Patent Description:
In particular the disclosure is concerned with a method of balancing a rotor for a gas turbine engine.

Gas turbine engines, which are a specific example of turbomachines, generally include a rotor with a number of rows of rotating rotor blades which are fixed to a rotor shaft. When a hot and pressurized working fluid flows through the rows of blades in the main passage of a gas turbine, it transfers momentum to the rotor blades and thus imparts a rotary motion to the rotor. As a result of any unbalance of the rotor, vibrations are caused which may adversely affect efficiency and durability of the gas turbine. Satisfactory operation therefore requires accurate balancing of the rotor to suppress vibrations. To this end, the rotor undergoes a balancing procedure by which unbalance is assessed and balancing weights fitted to the rotor.

A known procedure for balancing may comprise mounting the assembled rotor onto a balancing machine, running the rotor at the intended balancing speed and measuring the vibrations of the rotor as part of a so called base run. Subsequently a calibration weight is temporarily fitted to one of the available correction planes included in the rotor design. The rotor is again subjected to rotation and vibrations are measured with the calibration weight in place. This so-called influence run is performed for each available correction plane separately to assess its vibration response. Based on a comparison with the base run, balancing weights are fitted. The balancing weights are fitted to reduce the unbalance of the rotor and therefore generally differ from the calibration weights in terms of both mass and angular location.

It has been found that certain types of rotors, which may be referred to as 'insensitive rotors', are more difficult to balance using the known procedure. That is to say, while certain conventional rotors may be balanced by performing, say, four or five runs in the balancing machine, for insensitive rotors a significantly greater number of runs may be required in order to meet an applicable balancing standard. In certain cases an insensitive rotor requires more than <NUM> runs for balancing, resulting in at least an additional work day in comparison to a sensitive rotor.

<NPL>, discloses a method of balancing a multistage compressor.

Hence a rotor balancing method reducing the number of iterations needed for balancing over conventional methods is highly desirable.

According to the present invention there is provided a rotor balancing method as set forth in claim <NUM>.

Other features of the invention will be apparent from the dependent claims.

Accordingly there is provided a rotor balancing method for a gas turbine. The method comprises providing a rotor (<NUM>) comprising: a first bearing (<NUM>) and a second bearing (<NUM>), and a plurality of correction planes (<NUM>) comprising a first correction plane (<NUM>) and a second correction plane (<NUM>). A first balancing weight (W1) is attached to the first correction plane (<NUM>) and remains attached for all following influence runs. The method further comprises performing a first influence run by: running the rotor (<NUM>) at an intended balance speed and recording a first set of vibration measurements at the first bearing (<NUM>) and the second bearing (<NUM>), wherein the vibrations detected at the first bearing (<NUM>) have a smaller magnitude than the vibrations detected at the second bearing (<NUM>). The method further comprises providing a data set comprising a reference influence vector of the second correction plane (<NUM>), wherein the reference influence vector is an influence vector of a reference rotor (<NUM>) of the same production type as the rotor (<NUM>). The method further comprises fitting a first calibration weight (M1) to the second correction plane (<NUM>) using the reference influence vector to determine the mass and the angular location of the first calibration weight (M1). The method further comprises performing a second influence run by: running the rotor (<NUM>) at the intended balance speed and recording a second set of vibration measurements at the first bearing (<NUM>) and the second bearing (<NUM>), and removing the first calibration weight (M1) from the rotor (<NUM>). The method further comprises calculating an influence vector of the second correction plane (<NUM>) using the first set of vibration measurements and the second set of vibration measurements. The method further comprises carrying out balancing of the rotor by: fitting a final balancing weight (W1') to the first correction plane and a second balancing weight (W2) to the second correction plane (<NUM>) using the calculated influence vector. The mass of the first calibration weight (M1) is inversely proportional to the magnitude of the reference influence vector of the second correction plane (<NUM>).

