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HMT Electronics

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ELECTRICAL ASSEMBLYIt is the main section of HMT electric departments. There are

preparing the panel board for the various machines which are used in various operations they are mostly grinder machine and lathe machine panel prepare.

All the controls and relaying mostly for the panels of the machine such as - Push Button Contactor Thermal over load relay Timer Miniature circuit Breaker Fuses & limit Switches. Starters

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PUSH BUTTONA push button is a device that provides

control of an equivalent by pressing button. A push button is shown in figure. The contacts are operated by a button. Two sets of contact, one is normally open [N/O] and normally closed [N/C] are provided in a push button. When the push button is pressed by applying a force, the N/C contact opens and N/O contact closed. The push button stays in its depressed condition as long as it is held pressed. When the pressure on the push button is released, a spring inside the push button brings the contracts back to their initial positions.COLOUR CODING OF PUSH BUTTON

Colour Operation

Red Stop or Off

Green Start or On

Yellow Intervention

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CONTACTORSA contactor is a mechanical switching device

having one position of rest corresponding to the position of the main contacts either open or closed operated otherwise than by hand, capable of making, carrying and over load condition the speed of make and break being independent of the operator.

There are various types of contactors available. They are electromagnetic contactors, pneumatic contactors, electro pneumatic contactors, latched contactors etc. The detail of an electro magnetic contactor given below.

ELECTROMAGNETIC CONTRACTOR -Construction - Is has got a coil which is to

be connected across a voltage according to its rating. It will have contracts normally open [N/O] and some normally closed [N/C].

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Over load relayOverload relay is to be used in control

circuits for protection purpose against over load. It this relay a bimetallic strip is provided.

A heating coil is wound on the strip, which carries the line current of the circuit. In case of over load current flowing through the coil the bimetal bends considerably and opens a normally open contact or close a normally open contact as shown in fig. The opening or closing of the contact of the relay during overload can be utilized in tripping off the circuit in which this relay has been employed.

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These are two type of timers1.Electronic Timer2.Electro pneumatic timer

Timer are the electrical components used for setting the time in which contacts get changed. It is used for connection convert into star-delta depending on the timer rating breaking time period setting. It is use for the protection of the machine. It is used in interlocking CKL.

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MINIATURE CIRCUIT BREAKERMiniature circuit breaker consists of

a contact in series with over load thermal coil which mechanically causes the opening of contact to isolate the faculty circuit. In some of the MCB'S auxiliary contacts for initiating a remote alarm of visual induction is provided.

Fuse and MCB's are is fact used to isolate a system from the supply in case of

Over loadShort circuitUnder voltage

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FUSESA fuse is an over current protective

device with a circuit opening fusible member which may be a thin wire or a trip directly heated or destroyed by the current passing through it. The thin wire on strip is placed in series with the circuit to be protected.

Fuses are of two types:-1. Rewirable fuse 2. Cartridge fuse.

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LIMIT SWITCHESA limit switch is a mechanically operated

device, the prime function of which us to open or closed a contact in a circuit when a certain limit, physical distance covered by a device operated by a motor has been reached.

A limit switch is either stationary and actuated by some moving member or it moves with the machine and is actuated by a stationary member. A limit switch usually will have one normally open and normally closed contact.

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C.N.C. MACHINESCNC (Computer Numerically

Controlled) work on binary system Machining centre: A machine

which capable to performing multiple operations on a work piece in a single set up like milling, drilling, boring and tapping.Main parts of CNC Machine Center

Bed Saddle Column Table Servomotor Ballscrew

Spindle Tool Changer And Machine Control Unit

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Higher flexibility

Increase productivity

Consistent quality

Higher accuracy

Less rejection

Reliable operations

Reduce scrap rate

Reduce non-productive time

Reduce manpower

Shorter cycle time

Automatic tool change

Lesser floor space

Complex machining


Greater machine utilization

Tooling cost reduced (Jig &


Increase operational safety

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WINDING SECTIONIt is the main section of HMT where the maintenances and

repair of A.C. and D.C. machine winding is made by workers.Different types of machines came here for repairing,

maintenance and rewinding. Which are as follows.A. C. Induction motor.A. C. slip ring squirrel cage motorUniversal MotorTransformer.

