Design Is the most important step to success in any project.

Poor design lends itself to poor outcomes, expectations, viability, maintenance & serviceability, fault/issue diagnosis, meeting relevant standards and safety, most importantly borderline useless usability.

For example a plant with poor power quality is noticed and several key issues discovered. Unfortunately the immediate problems may be rectified but other concerns are discovered and dismissed as "do that later"

As most people know later never happens. A Issue is discovered a large VFD is running at a high THD or total Harmonic  

Distortion which express itself as many issues on the power betwork. The drive is discovered to be 315kW rating,

The motor is rated at 250kW but when simple calculations and measurement discover the maximum load is around 220kW. The drive is also located in a questionable area and has the possibility of being engulfed with Ammonia is something where to fail.

The quick fix is to place a choke or inductor in front of the drive to help with the high THD.

The cost of materials and labour is about 30% of the replacement drive but not including downtime. Lowering the THD is not going to meet Maximum requirements as per IEEE & IEC standards but will make a noticeable difference to the network.

Meeting the future of machine safety requirements and various safety standards not to mention engineering best practice are not thought of as above. A solution maybe install a Active Harmonic filter further upstream in the network which will also help when the VFD is not running.  The AHF  has ethernet comm which also allows to monitor the viability of the project and monitor for other issues. It has been found that with some simple tests before installation a suitable size was selected which allow for the Oversized drive to be replaced with a utlra low harmonic VFD in the future which will be installed in a purpose built swithcroom as well as ancillary and auxiliary equipment install in the previous poor environment. 

As the enginer selected Ethernet/ip DLR comms card now have redundancy comms, which also allowed for the drive to be commissioned and tested for production before the change over which only took several hours to connect to the existing motor.

By selecting comms option it meant the existing PLC hardware used to control and monitor the existing drive stayed in tact until the drive was decommissioned. Saving more money and now have that PLC hardware available for other projects. The original labelling was reused and the comms cable where marked in recognition the new identification system employed by the plant.

As it was identified in a risk assessment the drive will be allocated and STO shutdown in the future when the Control systems are upgraded.

If the choke was to be installed this is the largest Motor/VFD combination which if the drive was upgraded in the near future to a Ultra Low Harmonic VFD the choke would be useless and rendering it not uselful anywhere in the plant.