General Escalator

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    Electrical & Control System and Moving Walkways

    I indicated in a previous TopicEscalators Basic Components - Part Onethat EscalatorsBasic 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 fromseventh to tenth in the previous topicEscalators Basic Components Part Two.

    Today, I will explain the last item; Electrical & Control Systems, also I will explain theMoving walkwaysas 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/orflexibly coupled to the reduction gear. The motor is usually protected by thermal andelectro-magnetic overload devices as well as thermistors in the motor winding. The motoroperation 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 Conventionalelectromechanical starting systems, which include the following methods:

    1. Full voltage Wye Start/Delta Run connection starting.

    2. Part-winding starting.

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    3. Reduced voltage starting.

    4. Autotransformer starting.

    These Conventional starting methods were used along with relay logic to control thestarting 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 anEthernet 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 displayto allow immediate identification of the cause of a shutdown. The display is located withinthe 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 diagnosticsystem is possible at the display point via menus and keypads adjacent to or contained aspart of the display system. The escalator controller and fault diagnostic system may include a text display toallow immediate identification of the cause of a shutdown. The controller itself could belocated within the inner decking of the upper end of the escalator as well as the equipmentmachine room. Through the use of a keypad and the display, the technician is provided theability to display programmable messages and fault conditions. Operation of the faultdiagnostic system is possible at the display point by the use of menus and keypads adjacentto or contained as part of the display system.

    2.3 Escalator Controller Components

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    Escalator Controller Componentsa- A Circuit Breakeris a device designed to open and close a circuit by non-automaticmeans and to open the circuit automatically on a predetermined over-current. This isusually 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 Fusesare 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-rushcurrent when the equipment is energized.

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    c- A Step down Transformeris used to step down voltages normally from 480vac to120vac 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 dualcontactor Motor starter is used where one starter controls the motor in the up directionand the other starter is responsible for the down direction. It may also be, one starter foreach 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 willprovide power to the brake coil thereby disengaging the fail-safe brake for the motor toturn. When de-energized, the tension of the brake spring(s) will mechanically apply thebrake capable of stopping a down running escalator with brake rated load.

    f- Overload Protectionis normally a bi-metal normally closed contact that senses theheaters in line with the 480VAC power supply and the motor leads. When an overcurrentoccurs, the heaters will transfer heat to the bi-metal contacts to open and disconnect themotor 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 notnecessarily on a short circuit to cause the interruption of current flow to the electricmotor. 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 todisable a motor which has overheated due to bearing or winding failure.

    g- A Fault Indicating Deviceis part of the controller that operates to visually indicate theactuation of a safety device causing the escalator to shut down. It has an indication thatremains until manually canceled or reset by the maintenance person or by the StationAgent/Manager. Indicating lamps are of a neon type or LED used to display unitmalfunction or any activated safety devices.

    h- A PLC or programmable logic controller, or programmable controller,is a digitalcomputer used for automation of electromechanical processes, such as control of the

    drive machine, handrail speed, motor speed, motor frequency and voltage input as wellas the monitoring of all safety devices.

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    programmable controlleri- A Soft Start Controlleris a solid state AC drive which controls the speed of AC motorsby 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 arectifier so that DC power for the inverter can be provided from the main AC power. ACdrives are also called variable-frequency drives, frequency inverters, or inverters. Thespeed of an AC motor is determined by the cycle number of alternating current it receivesat 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 easilycontrolled by controlling the frequency.

    3- Escalator Control Cabinets

    3.1 Main Electrical & Control Cabinet

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    Usually,The Main Disconnect Switch, motor protection and control devices are typicallyinstalled in an electrical cabinet positioned in the upper machinery well-way of theescalator. The cabinet will typically correspond to NEMA 3, ANSI/ASME standards by theescalator manufacturer comprising a steel enclosure with all required relays, automatic

    circuit breaker, and terminals completely wired for the escalator control. Faultannunciation is generally provided to identify activation of spec