Elevators | Escalators
Introduction
Passenger transportation facilities such as moving walkways, escalators, and elevators, are commonly found in airports, supermarkets, and subway stations. These facilities are often operated continuously to transport people from one place to another, sometimes spanning several floors. They are all driven by a variable frequency inverter.
Working principle
A variable frequency inverter is connected to an electric motor via motor cables, with a gear or an elevator winch directly attached to the motor. The motor accelerates to its nominal speed at start-up and decelerates at the end of a cycle. The pulse-width modulated motor voltage of the inverter contains a typical common-mode voltage that can drive a common-mode ground current via the motor bearings, resulting in accelerated wear of the bearing raceways.
Damaging effects
If a bearing current flows at a sufficient current level, it results in electrical erosion in the bearing, which in the worst case results in fluting on the motor bearing raceway after a few thousand hours of operation. The mechanical vibrations increase, and in the worst case, the bearing fails. Additionally, electromagnetic noise conducted or radiated can occur due to the common-mode noise and the resulting leakage currents.
The Solution
Our Blueferrite-Nanocrystalline cores can be easily mounted above the motor cables at the inverter output. The high impedance of our ring cores combined with high saturation current level reduces the unwanted common-mode ground currents to a harmless level. This increases bearing lifetime and prevents unwanted maintenance costs.