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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
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University of Jordan Electrical Engineering DepartmentElectric 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: • 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 Hoistwaycomponents: • Guide rails for both the car & counterweight. • Counterweight. • Suspension (Hoisting) Ropes (Cables). • Landing (Hoistway) doors. • Buffers in the pit.
2.1.2 Counterweight • Counterweightis 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.
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 hoistwaydoor. • 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.
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:
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: • 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 • 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.
