Читать книгу Elevator Troubleshooting & Repair - David Herres - Страница 5
ОглавлениеAn appropriate subtitle for this introduction would be: DON’T GET IN OVER YOUR HEAD! Elevators move large numbers of people up and down in high-rise buildings on a daily basis and there is the potential for an accident to occur. A highly-developed system of safeguards is in place, and for this reason an elevator ride is statistically far less hazardous than crossing a street.
Fatalities are extremely rare due to the redundant safety mechanisms, but they have occurred, some because of faulty maintenance procedures. A documented instance involved two wires which were temporarily disconnected from a circuit board and then reversed, thus disabling the door interlock, which prevents an elevator car from moving when the door is not closed and latched. A child was crushed between the car floor and door opening. There are tremendous moral and legal issues, and it is the responsibility of each worker to understand the consequences of any errors.
In the popular imagination, if an elevator cable breaks, the car immediately falls to the bottom of the shaft, killing the occupants. In actuality, the car is connected by multiple cables, which are regularly inspected for wear, any one of which would hold a fully-loaded car. Additionally, elevator cars have mechanisms known as safeties, which clamp onto the guide rails in an overspeeding or slack-cable situation.
In performing elevator maintenance and repair, there are enormous moral and legal issues. Workers need to fully understand proper maintenance procedures so that all safeguards remain in effect. As a start, it is essential to become aware of applicable regulations and to comply with them.
Of course, a major aspect in elevator technology is electrical. The National Electrical Code (NEC), revised and issued every three years by the National Fire Protection Association (NFPA), governs most electrical installations with a few exceptions such as installations under the direct control of utilities, and underground in mines. (It does, however, govern non-mine installations such as lighting and signal wiring in underground traffic tunnels.) NEC has no legal standing on its own, but is offered up for adoption and enforcement by states, municipalities, and jurisdictions inside and outside the United States.
NEC Article 620, part of Chapter 6, covers elevators, dumbwaiters, escalators, moving walks, platform lifts, and stairway lifts. Each of these performs a different set of functions with different requirements. The section on elevators contains specific electrical requirements, which must be observed in new installations. It is not the intent of NEC that with each Code revision all existing installations are to be immediately upgraded to comply. Nevertheless, older installations should be critically evaluated to see where upgrades are feasible and/or warranted. Besides Article 620, new elevator installations must comply with the entire electrical code except where specifically exempted. Two very important articles are 250, Grounding, and 430, Motors, Motor Circuits and Controllers.
I will return to the very important subject of codes in this Introduction and in fact throughout the book, but first a few paragraphs about licensing.
If you are serious about engaging in elevator work, you should acquire the appropriate license(s)—electrician’s license and elevator mechanic’s license. This is not going to happen all at once. Most states require verified work experience and/ or completion of classroom or online training, including passage of an exam, plus the state exam. There is no single nationwide electrician’s or elevator technician’s license. For the most part in the United States these permits are issued and regulated by the individual states, or in a few instances jurisdiction is ceded over to separate counties or municipalities. Most states maintain electrical and elevator agencies, which inspect installations and issue technicians’ and other permits. Requirements vary widely from state to state. The best approach as a start is to check your state’s website for requirements and procedures for obtaining the appropriate licenses.
My home state, New Hampshire, requires electricians’ licensing for those who are performing electrical installations for heat, light, and power purposes regardless of the voltage. It is not the voltage of the circuit that determines the requirements of licensure, it is the type of circuit. Accordingly, an individual can work on a central fire alarm system without having an electrician’s license, because the electrical system is for signaling, not heat, light, or power. How does this apply to elevator work? Most inspectors, technically known as the authorities having jurisdiction, will recognize that elevators, as we shall see in the chapters that follow, are composed of both signaling and power electrical circuits. Therefore, the electrician’s license would not be required to work on the signaling and control circuitry, in the car, on individual floors where the call buttons are located, in the machine room, or in the motion controller. However, the electrician’s license would be required to work on the power path from the entrance panel, through the main disconnect, to the variable frequency drive (VFD) and motor. The electrician’s license would also be required to work on lighting and branch-circuit receptacles in the pit and machine room. (In most cases a licensed electrician would in fact work on the signal wiring, but for this the license would not absolutely be required.) The bottom line is that if you are serious about doing elevator work, you should obtain the electrician’s license.
