Electrical & Control System and Moving Walkways



I indicated in a previous Topic” Escalators Basic Components - Part One “that Escalators Basic components are as follows:
  1.  Landing Platforms.
  2. Truss.
  3. Tracks.
  4. Steps.
  5. Handrail.
  6. Escalator Exterior (Balustrade).
  7. Drive system.
  8. Auto-Lubrication System.
  9. Braking system.
  10. Safety devices.
  11. Electrical & Control Systems.

And I explained the first six items in this previous topic. Also, I explained the items from seventh to tenth in the previous topic “Escalators Basic Components – Part Two”.


Today, I will explain the last item; Electrical & Control Systems, also I will explain the Moving walkways as it is one of the transportation systems used in buildings.


Eleventh: Electrical & Control system


1- Escalator Motor

The escalator motor is typically an AC direct-on-line flange mounted unit, directly and/or flexibly coupled to the reduction gear. The motor is usually protected by thermal and electro-magnetic overload devices as well as thermistors in the motor winding. The motor operation is controlled by the main controller.


2- Main Controller


2.1 In Earlier Escalator Systems 


As I mentioned before, in earlier escalator systems it was common to use Conventional electromechanical starting systems, which include the following methods:
  1. Full voltage Wye Start/Delta Run connection starting.
  2. Part-winding starting.
  3. Reduced voltage starting.
  4. Autotransformer starting. 

These Conventional starting methods were used along with relay logic to control the starting method for the drive motor(s).

2.2 In Modern Escalators 


  • But in modern escalators, the main controller will use a soft start controller or a variable frequency drive along with a Programmable Logic Controller (PLC) to control and monitor the status of the escalator. The PLC may also be capable of communicating via an Ethernet to permit remote monitoring of the system. Modern escalator controllers incorporate an electronic fault diagnostic system. 
  • This fault diagnostic system is capable of logging statistical data on the operation of the escalator and includes memory to store escalator faults causing shut down. The escalator controller and fault diagnostic also includes an English language clear text display to allow immediate identification of the cause of a shutdown. The display is located within the inner decking at the upper end of the escalator. 
  • The display system normally provides a minimum of 2 lines of 20 characters for displaying programmable messages and fault conditions. Operation of the fault diagnostic system is possible at the display point via menus and keypads adjacent to or contained as part of the display system. 
  • The escalator controller and fault diagnostic system may include a text display to allow immediate identification of the cause of a shutdown. The controller itself could be located within the inner decking of the upper end of the escalator as well as the equipment machine room. Through the use of a keypad and the display, the technician is provided the ability to display programmable messages and fault conditions. Operation of the fault diagnostic system is possible at the display point by the use of menus and keypads adjacent to or contained as part of the display system. 


2.3 Escalator Controller Components 


Escalator Controller Components

a- A Circuit Breaker is a device designed to open and close a circuit by non-automatic means and to open the circuit automatically on a predetermined over-current. This is usually mounted near the control cabinet with accessibility of its red color handle or trip breaker. When opened, it isolates most electrical controls inside the controller.

b- Line Fuses are in line with each leg of the three-phase 480 VAC power supply located inside the controller or in a separate box. It is used as an over-current protection device, which has a similar function as the circuit breaker but normally used as a short circuit protection (catastrophic failure).

Typically, these fuses are of a time-delay category, capable of handling the initial in-rush current when the equipment is energized.

c- A Step down Transformer is used to step down voltages normally from 480vac to 120vac or other low ac voltages that may be used for controls and demarcation lighting.

d- A Motor Starter, when energized, its main contacts will provide power to the motor, and its auxiliary contacts may provide power to other control circuits. Typically, a dual contactor Motor starter is used where one starter controls the motor in the up direction and the other starter is responsible for the down direction. It may also be, one starter for each motors’ direction on two motors for dual drive or three for tri-motor drive escalator. Ideally, these contactors will be equipped with a mechanical interlock which would aid in preventing a phase-to-phase electrical short. Soft start starters are widely used in the modern escalators.

e- Brake Energizing Relay for the Main Drive Shaft, when energized, its contacts will provide power to the brake coil thereby disengaging the fail-safe brake for the motor to turn. When de-energized, the tension of the brake spring(s) will mechanically apply the brake capable of stopping a down running escalator with brake rated load.

f- Overload Protection – is normally a bi-metal normally closed contact that senses the heaters in line with the 480VAC power supply and the motor leads. When an overcurrent occurs, the heaters will transfer heat to the bi-metal contacts to open and disconnect the motor contactor coil thereby opening the contactors for the motor. Solid state versions use the same detection method but will provide low voltage protection to the control circuit thereby shutting down the power circuit as well as the control circuit.

