Save money think maintenance

During a recent plant shutdown, a wood products manufacturer needed an inspection and survey of the three large AC grinder motors it has on-site. The company had only a three-day window in which to complete the survey and approached ABB to manage the task.

A skilled team of technicians was sent to the site to perform white metal bearing and alignment checks, complete electrical testing and provide the customer with a survey of the winding and rotor conditions. 

The first requirement was for the ABB team to attend a safety toolbox meeting and familiarise themselves with safety requirements and protocols. Once all electrical isolations were observed, the team approached the first of the three motors to identify hazards in the area prior to removing the motor covers for inspection.

Visual inspections

Once removed, a visual inspection of the rotor and stator windings took place, with the technicians making observations of key points of interest.  

The rotor was visually inspected for signs of heating, movement of the winding or support blocking. The main rotor leads and associated blocking were also checked, along with the air gap, for signs of obstruction or stator wedge movement. 

The stator was then visually inspected for similar anomalies with the focus on checking for loose or missing blocking, signs of partial discharge (PD) about the coils and main leads from the connection ring. 

Winding coil clearances were noted as a guide to the likelihood of PD occurrence and coil bracing was inspected for tightness. 

The visual inspection for evidence of PD is important when confirming the severity of insulation decay and reporting on the potential for a sudden winding failure. Electrical testing is performed to gauge the condition of winding and judge the presence of PD in a measurable format. 

Once the visual inspection was complete the technicians tested the stator and rotor windings to gain data on winding and insulation resistance.

While the inspection of the rotor and windings was being carried out, the technicians removed the white metal bearing housing tops to gain access to the bearings for inspection. Both non-drive end and drive end bearings were inspected for signs of wear or damage and measurements of the oil clearance recorded. (By checking oil clearances against benchmarks technicians can advise whether repair or replacement of the bearing is needed.) 

Once the bearings were checked, cleaned and re-fitted, the housing oil seal clearances were checked and measurements recorded. The technicians also examined the bearing pedestals and stator feet for any signs of movement or looseness associated with loose fastenings.

All three machines were inspected in the same way and the work completed well within the timeline agreed.

Points of interest identified

As a direct result of this survey several points of interest were identified. Some of the bearings housing pedestal fastenings were found to be loose, and this was remedied. Furthermore, one bearing housing was found to be out of alignment. Although the misalignment of the housing was not significant enough to address immediately, plans have been made to remedy this during the next survey. More importantly, the report provided the customer with key information about the three critical machines and assisted it in introducing a yearly inspection programme. The team was invited back in 12 months to repeat the inspection in order to provide an accurate monitor of the condition of both the motor windings and the wear of the white metal bearings.

As a result of the timely inspection provided by ABB, this business now appreciates the need for regular inspections that will allow security in planning, and that supports consistent trouble-free production operations.

Such inspections are becoming increasingly important as over the recent years there has been a strong focus on increasing shareholder value and meeting the demands of a competitive market. This has led many businesses to concentrate on reducing costs to remain competitive and increase production capability to meet growth targets. 

Industry leaders have identified that by investing in an accurate understanding of the condition of their plant and equipment they reduce the cost not only of maintenance, but also associated costs of production loss due to plant downtime. 

Maintenance supports planning and budgeting

ABB offers industrial customers expertise in the field of preventative and predictive maintenance in support of good planning and budgeting, reducing unplanned breakdowns and maintaining a high level of plant performance.

Its predictive maintenance technical specialists perform on-site plant and equipment condition assessments that provide customers with a good understanding of the condition and performance of plant. These give customers the ability to plan for servicing equipment ahead of time.

Not only does this assessment ensure reliability during operations but it can also be used for managing maintenance costs and allowing accurate budgeting strategies.

The cornerstone of good preventative and predictive maintenance is regular and accurate survey inspection of critical plant and equipment. 

ABB in Hamilton, offers expert mechanical and electrical technical staff in the field of rotating machinery inspection, a service which has been favourably received by its customers.

This experienced team works within tight time frames anywhere in the Asia Pacific region. Once on-site, the team performs inspections on such equipment as mechanical bearings, seals, and other rotating ancillaries associated with HV and LV electric motors and generators. By not having to move the machine into a workshop, costs are further reduced.

Electrical testing can be undertaken on isolated equipment in-situ. This includes winding resistance, insulation resistance, Polarisation Index and Dobel testing, all of which provide useful information on the condition of the machine and assist in planning further servicing that may be identified during the inspection. 

During the inspection process all data taken is accurately collated for the preparation of the final technical report which includes recommendations and budget information to the customer.

The ABB site team also effect repairs and cleaning to both AC and DC electric motors and generators during a site inspection. Minor mechanical and electrical repairs can be made in areas of the machine that are easily exposed and that allow working access.

The observations made and the data gathered during an inspection result in an informative and accurate report to the customer, providing valuable information of the current condition of the equipment.