The New Hampshire Board licenses three categories: master, journeyman, and high/medium voltage electricians. In addition, it registers apprentice electricians and high/medium voltage trainees. All electrical work for which an electrician’s license is required must be overseen by a licensed master electrician. This individual need not be at the jobsite at all times, but is responsible for seeing that the work complies with the National Electrical Code. Journeyman electricians may perform the on-site electrical work, but they may not work on their own as independent contractors. Apprentice electricians may also perform electrical work, but they must be supervised by journeyman electricians, who must be on-site whenever apprentices are working. A one-on-one ratio must be maintained. If there are two apprentice electricians performing electrical work, there must be two journeyman or master electricians at the site.
To receive a master electrician’s license, the individual must have 8000 hours practical experience as an apprentice to a licensed electrician and at least one of the following:
■ 575 hours of electrical schooling in blocks of 144 hours per year or have an associate or higher degree in an electrical curriculum
■ Have ten years experience as a journeyman or master electrician as required in another jurisdiction; or Have taken the journeyman or master exam in New Hampshire previously
■ Acquired credit or school time, not to exceed 2000 hours, towards the practical experience requirement or completion of prescribed courses in electrical installations at an approved school
■ Pass the journeyman examination and obtain 2000 hours of experience as a journeyman in performing electrical installations prior to being examined
The master electrician exam consists of 50 NEC questions, 50 questions on practical installations, and 25 questions on applicable state laws and the Board’s administrative rules. The license fee is $270 for three years. To receive a journeyman electrician’s license, the requirements are substantially the same, but the exam is less difficult. The fee is $150 for three years.
The apprentice is not required to take an examination or have work experience prior to application, but must possess a high school diploma or equivalent. The fee for the apprentice card is $30, and it is valid for one year. During that period the apprentice is expected to complete 150 hours of vocational training and to study for the journeyman’s license. New Hampshire also issues an elevator mechanic’s license. Considerable practical experience working with a licensed individual is required to obtain this license, so it would be a long-range goal.
The American Society of Mechanical Engineers (ASME), through its Board on Safety Codes and Standards (BSCS), develops and maintains a comprehensive portfolio of codes and standards that governs elevators and escalators. A complete listing can be seen at ASME.org.
ASME A17, Safety Code for Existing Elevators and Escalators, is an essential reference for elevator maintenance workers and repair technicians. It can be ordered online at ASME.org. After a few paragraphs on Purpose and Exceptions, ASME A17 lists pertinent definitions. Here, by way of overview, are some highlights, with references to escalators, moving walks, and material lifts eliminated because they are outside the scope of this textbook.
■ Car annunciator: An electrical device in the car that indicates visually the landings at which an elevator landing signal registering device has been actuated.
■ Auxiliary power lowering device: An alternatively powered auxiliary control system that will, upon failure of the main power supply, allow a hydraulic elevator to descend to a lower landing.
■ Emergency brake: A mechanical device independent of the braking system used to retard or stop an elevator should the car overspeed or move in an unintended manner. Such devices include, but are not limited to, those that apply braking force on car rails, counterweight rails, suspension or compensation ropes, drive sheaves, and brake drums.
■ Buffer: A device designed to stop a descending car or counterweight beyond its normal limit of travel by storing or by absorbing and dissipating the kinetic energy of the car or counterweight.
■ Bumper: A device, other than an oil or spring buffer, designed to stop a descending car or counterweight beyond its normal limit of travel by absorbing the impact.
■ Car-direction indicator: A visual signaling device that displays the current direction of travel.
■ Car door interlock: A device having two related and interdependent functions, which are to prevent the operation of the driving machine by the normal operating device unless the car door is locked in the closed position; and to prevent the opening of the car door from inside the car unless the car is within the landing zone and is either stopped or being stopped.
■ Car door or gate electric contact: An electrical device, the function of which is to prevent operation of the driving machine by the normal operating device unless the car door or gate is in the closed position.
■ Overslung car frame: A car frame to which the hoisting rope fastenings or hoisting rope sheaves are attached to the crosshead or top member of the car frame.
■ Underslung car frame: A car frame to which the hoisting rope fastenings or hoisting rope sheaves are attached at or below the car platform.
■ Car lantern: An audible and visual signaling device located in a car to indicate the car is answering the call and the car’s intended direction of travel.
■ Car platform: The structure that forms the floor of the car and directly supports the load.
■ Compensating rope sheave switch: A device that automatically causes the electric power to be removed from the elevator driving-machine motor and brake when the compensating sheave approaches its upper or lower limit of travel.
■ Motion control: That portion of a control system that governs the acceleration, speed, retardation, and stopping of the moving member.
