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Entry type: FAQ Entry ID: 26556079, Entry date: 09/20/2007

Balancing of three-phase induction motors

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What does balancing mean for three-phase induction motors?


            Rotating motor parts that are not balanced generate vibration in operation that from a
            specific level onwards can damage the motor components. Balancing rotating parts
            reduces this vibration to a non-critical level for the components.

Balancing quality:
            The balancing quality Classes (G) is defined in DIN ISO 1940 Part 1.
            For motors, EN 60034-14 is binding, with vibration severity levels A and B

            The vibration severity levels are classified according to Class A or B;
                    A - for normal operation
                    B - for lower vibration values for specific applications (e.g. high speeds), SH
                    Catalog. Or special customer requirements.

Vibration severity levels:
The new Standard "Mechanical vibration of certain machines with a shaft height of 56
            and higher – measuring, evaluating and limit values of vibration severity:
            "DIN EN 60 034-14 has been valid since 01. Sept. 2004.
            In addition, up to 01.12.2006 it was permissible to apply the previous Standard
            DIN EN 60 034-14 1997-09.
            Low-voltage motors from the Standard Drives Business Division (Catalog D81.1)
            - for orders entered after 01.12.2006 - have been manufactured corresponding to the
            requirements of the new vibration Standard DIN EN 60034-14, Sept. 2004 with
            vibration severity level A.

            The vibration severity levels N, R, S - applicable up to 09/2004 - have been changed
            over to vibration severity levels A and B.
            The low-voltage motors are supplied as standard in level A.
            Vibration severity level B is available by specifying code K02.
            Vibration severity level B is stamped on the rating plate.
            The limit values of the vibration severity levels are maintained in the speed range
            600 rpm to 3600 rpm at a maximum line supply frequency of 60 Hz. An enquiry is
            required for speeds outside the specified range.

Balancing types:
The type of rotor balancing is stamped on the face side of the shaft (drive side) using
            the following letters.

            F = balancing with full key
            H = balancing with half key
            N = balancing without key (=“plain shaft“)

            The half key balancing type has been standard since 01.06.1998; full key balancing is
            possible by specifying option +L68

            For special customer requirements the rotor can be specially balanced in-line with
            customer requirements; for instance, high-speed motors etc. An enquiry is required.

            Additional information on balancing and vibration severity - as well as their limit values -
            are specified in the Catalog for Low-Voltage Motors, D81.1, P.1/55.


Version Issue Changes
1 August 2007 First Edition

Written by: A&D SD CST

Keywords: Three-phase induction motors, balancing,

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