U.S. patent application number 14/028829 was filed with the patent office on 2014-03-20 for rotor assembly and refit method.
This patent application is currently assigned to ALSTOM Technology Ltd. The applicant listed for this patent is ALSTOM Technology Ltd. Invention is credited to Christopher KENTISH, Timothy George SHURROCK, Nikola ZELENOVIC.
Application Number | 20140079547 14/028829 |
Document ID | / |
Family ID | 46967996 |
Filed Date | 2014-03-20 |
United States Patent
Application |
20140079547 |
Kind Code |
A1 |
ZELENOVIC; Nikola ; et
al. |
March 20, 2014 |
ROTOR ASSEMBLY AND REFIT METHOD
Abstract
A method of coupling at least two sections of a rotor designed
to carry the rotating parts of a turbine for the generation of
electrical power for a public grid and a modified rotor is
described with a coupling of increased diameter exceeding the
nominal diameter of the rotor, with the step of removing mass from
an volume lying exclusively within the interior of the sections
when coupled such that the lateral critical speed of the coupling
is moved away from the normal operating speed of the rotor
Inventors: |
ZELENOVIC; Nikola; (Wigston,
GB) ; KENTISH; Christopher; (Leamington Spa, GB)
; SHURROCK; Timothy George; (Rugby, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALSTOM Technology Ltd |
Baden |
|
CH |
|
|
Assignee: |
ALSTOM Technology Ltd
Baden
CH
|
Family ID: |
46967996 |
Appl. No.: |
14/028829 |
Filed: |
September 17, 2013 |
Current U.S.
Class: |
416/1 ;
416/204R |
Current CPC
Class: |
F01D 5/02 20130101; F05D
2230/10 20130101; F05D 2220/31 20130101; F01D 5/027 20130101; F05D
2230/80 20130101; F01D 5/026 20130101 |
Class at
Publication: |
416/1 ;
416/204.R |
International
Class: |
F01D 5/02 20060101
F01D005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 17, 2012 |
EP |
12184721.4 |
Claims
1. A method for shifting a critical vibrational mode of a rotor
further away from the normal operating speed of the rotor
comprising: providing the rotor with a coupling that couples
contact faces of two rotor sections; and removing mass from a
volume lying exclusively within the interior of the rotor sections
when coupled.
2. The method of claim 1 wherein the removing mass comprises
removing mass from a contact face of the coupling thereby creating
a cavity at a coupling end of at least one rotor section.
3. A rotor for carrying the rotating parts of a turbine for the
generation of electrical power for a public grid with the rotor
comprising at least two rotor sections coupled with a coupling of
diameter exceeding the nominal diameter of the rotor sections,
wherein at least one of the rotor sections includes one or more
cavities at the end of the at least one rotor section and in the
vicinity of the coupling such that the boundaries of the one or
more cavities are all interior surfaces when the rotor sections are
coupled.
4. The rotor of claim 3 wherein the one or more cavities at the end
of at least one rotor sections and in the vicinity of the coupling
extend from the wall of the rotor into a part of the coupling
exceeding the nominal diameter of the rotor sections or are placed
in a volume extending from the wall of the rotor sections into a
part of the coupling exceeding the nominal diameter of the rotor
sections.
5. The rotor of claim 3 wherein the at least one of the rotor
sections carries the rotating parts of a low pressure steam
turbine, such as the rotating blades or airfoils and their
respective platforms.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to European Application
12184721.4 filed Sep. 17, 2012, the contents of which are hereby
incorporated in it entirety.
TECHNICAL FIELD
[0002] This invention relates generally to a rotor assembly and
method of refitting a large rotor, particularly for turbines such
as low pressure steam turbines.
BACKGROUND
[0003] As described for example in the U.S. Pat. No. 6,837,685, at
least some known turbine rotor assemblies include a rotor wheel to
which a plurality of blades are coupled. The rotor is typically
assembled from several large cylindrical forgings or machined
sections. The sections are either welded, bolted or connected
through a heat shrinking process.
[0004] The rotor is supported at the ends or intermediate positions
along its length by bearings. In the case of a large multi-stage
steam turbine that includes high-pressure turbine, intermediate
pressure turbines and low pressure turbines there are typically
bearings to support the rotor at the end and between the
stages.