Using the exemplary method it may be possible to determine the mass and the angular location of the first calibration weight M1 so that an improved vibration response is caused. This improved vibration response is reflected in the second set of vibration measurements, from which an improved influence vector for the second correction plane <NUM> may be obtained. In turn, this allows fitting a balancing weight of optimised mass to an optimised angular location. Accordingly, the method may improve on conventional rotor balancing methods by reducing the time required to reduce vibrations to a tolerable level by using an improved first calibration weight M1. For example, the number of balancing runs may be reduced. Also, the number of correction planes needed for balancing may be reduced. This may be particularly desirable where certain correction planes are difficult to access.

According to some examples, the reference influence vector comprises a magnitude which is an average over the magnitudes of a plurality of reference rotors, and the reference influence vector comprises a phase angle which is an average over the phase angles of the plurality of reference rotors. Using an average may provide for a reference influence vector which more accurately describes the rotor (<NUM>).

According to some examples, fitting the first calibration weight comprises: calculating a calibration mass and a calibration angular location to reduce vibrations at the second bearing using the reference influence vector; selecting the first calibration weight to have a mass substantially corresponding to the calibration mass; and fitting the first calibration weight to an angular location of the second correction plane substantially corresponding to the calibration angular location. By calculating both the mass and the angular location of the first calibration weight, the resulting vibration response may be improved over calculating either the mass or the angular location and using an alternative method, such as knowhow, for determining the other.

According to some examples, the magnitude of the reference influence vector of the first correction plane (<NUM>) is greater than the magnitude of the reference influence vector of the second correction plane (<NUM>), wherein the second reference influence vector is either contained in the data set or computable from the vibration measurements of the data set. By comparing the magnitude of the influence vectors it may be possible to identify a sensitive correction plane. A sensitive correction plane is expected to possess a greater magnitude. The magnitude of the reference influence vector of the first correction plane (<NUM>) is greater than the magnitude of the reference influence vector of the second correction plane (<NUM>) by at least a factor of two. Where the magnitude of the influence vectors differs greatly this may indicate that the smaller influence vector describes an insensitive correction plane. The present disclosure is particularly applicable to balancing using an insensitive correction plane and may considerably improve over conventional methods for insensitive correction planes.

According to the present disclosure, the mass of the first calibration weight (M1) is inversely proportional to the magnitude of the reference influence vector of the second correction plane (<NUM>). Choosing the mass of the first calibration weight accordingly may provide for reduced vibrations.

According to some examples, the mass of the first calibration weight (M1) is proportional to the magnitude of the vibrations of the first set of vibration measurements, and is inversely proportional to the magnitude of the reference influence vector of the second correction plane (<NUM>). Choosing the mass of the first calibration weight accordingly may provide for reduced vibrations.

According to some examples, the mass of the first calibration weight is smaller than the magnitude of the vibrations of the first set of vibration measurements divided by the magnitude of the reference influence vector of the second correction plane (<NUM>). Due to the small magnitude of the reference influence vector the mass of the first calibration weight may be an overestimate. It may therefore improve the vibration reduction to select a smaller calibration weight. According to some examples, the mass of the first calibration weight is smaller by a factor of <NUM> to <NUM>. According to some examples, the mass of the first calibration weight is between <NUM> grams and <NUM> grams.

According to some examples, fitting the first balancing weight comprises: calculating a balancing mass and a balancing angular location to reduce vibrations at first bearing and/or the second bearing using the calculated influence vector; selecting the first balancing weight to have a mass substantially corresponding to the balancing mass; and fitting the first balancing weight to an angular location of the second calibration plane substantially corresponding to the balancing angular location. By calculating both the masses and the angular locations of the final balancing weight (W1') fitted to the first correction plane and the second balancing weight fitted to the second correction plane using the influence vectors, the resulting vibration may be improved considerably over conventional methods of rotor balancing.

The present disclosure is particularly applicable to balancing using an insensitive correction plane and may considerably improve over conventional methods for insensitive correction planes.

