JPH0161036B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load runback device, and more particularly to a load runback device suitable for controlling the operation of a turbine generator.

Figure 1 is a schematic diagram of a typical turbine generator plant, in which 1 is a boiler, 2 is a main steam stop valve, 3 is a control valve, 4 is a turbine, 5 is a reheater, and 6 is a Reheat steam stop valve, 7 is a generator, 8 is a power system, 9 is a current transformer, 10 is a current detector, 11
12 is a condenser, and 13 is a water supply pump.

In this configuration, steam generated in the boiler 1 passes through the main steam stop valve 2 and the control valve 3 to drive the turbine 4. As shown in FIG. 1, in the case of a reheat type system, the steam is further reheated in a reheater 5,
The turbine 4 is driven through the reheat steam stop valve 6. When the turbine 4 is driven in this way, the generator 7 connected to its shaft rotates,
Electric power is generated, and the generated output is connected to the power system 8. Further, the load current of the generator 7 is transformed by a current transformer 9 and monitored by a current detector 10. Further, the steam that drove the turbine 4 is condensed by a condenser 12 and supplied to the boiler 1 by a feed water pump 13.

By the way, the generator 7 is equipped with a cooling device that directly cools the stator windings with cooling water, and in order to detect a failure of this cooling device, a failure detector 11 consisting of a pressure switch, a temperature switch, etc. is installed.
is provided. On the other hand, the current detector 10 is set to operate at a load current value equal to or higher than the self-cooling capacity of the generator 7 that does not depend on the cooling device.

As mentioned above, in a turbine generator plant that employs a direct cooling method for the stator winding of the generator 7, if the cooling system fails, the cooling water flowing inside the stator winding conductor may stop or decrease. Accidents may occur such as cooling water being supplied to conductors before it is sufficiently cooled. In such a state, cooling is no longer possible, and the stator winding conductor becomes abnormally high in temperature, putting the generator 7 in a dangerous state, so it is necessary to quickly reduce the load current. Such an operation is generally called a load runback operation.

Such a load runback occurs when the failure detector 11, which detects a failure in the cooling system of the generator 7, is activated, and the output of the current detector 10, which detects that the load current of the generator 7 is greater than its self-cooling capacity, is While this is being done, a closing command is issued to the regulating valve 3. At the same time, a timer that detects the time during which the load runback command is issued monitors whether the load drops to the self-cooling capacity within the allowable time, and if the load does not drop, the generator 7 is tripped. On the other hand, if the load falls to the self-cooling capacity within the allowable time, the output of the current detector 10 disappears, and the load runback ends.

Figure 2 is a block diagram showing an example of a conventional load runback device, in which AND is an AND circuit;
A indicates an output signal of the AND circuit AND, 3M indicates a control device for the regulating valve 3, and 14 indicates a timer.

In this configuration, signal A is output under the conditions that there is an output from the failure detector 11 and an output from the current detector 10. This signal A is given to the control device 3M of the regulating valve 3 as a runback command, and the regulating valve 3 is closed. After this, when the load current falls below a value equivalent to the self-cooling capacity of the generator 7, the output of the current detector 10 disappears, so the signal A is restored and the closing operation of the control valve 3 is stopped. On the other hand, signal A
When this occurs, the timer 14 which has set the allowable runback time starts counting, and if the signal A does not return within the set time, the generator 7 is tripped by the output signal of the timer 14.

As mentioned above, in conventional load runback devices, when a failure called cooling water cutoff occurs due to low cooling water pressure or high cooling water temperature,
A load reduction command is issued to the turbine control valve, and the generator 7 is controlled to reduce the load within the allowable time to the self-cooling capacity load (26 or 30% of the rating) that can be operated without cooling water. If the load does not reach the self-cooling capacity load within a certain period of time, it is determined that the load runback has failed, and the generator 7 is immediately tripped.