■ Operation control: That portion of a control system that initiates the starting, stopping, and direction of motion in response to a signal from an operating device.
■ Automatic operation: Operation control wherein the starting of the elevator car is effected in response to the momentary actuation of operating devices at the landing, and/or of operating devices in the car identified with the landings, and/or in response to an automatic starting mechanism, and wherein the car is stopped automatically at the landings.
■ Motion controller: An operative unit comprising a device or group of devices for actuating the moving member.
■ Motor controller: The operative units of a motion control system comprising the starter devices and power conversion equipment required to drive an electric motor.
■ Elevator control room: An enclosed control space outside the hoistway, intended for full bodily entry, which contains the motor controller. The room could also contain electrical and/or mechanical equipment used directly in connection with the elevator, but not the electric driving machine or the hydraulic machine.
■ Control system: The overall system governing the starting, stopping, direction of motion, acceleration, speed, and retardation of the moving member.
■ Designated level: The main floor or other floor level that best serves the needs of emergency personnel for firefighting or rescue purposes identified by the building code or fire authority.
■ Displacement switch: A device actuated by the displacement of the counterweight, at any point in the hoistway, to provide a signal that the counterweight has moved from its normal lane of travel or has left its guide rails.
■ Door or gate electric contact: An electrical device, the function of which is to prevent operation of the driving machine by the normal operating device unless the door or gate is in the closed position.
■ Electrical/electronic/programmable electronic (E/E/PE): Based on electrical (E) and/or electronic (E) and/or programmable electronic (PE) technology.
■ Hydraulic elevator: A power elevator in which the energy is applied, by means of a liquid under pressure, in a hydraulic jack.
■ Roped hydraulic elevator: A hydraulic elevator in which the energy is applied by a roped-hydraulic driving machine.
■ Hoistway door or gate locking device: A device that secures a hoistway door or gate in the closed position and prevents it from being opened from the landing side except under certain specified conditions.
■ Hydraulic jack: A unit consisting of a cylinder equipped with a plunger (ram) or piston, which applies the energy provided by a liquid under pressure.
■ Driving machine: The power unit that applies the energy necessary to drive an elevator.
■ Geared driving machine: A direct driving machine in which the energy is transmitted from the motor to the driving sheave, drum, or shaft through gearing.
■ Traction machine: A direct driving machine in which the motion of a car is obtained through friction between the suspension ropes and a traction sheave.
■ Gearless traction machine: A traction machine, without intermediate gearing, that has the traction sheave and the brake drum mounted directly on the motor shaft.
■ Hydraulic driving machine: A driving machine in which the energy is provided by a hydraulic machine and applied by a hydraulic jack.
■ Direct hydraulic driving machine: A hydraulic driving machine in which the driving member of the hydraulic jack is directly attached to the car frame or platform.
■ Roped-hydraulic driving machine: A hydraulic driving machine in which the driving member of the hydraulic jack is connected to the car by wire ropes or indirectly coupled to the car by means of wire ropes and sheaves. It includes multiplying sheaves, if any, and their guides.
■ Elevator machine room: An enclosed machinery space outside the hoistway, intended for full bodily entry, which contains the electric driving machine or the hydraulic machine. The room could also contain electrical and/or mechanical equipment used directly in connection with the elevator.
■ Maintained pressure: The hydraulic pressure between the pressure source and the control valves of a maintained pressure hydraulic elevator.
■ Compensation means: The method by which unbalanced forces due to suspension means are reduced, utilizing one or more compensation members and their terminations.
■ Elevator nonstop switch: A switch that, when operated, will prevent the elevator from making registered landing stops.
■ Inspection operation: A special case of continuous-pressure operation used for troubleshooting, maintenance, repair, adjustments, rescue, and inspection.
■ Phase I recall operation: The operation of an elevator where it is automatically or manually recalled to the recall level and removed from normal service because of activation of firefighters’ emergency operation.
■ Phase II emergency in-car operation: The operation of an elevator by firefighters where the elevator is under their control.
■ Elevator pit: The portion of a hoistway extending from the sill level of the bottom terminal landing to the floor at the bottom of the hoistway.
■ Rated speed: The speed at which an elevator is designed to operate.
■ Car or counterweight safety: A mechanical device attached to the car, car frame, or to an auxiliary frame, or to the counterweight or counterweight frame in order to stop and hold the counterweight under one or more of the following conditions: predetermined overspeed, free fall, or if the suspension ropes slacken.