According to some examples, the method comprises carrying out partial balancing, before performing the first influence run, by fitting the first balancing weight (W1) to the first correction plane (<NUM>) in order to reduce vibrations at the first bearing (<NUM>). Using partial balancing, the vibrations at the first bearing (<NUM>) can be reduced effectively so that a more accurate influence vector can be calculated for the second correction plane (<NUM>), because a significant relative change in the vibrations detected at the first bearing (<NUM>) is expected in response to fitting the first calibration weight (M1). According to an example, during the second run increased vibrations are recorded at the first bearing (<NUM>) than during the first run.

According to some examples, the first correction plane (<NUM>) is located on a compressor turbine disk of the rotor (<NUM>). A correction plane located on the compressor turbine disk may be particularly suitable for carrying out partial balancing, as described above, and may be less suitable for receiving the first calibration weight (M1). Identifying the first correction plane with a compressor turbine disk may therefore improve the effectiveness of the rotor balancing.

According to some examples, the second correction plane (<NUM>) is located on an exit stub shaft (<NUM>) of the rotor (<NUM>). A correction plane located on the exit stub shaft (<NUM>) may be particularly suitable for receiving the first calibration weight (M1). Identifying the second correction plane (<NUM>) with an exit stub shaft may therefore improve the effectiveness of the rotor balancing.

According to some examples, the intended balance speed is a full operational speed at or around the first critical speed of the rotor (<NUM>) at which the first bending mode of the rotor becomes significant for balancing considerations.

The present disclosure relates to a method for balancing a rotor for use in a turbomachine, such as a gas turbine.

By way of context, <FIG> shows a known arrangement to which features of the present disclosure may be applied.

<FIG> shows an example of a gas turbine engine <NUM> in a sectional view, which illustrates the nature of the rotor and the environment in which it operates. The gas turbine engine <NUM> comprises, in flow series, an inlet <NUM>, a compressor section <NUM>, a combustion section <NUM> and a turbine section <NUM>, which are generally arranged in flow series and generally in the direction of a longitudinal or rotational axis <NUM>. The gas turbine engine <NUM> further comprises a rotor shaft <NUM> which is rotatable about the rotational axis <NUM> and which extends longitudinally through the gas turbine engine <NUM>. The rotational axis <NUM> is normally the rotational axis of an associated gas turbine engine. Hence any reference to "axial", "radial" and "circumferential" directions are with respect to the rotational axis <NUM>. The radial direction <NUM> is substantially perpendicular to the rotational axis <NUM>, while the circumferential direction is perpendicular to both the rotational axis <NUM> and the radial direction <NUM>.

The shaft <NUM> drivingly connects the turbine section <NUM> to the compressor section <NUM>.

In operation of the gas turbine engine <NUM>, air <NUM>, which is taken in through the air inlet <NUM> is compressed by the compressor section <NUM> and delivered to the combustion section or burner section <NUM>. The burner section <NUM> comprises a burner plenum <NUM>, one or more combustion chambers <NUM> defined by a double wall can <NUM> and at least one burner <NUM> fixed to each combustion chamber <NUM>. The combustion chambers <NUM> and the burners <NUM> are located inside the burner plenum <NUM>. The compressed air passing through the compressor section <NUM> enters a diffuser <NUM> and is discharged from the diffuser <NUM> into the burner plenum <NUM> from where a portion of the air enters the burner <NUM> and is mixed with a gaseous or liquid fuel. The air/fuel mixture is then burned and the combustion gas <NUM> or working gas from the combustion is channelled via a transition duct <NUM> to the turbine section <NUM>.

The turbine section <NUM> may comprise a number of blade carrying discs <NUM> or turbine wheels attached to the rotor shaft <NUM>. In the example shown, the turbine section <NUM> comprises two discs <NUM> which each carry an annular array of turbine assemblies <NUM>, which each comprises an aerofoil <NUM> embodied as a turbine blade. Turbine cascades <NUM> are disposed between the turbine blades. Each turbine cascade <NUM> carries an annular array of turbine assemblies <NUM>, which each comprising an aerofoil <NUM> in the form of guiding vanes, which are fixed to a stator of the gas turbine engine <NUM>.

