Gene Vogel
EASA Pump & Vibration Specialist

The EASA AC Motor Verification & Redesign - Version 4 software (ACR-MotorDb) is a powerful tool for service centers providing the capability to meet their customer’s needs for AC stator and wound rotor redesigns. In most cases, the data from the existing winding is recorded when that winding is removed from the core. But occasions arise where that original data is not available; it may have been recorded incorrectly or a different service center may have stripped the core but not completed the repair. In those cases, the service center must come up with a new “bare core” winding design. ACR-MotorDb has some specific features to address this need.

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HOW TO CALCULATE A WINDING FROM A BARE CORE

The MotorDb segment of the program is the EASA Winding Database compiled over decades from winding data submitted by EASA members. With over 300,000 winding records, it is likely that windings similar to the original winding are available in MotorDb. By simply searching the database for the core dimension criteria, a list of prospective matching windings is returned. A winding from the database does not have to match the original motor nameplate exactly to be used as basis for the bare core design. When a matching winding is selected, that data can be automatically transferred to the Redesign program where modifications needed to match the desired criteria can be adjusted. The process is smooth, effortless and accommodates most 3 phase induction motor windings.

The first step is to display a list of prospective windings that closely match the bare core dimension criteria. Enter the core length, bore diameter, number of slots and poles into the MotorDb search dialog box. As an example, we will search for a 12” core length, 14” bore diameter and 72 slots for a 125 HP, 6 pole Marathon motor. Initially enter only the core dimensions, number of slots and number of poles (Figure 1); the Get Count feature will quickly return the number of matching records. If the result is about 50 or fewer motors, click OK to retrieve those records into a spreadsheet format where the records can be sorted by columns and reviewed. If the Record Count is too large, enter additional criteria to narrow the search. For our example, 44 records were found, and the resulting spreadsheet is illustrated in Figure 2.

The spreadsheet can be sorted by columns to easily review the data. It is useful to sort by the AirDensity (AGD) and Power (Pwr) columns to assess if the bare core is a good candidate for the desired resulting winding. If there are several windings with the desired power rating and the AGD is within acceptable limits, there is assurance the redesign will be successful. For our example, there are 16 windings rated at 125 HP and 10 of them are Marathon motors. So, in this example, it is likely original factory data is available. Of course, that is not always the case. Suppose our bare core is a Siemens motor, which is not listed. We can still select a different manufacturer winding as the basis for our bare cored design. Select one of the windings from the spreadsheet that matches the desired nameplate data as closely as possible. The full winding data will be displayed in an editor (Figure 3).

This original data record was in the database so no redesign was necessary; the bare core can be wound directly from the database record. Such is not always the case, and the EASA software has a function in MotorDb to transfer data from a MotorDb winding record to ACR for redesign. The Send to ACR function in MotorDb creates a new record in ACR where all the ACR redesign functions are available. Taking our example motor, suppose the desired winding is 575 Volts. MotorDb records are only 230 or 460 Volts.

Figure 4 illustrates a MotorDb record sent to ACR and the Volts redesigned from 460 Volts to 575 Volts. The winding is redesigned for 575 Volts and the connection was changed from 6Y to 3Y to keep the Volts per Coil within acceptable limits (Figure 5).

The combination of the EASA Winding Database and the Verification and Redesign program is an easy-to-use solution when presented with bare core winding challenges. For complete step-by-step instructions on bare core redesign, view the tutorial video How to calculate a winding from a bare core available at go.easa.com/wbc.