Reactor Feedwater Pump Control System

Abstract

An object of the present invention is to provide a reactor feedwater pump control system, wherein when a condensate pump is tripped, the decrease in feedwater flow of feedwater supplied to a steam generator is minimized to suppress the decrease in water level of the steam generator, and at the same time preventing operating condensate pumps from continuing a run out operation. The feedwater pump control system is provided with a feedwater supply system, which includes a plurality of condensate pumps disposed in parallel for boosting condensate water from a condenser; a plurality of reactor feedwater pumps disposed in parallel for further boosting and supplying the condensate water to a steam generator; and variable frequency power supply systems each for driving an electric motor of the reactor feedwater pump at an adjustable speed.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to reactor feedwater pump control systems used in thermal power plants and reactor power plants.

2. Description of the Related Art

Generally, in a reactor power plant or a thermal power plant, steam generated by a nuclear reactor or a boiler as a steam generator is used to drive a steam turbine. After driving the steam turbine, the steam is cooled by a condenser to be used as condensate water. The condensate water is boosted by a feedwater supply system, and is then supplied to the steam generator. The feedwater supply system includes a plurality of condensate pumps and a plurality of reactor feedwater pumps both including a standby pump.

When one of the condensate pumps on an upstream side of such a feedwater supply system trips, the flow output from the condensate pumps decreases. In such case, if reactor feedwater pumps on the downstream side are operated normally, balance between the flow normally able to be provided by the condensate pumps on the upstream side and the flow provided by the reactor feedwater pumps on the downstream side would be disrupted. The remaining condensate pumps would be operated in a zone exceeding an excess flow zone (hereinafter referred to as “run out operating zone”) which is only transiently allowed for a certain period. This may damage the remaining condensate pumps. In addition, since the reactor feedwater pumps would not be able to obtain required suction pressure, cavitation may occur, possibly damaging the reactor feedwater pumps.

For the above reasons, it is necessary to take measures to keep balance between the flow of the pumps on the upstream side and the flow of the pumps on the downstream side in such a case.

There is disclosed a feedwater supply system provided with inverter devices which drive driving electric motors of reactor feedwater pumps with adjustable speed respectively, wherein: when it is detected that an operating condensate pump has been tripped, a controller executes control for tripping that outputs, to all inverter devices of operating reactor feedwater pumps, a decelerating operation instruction to perform decelerating operation based on set speed; and the controller then outputs a start-up instruction to a standby pump for the tripped condensate pump, and executes control for returning that outputs a return instruction to return to a normal state to all inverter devices of the reactor feedwater pumps (for example, refer to JP-2009-204255-A).

SUMMARY OF THE INVENTION

In the above-described JP-2009-204255-A, for example, when a normal plant feedwater flow is provided by operating three condensate pumps and three reactor feedwater pumps, the feedwater flow provided by each pump is 33% of the plant feedwater flow. Accordingly, in a case where one of the condensate pumps is tripped, the control for tripping is executed as the following: the inverter systems (hereinafter referred to as “ASD (Adjustable Speed Drive inverter system)”) of the reactor feedwater pumps output the decelerating operation command to decrease the feedwater flow of the plant from 100% to 66%. In the subsequent return control, the start-up instruction for standby condensate pump is output. After the standby pump is determined to be started, the ASDs of the reactor feedwater pumps output an accelerating operation command to increase the feedwater flow of the plant from 66% to 100%.

However, the behavior of the feedwater supply system upon tripping of a condensate pump has problems as below:

(1) Because of the characteristics of the ASDs, the rotational speed of the reactor feedwater pumps cannot be rapidly decreased. Therefore, even though the decelerating operation instruction is received, the actual rotational speed of each reactor feedwater pump decreases at a limited rate.

(2) A standby condensate pump is usually started shortly after one condensate pump is tripped. A start-up of the standby pump is determined by a closed contact signal of a power breaker. Thus, a time period of the output of the above-described decelerating operation instruction is short. After the standby pump is started, an accelerating operation instruction is output to return the flow to a normal rate.

(3) To be more specific, since the output time of the decelerating operation instruction for decreasing the feedwater flow of the plant from 100% to 66% is short, ASDs cannot rapidly decrease the rotational speed of reactor feedwater pumps even though the decelerating operation instruction is received. In addition, the accelerating operation instruction for increasing the feedwater flow of the plant from 66% to 100% is output soon after the receipt of the decelerating operation instruction. The actual rotational speed of the reactor feedwater pump may substantially not decrease.

(4) It may be possible to ensure a sufficient flow several seconds after starting the standby condensate pump in this case. However, the two condensate pumps which have not been tripped would continue to operate in a run out operating zone in order to compensate for the flow of the reactor feedwater pumps not decelerating.

(5) Further, even if the rotational speed of each reactor feedwater pump driven by a respective ASD is sufficiently reduced, the reactor feedwater pump cannot be rapidly accelerated due to the characteristics of the ASD. Therefore, in the returning control, it would take a certain time until the rotational speed reaches a speed corresponding to the required plant feedwater flow. The water level of the steam generator would largely decrease during this time.

(6) Furthermore, no control is prepared for a case where the standby condensate pump does not start up even when required. Continuing the deceleration control may decrease the water level of the steam generator to thereby cause plant trip, and other problems may occur as well.

The present invention has been made on the basis of the foregoing facts and circumstances. An object of the present invention is to provide a reactor feedwater pump control system such that, when a condensate pump trips, minimizes the decrease in feedwater flow supplied to a steam generator so as to suppress the water level decrease in the steam generator, and also prevents continuously operating condensate pumps from continuing run out operation.

In order to achieve the above-described object, the first invention provides a reactor feedwater pump control system provided with a feedwater supply system, the feedwater supply system comprising:

a plurality of condensate pumps disposed in parallel for boosting condensate water from a condenser;

a plurality of reactor feedwater pumps disposed in parallel for further boosting and supplying the condensate water to a steam generator; and

variable frequency power supply systems each for driving an electric motor of the reactor feedwater pump at an adjustable speed, the variable frequency power supply systems in the feedwater supply system receive frequency control instruction to thereby control the rotational speeds of the reactor feedwater pumps;

wherein:

the reactor feedwater pump control system includes:

control for tripping means for, when it is detected that one of the operating condensate pumps has been tripped, changing a maximum flow limit value for the frequency control instruction to the variable frequency power supply systems, in order to change a flow to the run out flow which is operational only for a short-time transition; and

control for returning means for, when it is detected that a standby pump for the condensate pump has started up, changing the maximum flow limit value from the run out flow to the normal operating flow.

A second aspect of the present invention is a reactor feedwater pump control system according to aspect 1, wherein:

the feedwater supply system includes pressure detection means for detecting discharge pressure of the condensate pumps; and

the reactor feedwater pump control system receives the discharge pressure of the condensate pumps from the pressure detection means, detects start-up of the standby condensate pump by comparison operation of the discharge pressure and pump start-up characteristics.

A third aspect of the present invention is a reactor feedwater pump control system according to aspect 1, wherein:

the feedwater supply system includes rotational speed detection means for detecting the rotational speeds of the condensate pumps; and

the reactor feedwater pump control system receives the rotational speeds of the condensate pumps from the rotational speed detection means, detects the start-up of the standby condensate pump by comparison of the rotational speeds and the pump start-up characteristics.

A fourth aspect of the present invention is a reactor feedwater pump control system according to any one of aspects 1 to 3, wherein:

the reactor feedwater pump control system includes the control for tripping means, and control means for, when it is detected that the standby pump for the condensate pump has not started up, changing the maximum flow limit value from the run out flow to the normal operation flow obtained by condensate pumps that are continuously operating.

A fifth aspect of the present invention is a reactor feedwater pump control system according to aspect 4, wherein:

the reactor feedwater pump control system includes control means for, when it is detected that the standby pump for the condensate pump has not started up, outputting an instruction to an automatic power regulator of the steam generator to request the automatic power regulator to decrease the power of the steam generator.

A sixth aspect of the present invention is a reactor feedwater pump control system according to aspect 5, wherein:

the reactor feedwater pump control system includes control means for, when it is detected that the standby pump for the condensate pump has not started up, changing the number of operating reactor feedwater pumps in such a manner that the number of operating reactor feedwater pumps becomes equivalent to the number of condensate pumps that are continuously operating.

According to the present invention, when a condensate pump is tripped, the decrease in feedwater flow of feedwater supplied to the steam generator can be minimized to suppress the decrease in water level of the steam generator. At the same time, operating condensate pumps can be prevented from continuing a run out operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a systematic diagram illustrating a steam turbine facility to which a first embodiment of the reactor feedwater pump control system of the present invention is applied;

FIG. 2 is a block diagram illustrating a configuration of the reactor feedwater pump control system according to the first embodiment of the present invention;

FIG. 3 is a characteristic chart illustrating the operation in which a standby pump has started up when a condensate pump is tripped in the first embodiment of the reactor feedwater pump control system of the present invention;

FIG. 4 is a characteristic chart illustrating the operation in which a standby pump has not started up when a condensate pump is tripped in the second embodiment of the reactor feedwater pump control system of the present invention;

FIG. 5 is a characteristic chart illustrating the operation in which a standby pump has not started up when a condensate pump is tripped in the third embodiment of the reactor feedwater pump control system of the present invention;

FIG. 6 is a characteristic chart illustrating the operation in which a standby pump has not started up when a condensate pump is tripped in the fourth embodiment of the reactor feedwater pump control system of the present invention; and

FIG. 7 is a table illustrating an example of determining pump operating conditions and an example of setting maximum flow limiters in each embodiment of the reactor feedwater pump control system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the reactor feedwater pump control system of the present invention will be described below with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a systematic diagram illustrating a steam turbine facility to which a first embodiment of the reactor feedwater pump control system of the present invention is applied. FIG. 2 is a block diagram illustrating a configuration of the reactor feedwater pump control system according to the first embodiment of the present invention. FIG. 3 is a characteristic chart illustrating the operation during start-up of a standby condensate pump for tripping in the first embodiment of the reactor feedwater pump control system of the present invention.

In FIG. 1, steam generated by a steam generator 1 is supplied to a high-pressure turbine 2 through a supply pipe. The steam expanded by the high-pressure turbine 2 is passed through a steam pipe to a moisture separator reheater 3. The moisture separator reheater 3 reheats the steam and then supplies the reheated steam to a low-pressure turbine 4. The steam expanded by the low-pressure turbine 4 is condensed by a condenser 5 so as to be used as condensate water. The condensate water is led out from the condenser 5 by a plurality of low-pressure condensate pumps 6 (in this example, four pumps) disposed in parallel. Then, the condensate water is boosted to be supplied to a plurality of high-pressure condensate pumps 7 (in this example, four pumps) disposed in parallel. The high-pressure condensate pumps 7 further boost the condensate water to send them to a low-pressure feedwater heater 8 through feedwater supply pipes. The low-pressure feedwater heater 8 heats and raises the temperature of the condensate water supplied by using extracted steam from the low-pressure turbine 4. The heated condensate water is supplied to a plurality of reactor feedwater pumps 10 (in this example, four pumps) disposed in parallel. Driving electric motors of the reactor feedwater pumps 10 are driven at adjustable speed by respective adjustable speed motors with variable frequency power supply systems 9. The reactor feedwater pumps 10 further boost the condensate water to supply them to a high-pressure feedwater heater 12. The high-pressure feedwater heater 12 heats and raises the temperature of the condensate water by using extracted steam from the high-pressure turbine 2. The heated condensate water is then supplied to the steam generator 1.

The extracted steam from the high-pressure turbine 2 is, as described above, supplied to the moisture separator reheater 3 and the high-pressure feedwater heater 12 as heating steam. After heat exchange with exhaust steam of the high-pressure turbine 2 or feedwater, the extracted steam turns into drain. The drain is collected in a high pressure drain tank 11 through a drain pipe. Drain generated in the moisture separator reheater 3 by moisture separation of the exhaust steam from the high-pressure turbine 2, is also collected in the high pressure drain tank 11. The drain stored in the high-pressure drain tank 11 is led out therefrom and boosted to be supplied to inlet sides of the reactor feedwater pumps 10 by a plurality of high-pressure drain pumps 13 (in this example, four pumps) disposed in parallel.

The water level controlling of the steam generator 1 in the turbine facility is conducted on the basis of: the water level of the steam generator 1; the amount of steam generated by the steam generator 1; and the feedwater flow supplied to the steam generator 1. According to these factors, the systems for controlling the water level in the steam generator 1, namely, the feedwater flow control system 16 and the reactor feedwater pump control system 15 output rotational speed instructions to the adjustable speed motors with variable frequency power supply systems 9. Thus, the rotational speeds of the driving electric motors and the reactor feedwater pumps 10 can be adjusted, thereby controlling the water level in the steam generator 1.

As shown in FIG. 2, the reactor feedwater pump control system 15 is provided with a pump operating condition determination circuit 14 for determining operating conditions of the low-pressure condensate pumps 6, the high-pressure condensate pumps 7, the reactor feedwater pumps 10 and the high-pressure drain pumps 13. The reactor feedwater pump control system 15 is also equipped with a maximum flow limit setting circuit 15A. The maximum flow limit setting circuit 15A receives operating conditions from the pump operating condition determination circuit 14. Based on the conditions, the maximum flow limit setting circuit 15A limits the maximum values of rotational speed instructions and sends them to the reactor feedwater pumps 10. In such manner, the maximum flow limit setting circuit 15A prevents the pumps from operating beyond capacity. Incidentally, two kinds of limit flows are set for each pump: a design flow and the run out flow. The design flow represents a flow in a normal operation, continuously operational and allows for fluctuations, etc. The run out flow represents a flow in a transitional situation and its operational time is limited.

Going back to FIG. 1, configurations of the low-pressure condensate pumps 6, the high-pressure condensate pumps 7, and the high-pressure drain pumps 13 are described. Assuming the plant feedwater flow during a normal operation as 100%, the condensate water flow and high-pressure drain flow of each of the pumps (one pump) are both approximately 33% in capacity. The three kinds of pumps each consist of four pumps connected in parallel. In a normal operation in which the plant feedwater flow is 100%, three of the four pumps operate while the remaining one is held as a standby pump.