<FIG> is a schematic cross-sectional view of an exemplary rotor <NUM> to which the rotor balancing method according to the present disclosure may be applied.

The rotor <NUM> (or 'rotor assembly') has an elongate shape. For example, the rotor assembly of the gas turbine of <FIG> comprises the generally cylindrical rotor shaft <NUM> carrying a plurality of turbine disks and compressor disks <NUM>. The longitudinal extent of the rotor <NUM> is bounded by a pair of axial ends <NUM>, <NUM>. The first axial end <NUM> is an upstream end with respect to the flow of working fluid, while the second axial end <NUM> is a downstream end.

The rotor <NUM> comprises an inlet stub shaft <NUM> and an exit stub shaft <NUM>. The inlet stub shaft <NUM> is located towards the first end <NUM>, while the exit stub shaft <NUM> is located towards the second end <NUM>. Further, the rotor <NUM> comprises a rotor shaft <NUM> carrying power turbine rotor disks <NUM> and compressor turbine rotor disks <NUM>. The rotor disks <NUM>, <NUM> are carried on the rotor shaft <NUM>.

The rotor <NUM> comprises a pair of bearings <NUM>, <NUM>. The bearings (or 'bearing portions' or 'lands') are configured to be received within bearing housings of the gas turbine. According to the present example, each bearing <NUM>, <NUM> comprises a smooth radial surface coaxially arranged about the rotational axis <NUM>. By means of the bearings the rotor <NUM> is radially located and supported against forces in the radial direction <NUM>. Such forces include the rotor weight as well dynamic forces, particularly those resulting from an unbalance of the rotor <NUM>.

A plurality of correction planes <NUM> is provided on the rotor <NUM> by means of which the unbalance of the rotor <NUM> may be reduced. In line with its use in the art, the term 'correction plane' is understood to refer to a structural feature of the rotor rather than a geometric plane. In other words, a correction plane is a region or segment of the rotor <NUM>. The correction planes <NUM> are configured to selectively receive and retain additional mass so that the mass distribution of the rotor <NUM> can be altered through the addition of said additional mass. That is to say, each correction plane <NUM> is configured to receive and retain weights in holes <NUM> (or 'recesses') defined by the rotor <NUM>.

The plurality of correction planes <NUM> is spaced apart along the rotational axis <NUM>. Thus means are provided for adjusting the mass distribution at each axial location where a correction plane is located. In certain known rotors, correction planes are located where the rotor designs allows rather than where it would be desirable. That to say, because of design limitations the correction planes are located where it is structurally possible to provide them, but not necessarily in regions which provide the maximal response to balancing adjustment. Furthermore, some correction planes may be difficult to access because other structures of the rotor may obstruct access thereto. It is therefore considered desirable to optimise efficacy of the available correction planes.

According to the present example, there is provided a first correction plane <NUM>, a second correction plane <NUM>, and a third correction plane <NUM>. The first correction plane <NUM> is provided on a compressor turbine rotor disk <NUM>. The second correction plane <NUM> is provided on the exit stub shaft <NUM>. The third correction plane <NUM> is provided on the inlet stub shaft <NUM>.

Each correction plane <NUM> comprises a plurality of holes <NUM>, where each plurality of holes <NUM> is arranged symmetrically about the rotational axis <NUM>. The holes <NUM> of a correction plane <NUM> are provided at a regular interval, i.e. equidistant angular separation, and at a fixed radial distance to the rotational axis <NUM>. Each hole <NUM> of a given correction plane <NUM>, <NUM>, <NUM> therefore has a particular angular location. This particular angular location may be used to identify a specific hole <NUM> of a specific correction plane <NUM>, <NUM>, <NUM>.

According to some examples, a correction plane <NUM> comprises between sixteen and twenty holes <NUM>. According to the present example, twenty holes <NUM> are provided, resulting in an angular separation between adjacent holes <NUM> of <NUM>° (degrees of an arc) or, equivalently, pi/<NUM> rad (radians). A weight can be fitted into each hole in order to change the mass distribution of the rotor <NUM> purposes of balancing the rotor <NUM>.

<FIG> is a schematic cross-sectional view of the rotor <NUM> and a balancing machine <NUM>. The balancing machine <NUM> is a piece of test equipment configured to simulate operation of the rotor <NUM> in a gas turbine and assess the performance of the rotor <NUM> under such operating conditions.

The rotor <NUM> is mountable onto the balancing machine <NUM> by means of a plurality of pedestals <NUM>. The pedestals <NUM> are configured to carry the rotor <NUM> by receiving and retaining the bearings <NUM>, <NUM>. According to the present example, there is provided a first pedestal <NUM> and a second pedestal <NUM>. The first pedestal <NUM> is configured to receive the first bearing <NUM>, while the second pedestal <NUM> is configured to receive the second bearing <NUM>.

The balancing machine <NUM> is configured to subject the rotor <NUM> mounted thereto to a rotational speed corresponding to an intended balance speed. The intended balance speed is a predetermined rotational speed which, according to some examples, corresponds to an operating speed of the rotor <NUM>. For purposes of high-speed balancing the balancing machine <NUM> may be configured to subject the rotor <NUM> to a rotational speed at or around a critical speed of the rotor at which a mode shape of the rotor becomes significant for balancing considerations. For example, the rotor may be subjected to a rotational speed at or around the first critical speed of the rotor <NUM> at which the first bending mode of the rotor becomes significant for balancing considerations.

The balancing machine <NUM> comprises a plurality of vibration sensors. According to the present example, there is provided a first vibration sensor <NUM>, and a second vibration sensor <NUM>. The first vibration sensor <NUM> is located at the first pedestal <NUM> and configured to measure vibrations to which the first pedestal <NUM> is subjected. Similarly, the second vibration sensor <NUM> is located at the second pedestal <NUM> and configured to measure vibrations to which the second pedestal <NUM> is subjected. Such vibrations may be caused at either or at both pedestals <NUM>, <NUM> by unbalance of the rotor <NUM>.

The balancing machine <NUM> comprises a phase sensor <NUM> configured to detect the revolutions of the rotor <NUM>. According to some examples, the phase sensor <NUM> is an optical sensor configured to register the revolutions of a visible feature on the rotor <NUM>, such as a mark applied to the surface of the rotor <NUM>. Using the phase sensor <NUM>, the phase of the rotor <NUM>, i.e. its orientation, may be determined.

<FIG> illustrates an exemplary method of balancing the rotor <NUM> using the balancing machine <NUM>. The exemplary method comprises steps S300 to S370.

The method comprises step S300 according to which there is provided a rotor <NUM> as described above. A first balancing weight W1 is attached to the first correction plane <NUM> of the rotor <NUM>. By means of the first balancing weight W1 the rotor <NUM> is partially balanced. That is to say, the vibrations at one of the bearings <NUM>, <NUM> or, correspondingly, one of the pedestals <NUM> are reduced by means of the first balancing weight W1, according to some examples to below or around <NUM>/s The first balancing weight W1 has a mass and an angular location which is chosen according to any suitable process, an example of which is described below.

The method comprises step S310 of performing a first influence run. The first influence run comprises running the rotor <NUM> at the intended balance speed and recording a first set of vibration measurements at the first bearing <NUM> and the second bearing <NUM>. The vibration sensors <NUM>, <NUM> provided at the pedestals <NUM> are used to measure the vibrations.

Any vibrations detected at the bearings are assessed and it is determined whether and to which extent these vibrations are caused as a result of unbalance of the rotor <NUM>. According to the present example, the only cause of vibrations is unbalance of the rotor <NUM>.

The first set of vibration measurements R comprises a first vibration signal R1 of vibrations recorded at the first bearing <NUM>, or the first pedestal <NUM>, and a second vibration signal R2 recorded at the second bearing <NUM>, or the second pedestal <NUM>. Each vibration signal R1, R2 contains information about the magnitude of the vibrations and the phase angle of the vibrations at the respective bearing <NUM>, <NUM> or pedestal <NUM>, <NUM>. In other words, a vibration signal contains information about a phasor.

According to the present disclosure, the vibrations at one bearing have a smaller magnitude than the vibrations detected at the other bearing as a result of the partial balancing by means of the first balancing weight W1. According to the present example, the vibrations detected at the first bearing <NUM> have a smaller magnitude than the vibrations detected at the second bearing <NUM> by approximately <NUM>/s. The first balancing weight W1 remains fitted for the subsequently performed first influence run and second influence run.

The method comprises step S320 of providing a data set comprising a reference influence vector of the second correction plane <NUM>. This step is carried out prior to step S340, which requires the data set, but not necessarily after the previous steps S300, S310.

The reference influence vector of the second correction plane <NUM> is an influence vector of a reference rotor <NUM>, rather than an influence vector of the rotor <NUM> being balanced. The rotor <NUM> and the reference rotor <NUM> are of the same production line, i.e. product type, and hence substantially identical. The data set in relation to reference rotor <NUM> is therefore used as an approximation for balancing the rotor <NUM>. Using the reference influence vector is considered particularly desirable as this has been found to provide an improved set of mass and angular location values.

The method comprises step S330 of fitting a first calibration weight M1 to the second correction plane <NUM>. Generally, a calibration weight is a test mass which is added to a correction plane <NUM> in order to determine the effect of the test mass on the vibrations at the bearings in order to infer the effect a balancing weight will have. Only a single calibration weight is added to the rotor <NUM> at any given time in order to determine the response to said single calibration weight (in addition to the first balancing weight).

The first calibration weight M1 is generally characterised by its mass and its angular position on the correction plane to which it is fitted. The mass and angular position of the first calibration weight may be determined using any suitable means, for example Equation <NUM> below. According to the present example, they are determined using the vibration measurement R and a reference influence vector H2'. The reference influence vector H2' is a quantity which describes or at least approximates the effect that a weight added to the second correction plane has on the vibrations detected at the bearings <NUM>, <NUM>. In particular, a first component H21' of the reference influence vector H2' describes the effect on vibrations at the first bearing <NUM> or pedestal <NUM>, and a second component H22' describes the effect on vibrations at the second bearing <NUM> or pedestal <NUM>. Each component has a magnitude and a phase, i.e. defines a phasor.

The step S330 comprises using the reference influence vector to determine the mass and the angular location of the first calibration weight M1. The mass and the angular location of the calibration weight are chosen dependent on the vibrations detected at a single bearing in order to reduce the vibrations at said single bearing. Notably, the vibration response of certain known rotors has been found to critically depend on the mass and angular location values. A set of randomly selected values may therefore yield a poor vibration response and, ultimately, an ineffective balancing weight. According to the present example, the first calibration weight M1 is attached to the second correction plane to reduce the vibrations at the second bearing <NUM>.

The method comprises step S340 of performing a second influence run. The second influence run comprises running the rotor <NUM> at the intended balance speed and recording a second set of vibration measurements at the first bearing <NUM> and the second bearing <NUM>. The vibrations are recorded in a second set of vibration measurements P comprising a first vibration signal P1 of the first bearing <NUM> (or first pedestal <NUM>) and a second vibration signal P2 of the second bearing <NUM> (or second pedestal <NUM>). As above, each vibration signal contains information about the magnitude of the vibrations and the phase of the vibrations at the respective pedestal.

The method comprises step S350 of calculating an influence vector of the second correction plane <NUM>. Step S350 comprises using the first set of vibration measurements and the second set of vibration measurements for calculating the influence vector of the second correction plane <NUM>. Any known means suitable for making this calculation may be used.

The method comprises step S360 of carrying out balancing of the rotor <NUM>. Step S360 comprises fitting a finial balancing weight W1' to the first correction plane <NUM> and a second balancing weight W2 to the second correction plane <NUM> using the influence vectors of the first correction plane <NUM> and second correction plane <NUM>. The masses and the angular locations of the final balancing weight W1' and the second balancing weight W2 may be determined using any suitable means, and in later sections of the present disclosure a particular example is discussed so that conventional calculation means can be used to efficiently obtain accurate results.

