IS 12075 : 2008 Mechanical Vibration of Rotating Electrical Machines with Shaft Heights 56 mm and Higher - Measurement, Evaluation and Limits of Vibration Severity

1 Scope

1.1 This standard specifies test and measurementconditions and fixes the limits for the level of vibrationseverity of an electrical machine when measurementsare made on the machine alone, at a testing departmentunder properly controlled conditions.

1.2 This standard is applicable to dc machines and three-phaseor single-phase ac machines with shaft centreheight 56 mm and higher and a rated power up to50 MW, at nominal speeds from 500 rpm up toand including 3 000 rpm.

NOTE - The mechanicalvibrations in rotating machines ofspeed lower than 500 rpm shall be subject to agreement betweenthe purchaser and the manufacturer.

1.3 For vertical and flange mounted machinesvibrations are to be measured in a state of freesuspension. However for vertical machines having shaftheight greater than 400 mm the vibration may also bemeasured with rigid mounting. Under this conditionthe vibration limits as applicable to horizontal machineswill be applicable (see 8.2).

1.4 This standard is not applicable to machines mountedin-situ, three-phase commutator motors, single phasemachines, three-phase machines operated on single-phasesystems, vertical water power generators,permanent magnet generators or series wound dcmachines and motors for submersible pumps.

NOTE - The shaft height of a machine without feet, or amachine with raised feet, or any vertical machines, is to betaken as the shaft height of a machines in the same basic Irame,but of tbe horizontal shaft mounted type IMB3 (see IS 2253 :1974 Designation for types of construction and mountingarrangementof rotating electrical machines).

1.5 Introduction

Vibration in rotating electrical machines are caused by:

a) Unbalance in the rotating masses;

b) Slight deformations in the frame or bed of themachine caused by certain magnetic attractionbetween the stator and rotor;

c) Rolling bearing; and

d) Aerodynamic loads and some secondaryeffects such as instability of the shaft in thebearings, passive resistance, asymmetricexpansion, etc.

Inspitc of accurate balancing that can be achieved,residual unbalance generally proves to be the maincause of once per revolution vibrations found in themachine.

The measurement of vibrations is closely linked withthe mounting of the machine and it is generallydesirable to carry out vibration measurements underactual installation and operating conditions. However,to estimate the quality of balance as far as balance andvibrations of rotating electrical machines areconcerned, it is necessary to measure the vibrationson the machine alone under proper test conditionswhich permit reproducible tests to be carried out andprovide comparable measurements.

2 References

The following standards are necessary adjuncts to thisstandard: