Transcript Document

University of Jordan
Electrical Engineering Department
Electric Drive
Electrical Elevators
Done By: Mohammad Abed Ashour
0086628
The Electrical Elevator
a permanent lifting equipment
serving two or more landing
levels, including a car for
transportation of passengers,
goods, running al least partially
between rigid guide rails.
Basic Components:
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Elevator Car.
Hoistway.
Machine/drive system.
Safety system.
Control system.
1. Elevator Car
• Elevator Car is the vehicle that travels
between the different elevator stops carrying
passengers.
• It is usually a heavy steel frame surrounding
a cage of metal and wood panels.
1.1 Standard car size:
• To prevent overloading of the car by persons,
the available area of the car shall be limited
and related to the rated load of the elevator.
The following table shows the standard car
sizes related to the elevator rated loads.
• # of passengers = rated load /75
Where:
75 represents the average weight
of a person in Kg.
• The value obtained for the
number of passengers shall be
rounded to the nearest whole
number.
• Car Width (CW): The horizontal dimensions between the
inner surfaces of the car walls measured parallel to the
front entrance and at 1m above the car floor.
Car Height (CH): The inside vertical distance between the
entrance threshold and the constructional roof of the car.
Light fittings and false ceilings are accommodated within
this dimension.
Car Depth (CD): The horizontal dimensions between the
inner surfaces of the car walls measured at right angles to
the car width and at 1m above the car floor.
1.2 Elevator Car Components:
• Car Sling, a metal framework connected to the
means of suspension.
• The elevator cabin.
• Mechanical accessories which are:
Car door and door operator.
Guide shoes.
Door Protective Device.
2. Hoistway
• Hoistway is the space enclosed by fireproof walls
and elevator doors for the travel of one or more
elevators, dumbwaiters or material lifts. It
includes the pit and terminates at the underside
of the overhead machinery space floor or grating
or at the underside of the roof where the
hoistway does not penetrate the roof. (Hoistway
is sometimes called "hatchway" or "hatch".)
• A simple definition for
the hoistway is the shaft
that encompasses the
elevator car.
• Note: Generally the Hoistway serving all floors
of the building but in high-rise buildings
hoistways may be banked with specific
hoistways serving only the lower floors and
others serving only middle or upper floors
while traveling in a blind hoistway until
reaching the floors that it serves. A blind
hoistway has no doors on the floors that it
does not serve.
2.1 Hoistway components:
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Guide rails for both the car & counterweight.
Counterweight.
Suspension (Hoisting) Ropes (Cables).
Landing (Hoistway) doors.
Buffers in the pit.
2.1.1 Guide Rails
2.1.2 Counterweight
• Counterweight is a
tracked weight that is
suspended from cables
and moves within its
own set of guide rails
along the hoistway
walls.
• The elevator car is balanced by a heavy
counterweight that weighs roughly the same
amount as the car when it's loaded half-full.
• When the elevator goes up, the counterweight
goes down and vice-versa .
Benefits of counterweight
• Balancing the mass of the complete car and a
portion of rated load, and it will be equal to
the dead weight of the car plus about 40% of
the rated load.
• Reducing the necessary consumed power for
moving the elevator.
• By using counterweight, the motor needs to
use much less force to move the car either up
or down. Assuming the car and its contents
weigh more than the counterweight, all the
motor has to lift is the difference in weight
between the two and supply a bit of extra
force to overcome friction in the pulleys and
so on.
• Since less force is involved, there's less strain
on the cables which makes the elevator a little
bit safer.
• If the motor is using less force to move the car
the same distance, it's doing less work against
the force of gravity so the counterweight
reduces the amount of energy the motor
needs to use.
• The counterweight reduces the amount of
braking the elevator needs to use so it makes it
much easier to control the elevator car.
• Imagine if there were no counterweight:
a heavily loaded elevator car would be really hard
to pull upwards but, on the return journey, would
tend to race to the ground all by itself if there
weren't some sort of sturdy brake to stop it.
