Automatic Rescue Device (ARD):
In countries such as India where power interruption is frequent, Automatic Rescue Device is widely used to rescue the passengers trapped inside the lift cabin.
1. Manual Rescue:
In the past, when Automatic rescue devices were not available, elevator mechanics used to lift the machine brake and rotate the fly wheel to bring the lift to the door level and then open the door using a key to free the passengers. This method is highly unsafe and was required to be conducted only by trained personnel. Remaining inside the lift cabin till the arrival of trained personnel caused lot of anxiety and panic for the trapped passengers. Lift industry has witnessed many incidents during and before rescue operations.
2. Stopping Jerk:
Apart from passenger entrapment, when the elevator stops suddenly due to power outage, the PM Gearless elevators seem to introduce heavy jerk as compared to equivalent geared elevators. This causes discomfort especially to elderly and pregnant women. This severe sudden stopping jerk is in addition to the passenger entrapment and anxiety till the person comes out of the lift. Typically most of MRL lifts are gearless.
At present, many lift manufacturers have improved the engineering design to reduce the stopping jerk on power failure.
3. Automatic Rescue Device Basic Operation:
At present, for rescuing a trapped passenger, automatic rescue devices are used which is a safe way of rescuing the passengers. ARD is a control device meant to bring a stuck elevator between floors, due to loss of power, to the nearest level and open the door in order to allow the trapped passengers to be evacuated. Such a device use auxiliary power such as batteries and it must comply with all the safety requirements of the lift as during normal run. In the case of manual door operation, the device shall allow the passengers to open the door on reaching the level and in case of power operated doors; the doors will automatically open on reaching the floor level. The speed during the ARD run is usually less and typically it is about 1/10 to 1/16 of the rated speed. Since the ARD’s take over automatically, the passengers are rescued shortly after power failure. But the ARD’s are useful only for entrapment due to power failure and not when the elevator stops due to failure of controller or any of the safety switches.
3.1 ARD Building Blocks:
There may be many variations between each manufacturer, but typically following are the major parts of an ARD system:
(a) Battery:
Generally 4 Nos of 12v Lead Acid Maintenance free batteries are used to power the elevator during rescue operation. The AH of the battery is chosen based on the power requirements of the elevator, typical ampere hour rating being 7.2AH, 12AH, 18AH or 24AH.
(b) Charger and Charger Transformer:
During normal power, the batteries are charged by the Charger transformer and the charger. The charger transformer steps down the three phase 400v AC mains power and feeds to the charger.
(c) Power Board and Power Transformer:
The power board converts the 48V DC battery supply to suitable three phase AC and the power transformer steps p the output to feed 400V AC 3 phase to the elevator. The power boar consists of IGBT’s or power MOSFET’s which are driven by drivers controlled by PWM circuitry.
(d) Logic Board:
The logic board typically dos the following functions:
- During normal power, it switches main contactor to provide 400V AC 3 Phase 50 HZ mains power to the elevator. On loss of mains power, it switches off main contactor and switches ON the ARD contactor to provide 400V AC 3 Phase 50 HZ emergency power to the Elevator.
- Detects the power failure signal from other external device such as single phase preventer and initiates ARD operation.
- Provide signal to the elevator controller / Main VVVF drive to indicate that the power available is emergency power.
- Provide signal to the voice annunciator to make emergency rescue announcement inside the car.
- Detects Door Zone signal from the elevator, terminates the ARD run.
- Continues and finishes Rescue operation even if mains power resumes in between.
- Detects the current drawn from the battery and provide command to the main drive to reverse the direction of travel in order to make the movement of elevator in the direction of gravity.
- Detect the health of the battery and provide prior indication during normal power.
- Has many timers, (a) 6 sec (approx.) timer to initiate ARD operation. (b) Initiate another timer typically 3 min to abort ARD operation if door zone signal was not received. (c) About 15 sec after receipt of Door Zone signal to allow the elevator controller to fully open the door and then completes ARD operation.
- Disconnects the battery from discharge inside the ARD circuitry if power is shut down for a prolonged time.
4. Advancement in main drive technology:
During rescue operation, first, the ARD tries to run the elevator in a pre-determined direction. If the battery current drawn is more, the elevator run is stopped and direction of travel reversed to take advantage of gravity. This feature drains the battery and also takes a little longer for rescuing the passenger. In the current designs, the main VVVF drive has been designed to remember the running current and direction of travel during each run. On power failure, during ARD run, the drive runs in the easy direction thus avoiding unnecessary current drain from the battery.
5. Seamless ARD run:
Prevention of “stopping jerk” due to power failure and subsequent ARD run can be overcome if the elevator is run on 3 phase un-interrupted power supply (UPS). Through few customers use UPS, it is an expensive solution.
5.1 GeN2 Switch by OTIS:
Switch works on single phase supply with the regenerative drive powered by lead acid battery. But a present, this is suitable only up to 8P, 1mps MRL elevator.
5.2 TOSMOVE NEO by Toshiba:
Uses Super Charge ion Batteries ( SCIB). When power failure occurs, gradually reduces elevator’s speed, and move to the nearest floor at slow speed. During continued power failure, moves at 1mps for 30 minutes.
5.3 Affordable seamless ARD:
Similar to OTIS and Toshiba, Schindler has a product which works n solar power and single phase supply. But, these products are not able to provide a low cost solution to the average Indian buyer. Basic block diagram of the seamless ARD given below:
Description:
During normal mains power, 3 phase mains power charges the battery. The main V3F drive and the Controller power is provided by the mains. During elevator run, the battery is also getting charged from the DC link bus of the drive. The bi-directional Converter transfers energy from the DC link to the battery / Super capacitor. In the event of power failure, the DC link is fed by the battery through the B-directional bus. Supply to the controller is maintained by the DC to AC inverter.
Above is mentioned only as an idea for future work as the solution tried was not fully tested at site and or commercialized.
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