Lifts: An Application to Electrical Drives. Prepared by: Al Harith Auda (0060772) Nazeeh Ammari (0076411) Iskander Imseeh (0077601). Brief history of Elevators.
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Prepared by:Al HarithAuda (0060772) Nazeeh Ammari (0076411)
An elevator consists of:
The figure in the next slide shows the components of an elevator.
Pneumatic Vacuum Elevators
These operate without cables or pistons and can be installed more easily and quickly than their alternatives since their housing is composed of prefabricated sections which are considerably narrower than conventional lift shafts. These sections are transparent and afford the passenger a near 360° view. Other notable features of the vacuum elevator are as follows:
• Installation within one to two days
• Two to four stops for residential, marine, and stage use (35 ft total rise)
• Ideal for new and existing homes due to the minimal space needed to fit the elevator
• Self-supporting structure: the elevator can rest on any existing ground floor
Configuration of Gearless traction lift
The elevator is composed of a motor and, most commonly, a gear reducer system, which functions as follow:
The motor component of the elevator machine can be either a DC motor or an AC motor, each has it’s advantages:
In an elevator system, it’s possible to regenerate some (if not all) of the power consumed, the elevator has four modes of operation:
In this mode, the system is consuming power, where both the torque and the speed are positive.
In this mode of, the system is regenerating (supplying) power, where the torque is negative and the speed is positive.
3. Third quadrant (reverse motoring):
In this mode, the system is consuming power, since both torque and speed are negative and their product is positive.
In this mode, the system is regenerating power again, since the torque is positive and the speed is negative.
The next slides show these modes in the four quadrants for better demonstration.
Torque-speed quadrant of operation
The voltage-fed three-phase pulse width modulation (PWM) rectifier is adopted so that dc bus voltage regulation, bidirectional power flow, and controllable power factor with reduced input current harmonics are possible.
Some additional hardware is adopted for the high performance and reliability of the whole drive system.
A number of traffic control algorithms have been developed that define the strategies undertaken in order to optimize the use of grouped lifts by, for example:
• minimizing passenger’s waiting time
• minimizing passenger’s journey time
• minimizing the variance in passenger’s waiting time
• maximizing the handling capacity
• minimizing the energy consumption
Before we solve a numerical example on elevator mechanics, we will give a brief introduction to the basic laws and definitions needed to understand it.
Let us consider an electric drive for an elevator with the data shown in figure 1.11. The motor rated speed nn = 1550rpm. The efficiency of the gearing system is = 0.8.
Calculate the total inertia (reduced to motor shaft), torque and power without and with counterweight.
Figure 1.11. Elevator electric drive with multiple mechanical transmissions and counterweight
The gear ratios may be defined as speed ratios - Wt /wm for J4+J5 and Wd /wm for J6 (figure 1.11).
Consequently the inertia of all rotating parts Jr, reduced to the motor shaft, (figure 1.11), is:
For the cabin and the counterweight, the inertia, reduced to motor shaft (Je) is:
Thus the total inertia Jt is:
In absence of counterweight the la of energy conservation leads to:
Consequently the motor torque, Tem, yields:
On the other hand in presence of counterweight (1.16) becomes:
So the motor electromagnetic P’em is: