Case Study: Wye Delta

SKF/Baker Industries received a request from a client to investigate standby gas treatment motor because of leaking grease from the motor and poor airflow through the motor. The motor, a 10 horsepower, 460-volt AC, was attached to an overhung squirrel cage type fan.

After investigating the setup, the culprit was the cooling fan. The fan had degraded and the decision was made to replace the motor.

The work order was planned and a new motor was ordered. The original motor was obsolete and engineering procured a replacement motor, which was evaluated to have the same critical characteristics (voltage, current, speed, horsepower, etc.).

The motor was bench tested electrically and installed on 9/16/2005. The PMT (Post Maintenance Testing) included vibration data was satisfactory at the time of the installation.

Eight months later, however, the motor was extremely hotter to the touch than previously noted, and more importantly, grease was leaking again.

This is where Baker’s expertise came into play. They devised a plan using a contact pyrometer – a thermography camera, strobe, handheld vibration and the Explorer.

The data revealed vibration values below the normal levels, but higher when compared to the installed PMT data. The casing temperature was greater than 200 degree F and the speed, confirmed with the strobe, was 1675 rpm.

The Explorer data showed that the motor was operating significantly lower than the nameplate data.

Detailed analysis of all of the data suggested that an investigation was required into the design of the motor and it’s application.

After contacting the vendor of the replacement motor and a subsequent check of the wiring, it was determined that the new motor was a delta run motor. The motor had been connected in a wye configuration (as per the removed motor).

Because of technology and common sense, you should be able to pinpoint a problem with a motor and provide a solution that will save you time, money, and a headache.

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