According to the present example, the magnitude of the influence vector of the second correction plane is smaller than the magnitude of an influence vector (or reference influence vector) of the first correction plane. In other words, the second correction plane <NUM> is less sensitive than the first correction plane <NUM>.

According to some examples, using the reference influence vector H2' a calibration mass and a calibration angular location to reduce vibrations at the second bearing <NUM> are calculated. The first calibration weight M1 is selected to have a mass substantially corresponding to the calibration mass or 'calibration mass value' and fitted to second correction plane <NUM> at an angular location substantially corresponding to the calibration angular location or 'calibration angular location value'.

The mass and the angular location of the first calibration weight M1 are in some examples calculated using: <MAT> i.e. M1 equals minus R1 divided by H22'. According to the above Equation <NUM>, the calibration weight is expressed as a function of mass and angular location. The mass is expressible in units of grams, while the angular location is expressible in units of degrees of an arc. The vibration response R1 depends on the amplitude of the vibrations, expressible in millimetres per second, and the phase angle of the vibrations, expressible in degrees of an arc. The influence vector possesses a magnitude, expressible in units of millimetres per second per gram, and a phase angle, expressible in degrees of an arc.

According to some examples, the calculated mass of the first calibration weight M1 is considered too large, for example up to <NUM> gram, due to the very small reference influence vector H2' of the second correction plane <NUM>. The first calibration weight M1 may have a mass corresponding to a fraction of the calculated mass; for example half or a third. According to the present example, the first calibration weight M1 is chosen to have a mass between <NUM> gram to <NUM> gram, and the calculated angular location from Equation <NUM>.

According to some examples, the magnitude of the reference influence vector of the first correction plane <NUM> is greater than the magnitude of the reference influence vector of the second correction plane <NUM>. By comparing the magnitude of the influence vectors it may be possible to identify a sensitive correction plane. A sensitive correction plane is expected to possess a greater magnitude. For example, the magnitude of the first reference influence vector is greater than the magnitude of the second reference influence vector by at least a factor of two. Where the magnitude of the influence vectors differs greatly this may indicate that the smaller influence vector describes an insensitive correction plane. Additionally, it has been found that the phase angle of a reference influence vector of a reference rotor <NUM> may differ substantially from the actual phase angle of the rotor <NUM>. The method according to the present disclosure compensates for this with the calculated calibration weight M1, and the reduced vibrations at the first bearing <NUM>, such that a relatively large and accurate vibration response difference to the first set of vibration measurements R is expected.

The accuracy of approximating H2 using H2' can be optimised by using an average reference influence vector. That is to say, the reference influence vector H2' is calculated using influence vectors of a plurality of reference rotors <NUM>. The average reference influence vector H2' has a magnitude corresponding to the average of the magnitudes of influence vectors of the reference rotors <NUM> and, similarly, a phase angle corresponding to an average of the phase angles of the influence vectors. The average may be calculated in any suitable form, such as the mean, the median or the mode.

The mass and the angular location of final balancing weight W1' and the second balancing weight W2 are calculated according to the influence vectors of the first correction plane and second correction plane. The influence vector of the second correction plane has been calculated from the first and the second sets of vibration measurements. In particular, this influence vector is expected to accurately describe the effect of a balancing weight added to the second correction plane because the reference influence vector H2' will have yielded an improved vibration response. More particularly, this procedure comprises calculating balancing masses and their balancing angular locations to achieve vibrations at the first bearing and the second bearing within an acceptable vibration limit using the calculated influence vector. According to the present example, this procedure comprises selecting the first balancing weight to have a mass substantially corresponding to the balancing mass; and fitting the second balancing weight W2 to an angular location of the second correction plane substantially corresponding to the balancing angular location. According to the present example, this procedure also comprises selecting the final balancing weight W1' to have a suitable mass and angular location.