Now, the load runback mentioned above is carried out by reducing the amount of steam to the turbine 4 using the regulating valve 3, but this is because the amount of heat retained in the boiler 1 is large if the output cooling to the boiler 1 is reduced. This is because the load cannot be lowered rapidly. However, especially in once-through boilers used in recent large-capacity thermal power plants, when carrying out load runback, it is necessary to reduce the water supply flow rate in cooperation with the regulating valve 3. In other words, the furnace pressure in the boiler 1 where the feed water flow rate is insufficiently throttled compared to the throttle valve 3 will result in high furnace pressure, and conversely, if the feed water flow rate is throttled too much, the furnace pressure in the boiler 1 will be low. In either case, it is dangerous for the boiler 1 and may even lead to boiler trip. Therefore, the speed at which the regulating valve 3 is throttled is required to be constant from the viewpoint of controllability on the water supply side.

Further, in general, the steam turbine 4 has an output time constant between the steam input and the output of the generator 7, and in particular, in a reheat turbine, the time constant is large depending on the amount of steam held in the reheater. For this reason, the output of the generator 7 decreases with a delay with respect to constant speed throttling of the regulator valve 3 during load runback.

FIG. 3 is a characteristic diagram showing the relationship between the regulating valve opening P, the load current I of the generator 7, and the time T when the above-mentioned load runback occurs in the turbine generator operating at the rated load.

As is clear from FIG. 3, as soon as the load runback is started at time _T0 , the regulator valve 3 starts throttling at a constant speed, but the load current starts to reduce the delay. At time t ₁ , the regulating valve 3 is narrowed down to the opening P ₁ corresponding to the generator's self-cooling capacity, but at this time,
Since the load current has not yet reached the self-cooling capacity equivalent current I ₁ , the load runback continues, and at time t ₂ the load runback stops when the load current reaches I ₁ . At this time, the regulating valve 3 has been throttled down to the opening degree _P2 , so the load current continues to decrease even after the load runback is stopped, and drops to the value of the load current _I2 corresponding to the opening degree _P2 .

As described above, with the conventional load runback device that stops load runback when the current drops below the self-cooling capacity of the generator 7, the final set load may drop too much due to excessive throttling of the regulator valve 3. Become. In such cases, boiler controllability,
Since the controllability of the water supply flow rate, etc. deteriorates, load runbacks due to failure of the cooling system have almost never been successful and have led to tripping.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a load runback device that eliminates the drawbacks of the prior art described above, improves the control characteristics during load runback, and enables reliable completion of load runback and return operation.

More specifically, during load runback, the present invention provides
By detecting that the generator output current has fallen further below the current corresponding to the self-cooling capacity and opening the regulating valve once again, which has been throttled down, the regulating valve is opened again to prevent the settling load from dropping too much after load runback. The present invention provides a new load runback device with improved control characteristics during load runback.

Hereinafter, the load runback device of the present invention will be explained in more detail with reference to the drawings.

FIG. 4 is a block diagram of a load runback device according to an embodiment of the present invention, in which 15 is a second current detector, AND2 is an AND circuit, 8 is an output signal of the AND circuit AND2, and 3M-1 3M-2 is a closing controller for the regulating valve 3, and 3M-2 is an opening controller for the regulating valve 3. By the way, as shown in the partial circuit diagram of FIG. 5, the second current detector 15 is added to the current transformer 9 of FIG. It is set so that the output is output below a slightly lower set value.

The operation of the configuration as described above will be explained below with reference to the characteristic diagram shown in FIG. In Figure 6, P
is the opening degree of the adjusting valve, and I is the load current.

Now, when a failure occurs in the cooling system of the generator 7 and the failure detector 11 is activated, if the load current is equal to or greater than the current value equivalent to the self-cooling capacity of the generator 7, the first current detector 10 is activated. Since it is operating and outputting an output, a signal A is output from the AND circuit AND as a runback command and is given to the control device 3M of the regulating valve 3. As a result, the closing controller 3M-1 operates to close the regulating valve 3 at a constant speed. As a result of this operation, if the load current falls below the self-cooling capacity of the generator 7, the output of the current detector 10 disappears, and the signal A
is restored, and the closing operation of the regulating valve 3 is stopped. on the other hand,
The timer 14, which has a set runback allowable time, starts counting until the time when the signal A is generated, and if the signal A does not return within the set time, the output signal of the timer 14 causes the generator 7 to trip.