• In a different design, known as a duplex
counterweight-less elevator, two cars are
connected to opposite ends of the same cable
and effectively balance each other, doing away
with the need for a counterweight.
Counterweight components:
2.1.3 Suspension (Hoisting) Ropes
(Cables)
• Suspension Ropes are Suspension means for car
and counterweight, which are represented by
steel wire ropes.
• They are used on traction type elevators, usually
attached to the crosshead and extending up into
the machine room looping over the sheave on
the motor and then down to the counter
weights.
• The term Roping system can be defined as the
arrangement of cables supporting the elevator
and which has many types or arrangements as
follows:
• Single wrap: rope passes over sheave once and
connected to counterweight.
• Double wrap: rope wound over sheave twice in
high speed elevators for additional traction.
• 1:1 roping: when rope connected to
counterweight where cable travels as far as
car in opposite direction.
• 2:1 roping: rope wraps sheave on
counterweight and connects to top of the
shaft, rope moves twice as far as cab.
2.1.4 Landing (Hoistway) Doors
• The door that is seen from each floor of a
building is referred to as the outer or hoistway
door.
• This hoistway door is a part of the building (each
landing).
• It is important to realize that the car door does all
the work; the hoistway door is a dependent.
These doors can be opened or closed by electric
motors, or manually for emergency incidents.
• Safety devices are located at each landing to
prevent inadvertent hoistway door openings and
to prevent an elevator car from moving unless a
door is in a locked position.
• The difference between the car doors and the
hoistway doors is that the elevator car door
travels through the hoistway with the car but the
hoistway doors are fixed doors in each landing
floor.
2.1.5 Buffers in the pit
• A Buffer is a device designed to stop a
descending car or counterweight beyond its
normal limit and to soften the force with
which the elevator runs into the pit during an
emergency. They may be of polyurethane or
oil type in respect of the rated speed.
• There are two principal types of buffers in
existence:
• Energy accumulation: accumulate the kinetic
energy of the car or counterweight.
• Energy dissipation: dissipate the kinetic
energy of the car or counterweight.
The main types of elevator buffers
• A Spring Buffer is one type of buffer most
commonly found on hydraulic elevators or
used for elevators with speeds less than 200
feet per minute. These devices are used to
cushion the elevator and are most always
located in the elevator pit.
• An Oil Buffer is another type of buffer more
commonly found on traction elevators with
speeds higher than 200 feet per minute.
• This type of buffer uses a combination of oil and
springs to cushion a descending car or
counterweight and are most commonly located in
the elevator pit, because of their location in the
pit buffers have a tendency to be exposed to
water and flooding.
• They require routine cleaning and painting to
assure they maintain their proper
performance specifications. Oil buffers also
need there oil checked and changed if
exposed to flooding
3. Elevator Machine and Drive System
• Driving machine is the power unit of the elevator,
and usually located at the elevator machine
room.
• The Driving machine used to refer to the
collection of components that raise or lower the
elevator.
• These include the drive motor, brake, speed
reduction unit, sheaves and encoders.
3.1 Types of Driving Machines:
• 1- Gearless Machine
• 2- Geared Machine
• 3- Drum Machine
• Look at the figures:
• Gearless Machine
• Geared Machine
• Drum Machine
3.1.1 Gearless Machine
• It used in high rise applications whereby the
drive motor and drive sheave are connected in
line on a common shaft, without any
mechanical speed reduction unit located
between the drive motor and drive sheave.
• Their sizes and shapes vary with load, speed
and manufacture but the underlying principles
and components are the same.
• Generally, Gearless machines are used for high
speed lifts between (2.5 m/s) to (10 m/s) and
they can be also used for lower speeds for
special applications.
Gearless Machines Components:
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Electrical Motor.
Traction Sheave or drum.
Direct current armature in case of DC motor.
Rotor in case of AC motor.
Brake.
Machine Bedplate.
Supporting bearings.
Deflector or double warp sheave.
