Electricity: single generator systems – Automatic control of generator or driving means – Power factor or phase relationships
Reexamination Certificate
2001-01-16
2001-09-25
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Power factor or phase relationships
C322S037000, C322S036000
Reexamination Certificate
active
06294898
ABSTRACT:
BACKGROUND
Exciters designed for operation with synchronous generators have traditionally been required to protect the generator field by limiting operation of the generator in the overexcited region of a generator's capability curve which is restricted by field heating. In the underexcited region of the generator capability curve, operation must be limited because of stator end turn heating and stator lamination over-voltage effects. Operation between rated KVA at rated lagging power factor and rated KVA at unity power factor must be limited because of overheating caused by excessive stator current. While conventional fixed hardware or software algorithms used to implement this functionality such as General Electric's GENERREX-CPS, GENERREX-PPS, SHUNT-SCR, ALTERREX, STATIC BUS FED EXCITATION and SILCO 5 control implementations, can properly protect the generator these prior art implementations do not have any capability of being responsive to coolant conditions as they deteriorate from nominal. A further problem is that prior art limiter implementations do not account for improved coolant conditions and the possible increase in generator rating associated with such improved coolant conditions. Indeed, “ambient following” combustion turbine applications are particularly sensitive to changes in coolant conditions as the output power capability thereof varies significantly with coolant conditions.
It is thus seen to be desirable to coordinate the limit and protection functions of a generator exciter as a function of coolant conditions to provide improved overall generator performance.
SUMMARY OF THE PREFERRED EMBODIMENTS
The apparatus and method described herein accurately protect the generator as coolant conditions vary from nominal in the areas limited by (1) field heating, (2) stator current heating and (3) underexcited capability while maintaining full output capability from the generator. In a preferred embodiment, appropriate algorithms implemented in hardware or software are automatically selected to optimize the compensation for either hydrogen cooled or air cooled generators in the area of the capability curve characterized by field current or stator current heating while a jumper, or other suitable switching device, is implemented to select the proper compensation in the underexcited area. The advantages of the preferred embodiment include implementation of very accurate compensation of limiters with automatic coordination of the limiters and protection algorithms, whereby a more efficient use of a generator across varying cooling conditions is realized.
Since both limit and protection algorithms can be supplied in an exciter of a generator, it is, in accordance with the preferred embodiment, desirable that the limit and protection functions be coordinated and maintain coordination as coolant conditions change. Thus, described herein, is a very accurate apparatus and method for coordination of the limit and protection functions, as a function of coolant conditions, permitting full output capability from a turbine generator while maintaining very accurate protection functions. As an added benefit, a coolant compensated stator current limit function can be added for operation in the area of the capability curve from rated KVA at rated lagging power factor to operation at rated KVA and unity power factor.
More specifically, generators have different ratings based on the coolant conditions at the existing operating point. As noted above, prior art exciter implementations use fixed limit and protection hardware or software algorithms which either do not offer protection at other than rated coolant conditions or do not permit generator operation to increase as coolant conditions improve to obtain full capability operation of the generator. This is especially important for ambient following combustion turbine applications, as previously explained. Thus, the methodology described herein implements fixed parameter limits and protection algorithms yet provides full limit and protection compensation keyed either to temperature or hydrogen pressure (depending on the type of cooling system) to match the capability of the exciter to the generator rating. And, as a consequence, there is provided automatic coordination between the limit and protection algorithms.
In accordance with the preferred embodiment, a two part characteristic is used to implement the under excited limit (UEL). Utilizing such a two part characteristic for the under excited limit has the added benefit of providing a compensating signal for operation in the area of the generator capability curve determined by stator current heating or stator KVA. This permits the use of a fixed parameter stator current limit that is compensated for coolant conditions.
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Curran James E.
Lawson Rodney A.
Pearson William R.
Duncan Kevin T.
General Electric Company
Horton Carl B.
Hunton & Williams
Ponomarenko Nicholas
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