EMA has been servicing the electric motor drives on large tunnel boring machines for some time now. A Drive Lines newsletter article, Boring Service Call, was published in January of 07 about a specific call here in Georgia.
The largest TBM company in the world is Herrenknecht in Schwanau Germany. Trey and I were privileged to visit their facilities earlier this year, and it was a fascinating experience. The image on the right is the entrance to the plant, and the concrete circles are actual casings from one of their various world-wide tunnel projects.
We seldom see these giant machines out of the ground, and within the tunnels it’s difficult to get a perspective on the entire machine.
While in Germany, we were able to actually walk around and inspect a complete machine. No one seeing one of these behemoths in clear view can help but be impressed at the genius of Martin Herrenknecht when he developed this technology and formed Herrenknecht in 1977. To say the least, they are engineering marvels.
Tunneling through various types of earth is challenging, and Herrenknecht has developed great expertise in this area. Sometimes in soft earth, they must pressurize the cutting head area, and anyone needing access to that part of the machine must enter via an airlock system. Similar to deep sea diving, the workers can only stay there for a short period of time, and must endure decompression chambers upon exiting. Very careful geologic analysis is required and the engineers have to be prepared for penetrating large pockets of water in addition to the various types of soil, sand, and rock.
In addition to air pressurization, the machine must often inject materials at high pressure into the earth surrounding the cutter head to avoid a collapse. Once the head of the machine passes, prefabricated concrete walls are installed to shore up the tunnel. TBMs do NOT back up well, so it’s imperative that great care be taken to insure that the machine doesn’t get stuck or off course.
One question often asked, is “how do they keep this huge machine going in the correct path?” (Keep in mind, that it isn’t uncommon for two machines to be starting at opposite ends and tunneling toward each other, so precision is necessary. )
They do this by carefully using lasers on a frequent basis to check the path, and by making minor adjustments to the cutting head. As we’ve often noted here at EMA, astonishing feats of engineering are commonplace at Herrenknecht.
The motor drives are specialized large horsepower VFD s manufactured by Schneider Power Drives in Austria. We were also privileged to visit Schneider early this year. Schneider Power Drives is a high quality company with very skilled people, of whom we think highly.
EMA has been blessed to have a great relationship with both Schneider and Herrenknecht, and we’re proud to serve as the north American service center for both. It’s not just quality equipment that makes great companies; it’s great people. We find that to be true for both of these companies; friendly, results oriented, and competent are the best descriptions of the folks at both Herrenknecht and Schneider Power Drives.
TBM service calls are usually performed under ground, sometimes, several miles into the tunnel. You often enter via a vertical shaft, and then climb aboard a special locomotive used both to transport personnel and equipment. The materials generated by the tunneling, are either removed by a long conveyor, or are liquefied and pumped out.
The motor drives can be either air-cooled or liquid cooled, and are usually high horsepower open loop vector drives. There are both variable and constant torque loads, and while at times the units are readily accessible for service, at other times, the working space is very tight. TBM service is not a place for the claustrophobic. Downtime is very costly on a TBM, and so a quick and efficient response is necessary. The tunnel operators often stock spare parts, and additionally, we keep parts here at EMA.
While not widely known, TBMs are at work all over the world. Since TBMs can construct large tunnels with very little surface disturbance, it’s possible for even those near the vicinity of a tunnel project to be completely unaware of the machine’s presence. TBMs are an economically and environmentally attractive solution for utility, traffic, water and sewer construction, and they’re more and more becoming the standard way to construct tunnels in urban or environmentally sensitive environments. Because TBMs don’t use dynamite, they’re safer, and for those living in the area of the tunnel, a better neighbor.
As we say.. it’s an underground business, but we like it!