Electrical Machines

MODES OF OPERATION OF PLC The various modes of operation of PLC's are 1. CLEAR program memory mode 2. PROGRAMMING mode 3. RUN mode 4. TESTING program mode 5. DIAGNOSTIC test mode 6. ENTER/CHANGE Access Code When PLC is put in CLEAR mode, the user program stored in the PLC memory can be cleared. Now all the memory is free for entering a new program. A new program can now by bringing the PLC into PROGRAMMING mode. Program instructions are entered one by one. After entering the program, the program execution can be checked by putti be checked by putting PLC in TEST program in test mode, PLC executes the user program but energise the outputs, only LED displays for outputs energised. Thus program working can be checked thout actually energising the outputs. This avoids damage machinery on account of incorrect program. The machine an be run continuously by bringing the PLC in RUN mode. In RUN mode, the PLC first reads the status of input devices and store then in the memo...

In the control circuit start relay 'S' gets energised arremains held only when the "O" contacts of all the master controllers (Hoist, LT and CT) are in closed position ie., levers are in OFF position. On moving the drum switch handle to position  1. on the right for hoist operation contact UF losing of this contact energises contactor 1M ed the up limit switch contact is closed. When actor TM energises it starts the motor to raise weight up at a slow speed because all the resistances are included in the rotor circuit of the electrical motor . 2. When contact 1M is energised its NC contacts 1M and 1M are open and acts as interlock for downward operation. Contact 1M closes and timer 1T is energised. 3. After a preset time the contacts of 1T, 1T, closes. Now if the drum switch is moved to position 2. The NO, closes and 1 contactor is energised and a set of resistance is removed from rotor circuit of hoist motor and it runs at a higher speed. Contact 1R...

head cranes are used for shifting heavy weights limited area. The area is decided by the span of long travel motion and cross travel motion of the crane. Weight in the defined area are picked up and shiftesta tony desired position with the help of three motions. 1. Hoisting, lowering 2. Longtravel (ie. Forward, Reverse) 3. Cross travel (which is ir to long travel) An overhead crane has to handle heavy weights in terms of thousands of kgs requiring high starting torques in all the motions. So we use slip ring induction motor for all. motor The crane moves on the rails for long travel driven by slipning induction motor known as long travel (LT) motor. This motor is installed on the structure itself. On the structure itself rails are mounted for cross travel (CT) trolley: The CT trolley moves on these rails by a CT motor mounted on the trolley itself. The hoisting motor is also installed on the trolley. Hoisting is done by a rope wound on the drum attached to the moto...