE OIL-FILLED CAPACITOR                 This capacitor is used mainly in the permanent-split capacitor motor and for the two-value capacitor motor. The capacitor use an oil-impregnated paper as the dielectric and are permanently conne
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Auto- transformer starter

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     The starter of this type are used upto 25H.P. motors. This type of starter has autos transformer from which many tapping are taken out which give different voltages by which a big motor can be be supplied by low voltage. While in the in the star delta starter only 1/√3 times the full voltage can be given to the motor. The torque also varies with the voltage.        This starter also has overload relay, no volt coil and "OFF" switch.       In this starter the overload coil works on the magnetic effect I.e. when the current in the flows more than the normal, overload relay opens overload switch.
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Star delta starter

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.This starter is fitted above 5H.P and upto 10H.P. in this starter there is two way switch which connects the 6ends of the motor once in star then in Delta. Like D.O.L.starter it also has overload relay ,no volt coil,current adjuster and "off" switch.    When we operate the handle down it is started, the ends A2,B2,C2,of the motor become short circuited and A1,B1, C1,get the supply. The motor becomes in star and gets 1/√3times or 58% of the full voltage by which the motor takes 1/3r current of that which the motor takes by starting in delta giving full voltage. It dropping of voltage in the line. By decreasing the current the torque of the motor also decreases to 1/3rd of the torque which it will give by direct star in deta. After taking 75% speed when the handle is done on delta, the ends,C1A2,A1B2,B1C2,are short circuited and each joint gets supply which connects the supply in delta and now since the motor is full speed the back e.m.f.is full. The motor is taking full cu
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Direct on line starter.

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Direct on line starter.       This starter gives the line voltage direct to the motor. It dose not reduce the voltage. This starter is used up to 5H.P.  To connect the motor from the I.C.T.P. main switch or isolator is sufficient but the starter has the following advantage:-   (A) The motor can be made on and off quickly.     (B)It cuts the motor from the line on overloads.     (C) It prevents the motor from burning on single phase.    It has the following parts:    (1) Three straight strips which join the line direct to the motor. When "On" push is pressed these strips contact the lower strips.     (2) Forth strip works as interlock switch I.e when " On" posh is released after pressing,the 4th strip passes the current.     (3) Overload relay. This has thick wire like heater from which if more than normal current (in any one phase) flows then heating element becomes hot and the bimetallic strip placed inside it bends and it opens the overload switch which
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Starting of three phase induction motors

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Starting of three phase motors. When the motor is in standstill position and supply is given to it, the motor works like that transformer of which the secondary is short-cricuited. Thus the rotor (sec. of transformer) will take high current and thereby the stator will also take high current from the line. The following are the disadvantage of this high current:-     1.This may brunt the stator winding I.e. the installation may burst anywhere in the winding.      2.It may bring the supply voltage down and due to this the relays of other motor, running near to this motor,may trip (due to low voltage). This type of voltage drop is not allowed by supply company also. Therefore big H.P. motors are provided starters to minimise the starting current.      Motors up to 5 H.P.(A class motor upto7.5H.P.)may be connect direct to line.       TYPES OF STARTER The following are the types of the starter:-     (A) Direct on line starter.     (B) Star Delta Starter.     (C) Auto star delta
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Induction Motor

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This motor is quite different from a D.C. motor because supply is not given to its rotor (armature) but the e.m.f. is induced in the rotor  when stator is supplied which produces current in the rotor and the motor runs. Thus this motor is called induction motor. Nowadays for each work at each place A.C. single phase or 3phase motor is used. The parts of this motor are as follows:- 1.Stator. 2.Rotor. 3.End cover. 4.Bearing. 5.Fan. 1.Stator: This is made of high silicon steel strips 0.3 to 1.35mm thick combining together which are called laminated strips and combination is called laminated core. The core has open or semi closed slots. In these slots winding is done. This core is fitted in a frame so that any external mechanical injury may not take place and rotor may rotet easily. 2.Rotor: It is also made of high Silicon steel strips 0.3 to 1.35 mm thick combining together. It has closed type slots in which winding is done. The winding is done with thick strips or rods. Nowada
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