3.1.2 Geared Machine
• It used in low and mid rise applications. This
design utilizes a mechanical speed reduction
gear set to reduce the rpm of the drive motor
(input speed) to suit the required speed of the
drive sheave and elevator (output speed).
• Their sizes and shapes vary with load, speed
and manufacture but the underlying principles
and components are the same.
• Generally, geared machines are used for
speeds between (0.1 m/s) and (2.5 m/s) and
are suitable for loads from (5 Kg) up to (50,000
Kg) and above.
Geared Machines Components
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Drive motor.
Brake.
Speed reduction unit or gearbox.
Drive sheave.
Bedplate.
Deflector sheave (if mounted as integral part
of the bedplate assembly).
Types of geared machine drive
according to location of installation:
• 1-Overhead traction: The drive machine
located directly over top its hoistway or shaft.
• 2-Basement traction:
The drive machine
located at a basement.
• 3-Offset traction:
The drive machine
located at the side of
the hoistway.
• Note:
Basement and offset applications require
additional deflector sheaves to properly lead
suspension ropes off the drive sheave and to the
car top or counterweight.
3.1.3 Drum Machine
• It widely used in older passenger and freight
elevator applications, though now rarely seen
except for dumbwaiters.
• A drum design has one end of the suspension
rope affixed to the inside of the winding
drum’s drive sheave, and then allows to rope
to reel in or off the outer surface of its sheave,
depending upon the car direction of travel.
3.2 Main Components of machine
drive system
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1- Electrical Motor
2- Traction (Drive) Sheave
3- Secondary Sheave
4- Deflector Sheave
5- Brake
6- Speed reduction unit or gearbox
7- Machine Bedplate
3.2.1 Electrical Motor
• Electrical Motor is used to raise and lower the
elevator cab, the direction of motor rotation
and speed (rpm) are directed and supervised
by devices located within the elevator
controller.
• The motor component of the elevator
machine can be either a DC motor or an AC
motor .
A) DC Motor:
• DC motors use carbon brushes to control or
regulate the operational speed of its motor.
• It is an important maintenance task to regularly
inspect, repair and replace these brushes.
• Failure to do so in a timely fashion can result in
equipment mis-operation and lead to significant
motor damage.
Advantages of using DC motors:
• Has a good starting torque.
• Ease of speed control using a DC generator
with a variable output or static converters.
B) AC Motor
Advantages of using AC motors:
• More regularly used because of its ruggedness
and simplicity.
• More ride quality.
Types of Electrical Traction Drive
Systems
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A- Geared traction control, which includes:
Single speed AC motor.
Two speed AC motor.
Variable voltage AC motor (VVAC).
Variable voltage, variable frequency AC motor
(VVVFAC).
Variable voltage DC motor(VVDC).
B- Gearless traction drives, which include:
• Variable voltage DC motor (VVDC).
• Variable voltage, variable frequency AC
motor(VVVFAC).
3.2.2 Traction (Drive) Sheave
• The powered pulley connected to either the elevator
drive motor’s output shaft (gearless) or to the output
side of the mechanical speed reduction unit (geared).
• The circumference of the sheave has a series of “U” or
“V” shaped grooves cut into it , in which sit the
elevator suspension or hoist ropes.
• The friction loads created as the suspension ropes pass
over the grooved surface of the sheave causes motion
to be transmitted from the drive motor to the elevator
cab or counterweight.
3.2.3 Secondary Sheave
• Pulley that is normally used on gearless
elevators and is located directly beneath the
machine or drive sheave.
• It has a grooved surface over which pass the
suspension or hoist ropes.
3.2.4 Deflector Sheave
• Pulley used to offset or direct the vertical drop or
location of the steel hoist ropes running between
the elevator car and its counterweight.
• Where the horizontal distance between the hitch
point for the car and the counterweight is larger
than the diameter of the drive sheave, one or
more deflector sheaves are used to guide the
hoist ropes.
• These devices are grooved sheaves that lead
elevator suspension ropes off the drive sheave
down to the car top and counterweight.
