Electrical transmission or interconnection systems – Plural load circuit systems – Selectively connected or controlled load circuits
Reexamination Certificate
1999-08-09
2001-05-29
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Plural load circuit systems
Selectively connected or controlled load circuits
C307S018000, C307S023000
Reexamination Certificate
active
06239511
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of power station technology. It relates to a power station comprising a generator which is driven by a turbine, produces electrical power and outputs to a network via a generator switch. Such power stations are known in a wide range of forms from the prior art. The invention furthermore relates to a method for operation of such a power station.
2. Discussion of Background
As can be seen from the greatly simplified illustration in
FIG. 1
, the generator
13
which produces electrical power and is driven by a turbine
11
via a shaft
12
is connected, in a power station
10
, via a generator switch
14
, a transformer
15
and a network switch
16
to a network
17
. If serious faults occur in the network
17
, the generator
13
is isolated from the network
17
by opening the generator switch
14
immediately downstream of the generator terminals. Such a known fault is, for example, a line short. Normally, a time of up to 300 ms is available for subsequent reconnection, within which the criteria of incorrect angle and incorrect slip can still be tolerated.
If the fault cannot be sorted out or rectified before this time period has elapsed, time-consuming resynchronization of the generator
13
to the network
17
is required, during which the weakened network (other power stations may also have to be resynchronized first of all) may finally collapse. This risk will occur increasingly often in the future, since such networks are increasingly being operated at their capacity limit.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel power station and a novel method for its operation, by means of which reconnection of the generator which has been disconnected from the network after a fault can be ensured without tedious speed matching which may last up to several seconds.
In accordance with exemplary embodiments of the invention, an electrical standby load is provided within the power station. The electrical standby load is connected to the generator or power output of the power station when the network is disconnected, for example when a network fault occurs. This ensures that the generator will continue to operate in a mode that will allow the generator to be directly reconnected to the network, without undergoing a lengthy resynchronization process.
In accordance with exemplary embodiments of the invention, the electrical standby load is adjustable. This ensures that the electrical standby load can be optimally set to the respective operating conditions which exist shortly before a fault occurs in normal operation and causes the network to be disconnected from the power output of the power station. In other words, the electrical standby load is set to emulate the load presented by the network to the power station shortly before the occurrence of the fault.
In accordance with exemplary embodiments of the invention, the electrical standby load includes at least one resistor which can be connected to the output of the power station. This resistor is designed to be adjustable. In particular, the resistor includes a plurality of resistor elements which can be independently connected in parallel and which can have graduated resistance values. Thus, the value of the resistor can be adjusted by connecting and/or disconnecting appropriate ones of the plurality of resistor elements. The connection of the resistor elements can be performed via power semiconductor switches, preferably pairs of thyristors connected back-to-back. This provides a functionally reliable, easily adjustable, compact standby load that uses proven technology.
In accordance with exemplary embodiments of the invention, when a fault occurs in the network and the power station generator is isolated from the network by opening the generator switch, the terminals of the generator are connected to the electrical standby load at the same time that the generator switch is opened. The generator is then operated in an isolated mode while connected to the electrical standby load and disconnected from network. Once the network fault has been rectified, the electrical standby load is disconnected from the generator terminals again when the generator switch is closed to reconnect the generator to the network.
In accordance with exemplary embodiments of the invention, the resistance value of the electrical standby load is set to a value which corresponds approximately to a real load that was present during previous operation when the generator was connected to the network. This value is determined roughly from the immediately preceding magnitudes of the real load and field current of the generator. During isolation of the generator (i.e., while the generator is connected to the electrical standby load and disconnected from the network), the generator is operated to maintain a constant phase difference between the generator voltage and the voltage of the network by adaptation of this value and/or by fine-control of the field current. Thus, for the resistor standby load: I
gen
′·U
gen
′=I
gen
·U
gen
·cos &phgr;, where I
gen
is the generator current in normal operation before the fault, U
gen
is the generator voltage in normal operation before the fault, and I
gen
′ is the generator current in the isolated mode and U
gen
′ is the generator voltage in the isolated mode. This results in the phase difference &Dgr;&phgr; between the generator voltage U
gen
′ and the network voltage U
net
remaining constant. Thus, when the generator is reconnected to the network, the generator immediately feeds power into the network. This ensures that the generator can be reconnected to the network at any desired time, and makes a considerable contribution to network stability. The isolated mode works particularly advantageously if the operation of the turbine is controlled by a turbine regulator, and the control setting of the turbine regulator is kept constant (“frozen”) in at least a first phase while operating in the isolated mode.
In accordance with another embodiment of the invention, the operation of the turbine is controlled by a turbine regulator, and the generator voltage is controlled by a voltage regulator. An adjustable electrical standby load is used, and the power and/or the generator voltage are/is varied during operation in the isolated mode by matched control of the turbine regulator, of the voltage regulator and of the adjustable electrical standby load and adaptation, resulting from this, of the phase difference of the generator voltage to the voltage of the network with the generator at a constant speed. This allows specific generator parameters to be varied in a controlled manner, in order to influence the reconnection capability to the network in an advantageous manner.
In accordance with another exemplary embodiment of the invention, the electrical standby load is connected when load shedding takes place in the network. This allows power oscillations to be prevented in a controlled manner. This is achieved particularly if the turbine is controlled by a turbine regulator, an adjustable electrical standby load is used, and the electrical standby load is continuously reduced to the value zero after being connected, matching the action of the turbine regulator.
REFERENCES:
patent: 3643437 (1972-02-01), Birnbaum et al.
patent: 4529887 (1985-07-01), Johnson
Asea Brown Boveri AG
Ballato Josie
Burns Doane Swecker & Mathis L.L.P.
Polk Sharon
LandOfFree
Power station having a generator which is driven by a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power station having a generator which is driven by a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power station having a generator which is driven by a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2506388