Product category:
Industrial Drives/Controls
News Release from: ABB Automation Tech (Drives and Motors) | Subject: 160kW ABB AC drive for Sentridge Control
Edited by the Engineeringtalk Editorial
Team on 18 May 2000
ABB power helps pull mole out of sticky
situations
Expensive downtime on a tunnel boring machine has been eliminated following the use of an ABB drive with Direct Torque Control (DTC) by Coventry-based Sentridge Control
Expensive downtime on a tunnel boring machine has been eliminated following the use of an ABB drive with Direct Torque Control (DTC) by Coventry-based Sentridge Control The 52 tonne microtunnelling machine, provided by Euro Iskei for the West of Scotland Water Authority's 1.7km-long storm water interceptor sewer in Ayr, uses the DTC technology in a 160kW ABB AC drive to avoid damage to the drilling head
The drive controls four 30kW motors that turn the machine's cutting head at a rate of 1 rpm.
DTC uses an advanced motor model that calculates the motors' parameters 40,000 times every second.
This gives an extremely fast response, which means that when the drilling head hits various substrates, from shingle to boulder clay, the speed of the motor can be adjusted instantaneously.
Furthermore, DTC provides 100% torque at zero speed, giving the machine four-times as much starting torque than the traditional star-delta control method, thereby making it difficult to jam the cutting head.
Should the cutting head get stuck, DTC allows the drive to be ramped up to 200% of the normal running torque for about three seconds.
"If this doesn't crush the obstacle then nothing will," says Steve Brooks Project Manager at Euro Iseki.
The drive's fast response times also help reduce machine maintenance costs.
"With Star-Delta control, the transmission of power from the motors to the cutting head can be very aggressive and we would normally have to replace the gears for every 1,800 m of completed tunnel which can be costly," explains Brooks.
"We are already half way through this tunnel and there are no visible signs of wear on any of the gears." The star-delta starter reduces a motor's current and starting torque to about 25% of that of direct-on-line (DOL) starting.
This makes it very difficult for the machine to work its way free once it encounters an obstruction and stops turning.
When a tunnelling machine does get stuck it has to be dug out of the tunnel from above, an expensive operation especially if the machine is beneath a building or a main road.
"If a tunnelling machine this size gets stuck the dig out operation can delay operations by up to twelve weeks and the costs can become very substantial," explains Brooks.
"So far, the DTC technology of ABB's ACS 600 has eliminated the stalling that we would otherwise expect from the star-delta drives." The performance benefits of the ACS 600 are so great that Euro Iseki are now recommending that they are used in all of their tunnelling machines.
The drive has also proved to be very energy efficient.
"For a 120kW drilling machine like this one that is controlled by a star-delta drive we would expect to use a 900 -1,000kVA generator to run the drilling operation," explains Brooks, "But we have replaced it with a 500kVA generator, cutting the installation and running costs in half." With a 2,845mm diameter cutting-head, the machine is the largest of its type ever used by Euro Iseki.
The sewer is 1,700m long and is being constructed in runs of between 90 to 250 metres.
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