APPLICATION BULLETIN - JULY 1997 | BACK TO INDEX  

Putting history on paper - PDL Electronics make history at the CHH Mataura Paper Mill

Ranking among the world leaders in their field has earned PDL Electronics Ltd a place in paper making history in New Zealand at Carter Holt Harvey's Mataura Mill. Therefore, when the worlds southern most mill was looking to upgrade the DC drives on its No.2 paper making machine to AC drives, it was PDL's high performance AC motor control Microvectors which were selected to drive the machine.

In a paper making machine, precise coordination of the relative speeds of the various rolls and calenders in each section of the machine is essential. This ensures a uniform quality of paper and eliminates costly downtime resulting from paper breaks. It has always been considered to be one of the most challenging applications of variable speed drive technology. It has traditionally been the domain of DC motors and drives, but recent advances in AC flux vector control technology now means that AC squirrel cage induction motors can be used. AC motors have significant benefits in terms of size, cost and reduced maintenance.

When planning their machine upgrade, Carter Holt Harvey had searched worldwide for the project controller, settling on an English company, Emerson and Renwick, whose engineering experience has allowed them to deal with the specialised aspects of the pulp and paper industry. However when it came down to procuring the key components for the system Carter Holt Harvey was quite specific about where these should be sourced. "We had a preference towards using local companies because of the technical support and back up they could provide," said Carter Holt Harvey Project Engineer, Craig Allan. "Given our post association with PDL Electronics Ltd and Clive Wilson of Dunedin we were very keen to evaluate their capability to meet the quality and service criteria. We have not been disappointed in our decision to select them as our suppliers".

The upgrade was one of Mataura Mill's biggest capital project in recent years and involved a number of unique challenges that had to be overcome. One of the major considerations was the space restriction around the No. 2 paper machine. This resulted in the unique vertical placement of the AC motors which gave improved access to the rear of the machine. It also allowed very simple motor changing and as the motor was flange mounted, it required no realignment. The shaft coupling is of the gear spline type and separates as the motor is lifted clear. Therefore, what used to be a 4 to 6 hour motor change can now be done in one, Mr Allen said.

The biggest challenge though, was introducing four new AC drives to work compatibly with the six older DC drives which the mill would retain. Never before have AC and DC drives been used in tandem. Moreover, if this was not enough groundbreaking work for the project team, it also notched up another milestone by being the first operation in New Zealand where AC drives were employed on a paper making machine.

Traditionally, the mill had run its No. 2 machine with 9 DC drives, installed in the late 1960's. However, by the 1990's these machines were being pushed to their limit. "The DC motors were originally sized to run at 280 metres a minute, however, they were being pushed to 350 metres a minute on some production runs" said Craig. The success of the new upgrade now enables the machines to run at 350 metres a minute comfortably and the drives have the potential to be run at 500 metres per minute.

The PDL Electronics Microvector was a lot easier to install and commission which meant much of the modification work needed on the control equipment was avoided. "This was a major benefit on a project which already had enough obstacles to overcome" said Craig. He went on to explain "Often on a job of this size a number of weeks are allowed to get a section completely tuned. However, the conversion for this project was very smooth, even exceeding Emerson's expectations".

He admits the shut down of Machine No. 2 to complete the project was a high pressure shut down for the mill, yet staff managed to have the system in place in five days. Since then the lack of maintenance and easy control of the PDL Microvector has met with high acclaim for the Mataura Engineering personnel. "With the PDL Electronics digital drives everything is carried out from the control panel", said Craig. "This is a huge improvement from the old regime. The Microvector holds the speed more accurately and has a better response to changes and reacts a lot faster."

The main object of the project was to obtain all round, improved flexibility and that has been delivered. "Being involved in such a project has been exciting for PDL Electronics" said the Southern Area Sales Manager, Hamish Robertson. "Although PDL Electronics is a relatively small company on the global scene its financial and human resources commitment to research and development have meant PDL Electronics' AC motor controllers are extremely competitive with anywhere else in the world".

Mr Robertson attributes the company's leading edge in rapid development of new products to the readiness of New Zealand companies to accept new technologies - an ethic PDL Electronics thrives on. "The New Zealand market as a whole has been very receptive to change which has enabled PDL Electronics to develop our products at a rate far faster than other AC manufacturers in the world," he said.

Mr Robertson also said PDL Electronics had no worries regarding the challenge of putting in their Microvectors to control the new combination of AC and DC motors on the paper making machine.

That confidence has been confirmed by the success of this innovative project and the accolades it has received from Engineering staff.