According to the present example, the method comprises partially balancing the rotor <NUM>. Partial balancing is carried out before the first influence run, by fitting the first balancing weight W1 to the first correction plane <NUM>, in order to reduce vibrations at a single bearing. In this case, the vibrations at the first bearing <NUM>, or the pedestal <NUM>, are reduced by partial balancing. That is to say, the mass and the angular location of the first balancing weight W1 are chosen dependent on the vibrations at the first bearing <NUM>. The first balancing weight W1 may reduce or increase vibrations at the second bearing <NUM>.

Similar to how the first balancing weight W1 is configured dependent on vibrations at the first bearing <NUM>, the first calibration weight M1 is configured solely dependent on the vibrations at the second bearing <NUM>. Accordingly, the first calibration weight M1 may reduce or increase the vibrations at the first bearing <NUM>. In the present example, the effect of the first calibration weight M1 is to increase the vibrations at the first bearing <NUM>. Therefore greater vibrations are measured at the first bearing <NUM> during the second run than are measured during the first run. Given that the vibrations at the first bearing <NUM> are small, the impact of the first calibration weight M1 will be significant even though the second balancing plane <NUM> is insensitive. Accordingly, a more accurate influence vector may be obtained as a result.

According to the present example, the method as described above is provided on a computer-readable medium, such as a hard disk or an optical disk. That is to say, instructions for carrying out the above method, particularly with reference to steps S300 to S370, are provided on the computer-readable medium. For example, using a suitable programming language a software application may be so provided for carrying out the method. More particularly, the computer-readable medium may be configured to instruct a processing unit to carry out certain steps of the method, and may be configured to instruct an operator to carry out other steps of the method. For example, the steps S300, S310 may be carried out by the operator. Other steps that may be carried out by the operator include the fitting of the weights S330.

The computer-readable medium is configured to instruct a processing unit, e.g. a central processing unit, to calculate the mass and the angular location of the first calibration weight M1 using the reference influence vector H2', calculate the influence vector of the second correction plane <NUM>. In the present example the computer-readable medium also contains the reference influence vector H2' or, as the case may be, the average reference influence vector.

The computer-readable medium may be part of the balancing machine <NUM>. That is to say, the balancing machine <NUM> comprises the computer-readable medium.

Claim 1:
A rotor balancing method for a gas turbine, the method comprising:
providing a rotor (<NUM>) comprising: a first bearing (<NUM>) and a second bearing (<NUM>), and a plurality of correction planes (<NUM>) comprising a first correction plane (<NUM>) and a second correction plane (<NUM>), wherein a first balancing weight (W1) is attached to the first correction plane (<NUM>) and remains attached for all following influence runs;
performing a first influence run by: running the rotor (<NUM>) at an intended balance speed and recording a first set of vibration measurements at the first bearing (<NUM>) and the second bearing (<NUM>), wherein the vibrations detected at the first bearing (<NUM>) have a smaller magnitude than the vibrations detected at the second bearing (<NUM>);
fitting a first calibration weight (M1) to the second correction plane (<NUM>);
performing a second influence run by: running the rotor (<NUM>) at the intended balance speed and recording a second set of vibration measurements at the first bearing (<NUM>) and the second bearing (<NUM>), and removing the first calibration weight (M1) from the rotor (<NUM>);
calculating an influence vector of the second correction plane (<NUM>) using the first set of vibration measurements and the second set of vibration measurements;
carrying out balancing of the rotor by: fitting a final balancing weight (W1') to the first correction plane (<NUM>), and fitting a second balancing weight (W2) to the second correction plane (<NUM>) using the calculated influence vector,
characterised by providing a data set comprising a reference influence vector of the second correction plane (<NUM>), wherein the reference influence vector is an influence vector of a reference rotor (<NUM>) of the same production type as the rotor (<NUM>);
using a reference influence vector of the second correction plane to determine the mass and the angular location of the first calibration weight (M1), wherein the mass of the first calibration weight (M1) is inversely proportional to the magnitude of the reference influence vector of the second correction plane (<NUM>).