Elevator buffers are safety devices which are required to be mounted at the base of an elevator shaft. As with any safety device elevator buffers have to meet with a variety of specifications but probably the most important of these is the manner in which the buffers must bring an impacting elevator car to rest. There are different technical specifications for elevator buffers in different regions worldwide however all employ the same basic performance criteria.
Since the very early days of elevators, a variety of safety systems have been employed to ensure that the elevator will not free fall. The purpose of elevator buffers is to provide protection against the malfunction of an elevator control system resulting in the elevator continuing to travel past the lowest stop to the base of the elevator shaft. The buffers are specified in accordance with the operating velocity and mass of the elevator.
Although freefall is not a realistic event for an elevator, the specification and code requirements are based on the assumption of freefall.
The requirement for elevator buffers fall into two categories depending on the type of buffer.
1. Energy accumulation buffers: These can take the form of simple mechanical springs or polymer buffers which store the absorbed energy of the impact in the form of strain energy. In some accumulation buffers this stored energy can be dissipated on the return movement of the buffer leading to two separate requirements:
a) Buffers with linear and non linear characteristics – these can be used if the elevator does not exceed 1.0m/s
b) Buffers with buffered return movement – these can be used for elevators that do not exceed 1.6m/s.
2. Energy dissipation buffers: These are usually hydraulic buffers which dissipate the energy of the impact in the form of heat during the travel of the buffer. This type of buffer can be used for all rated speeds, but must be used for speeds of 1.6m/s or over.
BUFFER PERFORMANCE CRITERIA – ENERGY DISSIPATION BUFFERS
Performance criteria in all specifications is governed by 2 underlying rules which state that the buffer must arrest a freefalling mass travelling at 115% of the rated speed of the elevator:
(i) With an average deceleration not exceeding 1g.
(ii) Without exceeding a deceleration of 2.5g for a time period greater than 0.04 seconds.
In addition a further, but separate requirement, states that the buffer stroke must be at least as great as freefall distance required to reach 115% of the rated elevator velocity. It is this requirement that dictates the stroke and consequently the installation height of elevator buffers. Due to customer demands, most elevator buffers do not deviate far from the minimum stroke requirement.
Power Quality and Elevators
Below is a high-level over-view of PQ issues and Standards that is critical for commercial establishments.
PQ & Reliability is key to proper operation of Elevators, Escalators and other loads driven by sensitive electronic controllers.
Poor Power Quality can cause costly malfunction of equipment due to the following :
Unbalance resulting from asymmetric load conditions
Sag & Flicker problems,
Power Factor and Reactive Power Demand
The good quality of power can be specified as :
– the supply voltage should be with-in guaranteed tolerance of declared value. In India, the specifications related to PQ are + 10% variation in Voltage and +2% of frequency.
– The wave should be a pure sine wave within allowable limits of distortion
-Voltage should be balance in all 3-Phases
-Loads must be equally distributed in 3-Phases
-Supply must be reliable
-The Earthing system should serve its purpose properly.
The following is a brief description about various PQ Standards (Detailed info can be shared on request)
IEEE644 – Standard procedure for measurement of Power Frequency electric and magnetic fields from A.C. Power Lines
IEEE C63.12 – Recommended Practice for Electromagnetic compability Limits
IEEE 518 – Guide for Installation of Electrical Equipment to minimize Electrical noise inputs to controllers from external sources
IEEE 519 – Recommended practices and requirements for Harmonic Control in Electrical Power systems
IEEE 1100 – Recommended Practice for Powering and grounding sensitive electronic equipment
IEEE 1159 – Recommended Practice for monitoring electric power quality
IEEE 141 – Recommended Practice for Electric Power Distribution for Industrial Plants
IEEE 142 – Recommended Practice for grounding of industrial and commercial power systems
IEEE 241 – Recommended Practice Electric Power System in Commercial Buildings
IEEE 602 – Recommended Practice Electrical Systems in Health Care Facilities
IEEE 902 – Guide for Maintenance, Operation and Safety of Industrial and Commercial Power System
IEEE C57.110 – Recommended Practice for Establishing Transformer Capability when supplying Non-sinusoidal load
IEEE P1433 – Power quality definitions
IEEE P1453 – Voltage Flicker
IEEE P1564 – Voltage Sag Indices
IEC/TR3 61000-2-1 – Electromagnetic Compatibility – Environment
IEC/TR3 61000-3-6 – Electromagnetic Compatibility – Limits
IEC 61000-4-7 – Electromagnetic Compatibility – Testing and Measurements Techniques – General Guides on Harmonics and Inter-Harmonics Measurements and Instrumentation
IEC 61642 – Industrial A.C. Networks affected by Harmonics – Application of Filters and Shunt Capacitors
IEC SC77A – Low frequency EMC Phenomena
IEC TC77/WG1 – Terminology
IEC SC77a/WG1 – Harmonics and other related Low Frequency Disturbances
IEC SC77a/WG6 – Low Frequency Immunity Tests
IEC SC77a/WG2 – Voltage Fluctuations and other Low Frequency Disturbances
IEC SC77a/WG8 – Electromagnetic Interference related to Network Frequency
IEC SC77A/WG9 – Power Quality Measurement Methods