Modular design and manufacture of a stator core

Details Modular design and manufacture of a stator core Modular design and manufacture of a stator core

1999-01-06

2001-03-13

Nguyen, Tran (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S216006, C310S256000, C310S256000

Reexamination Certificate

active

06201334

ABSTRACT:

FIELD OF THE INVENTION
The invention relates the design and manufacture of electrical generation equipment. More particularly, the invention relates to the modular design and manufacture of stator cores for use in electrical generators.
BACKGROUND OF THE INVENTION
The generator stator core is the largest single component in the train of a turbine generator set. The stator cores are generally manufactured from thousands of laminations of relatively thin steel plates which are stacked, pressed and clamped together into a large cylindrical form, i.e., the shape of the stator core. The clamping is necessary to accommodate variations in thickness (commonly referred to as “crown”) of the stock steel plates from which the laminations are punched. Improperly clamped laminations can result in plate vibration during generator operation, which results from magnetic impulses or core elliptical dilation. Moreover, air space between the laminations leads to high thermal resistance and decreased cooling efficiency. Fillers are often inserted into the stack of plates to compensate for voids caused by plate crown. Additionally, the fillers ensure that the clamping pressure is evenly distributed over the full plate area.
Typically, the stator core is assembled from the steel plates directly at the final installation site. However, the large size of the stator core and the need for proper clamping results in stator core manufacturing difficulties, including generous floor space and high crane requirements. Traditionally, two assembly procedures have been employed to form the cylindrical shaped stator core: In one procedure, the steel plates are stacked directly in a stator frame; in the other procedure, the steel plates are first stacked and clamped in an external stacking fixture. The complete stator core is then lifted into the stator frame via a large crane.
The manufacture of stator cores via the traditional methods results in manufacturing lead time and other associated manufacturing difficulties. For example, if the core is stacked directly in the stator frame, the frame must be delivered to the site before any manufacturing steps can occur. Additionally, intermediate core pressing equipment is needed to press and clamp the steel plates together at incremental lengths. If, on the other hand, the stator core is manufactured in an external fixture, the frame does not have to arrive on site before the manufacturing; however, the external fixture itself adds to the manufacturing costs and requires additional floor space on site. Moreover, the external fixture method requires a heavy duty crane of sufficient height to lift the assembled core into the stator frame. In either traditional manufacturing procedure, the core stacking process requires several days to complete.
In addition to assembly difficulties, stator cores assembled according to traditional methods experience operational problems. Such cores have a tendency to settle or relax during service. To help alleviate this tendency, various consolidation techniques and high clamping forces are required during assembly, further increasing the assembly time and costs. Moreover, heavy structural members are required at the core ends to hold the laminations in place, and access for future retightening may be required.
Thus, there is a need for an improved stator core design and manufacturing technique that increases the operational stability, while decreasing the time and cost of manufacturing a stator core.
SUMMARY OF THE INVENTION
The present invention meets the needs above by providing an improved stator core and a method for assembling the improved stator core. According to the method, stator core modules are prefabricated. The prefabricated modules are then inserted in the stator frame at any convenient assembly time. Each module is manufactured by clamping a stack of ferrous plates in a module fixture. The clamped stack of plates is placed in a vacuum chamber where a resin is applied to the stack of ferrous plates. The chamber is further pressurized to increase the impregnation of the resin between the plates. The prefabricated modules can then be stored or inserted into a stator frame to construct a stator core.
During assembly of a stator core, a selected number of modules are inserted into a stator frame. Thereafter, the stator core is clamped together. For example, through bolts are inserted through the axial length of the stator core, engaging each module and providing the force to hold the stator core together. Alternately, disk springs are inserted into the stator frame locking the modules together. The assembly is then complete, saving several days of on-site assembly while providing a stator core with improved operational characteristics.


REFERENCES:
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patent: 4651039 (1987-03-01), Yamamoto et al.
patent: 5267393 (1993-12-01), Purohit et al.
patent: 5365137 (1994-11-01), Richardson et al.
patent: 5461772 (1995-10-01), Puri
patent: 5866961 (1999-02-01), Suzuki et al.

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