Note that the load runback operation described above is performed by the timer 14.
Even after the load is completed within the allowable time stipulated by The current detector 15 of No. 2 operates and outputs an output. The output of the second current detector 15 is given to an AND circuit AND2, and as a result, a signal B is output from the AND circuit AND2.
The signal B is given to the control device 3M of the control valve 3, and the control valve 3 is opened by the opening controller 3M-2. Therefore, the regulating valve 3 opens and the load current increases, but when this load current exceeds the set value of the second current detector 15, the signal B returns and the first
The opening operation of the control valve 3 shown in the figure is stopped. After this, if the load current decreases further, the above-described operation is repeated, and the load current of the generator is adjusted to a value slightly lower than the current value corresponding to the self-cooling capacity, and is finally settled. In this case, hunting will not occur if the on/off setting values of the current detector are set a little wider. Further, once the narrowing down is completed, water supply control is automatically performed based on the main steam flow rate, fuel flow rate, load, etc., so there is no problem.

The relationship between the opening degree P of the regulating valve 3 and the load current I during the above operation is as shown in FIG.
When the load runback starts at time _t0 , the regulator valve 3 immediately starts throttling down at a constant speed, and the load current I starts to decrease after a short delay. At time _t1 , the regulating valve 3 is narrowed down to the opening _P1 corresponding to the generator's self-cooling capacity, but at this time the load current I has not yet reached the current _I1 corresponding to the self-cooling capacity, so the load runback continues. At time _t2 , load current I reaches _I1 and runback stops. At this time, the control valve 3 has been narrowed down to the _P2 position. Therefore, the load current I
decreases further after the runback stops, but soon reaches the current value _I3 , which is set slightly below the current value equivalent to the self-cooling capacity, and at this point _t3 , an opening command is issued to the control valve 3. The current value does not fall below _I3 . Then, as described above, the regulating valve 3 repeats opening and closing operations, and finally settles to the opening degree P ₃ corresponding to the self-cooling capacity.

As described above, according to the present invention, when carrying out a load runback when the cooling system of a generator equipped with a cooling device fails, the load is not lowered too much and coordination with other Accent equipment is maintained. It is possible to obtain a load runback device that allows stable control and enables load runback with a high success rate.

In addition, in the above embodiment, the case where the generator stator winding is water-cooled is illustrated, but the present invention is applicable to a generator that is cooled using another cooling medium instead of water cooling. Of course, it can also be applied in the same way. Furthermore, in the above embodiment, the case where there is one monitoring circuit for checking whether the load is reduced to the self-cooling capacity within the allowable time is exemplified, but it is also possible to provide multiple monitoring circuits using a combination of multiple current detectors and timers. It is possible to obtain similar effects.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a general turbine generator plant, Fig. 2 is a block diagram showing an example of a conventional load runback device, Fig. 3 is a characteristic diagram explaining the operation of the configuration shown in Fig. Figure 4 is a block diagram of a load runback device according to an embodiment of the present invention;
This figure is a partial circuit configuration diagram explaining the arrangement of the second current detector of FIG. 4, and FIG. 6 is a characteristic diagram explaining the operation of the configuration of FIG. 4. 1... Boiler, 2... Main steam stop valve, 3... Control valve, 4... Turbine, 7... Generator, 10,1
5...Current detector, 11...Failure detector, 14...
...Timer, 3M...control device.

Claims (1)

[Claims] 1 A failure detector for detecting a failure of the cooling device of a generator having a cooling device; and a current detector that outputs a second output at a set value slightly lower than the self-cooling capacity, and a load runback command to the prime mover that drives the generator based on the failure detector output and the first output. a first load control circuit that outputs a load runback command; a second load control circuit that commands the prime mover to increase the load based on the failure detector output and the second output; and a second load control circuit that commands the prime mover to increase the load, and outputs the load runback command. A load runback device comprising a monitoring circuit that monitors and trips the generator.