AC DRIVES AND VIBRATION
The question of whether an AC drive is suitable to survive a seismic event is dependent on the drive and the severity of the event.
Drives are tested to withstand certain vibration levels. When considering the vibrations caused by machinery, this is usually classed in terms of amplification. Vibrations caused by machinery would normally be measured by millimeters of amplification, whereas seismic events would normally reach centimeters of amplification.
If your drive is destined to operate in environments exposed to high machinery vibration or high seismic activity, then you’ll need an AC drive tested to withstand those particular stresses.
AC drives and seismic stress
AC -156 - Seismic Certification by Shake-Table Testing of Nonstructural Components by the International Code Council is one of the most common tests of how electronic engineering components cope under seismic stress. To test drives so they are capable of reaching this standard, leading manufacturers like Danfoss will test three main factors, these are:
SDS - (Spectral response acceleration at short period)
IP - (Importance Factors)
z/h - (height factor ratio)
When components are tested for these factors, those which are rated at 2.6g SDS or higher, IP of 1.5 and z/h of 1 they can be mounted in any kind of building on any kind of floor. This is particularly important for areas of the world which are vulnerable to seismic events. Of course, if you are unsure as to the suitability of your AC drive, whether it is currently in operation or you are planning to install a new drive then contact Northern Industrial. Our engineers have experience with thousands of parts and drives, so will happily advise on the suitability of your installation.
Functionality and reliability
A further standard worth considering is IEC 60068 - 2 - 64. This standard tests both short term functionality and long term reliability. By running tests on the component in three different directions, its possible to build a clear picture of how the part copes under stress. The part is tested through a Power Spectrum Density (PSD) curve up to 1000 Hz to build a thorough understanding of the stress a part can withstand before it is vulnerable to failure.
With these tests, manufacturers build a comprehensive understanding of the stresses their components can withstand. However, when considering real life applications, choosing the correct drive isn’t always that simple, but the IEC 60721-3-3 standard is a good place to start. This standard defines mechanical conditions as classes - known as M classes. These classes range from stationary (sinusoidal) and non-stationary vibrations which are rated from 3M1 to 3M8. Consulting this guidance makes choosing the right drive much easier. For example, if you require a drive capable of withstanding 2g vibrations and 25g shock, then you’ll require a 3M6 class drive. In this instance, an option would be the VACON 20x or the VLT DriveMotor.
Marine environments pose further challenges. Many manufacturers offer ranges which include additional marine type approvals. These approvals require additional mounting hardware designed to dampen the intense vibrations experiences on a ship's bridge.
Northern Industrial can help you choose the right AC drive
Whether installing drives intended to withstand shock vibrations, or the unpredictability of a seismic environment, choosing the correct drive is vital to ensure reliability and performance. If you are unsure about which drive you need, get in touch with Northern Industrial today. Our engineers have the benefit of over 40 years of experience installing automation parts in a huge range of environments, so are sure to find you the right solution for your particular application.