■ Traveling cable: A cable made up of electric conductors, which provides electrical connection between an elevator car or counterweight and a fixed outlet in the hoistway or machine room.
■ Unintended car movement: Any movement of an elevator car that is not intended car movement, resulting from a component or system failure.
Besides the foregoing definitions, which give us a valuable overview, Part II (Hoistways and Related Construction for Electric Elevators), Part III (Machinery and Equipment for Electric Elevators) and Part IV (Hydraulic Elevators) provide specific mandates and construction details. It is necessary to comply with these ASME A17 provisions in order to ensure that existing installations remain safe for workers and users. In performing repairs, it is essential that safety mechanisms remain in place, intact and fully functional. Moreover, workers should constantly evaluate the overall installation in the context of NEC and ASME A17 compliance. Additionally, Occupational Safety and Health Administration (OSHA) regulations are relevant to workplace safety. Keep in mind that most elevator accidents involve not members of the public who are using the equipment, but workers who are installing, maintaining, and repairing it. The obvious hazards are falling, being crushed, and being electrocuted. Additionally, there are long-term health hazards. Proper workplace procedures protect technicians and workers.
ASME A17 Part II applies to hoistways and related construction for electric elevators. It begins with the very basic statement that hoistways are to be enclosed throughout their height. The enclosure protects elevator machinery to a limited but very significant extent from fire that may occur in an adjacent area. This buys time for elevator occupants to descend to the ground floor (Phase I) and for firefighters to take manual control of the elevator (Phase II) so that they can endeavor to halt the fire and perform rescue operations.
Notwithstanding the fact that the hoistway protects the car and occupants from an external fire, the fact must be recognized that in some instances this vertical shaft can act as a highly efficient flue, increasing a fire’s temperature and facilitating its spread to upper floors. We shall see in Chapter 1, History, some attempts to confront this problem, for example by installing safety hatches, which consisted of sliding or hinged panels at each floor to create a series of closed compartments to control the draft. These panels would open to allow the car to pass. The hoistway moreover serves as a supporting structure for cable sheaves, counterweight guards, doorways at landings, control wiring, guide rails, and safeties.
Protection is to be provided around elevators adjacent to areas permitting passage of people and adjacent to areas permitting storage. This protection is permitted to be fixed guards, or sufficient distance from the moving portion of the elevator, or a combination of both, so that no one can accidentally come in contact with the elevator. Hoistway enclosures must have substantially flush surfaces on the hoistway sides used for loading and unloading. Landing sills, hoistway doors, door tracks, and hangers are permitted to project inside the hoistway enclosure.
■ Where a car leveling device is provided and the hoistway edge of the sill is either flush with or projects into the hoistway, the guard is to have a straight vertical face extending below the sill not less than the leveling zone plus three inches.
■ Where the sill projects inward from the hoistway enclosure, the bottom of the guard is to be also beveled at an angle of not less than 60 degrees nor more than 75 degrees from the horizontal or the guard is to be extended from the hoistway edge of the landing sill to the top of the door hanger pocket of the next entrance below.
■ Where no car leveling device is provided and the sill projects inward from the general line of the hoistway, the guard is to be either beveled at an angle of not less than 60 degrees nor more than 75 degrees from the horizontal, or it is permitted to have a straight vertical face extending from the hoistway edge of the landing sill to the top of the door hanger pocket of the next entrance below.
■ Metal guards are to be installed in the pit and/or machine room located underneath the hoistway on all open sides of the counterweight runway except that where a compensating chain(s) or rope(s) is attached to the counterweight; the guard is permitted to be omitted in the pit on the side facing the elevator car to which these chains or ropes are attached.
■ Where pit-mounted buffers are used, the guard is permitted to be omitted where the bottom of the counterweight resting on its compressed buffer is seven feet or more above the pit floor or above the machine or control room floor if located under the hoistway.
■ A permanent means of access to elevator machine rooms and machinery spaces is to be provided for authorized persons. Access doors to machine rooms and machinery spaces are to be kept closed and locked. The only means of access to a machine room is not to be through the hoistway. Permanent lighting is to be provided in all machine rooms and machinery spaces.
■ Means of access for authorized personnel is to be provided to all pits. A stop switch is to be provided in the pit for every elevator.
■ For hoistway doors, interlocks are required for passenger elevators.
■ Elevators that are operated from within the car are to have elevator parking devices installed at every landing that is equipped with an unlocking device.
ASME A17 Part III covers machinery and equipment for electric elevators.
■ Car and counterweight buffers or bumpers are to be provided. Solid bumpers may be permitted in lieu of buffers.
