Mechanical Design

Identifying replacement parts should have been straightforward, but it was not. The manufacturer fan drawings had generic descriptions without sufficient detail: no specific manufacturer information, model number, or datum diameter. Specific sheaves could not be identified through the drawings alone.

Field walkdowns were unreliable. Some fans had already been fitted with replacement components that differed from what the drawings showed, meaning you could not trust what was physically installed to match the engineering records. These walkdowns were also time-consuming.

Making this more critical: many of these fans were safety-related equipment at a nuclear generating station. Getting the replacement right was not optional.

I worked with the Plant Design – Mechanical team to identify and select new specific belt drive components (sheaves, sheave bushings, and belts) for two Darlington AC system fans:

• 3/4-73960-F7 (10 HP motor, 1164 rpm required fan speed)
• 2-73960-F11 (1.5 HP motor, 2052 rpm required fan speed)

The goal was to provide new belt drives equivalent to the original drives specified on the manufacturer's fan drawings, with components selected from a single manufacturer for consistency in reliability and maintenance.

The work followed a structured engineering approach, from input gathering through to formal documentation.

1. Gathered input data from engineering drawings, belt drive data sheets, and manufacturer documentation: motor speed, motor power, fan speed, shaft sizes, center distances, and service factor requirements.
2. Input parameters into TB Woods Belt Drive Selection software (version A-2005) using the "Check MTO/Drives" function for manual drive specification.
3. Software calculated optimal components: speed ratio, sheave diameters, belt length, tensioning force, and service factor.
4. Selected specific components from the TB Woods catalog, ensuring shaft bore sizes, keyway dimensions, and bushing types would fit the existing motor and fan shafts.
5. Specified performance test acceptance criteria for field verification after installation.
6. Wrote the Engineering Calculation report documenting all inputs, methods, results, and recommendations.

B belts transmit more power than A belts but require higher tensioning force, which translates to greater bearing load. 5L/4L belts are lighter-duty alternatives. Single-belt drives were preferred where possible to avoid non-uniform tensioning in multi-belt configurations. The belt cross-section was selected based on the power transmission requirements of each fan.

AK sheaves were used for drives under 3 HP with A/4L belts. BK sheaves were used for drives under 3 HP with B/5L belts. A/B combination sheaves were used for drives above 3 HP. On combination sheaves, B/BX belts were preferred because they ride near the top of the groove, making it easier to visually detect wear.

A minimum service factor of 1.5 was required, exceeding the industry recommendation of 1.3. However, excessive service factors (above 3.0) were avoided because they would result in excessive bearing loads from high belt tension. The goal was to land in the range that provided adequate safety margin without overloading the bearings.

The following input data for F7 was obtained from the Belt Drive Datasheet and associated drawings and input to the TB Woods drive selection software. The output components were selected from the TB Woods catalog based on the software's recommendations and added to the new Bill of Materials.

The shaft center distance (SCD) for F7 illustrates the kind of investigative work this project required. The belt drive datasheet listed a minimum SCD of 1 inch and a maximum of 4.5 inches. Calculating the average gave 2.75 inches. When this value was input to the TB Woods software, no results were returned, indicating an error with the recorded values. An SCD of 2.75 inches for a 10 HP fan drive is physically implausible; the sheaves alone would be larger than that.

Instead, I used the SCD of 42.4 inches obtained from the fan drawing itself. This kind of data discrepancy investigation, rather than blindly trusting recorded values, was a recurring part of the work. The unreliable datasheet values were likely legacy entries that had never been corrected, further reinforcing why the existing documentation could not be relied upon without cross-referencing multiple sources.

A performance test was specified to provide additional confidence in the selection of the new components. Before placing any fan in service after component replacement, two criteria had to be met:

1. Actual measured fan shaft speed must be within +/- 5% of the required fan speed.
2. Fan motor running current must be measured and determined to be at or below the Full Load Amperage (FLA) rating on the motor nameplate before placing the fan in service.

These criteria ensured that the selected components would not only deliver the correct fan speed but also that the motor would not be operating beyond its rated capacity under the new drive configuration.

The Engineering Calculation report went through a formal three-tier approval chain within the Plant Design – Mechanical organization:

1. Prepared by: Myself (University Student, Plant Design – Minor Modifications) alongside an Assistant Technical Officer, Plant Design – Mechanical. He provided technical guidance; I performed the actual work.
2. Verified by: Senior Technical Engineer, Plant Design – Mechanical.
3. Approved by: Section Manager, Plant Design – Mechanical.

The document was classified as an Engineering Calculation. The verification method was field verification of acceptance of test results as determined by the System Engineer. The scope was explicitly noted as not affecting the design basis of these fans, making the report exempt from N-PROC-MP-0044 (the Engineering Calculations procedure). The procedure was used as guidance only, per agreement between the Plant Design – Mechanical and Components & Equipment – Mechanical Section Managers.

Occasionally I worked on process flow diagram (flowsheet) updates, reviewing and marking up station flowsheets to reflect design changes from modifications. This involved reviewing engineering drawings and modification packages, identifying components to be added or deleted from flowsheets, and marking up drawings with redline annotations showing the changes. Each annotation included ADD/DELETE callouts with component identifiers: valves, pressure indicators, solenoids, and other instrumentation.

These flowsheets depicted safety-critical systems at the component level, including trip and reset relays, safety circuits, and solenoid controls. This was infrequent work, but it reinforced my ability to read and interpret complex engineering drawings and understand system-level configurations at a nuclear plant.

Beyond the SPOC role and the mechanical design work, day-to-day duties included supporting Modification Team Leaders with ECC process paperwork. This meant performing EC Closeouts (Phase 11 of the ECC process, covering equipment revision updates and documentation to Information Management Services), launching Authorization Requests (ARs), and filing and processing documentation required at various ECC gates.

This was not glamorous work, but it meant I touched the ECC process end-to-end: from tracking projects through the pipeline as SPOC, to performing the actual closeout paperwork, to understanding the design work that happened in between.

Component selection and sizing for belt drive systems in a nuclear facility. Understanding of power transmission fundamentals: belt types, sheave geometry, speed ratios, service factors, tensioning forces, and bearing loads. The ability to gather information from multiple sources (engineering drawings, data sheets, field walkdowns, manufacturer catalogs) and synthesize it into engineering decisions. Investigation of data discrepancies, such as the SCD mismatch on F7, rather than blindly trusting recorded values.

Authored a formal Engineering Calculation report that went through three-tier verification and approval. Worked within (or adjacent to) N-PROC-MP-0044, the Engineering Calculations procedure. Recommended new Bill of Materials entries and CAT ID creation for selected components. Understood the relationship between engineering calculations, field verification, and operational acceptance.

Worked with manufacturer fan drawings, belt drive data sheets, and process flowsheets. Performed flowsheet redline markups for safety-critical systems. Interpreted component-level detail: valves, pressure indicators, solenoid controls, and trip circuits.

This work came from proactively building relationships with other teams, not from my assigned duties. My primary SPOC role was coordination-focused, but I sought out deeper technical engineering work to round out the internship. The Plant Design – Mechanical manager did not come looking for me because he needed help; the collaboration happened because I had made myself known as someone interested in doing more than what was on my job description.