[0005] It should be noted that rotors for large turbines weigh may
weigh 155 tons or more and in spite of this considerable weight
have to rotate at typically full or half-frequency of the power
grid frequency, i.e. at 50 Hz or 60 Hz. In view of the high
rotational speed, an unbalanced mass of the rotor causes the rotor
to bend or buckle. As the speed of rotation increases the amplitude
of such vibrations often passes through a maximum that is called a
critical speed. Given the high tolerances to which modern turbines
are manufactured, such out-of-position movement can cause damage
and malfunction of the turbine.
[0006] It is therefore an object of the present invention to
provide a rotor coupling and methods to couple rotor sections, for
example as part of a repair or retrofit of the rotor. It is a
particular object of the present invention to provide such rotor
couplings and methods which are capable of reducing the risk of
failure due to critical speeds.
SUMMARY
[0007] According to an aspect of the present invention, there is
provided a rotor to carry the rotating parts of a turbine for the
generation of electrical power for a public grid with the rotor
including at least two sections coupled with a coupling of
increased diameter exceeding the nominal diameter of the rotor,
wherein at least one of the rotor sections includes one or more
cavities at the end of at least one rotor section and in the
vicinity of the coupling such that the boundaries of the one or
more cavities are all interior surfaces when the rotor sections are
coupled.
[0008] In a preferred variant the one or more cavities at the end
of the at least one rotor section and in the vicinity of the
coupling extend from the wall of the rotor into a part of the
coupling exceeding the nominal diameter of the rotor or are placed
in a volume extending from the wall of the rotor into a part of the
coupling exceeding the nominal diameter of the rotor.
[0009] In a preferred variant the at least one of the rotor
sections carries the rotating parts of a low pressure steam
turbine, such as the rotating blades or airfoils and their
respective platforms.
[0010] According to another aspect of the present invention, there
is provided a method of coupling at two sections of rotor to carry
the rotating parts of a turbine for the generation of electrical
power for a public grid with a coupling of increased diameter
exceeding the nominal diameter of the rotor, the method including
the step of removing mass from a volume lying exclusively within
the interior of the sections when coupled.
[0011] In a preferred variant of the method, mass is removed to
increase the critical lateral speed of the coupled rotor sections
such that the difference between operational speed and the critical
lateral speed is enlarged compared to coupled rotor sections with
flat ends.
[0012] The above and further aspects of the invention will be
apparent from the following detailed description and drawings as
listed below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Exemplary embodiments of the invention will now be
described, with reference to the accompanying drawings, in
which:
[0014] FIG. 1 shows a coupling between two rotor sections after a
modification according to known methods;
[0015] FIG. 2 shows couplings between two rotor sections
illustrating an example of the invention;
[0016] FIG. 3 shows a couplings between two rotor sections
illustrating examples of the invention; and
[0017] FIG. 4 shows two plots of an excitation spectrum of rotor
vibrations illustrating the effect of a modification in accordance
with an example of the present invention.
DETAILED DESCRIPTION
[0018] Aspects and details of examples of the present invention are
described in further details in the following description.
Exemplary embodiments of the present invention are described with
references to the drawings, wherein like reference numerals are
used to refer to like elements throughout. In the following
description, for purposes of explanation, numerous specific details
are set forth to provide a thorough understanding of the invention.
However, the present invention may be practiced without these
specific details, and is not limited to the exemplary embodiments
disclosed herein.
[0019] FIG. 1 shows a schematic diagram of two rotor sections 11,
12 linked by coupling 111, 112. The rotor section can be, for
example, two sections of a rotor for low pressure steam turbines.
Such rotor sections are typically either solid or else have
cylindrical shape with thick walls. At the coupling area 111, 112
the thickness of the wall and hence the outer radius of the rotor
exceed the nominal outer radius of the rotor to provide openings
for bolts or screws. The nominal radius can be regarded as the
radius of the rotor in the coupling area derived by linearly
extrapolating the radius of the rotor before the coupling section
up to the end of the rotor section.
[0020] The rotor when provided may be optimized to provide,
integrity at the lowest possible weight, lowest use of material, or
else to ensure the interchangeability of components in order to
minimize the number of spares. In a retrofit, however, the original
rotor can be replaced by an improved rotor leaving some limited
degrees of freedom to change the overall dimensions of the
rotor.
