BS ISO 7919-2:1996 pdf free download.Mechanical vibration of non-reciprocating machines — Measurements on rotating shafts and evaluation criteria — Part 2: Large land-based steam turbine generator sets.
Introduction
This part of ISO 7919 deals with the special features required for measuring transverse shaft vibration on the coupled rotor system of steam turbine generator sets for power stations. Evaluation criteria, based on previous experience, are presented which may be used as guidelines for assessing the vibratory conditions of such machines.
A general description of the principles which are generally applicable for the measurement and evaluation of shaft vibration of non-reciprocating machines is given in ISO 7919-1.
1 Scope
This part of ISO 7919 gives guidelines for applying evaluation criteria for shaft vibration under normal operating conditions, measured at or close to the bearings of steam turbine generator sets. These guidelines are presented in terms of both steady running vibration and any magnitude changes which may occur in these steady values. The numerical values specified are not intended to serve as the only basis for vibration evaluation since, in general, the vibratory condition of a machine is assessed by consideration of both the shaft vibration and the associated structural vibration (see the introduction to ISO 7919.1).
This part of ISO 7919 applies to large land-based steam turbine generator sets for power stations, having rated speeds in the range 1 500 r/min to 3 600 r/min, and power outputs greater than 50 MW.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part of ISO 7919. At the time of publication. the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO 7919 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of TEC and ISO maintain registers of currently valid International Standards.
ISO 7919-1:1996, Mechanical vibration of non-reciprocating machines — Measurements on rotating shafts and evaluation criteria — Part 1: General guidelines.
ISO 10816-1:1995, Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 1: General guidelines.
ISO 10816.2:1996, Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 2: Large land-based steam turbine generator sets in excess of 50 MW.
3 Measurement procedures
The measurement procedures to be followed and the instrumentation used shall be as described in
ISO 7919-1.
Early experience on large steam turbine generator sets was restricted to the measurement of absolute shaft vibration using shaft-riding transducers. More recently, as non-contacting transducers were developed, relative shaft vibration measurements have become more common but, if required, the absolute shaft vibration can be obtained by vectorially combining the outputs of a non-contacting transducer and a seismic transducer on a common mounting which measures the structural vibration. Both approaches are at present in common use and measurements of relative shaft or absolute shaft vibration are therefore equally acceptable for the purposes of this part of ISO 7919. For monitoring purposes, the measuring system shall he capable of covering overall vibration up to a frequency of not less than 160 Hz, which is the practical limit for most shaft-riding transducers. However, it should be noted that for diagnostic purposes it may be desirable to cover a wider frequency range.
Prior to running large steam turbine generator sets up to speed, slow-roll measurements of shaft displacement may be carried out. The results obtained are compared with expected values and maybe used as a basis for judging whether the state of the rotor line is satisfactory; for example whether a temporary bend is present in the rotor or whether there is a degree of bearing-support misalignment. Such measurements cannot normally be regarded as giving a valid indication of shaft runout under normal operating conditions since they can be affected by, for example, temporary bows, erratic movements of the journal within the bearing clearance, axial movements, etc. In particular, it is recommended that vector subtraction of slow-roll measurements from rated speed vibration measurements should not be carried out without consideration of the above factors, since the results may provide a misleading interpretation of the machine vibration (see Iso 7919-1).
NOTE 1 If1ow-ro1I measurements are taken, it is important to ensure that the low-frequency characteristics of the measuring system are adequate.
4 Evaluation criteria
Criteria for vibration magnitude, changes in vibration magnitude and operational limits are presented in annex A.
The vibration magnitude is the higher value of the peak-to-peak displacement measured in two selected orthogonal measurement directions. The values presented are the result of experience with machinery of this type and, if due regard is paid to them, acceptable operation may he expected. If only one measuring direction is used, care should be taken to ensure that it provides adequate information (see Iso 7919- 1).
The criteria are presented for the specified steady-state operating conditions at the rated speed and load ranges. They apply for normal slow changes in electrical loading of the generator but do not apply when different conditions exist or during transient changes, for example during start-up and shut-down and when passing through resonance ranges. In these cases alternative criteria are necessary.
It should be noted that an overall judgement of the vibratory state of a machine is often made on the basis of both shaft vibration as defined above and of measurements made on non-rotating parts (see ISO 10816-1 and ISO 10816-2).