• The number and size of deflector sheaves will
be a function of the elevator’s size, machine
placement and roping arrangement.
Drive Sheave without
Deflector Sheave
Drive Sheave with
Deflector Sheave
3.2.5 Brake
• Traction and drum machines are provided with a
mechanical brake, designed to stop and safely hold an
elevator.
• A centrifugal force governor is provided on most
elevators to guard against over speeding (when a car
travels in excess of 20% of top speed, the governor will
activate a safety stop device).
• Safeties are installed at the bottom of an elevator car
and occasionally on counterweights to provide positive
emergency stopping when activated by the governor.
• During typical operation, this
brake is electrically lifted or
“picked” against adjustable
tensioned springs.
• In the event electrical power is
removed from the brake, these springs ensure it immediately
drops back against its drum or disk, bringing the car to a safe
stop.
• While applied, the brake will securely hold in place the
elevator and its counterweight.
• Some older elevators have a control design
whereby the brake is used to decelerate the car
from full speed to a stop.
• Modern elevator controls use electrical circuitry
to slow and stop the car under normal operation.
• Once the car has stopped, the brake is released to
hold the car in position.
• However, in the event an elevator’s safety
circuit is actuated, the brake is immediately
applied to stop and hold the car and its
counterweight, regardless of the type of
control.
Brake Components and Configurations:
• The most common form of elevator brake
consists of a machined drum onto which two
curved shoes or pads drop onto the surface of
the drum.
• The brake drum or disk is directly coupled to the
elevator drive shaft. On some machines, the
brake is an external element whereby the brake
arms and their shoes are located outside and
above the rotating drum surface as shown:
• There is one type of gearless machine that has
its two brake arms applying force against an
inside or interior rim on the drive sheave as
shown:
3.2.6 Speed reduction unit or gearbox
• The most common type of speed reduction unit
consists of a hardened steel worm shaft, mated
with a bronze ring or crown gear (worm-gear set).
• The mating surfaces of these two elements are
contained within an oil bath for lubrication.
• Regular access to the machine to check the level
of oil, as well as the condition of the oil and the
ring gear is an important aspect of ongoing
equipment maintenance.
3.2.7 Machine Bedplate
• The gear box, motor and brake may be
assembled on a common bedplate. This
fabricated steel structure serves to keep all
parts in accurate alignment and allows onepiece shipment.
• Some machines have the motor and brake as
an integral part of the gear case, removing the
need for a separate bedplate.
4. Safety system:
• Safety system components:
• 1- Device for locking landing doors (Hoistway
Door Interlock).
• 2- Progressive safety gear.
• 3- Overspeed governor.
• 4- Buffers.
• 5- Final Limit switches.
• 6- Other safety devices and switches.
4.1 Device for locking landing doors
(Hoistway Door Interlock).
Device for locking landing doors
Hoistway Door Interlock
• It shall not be possible in normal operation to open the
landing door (or any of the panels in the case of a multipanel door) unless the car has stopped, or is on the point of
stopping, in the unlocking zone of the door.
• The unlocking zone shall not extend more than 0.2 meter
above and below the landing level.
• The hoistway door locking mechanism provides a means to
mechanically lock each hoistway door and the elevator
cannot leave a landing unless the doors are fully closed and
secured.
• They are also interconnected electrically to prevent
operation of the elevator if any of the elevator’s hoistway
doors are open. Should the doors be forced open, the
interlock circuit will be broken, causing the elevator to
immediately stop.
• Each landing door shall be provided with a locking device
satisfying the previous conditions. This device shall be
protected against deliberate misuse.
• Landing doors shall be capable of being unlocked from the
outside with the aid of key , which fit the unlocking triangle
(Hoistway Emergency Door Keys).
• Hoistway Emergency Door Keys permit the
unlocking of the hoistway door interlock.
4.2 Progressive safety gear
• Safety gear is a mechanical device for stopping the car
(or counterweight) by gripping the guide rails in the
event of car speed attaining a pre-determined value in
a downward direction of travel, irrespective what the
reason for the increase in speed may be.
• Progressive safety gear retardation is affected by
a breaking action on the guide rails and for which
special provisions are made so as to limit the
forces on the car, counterweight o balancing
weight to a permissible value.
• Pair of safety gears is mounted in the lower part
of car sling and operated simultaneously by a
linkage mechanism that actuated by overspeed
governor.
Safety Mechanism
• The progressive safety
gear and the braking
device are activated by
means of a linkage with
a shearing mechanism as
shown beside.
Operation of Safety Mechanism
• Dependent on the direction the safety lever is pulled upwards or
downwards; the movement of the lever is transmitted to the
shearing mechanism by means of a rocker.
• The grip wedges of progressive safety gear or braking device
which are linked with the safety-gear levers are released from
their rest position between rail and jaw body which is
maintained by a spring assembly.
• The safety-gear lever assembly which is arranged in the form of
a shearing mechanism ensures that the progressive safety gears
and/or braking device are activated simultaneously and in pairs.
Reset
• The progressive safety gear and the braking
device are reset by moving the car opposite to
direction of safety gear operation.
• (Move car in electric recall mode, or if
necessary, by releasing the car from the
engaged position).
Safety switch
• Safety switch is mounted on the bottom transom
on the side of the safety-gear.
• The switch is operated by the movement of the
safety-gear lever up or down according to
actuation direction if the car travels at over
speed.
• The switch interrupts the safety circuit causing
machine drive power off.
4.3 Over Speed Governor
• Over speed governor function is to actuate the safety
gear if the car speed exceeds 115% of its rated value.
• Usually a cable is attached to the safeties on the
underside of the car, called the governor rope. This
rope runs down through a pulley at the bottom of the
shaft and back up to the machine room and around the
governor sheave.
• When over-speeding is detected, the governor grips
the cable which applies the safeties that wedge against
the guide rails and stops the car.
• The over speed governor works on the floating
principle with a cam curve and roller guided
rocker.
• It is situated either in the machine room or in the
head room.
• Over speed governor is provided by a factory
adjusted switch activated when the tripped speed
is reached to disconnect the machine drive
starting with governor pulley blocking.
4.4 Buffers
• A Buffer is a device designed to stop a
descending car or counterweight beyond its
normal limit and to soften the force with
which the elevator runs into the pit during an
emergency.
• They may be of polyurethane or oil type in
respect of the rated speed.
• There are two principal types of buffers in existence:
A- Energy accumulation: accumulate the kinetic energy
of the car or counterweight.
B- Energy dissipation: dissipate the kinetic energy of
the car or counterweight.
• Polyurethane buffers which are energy accumulation
type with non-linear characteristics are used for lifts
that have rated speed not more than 1 m/sec.
• The main types of elevator buffers are:
• look at slides (30,31,32) to get more details.
4.5 Final Limit Switches
• Final limit switches shall be set to function as close as
possible to the terminal floors (the highest or lowest
landing of lifts), without risk of accident.
• Final limit switches shall operate before the car comes
into contact with the buffers. The action of the final
limit switches shall be maintained whilst the buffers
are compressed.
• After the operation of final limit switches, the return to
service of the lift cannot occur automatically.
4.6 Other Safety Devices and
Switches
• A- Overload Device.
• B- Door Protective Device such as: (photo-electric
and infrared sensors, safety edges).
• C- Emergency Stop Switch.
• D- Emergency Alarm Switch.
• E- Anti-Egress Lock Device.
5. Elevator Control System
• Elevator Control System is the system responsible
for coordinating all aspects of elevator service
such as travel, speed, and accelerating,
decelerating, door opening speed and delay,
leveling and hall lantern signals.
• It accepts inputs like (button signals) and
produces outputs like (elevator cars moving,
doors opening, etc.).
5.1 Aims of the control system
• To bring the lift car to the correct floor.
• To minimize travel time.
• To maximize passenger comfort by providing a
smooth ride.
• To accelerate, decelerate and travel within safe
speed limits.