[0021] In FIG. 1 it is assumed that coupling material 15 from the
original coupling 111, 112 as outlined by the dashed lines can be
removed to result in a smaller coupling 111a, 112a outlined by
solid lines. Normally such a reduction in mass is sufficient to
move the lateral critical speed of the coupling or overhang modes
far enough away from the normal operating speed.
[0022] In principle it is also possible to increase mass, to move
the lateral critical speed of the overhang mode sufficiently below
normal operating speed. However, this variant would be more
expensive and might require costly and time-consuming modifications
to coupling guards and/or the turbine casings. It can also be
expected to have a greater sensitivity to unbalance; and might move
the torsional natural frequencies of coupling modes, close to grid
or twice grid frequency.
[0023] However the reduction of the coupling dimension may lead to
an unacceptable loss of mechanical strength of the coupling. In
such a case, or other cases where for example the outer rotor
dimensions are fixed, removal of coupling material 15 from the
couples is not possible.
[0024] Considering these problems, FIG. 2 shows an alternative way
of shifting the lateral critical speed of the coupling or overhang
modes far enough away from the normal operating speed.
[0025] In FIG. 2 there is shown a coupling with an original rotor
section on the left side and an altered section on the right side
thus illustrating the alterations as per an example of the
invention. The coupling 111,112 of this example is shrunk onto the
actual rotor. The original rotor section 12 has an essentially
plane surface 13 facing the other section. The surface may have a
very shallow indention (not shown) machined into it to restrict the
contact areas with the other section. When modified in accordance
with an example of the invention a cavity 14 is machined into the
previously flat surface 13 by removing part of the wall of the
rotor section 12. In the example shown it extends further radially
into the coupling area or volume outside the nominal radius of the
rotor. The nominal radius is again defined as the radius of the
rotor in the coupling area derived by linearly extrapolating the
radius of the rotor before the coupling section up to the end of
the rotor section.
[0026] It should be noted that when the sections are coupled, the
cavity 14 is fully enclosed within the interior of the rotor. The
walls of the cavity are thus not exposed to the air flow along the
outside of the rotor. The cavity is rotationally symmetric to
facilitate the balancing of the rotor.
[0027] Another example is shown in FIG. 3. The rotor has a forged
solid coupling 111,112 on both ends of the rotor sections 11, 12. A
cavity 14 is machined into the walls of the rotor and part of the
coupling. In addition, a ring of coupling material 15 is removed
from the outside of the coupling.
[0028] The exact dimensions of the cavities shown are calculated
using FE analysis to ensure that the mechanical integrity of the
assembled rotor is not critically weakened. With the parameter in
mind, it be regarded as beneficial to remove as much material as
possible, thereby achieving a greater difference between the
lateral critical speed of the coupling or overhang modes and the
normal operating speed.
[0029] The plots of FIG. 4 show the shift of the vibrational
spectrum of a rotor before (top plot) and after (bottom plot)
creating a cavity at the coupling. The spectrum between the top and
bottom plot is essentially identical but slightly shifted to the
right. The cavity causes critical lateral speed to move away from
the operational speed of the rotor. More precise measurements show
a shift of the critical lateral speed from 1840 rpm to 1870 rpm,
with a corresponding reduction in vibration amplitude at 1800 rpm
(normal operating speed) of 20 .mu.m peak to peak (from 45 .mu.m to
35 .mu.m zero-to-peak).
[0030] The present invention has been described above purely by way
of example, and modifications can be made within the scope of the
invention, particularly as relating to the desired geometry of the
cavity 14 or the arrangement of cavities 14. The invention may also
comprise any individual features described or implicit herein or
shown or implicit in the drawings or any combination of any such
features or any generalization of any such features or combination,
which extends to equivalents thereof. The breadth and scope of the
present invention should not be limited by any of the
above-described exemplary embodiments.
[0031] Each feature disclosed in the specification, including the
drawings, may be replaced by alternative features serving the same,
equivalent or similar purposes, unless expressly stated
otherwise.
[0032] Unless explicitly stated herein, any discussion of the prior
art throughout the specification is not an admission that such
prior art is widely known or forms part of the common general
knowledge in the field.
* * * * *