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Lift branch


									GIT                                                                                                 Chapter 2
CEB                                                                                                Lift Branch

2.1 Introduction
         Lift, or elevator, device for vertical transport of passengers or freight to different floors or levels,
as in a building or a mine. Elevators consist of a platform or car traveling in vertical guides in a shaft or
hoist way.
         During my training period I was able to train in the General Hospital lift branch. The depot
includes an electrical superintendent and a gang of technicians. They provide 24-hour breakdown service
in the hospital.
         Designs of lift equipments are strictly related to the long standing, progressively updated, which
referred to two vital matters.
                          (a)     Safety in operation.
                          (b)     Recommended dimension related to load and speed, and based on the
                                  conditions for safe operation.
         Normally the lifts are operated by electric power, where AC motors and some times DC motors
are used to move the elevator. By controlling the speed of the motor the speed of the elevator can be
changed. The direction the movement of the car can be changed by changing the current direction of the
DC motor in the case of a Dc motor or by inter changing the two phases in the case of an ac motors.
2.2 Main types of lifts
       Lifts can be categories in the view of applications used in different places.
                - Passenger lifts
                - Hospital or Bed lifts
                - Freight lifts
                - Good lifts (Dumbwaiters)
2.3 Main Components of a Lift
        All machine room we saw was in top most floor of a building. But the machine room can be
situated in the bottom of the building also. Inside it there are electric motor, control panel, over-speed
governor, etc. Control panel consists of relays, indicators, MCB and etc.

2.3.1 Motor
         Main motor is AC induction motor and other motors are DC motors used for the lift. Normally,
the motor use for lift is a three-phase induction motor. This motor is use to travel the Lift car one floor
level to another floor level. Direction of rotation of the motor is change by changing two current phases. It
is automatically changed inside the control panel. Motor operates at two deferent speeds. Because car is
moving faster speed as soon as start to move and getting slowdown before stop as the floor level.

NDES                                                                                                   Page 5
GIT                                                                                               Chapter 2
CEB                                                                                              Lift Branch

2.3.2. Ropes
         All electrical connection to the car is made by means of the multi core hanging flexible cable.
One end of which is connected to a terminal box fitted under the car floor. The other end to a terminal box
fitted in at approximately the mid- position. This is used to hold lift car. Breaking strength of the rope
should be 10 to 12 times the capacity of the car. There are two roping methods.
     1. One to One
         In this case, the ends of the elevator ropes are connected on the car and the counter weight as
         shown in figure.
     2. Two to One
         In this type, the both ends of the ropes are tied on suitable places of the control room.

2.3.3 Control system
         Control unit consists of relays, operating switches, contactors, rectifiers, resisters and capacitors.
It receives signals from the selector and the lift. Then it controls lift according to these signals. In early
days, electro-mechanical relay panels are used as controllers. Now, microprocessor based controllers are

NDES                                                                                                 Page 6
GIT                                                                                               Chapter 2
CEB                                                                                              Lift Branch

2.3.4 Counter weight
       The object of the counter weight is to provide traction and to balance the weight of the car plus a
predetermined proposition, usually 40 to 50 percent of the maximum car load and there by to reduce the
size of the motor. Incidentally the counter weight provider a certain measure of safety when landing on its
buffer and removing traction from the car. This can be identifying as main part of the lift. Controller is
received signal from endings. Lift car, Lift motor etc. The signals are used to activate the lift to various
2.3.5 Brake System
         Break unit should be capable of handling 125% of load. Normally break is kept applied. When
the lift works, solenoid will activate and it pulls back break pads. After that, break releases and lift starts
to function. When the lift is stucked due to a power-cut or any other failure, break is released using a
handle manually.

2.3.6 Lift Car
        This is the container like structure that used to carry something in it belong to the requirement of
it is designed. There are floor level indicators, over weight alarm, telephone to use in the case of
emergency, switches to send the position we want to stop the lift.

2.3.7 Guiders
       Some form of guiding is necessary for both the car & counter weight so that they will travel in a
uniformly vertical direction. The guides must be of such length that it will be impossible for any of the car
or counter weight shoes run of the guides. In the most common arrangement two guides are required for
the car &to for the counter weight.

2.3.8 Over Speed Governor

        This is a safety device. Governor is adjusted so that,
         If speed is 115% of normal speed, electrical trip occurs due to the breaking fails or control
            panel fails.
         If speed is 130% of normal speed, mechanical trip occurs due to rope breakdown.

When rope breaks, if load is applied to the rope attached to over speed governor then rope operates by the
safety gear. When the car speed exceeds more than 20 % of the maximum speed of the car and power
supply did not cut off or by cutting off the power supply does not stop the car then Over Speed Governor
operates. Over Speed Governor operates the safety gears located at the bottom of the car. Safety gear is a
mechanical lock that car can be stop by locking it to the car guide.
NDES                                                                                                 Page 7
GIT                                                                                            Chapter 2
CEB                                                                                           Lift Branch

2.3.9 Travelling Cables
        Control signals and communicating signals are passed through this flexible electrical cable. It
consists of number of wires inside it. One end of this flexible cable has connected to the control panel and
the other end has connected to the bottom of the car.

2.4 Typical arrangement of a Lift
                         Traction Sheave
           Worm Reduction Gear

           Controller                                                Motor

        Machine Room
                                                                       Diverting Pulley
                 Car Guides
                                                                       Suspension Ropes
                                                                       Door Operator
                        Lift Car

                                                                           Car Door
                         Lift   wall

                    Safety Gear
                    (Under car)                                        Traveling Cables
          Counter Weight Guides

                                                                     Landing Indicator

                                                                       Landing Push

           Car and Counterweight
           Buffers in pit                                           Landing Entrance

NDES                                                                                              Page 8

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