5.2 Types of elevator control systems
• 1- Single Automatic operation:
• First automated system w/o single call button
on each floor and single button for each floor
inside car.
• Called if no one is using it.
• Passenger has exclusive use of the car until rip
is complete.
• 2- Selective collective operation:
• Most common, remembers and answers calls in
one direction then reverses. When trip complete,
programmed to return to a home landing.
• 3- Group automatic operation:
• For large buildings with many elevators which are
controlled with programmable microprocessors
to respond.
5.3 Elevator control system
components
• 1. Inputs (sensors, buttons, system controls).
• 2. Outputs (actuators, bells, displays).
• 3. Controllers such as:
a. (Relay based controller “electromechanical
switching”)
b. (Solid-state logic technology,
c. PLC controller “computer based technology”).
5.3.1.A Sensors
• A.1 Magnetic and/or photo electric:
• These pick up signals regarding the location of the car. This
sensor is usually placed on the car itself and reads the
position by counting the number of holes in the guide rail as
they pass by in the photo-electric sensor or in the case of the
magnetic sensor, the number of magnetic pulses.
• A.2 Infrared:
• This is used to detect
people entering or
leaving the elevator.
• A.3 Weight sensor (Over Load Device):
• This is placed on the car to warn the control
system if the design load is exceeded.
• A.4 PVT (primary velocity transducer):
• Velocity of the drive sheave is sensed with this
encoder
5.3.1.B Buttons
5.3.1.C System Controls
• They are used to turn the elevator system on
and off.
• They are only accessible from an elevator
control room.
• They would typically be used quite
infrequently.
5.3.2.A Actuators
• 5.3.2.A.1 Door Opening Device:
• It opens the inner door of the elevator cab and the outer
door of the elevator shaft simultaneously at each floor.
• 5.3.2.A.2 Electric Motor:
• The controller interacts with the elevator engine by sending
it a signal that specifies at which speed and in what
direction the engine should be going in.
• A stop signal is constructed by setting the speed parameter
of the signal to zero.
• 5.3.2.A.3 Brake:
• Brakes in elevator system are electromagnetic and
mechanical.
• The electromagnetic brakes activate automatically if
there is sudden loss of power or when the car is
stationary.
• The mechanical brakes at the sheave itself also stop the
car from moving when the car is inactive.
5.3.2.B Bells
• 5.3.2.B.1 Emergency Bell:
• It is used to alert people outside of the elevator system
when someone is trapped inside the elevator cab.
• 5.3.2.B.2 Load Bell:
• It is used to alert the passengers inside the cab that
there is too much weight in it.
• The controller interacts with the emergency bell and
the load bell by sending each one of them a signal to
ring.
5.3.2.C Displays
5.3.3 Controller
• It is a device which manages the visual
monitoring, interactive command control and
traffic analysis system to ensure the elevators
are functioning efficiently.
What is the function of the elevator
controller?
• It controls the speed of elevator engines.
• Processes elevator summons and floor
requests from passengers.
• Controls the operation of the elevator doors
of a cab through communication with door
opening devices.
5.3.3.1 Relay Based Controller
(Electromechanical Switching)
• A simple elevator with few
stops and manual door
operation can be served
well by a relay controller.
5.3.3.2 Solid State Logic Technology
• It includes both discreet
transistors circuits and
integrated circuit boards.
• It gives improved reliability,
lower power consumption
and easy fault diagnosis than
electromagnetic relay technology.
5.3.3.3 PLC Controller (Computer
Based Technology)
• Elevator concepts utilizes a
special type of industrial
computer called a (PLC) or a
Programmable Logic Controller
to control the logic of more
complex jobs.
• They are very dependable, compact and simple
to troubleshoot.
5.4 Elevator Control System Sequence
Diagrams
• The elevator control system may be viewed
either from:
• The point of view of an individual user.
or as:
• A system being acted on by many users.
5.4.1 The Point of View of an
Individual User
5.4.2 A System Being Acted On By
Many Users
Thank you