Overload protection is the result of a device that operates on excessive current, but not necessarily on a short circuit to cause the interruption of current flow to the electric motor. Overload protection is not meant to protect the system from direct shorts, but rather to provide protection from excessive mechanical overload of the motor or to disable a motor which has overheated due to bearing or winding failure.

g- A Fault Indicating Device is part of the controller that operates to visually indicate the actuation of a safety device causing the escalator to shut down. It has an indication that remains until manually canceled or reset by the maintenance person or by the Station Agent/Manager. Indicating lamps are of a neon type or LED used to display unit malfunction or any activated safety devices.

h- A PLC or programmable logic controller, or programmable controller, is a digital computer used for automation of electromechanical processes, such as control of the drive machine, handrail speed, motor speed, motor frequency and voltage input as well as the monitoring of all safety devices. 

programmable controller

i- A Soft Start Controller is a solid state AC drive which controls the speed of AC motors by controlling the frequency and voltage of the power supplied to the motor.

An inverter provides the controlled power, and in most cases, the AC drive includes a rectifier so that DC power for the inverter can be provided from the main AC power. AC drives are also called variable-frequency drives, frequency inverters, or inverters. The speed of an AC motor is determined by the cycle number of alternating current it receives at each second and by the number of poles in the motor.

Since the number of poles of most industrial motors is fixed, the speed is more easily controlled by controlling the frequency.


3- Escalator Control Cabinets


3.1 Main Electrical & Control Cabinet 



Usually,The Main Disconnect Switch, motor protection and control devices are typically installed in an electrical cabinet positioned in the upper machinery well-way of the escalator. The cabinet will typically correspond to NEMA 3, ANSI/ASME standards by the escalator manufacturer comprising a steel enclosure with all required relays, automatic circuit breaker, and terminals completely wired for the escalator control. Fault annunciation is generally provided to identify activation of specific escalator safety devices.



3.2 Landings Control Station 

Landings Control Station
  • A control station at both upper and lower landings is provided which includes a key-actuated directional starting safety switch and a key actuated stop switch. 
  • The control station is located in the newel end skirt deck at the ends of the balustrades. 
  • A Code compliant emergency stop station is provided at each end of the escalator. The emergency stop is located in accordance with governing Code requirements and is covered by a transparent cover and alarm. 
  • Starting of the escalator in normal continuous operation mode shall only be possible using a dedicated key switch at upper and lower ends. (Some units have key switches at one end only.) 


3.3 Maintenance Control Station
Maintenance Control Station

Each escalator is provided with a pendant-style hand station to operate the escalator during maintenance or service work. Plug-in connection points for the pendant handset are provided at both ends of the escalator within the truss enclosure beneath the landing plates.

The handset includes continuous pressure push buttons to operate the escalator in either direction. A maintenance stop button is included. When plugged into the receptacle, there should be no means of operating or permitting the escalator to run other than through the use of the handset.


4- Escalator Electrical Lighting


4.1 Balustrade Lights 

The entire length of the escalator between the interior balustrade panels is illuminated by continuous fluorescent lighting called the Balustrade Lights. Only the steps and the side sections up to the skirt panels require light so that escalator passengers can see where they’re walking without having bright lights shine in their faces.

An emergency circuit will light every other lamp section on one balustrade in case of a power outage.



4.2 Comb Lights 

Comb Lights 

The Comb Lights illuminate the area where the comb-fingers meet the steps. They are located in the end skirts above the upper newel and lower newel comb-fingers. These lights are also on the lighting emergency circuit.



4.3 Maintenance Lights 

Maintenance & Step Demarcation Lights
  • Areas inside the upper truss, the lower truss, and the machine rooms are illuminated by Maintenance lights. 
  • Light switches next to each light turn them off and on. 
  • These lights are on the emergency circuit and will work if the escalator breaks down. 
  • No special procedure should be necessary for changing these lamps. 



4.4 Step Demarcation Lights
Gaps between steps at the upper and lower newels are lighted by green fluorescent tubes below the steps. These Step Demarcation Lights shine between steps to makes it easier and safer for passengers stepping on and off of the escalator. Demarcation Lights are on the emergency circuit.



4.5 Direction Indicators 

Direction Indicators

A red and a green light mounted on the right side of each newel indicate the escalator direction of travel when approaching the steps. A rider will usually want to enter the newel with the lighted green indicator and avoid the lighted red indicator. Each of these lights is made up of LED clusters and can be replaced after taking off the faceplate and the indicator box cover. By removing the retaining nuts on the back side of the plate, either lens can be replaced. The red light should be replaced in the top position.



