Tech Articles | EMA Inc.

Pre Charge on Siemens Robicon Perfect Harmony VFD

One of the key features of all low voltage VFDs is their ability to softly charge the DC bus capacitors. This feature is not a readily available on the Siemens/Robicon Perfect Harmony MV VFDs. The Perfect Harmony VFD can be easily modified to include this feature. Soft (or Pre) charging the bus capacitors limits the inrush current upon power up, and prevents damage to transformers, power devices, and other connected devices. Within the Siemens Robicon Perfect Harmony medium voltage VFD…

Low Cost Medium Voltage VFDs

Medium Voltage VFDs are coming down in price as the market grows more competitive. Nonetheless, they remain expensive. The cost is not only the initial price, but the size of medium voltage VFDs means the installation costs are significant. All that said, at EMA we love medium voltage VFDs, enjoy repairing them, and selling them. They are very reliable, and are becoming more and more commonplace. One way to greatly reduce the purchase price and get low cost medium…

Pipelines: The safest transportation of all

The United States has become the worlds leading producer of petroleum. Credit the oil and gas industry, and their cutting edge technologies. It has never been cheaper or safer to extract oil and gas, and the industry future is bright. By far, the safest transportation method known for this product is pipelines. Emotional and anecdotal arguments against pipelines abound, but the actual data is inarguable. Pipelines are the safest method known to carry petroleum products. Pipelines already carry the…

Water Treatment: Making America Great

(Eddie Mayfield is the President of EMA, a company specializing in Electronic Motor Controls with particular expertise in Water and Water Treatment facilities) I had the opportunity to visit St. Petersburg and Moscow a few years ago. Both are beautiful cities, much nicer than I anticipated. St Petersburg, with its beautiful art and history is striking. I was amazed at how picturesque Red Square in Moscow was. Both cities were great to visit, the people were wonderful, and I hope…

Rockwell Allen Bradley Powerflex 7000 Shorting Issue

We recently had a customer sustain significant damage on their 2500 HP Allen Bradley Powerflex 7000 medium voltage VFD due to degraded rubber O-rings designed for reducing noise between the SGCT and the heat sink it sits on. After some digging, we found this to be a known problem in this Rockwell medium voltage VFD. In November of 2016 an engineering note was released in the Rockwell Knowledge base regarding the Powerflex 7000 medium voltage VFD: note 969771 states: “In…

Precharge Circuit for Medium Voltage MV VFD

It is common practice to have a precharge circuit in almost all low voltage VFDs, although this is not the case in MV VFD design. Inrush current can cause major damage to a medium voltage VFD. This blog describes how and why this damage occurs.