Elevator is basically a vertical transport system for human being and material. Mr. Otis after different inventions in other applications decided to invent an vertical transport machine for human. But the major concern in this was safety. So he develop such a mechanical brakes that even after hanging rope fails machine will not fall down. With this successful experiment he named it as elevators. Then he started manufacturing elevators. With the time peoples start accepting these products and over such a long period elevators have become a essential for our life style.
With the time elevators have become much safer and smooth. Now there are two main types of Elevators
1. Geared machine elevators (generally open loop)
2. Gearless Machine Elevators (Generally Close Loop)
Geared Machines consists of Ac induction motor and Gear box. Whereas Gearless machines are compact and permanent magnet synchronies motors. They don’t need gearbox due to low speed maximum output torque of motor.
In the period of 90’s Ac drives were started to use for elevators. But standard industrial Ac drives were not much successful because for different application needs.
Role of Ac drives in Elevator
In this post we will discuss about Open loop elevator ac drives. Gearless we will discuss in other post.
Elevator drive should have following features to work at its best
1. Brake Logic
2. S-curve pattern for acceleration and deceleration
3. High starting torque
4. Base block signal Input.
5. Relay output
6. Multi speed function for slow speed and fast speed
Why need above functions
1. Brake logic is most important feature of ac drive. Starting and stopping jerk are mostly dependent on this logic. . VFD generates set Percentage of toque at a selected frequency in motor before it releases brake. VFD has such function inbuilt to control Motor Brake. Same thing happens while stopping the motor. Brake should be released and engaged properly so that Elevator either should not roll back or nor should over travel or get jerks
2. S-Curve is second most important feature. After the brake is released Elevator will go high speed. While going to high speed if We keep Linear Curve than we will feel jerks while speeding of elevator. So ac drive should have proper S curve suitable for elevator.
3. When Elevator is Fully loaded (equal to Passenger capacity) or Empty than Elevators needs maximum torque to start the elevator. (Empty and full loaded needs full torque due to counter balancing weight of Elevator.) For this reason Drive should have more starting torque, typical 180% or more.
4. Base block input is like an emergency stop input. When base block elevator signal is given to ac drive will work but it does get that signal it should not run even if drive get a forward or reverse run command.
5. Relay outputs are needed because most of the Elevator controls comes with 110V supply. With transistor Digital output you need to put external relay. So it is convenient to have to relay outputs for Brake and Output contactor.
6. Multi Speed input feature. Typically you will find this feature in each and every VFD as it is basic feature of drive. After drive accelerate to full speed it runs continually on full speed till reaches near to destination floor, then elevtor control gives slow command just few feet before it reaches destination where second speed or slow speed is used. Apart from this ac drive get a another speed command during maintenance speed.
Fuji Electric, Yasakawa, L&T, Gefran and Hitachi
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