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In induction motor has two types.Squirrel cage induction motor.Slip ring induction motor.

An induction motor consists essentially of main two parts.Stator.Rotor.

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STATOR & ROTORStator is a stationary part of an induction motor.

It is cylindrical structure built up of dynamo grad laminations. The laminations are either 0.35 or 0.50 MM thick. Stator carries a three-phase wdg and is perform a 3-phase supply. It is wound for a definite number of pales, the exact no. Of poles being determined by the requirement of speed. Greater the no. Of poles, lesser the speed and vise versa. When three phase supply given to the stator wdg. It produces a magnetic flux which is of constant magnitude but which rotates at synchronous speed. This revolving magnetic flux induced an e.m.f. In the rotor by mutual inductance.

Rotor is the rotating part of induction motor. Various types of rotor are used in the Induction motor such as -

Squirrel cage induction motor.Double squirrel cage induction motor.Phase wound Rotor

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SLIP RING MOTORStarting torque of these motor are better than squirrel cage

motors when we drives these motors the starting condition high resistance wedgs of motor are used but after coming in its synchronous speed then only works low resistance wdg. The slip ring motors are used where high starting torque is required. For Instance

In the hoistFor liftIn the craneFor Power HammerFor battle ship purposeThe squirrel cage motor is not useful where the motor has to

start against heavy load.

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There are four main points: -1. No of slots 2. No of pitch 3. No of turns 4. Gauge of wire

Winding material:- 1. Conducting material 2. Insulating material3. Solder & flux

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ARMATURE WINDING FAULTSThere are three faults in armature winding: -

SHORT CIRCUIT FAULT: When the leads of armature coil touches each other electrically, it is called short ckt fault.

OPEN CIRCUIT FAULT: When the leads of the armature coil are released commutator segment in breakdown position called open circuit fault.

EARTH FAULT:- When coil or coil lead or commutator segment touches the body of rotor, it causes the earth fault.

TESTING METHOD OF ARMATURE 1.Series test lamp method 2.Growler testing method 3.Genral method of testing

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FAN WINDINGIt has two winding one in inner side and other is or second is in

outer side and is called running and starting wdg respectively. Starting winding have more turns on coil comparative to running wdg. Due to increase it’s starting resistance. Each coil are wounded in opposite direction or we can say that, these coils are wounded first in clock wise and then anti clock wise.

Generally super enameled copper of 33 and 35 S.W.G. are used in fan wdg. Four wires or terminal are taken out from starting and running winding.

According to the circuit, a capacitor is connected to the starting winding to start the motor so this motor is called capacitor start motor.

Exchange is provided where is water cold angse waste is utilize to cool the refrigerants from the condenser coil before entry to drier.

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SUB-STATIONThe Sub Station is an assembly of apparatus which is used to

transfer of electric supply, is called an sub station.HMT sub station is situated at Beawer Road, Ajmer. It is a source

of electrical energy for HMT Machine Tools Ltd. HMT Township and general stores.

Power house is basically a 33/11 K.V. S/S and its line dia 33KV feeders have come here one is from RSEB Madar by crossing Nasirabad road and other one is from RSEB Saradhana by crossing national hiway No. 8

Different safety equipment and precautions are arranged in these feeders, which are already shown in diagram. These feeders are coming at AVVNL Grid sub station .At a time only one feeder can be use.

In the HMT’S sub station the 11 kV supply is step down to 440 volt & then distributed to various sections of HMT factory & town ship

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The majority of the sub station in the power system are concerned with the changing of voltage level of electric supply. These are known as TRANSFORMER SUB STATION bozo transformer is the main component employed to change the voltage level.

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1. STEP UP SUBSTATION:-The generating 11kv is step up to high voltage 220kv to affect economy in transmission to electric power.

2. PRIMARY GRID SUBSTATION:- The 220 kv is transmitted by 3 phase 3 wire over head system to the city.

3. SECONDARY GRID SUBSTATION:- The 220 kv is step down into the 66 kv. The secondary sub station is out door type.

4. DISTRIBUTION SUBSTATION:- The 66/11kv are known as distribution substation. & This change to 440 or 230volt.

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