It's cool to match motors with drives

Edited by the Engineeringtalk editorial team Apr 20, 2004

WEG distributor Dorlec has applied a matched WEG 200kW motor/drive package to solve a recurring problem of motor and inverter failures.

WEG distributor Dorlec has applied a matched WEG 200kW motor/drive package to solve a recurring problem of motor and inverter failures, which was costing thousands of pounds in repair bills and resulting in considerable lost production at SCA Hygiene in Chesterfield.

The WEG package gives SCA the benefits of a three-year warranty, which is now standard on all UK supplied WEG drives and motors.

SCA is a truly global company, manufacturing some of the most well known brands of absorbent hygiene products in the world.

At the company's Chesterfield mill, paper, for use in tissues and paper towels, is produced in a continuous process, 365 days a year.

The paper is produced on a 50m-long manufacturing line, which includes a large drying cylinder.

Serving this dryer are large wet end and dry end fans, which are crucial to the final stages of the production process.

The wet end fan is controlled by a 200kW inverter/motor combination, which had, until recently, proved to be unreliable, the motor and/or the inverter failing on several occasions, all of which resulted in total line stoppages and considerable lost production.

Faced with this continuing problem, Steve Nam, the engineer in charge of the paper line, enlisted help from WEG distributor Dorlec.

Based locally to SCA in Chesterfield, Dorlec is a specialist in drives and motor control and offers a well-established trouble shooting/fault finding service on drive systems.

Subsequent investigations into the cause of the failures revealed the problem to be a lack of direct short circuit protection against over currents on the main motor output circuit.

In view of this, Dorlec advised replacement of the existing equipment.

SCA agreed, and subsequently a matched 200kW motor/drive package from WEG was installed.

Because of the criticality of the production environment, and the costs of lost production, WEG undertook to back the package from Dorlec with a 3 year warranty - a guarantee which is now offered on all UK supplied WEG motors and drives when provided as packages (motor and drive).

In addition, WEG also undertook to keep a spare drive and motor in stock at Dorlec as an additional backup safeguard for SCA.

Since installation some months ago, the WEG package has performed perfectly under demanding humid conditions, prompting Steve Nam to comment: "No news is good news.

We have worked with Dorlec over many years and they have always come up with the goods.

We like the fact that, with the WEG equipment, we have a the security of a 3-year warranty, a readily available spare, should we require it, and a single source responsibility for the equipment, which is based locally".

The positive results achieved by SCA with the WEG inverter/motor combination directly support those obtained in exhaustive tests carried out at WEG's headquarters in Brazil.

These tests allied WEG's own, and other manufacturers' ranges of drives, with WEG's W21 line of high efficiency motors.

The only variable in the tests was the make of drive, all other conditions being maintained the same The tests revealed that motor temperature increase (delta T) was up to 11% lower using WEG drives, when compared to the other VSDs tested.

This is important for motor longevity, because when motor operating temperature is lower, the benefit is a longer insulation life.

Also aiding motor life is the fact that WEG motors are designed specifically for use with VSDs.

This means that their insulation is not subject to the damage that can arise from rapid voltage rises, this the result of mismatching of motor cable impedance and motor impedance.

However, to protect motors that are not so well insulated, WEG has ensured that the turn on time of the output devices in its new drives is set at a level that reduces voltage rise time.

As this feature is internal to the drive, no additional external output chokes or special output filters are required, ensuring that greater motor reliability is not bought at the expense of additional cost.