■ On rod-type counterweights, the rod nuts are to be cotter-pinned and the tie rods are to be protected so that head weight cannot crush the tie rods on buffer engagement. The weights are to be protected so they cannot be dislodged.
■ Every elevator car is to have a platform consisting of a non-perforated floor attached to the platform frame supported by the car frame, and extending over the entire area within the car enclosure.
■ Hinged platform sills, where provided, are to have electric contacts that will prevent operation of the elevator by a normal operating device unless the hinged sill is within two inches of its fully retracted position.
■ The elevator is permitted to be operated by the leveling device in the leveling zone with the sill in any position.
■ Floating (movable) platforms that permit operation of the elevator when the car door or gate is not in the closed position are prohibited.
■ Cars are to be fully enclosed on all non-entrance sides and on top.
■ Cars are to have a car door or gate provided at each entrance equipped with a car door or gate electric contact. It is to be positively opened by a lever or other device attached to and operated by the door or gate.
■ For elevators installed in enclosed hoistways, cars are to be provided with a car top emergency exit with a cover hinged or otherwise attached to the car top so that the cover can be opened from the top of the car only, and opens outward. Interiors of cars are to be provided with electric light or lights. No less than two lamps are to be provided.
■ The car of every elevator suspended by wire ropes is to be provided with a safety capable of stopping and sustaining the car with rated load. When the safety is operated by a governor, the safety is to be capable of stopping and sustaining the car with rated load from governor tripping speed. Counterweight safeties are to be provided and are to be capable of stopping and sustaining the counterweight.
■ Safeties are to be applied mechanically. Electrical, hydraulic, or pneumatic devices are not to be used to apply the safeties nor to hold the safeties in the retracted position. Safeties that depend upon traction for application are prohibited. When car safeties are applied, no decrease in tension in the governor rope nor motion of the car in the down direction is permitted to release the safeties, but the safeties are permitted to be released by the motion of the car in the up direction.
■ Rail lubricants or coatings that will reduce the holding power of the safety or prevent its functioning as required are not to be used.
■ The car and counterweight guide rails are to extend at the top and bottom to prevent the guiding member from disengaging from the guide rails in the event that either the car or counterweight reaches its extreme limit of travel.
■ Sheaves and drums are to be of cast iron or steel and are to have finished grooves for ropes.
■ Winding drum machines are to be provided with a slack rope device having an enclosed switch of the manually reset type that will cause the electric power to be removed from the elevator driving-machine motor and brake if the hoisting ropes become slack or broken.
■ In indirect-drive machines, each chain or belt in a set is to be continuously monitored by a broken belt or chain device of the manually reset type, which will function to automatically interrupt power to the machine and apply the brake in the event any belt or chain in the set breaks or becomes excessively slack. If one belt or chain of a set is worn, stretched, or damaged so as to require replacement, the entire set is to be replaced. Sprockets and toothed sheaves are also to be inspected on such occasions and to be replaced if noticeably worn.
■ The elevator-driving machine is to be equipped with a friction brake applied by a spring or springs, or by gravity, and is to be released electrically. The brake is to be designed to have a capacity sufficient to hold the car at rest with its rated load.
■ Enclosed upper and lower normal stopping devices are to be provided and arranged to slow down and stop the car automatically, at or near the top and bottom terminal landings. These devices are to function independently of the operation of the normal stopping means and of the final terminal stopping device.
■ Manually operated rope (shipper rope) or rod-operating devices, or rope-operating devices actuated by wheels, levers, or cranks are not to be used.
■ Handles of lever-type operating devices of car-switch operation elevators are to be so arranged that they will return to the stop position and latch there automatically when the hand of the operator is removed.
■ Elevators with automatic or continuous-pressure operations are to have a continuous pressure button operating switch mounted on the top of the car for the purpose of operating the car solely from the top of the car. The device is to operate the car at a speed not exceeding 150 feet per minute.
■ The means for transferring the control of the elevator to the top-of-car operating device is to be on the car top and located between the car crosshead and the side of the car nearest the hoistway entrance normally used for access to the car top.
Electrical Protective Devices, as covered in ASME A17, Part III, will be discussed in detail in Chapter 5, Troubleshooting Elevator Systems.
Hydraulic elevators, as covered in ASME A17, Part IV, will be discussed in detail in Chapter 2, Types of Elevators.
The requirements listed above are a small part of the entire elevator Code. They are presented by way of introduction to the general topics covered in this book.