5- Heating Systems and Controls 


5.1 Heater Operation
Heating elements are located in the upper, lower, and incline sections of each escalator installed from the entrance to the mezzanine levels. Their design purpose is to prevent ice from forming on the steps.


5.2 Heater Elements
  • These heaters are 2000 watt, 480 volt, single-phase tubular electrical elements that are controlled by a thermostat that is adjustable from 30°F to 110°F. 
  • To replace a heating element, it is necessary to first remove four step sections. Move the missing step section over the heater to be removed and disconnect the conduit box cover. 
  • Disconnect the heater wiring and conduit. 
  • It will be a lot easier to replace an element if the wires are tagged before they are disconnected. 

5.3 Heater Thermostatic Controls
The thermostat can be removed after taking out two steps and positioning the missing step section over the control. Turn the heater disconnect switch off before removing the box cover. Disconnect the wires and tag them for easy re-connection.


Moving Walkway


Moving Walkway

A moving walkway sometimes called Travelator, Horizontal Escalator is a slow moving conveyor mechanism that transports people, across a horizontal or inclined plane, over a short to medium distance. Moving walkways can be used by standing or walking on them. They are often installed in pairs, one for each direction.

Moving walkways, usually found in airports, are designed to move people over long distances, usually between different terminals. Moving walkways are similar to an escalator. The only difference is that the steps lay flat, like a conveyor belt. Passengers are able to move from gate to gate or from one baggage area to the next. Moving walkways, like elevators and escalators, offer a smooth and convenient ride for people while providing outstanding energy efficiency for commercial building operators.


Types of Moving walkways


1-According To Inclination Angle 


Horizontal and Inclined Moving Walkways
a- Zero degrees inclination “Horizontal” Moving Walkways.

b- Up to 15 degrees inclination “Inclined” ” Moving Walkways.



2- According To the Flat Moving Surface 


Moving walkways have two basic styles according to the flat moving surface:

a- Pallet Type 

Pallet Type Moving walkways

A continuous series of flat metal plates mesh together to form a walkway. Most have a metal surface, though some models have a rubber surface for extra traction.

b- Moving Belt 

Moving Belt Moving Walkway

These are generally built with mesh metal belts or rubber walking surfaces over metal rollers. The walking surface may have a solid feel or a "bouncy" feel.

Both types of moving walkway have a grooved surface to mesh with comb plates at the ends. Also, all moving walkways are built with moving handrails similar to those on escalators.

3- According To the Speed 


Moving walkways have two basic styles according to the flat moving surface:

a- Slow- speed Standard type 


The speed of these walkways is determined by the need for safety upon entry and exit, which generally limits it to approximately half normal walking speed, or 30–40m/min. The slow speed of the walkway causes impatience, and passengers often walk on the walkway itself or on the adjacent floor rather use the slower walkway.


b- High-speed walkways 

High-speed walkways

Using the high-speed walkway is like using any other moving walkway, except that for safety there are special procedures to follow when joining or leaving.

On entering, there is a 10 m acceleration zone where the "ground" is a series of metal rollers. Riders stand still with both feet on these rollers and use one hand to hold the handrail and let it pull them so that they glide over the rollers. The idea is to accelerate the riders so that they will be traveling fast enough to step onto the moving walkway belt. Riders who try to walk on these rollers are at significant risk of falling over.

At the exit, the same technique is used to decelerate the riders. Users step on to a series of rollers which decelerate them slowly, rather than the abrupt halt which would otherwise take place.



Moving walkways basic components: 

Moving walkways basic components

The moving walkways are identical to escalators in the basic components of their construction, but they differ in the following:
  • Moving walkways may run horizontally or on an incline of up to 15 degrees. 
  • The flat moving surface of the moving walkways may consist of a continuous rubber belt or a series of jointed treads. 
Moving walkways basic components
The main basic components of the moving walkways will be as follows: 

  1. Truss.
  2. Tracks.
  3. Drive motor.
  4. Gear box.
  5. Service track.
  6. Handrail drive wheels.
  7. Pallet chain sprockets.
  8. Pallets.
  9. Pallets chain.
  10. Handrail.
  11. Lower reversing station.
  12. Balustrade panels.
  13. Decks.
  14. Newel ends.
  15. Skirts.
  16. Access cover.
  17. Comb plates.
  18. Front plates.
  19. Controller.

Moving walkways Safety Devices: 


The safety devices that be included in most of the moving walkways are as tabulated in the below image.

 



In the next Topic, I will explain the Electrical Pumps and Motors. So, please keep following.



Note: these topics about Escalators in this course EE-1: Beginner's electrical design course is an introduction only for beginners to know general basic information about Escalators as a type of Power loads. But in other levels of our electrical design courses, we will show and explain in detail the Escalators Loads Estimation calculations.



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