The reactor feedwater pumps 10 driven by the adjustable speed motors with variable frequency power supply systems 9 have similar configurations. When the plant feedwater flow is assumed to be 100% during normal operation, the feedwater flow of each reactor feedwater pump 10 is approximately 33% in capacity. During normal operation, three of four pumps are operated and the remaining one is held as a standby pump.

A case is assumed where one low-pressure condensate pump 6 is tripped due to a failure in the one of the plurality of low-pressure condensate pumps 6 during normal operation. A feedwater flow would decrease to a level that can be supplied by two low-pressure condensate pumps 6. In such case, if the pumps on the downstream: the high-pressure condensate pumps 7 and the reactor feedwater pumps 10 driven by the adjustable speed motors with variable frequency power supply systems 9 continue to operate as usual at a feedwater flow of 100% together, an unbalance in flow between the upstream and downstream pumps may cause problems. More specifically, due to the unbalance between the flow available from the upstream pumps (i.e. the low-pressure condensate pumps 6) and the flow of the downstream pumps (i.e. the high-pressure condensate pumps 7 and the reactor feedwater pumps 10 driven by the variable frequency power supply systems 9), the two low-pressure condensate pumps 6 would be operated beyond the run out operating zone. This may cause damage to the operating low-pressure condensate pumps 6. In addition, since the high-pressure condensate pumps 7 and the reactor feedwater pumps 10 driven by the variable frequency power supply systems 9 would not be able to obtain the required suction pressure, the pumps on the downstream side may also be damaged due to cavitation.

In this embodiment, in order to eliminate the flow unbalance between the upstream and the downstream in the feedwater system upon pump tripping, the reactor feedwater pump control system 15 is provided with the maximum flow limit setting circuit 15A. A configuration of the reactor feedwater pump control system 15 will be described with reference to FIG. 2.

As shown in FIG. 2, the reactor feedwater pump control system 15 is provided with the pump operating condition determination circuit 14, the maximum flow limit setting circuit 15A and a steam generator power changeover demand circuit 15B. The pump operating condition determination circuit 14 receives the operating conditions of the low-pressure condensate pumps 6, the high-pressure condensate pumps 7, the reactor feedwater pumps 10 and the high-pressure drain pumps 13. As an indication of the operating condition, opened/closed contact of the power breakers of the electric motors for driving the pumps may be used for instance. The maximum flow limit setting circuit 15A outputs a rotational speed instruction to the variable frequency power supply systems 9 as to control each of the reactor feedwater pumps 10. The steam generator power changeover demand circuit 15B outputs a power changeover instruction to the steam generator automatic power regulator 100 to control the power of the steam generator 1.

Here, when one of the low-pressure condensate pumps 6 or one of the high-pressure condensate pumps 7 tripped, a control for tripping means included in the reactor feedwater pump control system 15 is executed as below. First, the reactor feedwater pump control system 15 receives operating conditions of the pumps from the pump operating condition determination circuit 14. According to the conditions, the reactor feedwater pump control system 15 outputs a setting change instruction to the maximum flow limit setting circuit 15A that limits a maximum value of a rotational speed instruction for each of the reactor feedwater pumps 6 driven by the variable frequency power supply systems 9. Then, the maximum flow limit setting circuit 15A changes the maximum flow limit value from the design flow to the run out flow which is operational for only a short-time transition. The rotational speeds of the reactor feedwater pumps 10 decrease and in turn the feedwater flow is decreased. As a result, the flow unbalance between upstream pumps i.e. the condensate pumps 6, 7 and the downstream pumps i.e. the reactor feedwater pumps 10 can be eliminated.

Further, when the standby pump is detected to be started, a control for returning means included in the reactor feedwater pump control system 15 is executed as below. The reactor feedwater pump control system 15 outputs a setting return instruction to the maximum flow limit setting circuit 15A. Upon receipt of the instruction, the maximum flow limit setting circuit 15A changes the maximum flow limit value from the run out flow to the design flow. The control is thus moved to a normal operation state, and the mismatch between the required feedwater flow needed for the steam generator 1 and the supplied feedwater flow can be minimized. As a result, the decrease in water level of the steam generator 1 can be suppressed.

Next, a description is made for an example of setting changes of the maximum flow limit setting circuit 15A where one of the plurality of low-pressure condensate pumps 6 is tripped, with reference to FIG. 3.

Here, for the sake of convenience, the design flow is assumed to be 110% of the plant feedwater flow. The run out flow is set as 130% of the plant feedwater flow, and its operational time is set as two minutes or less. The run out flow supplied from two low-pressure condensate pumps 6 is calculated as follows: 33.3×2×1.3=86.8%.

In FIG. 3, it is presumed that one of the plurality of low-pressure condensate pumps 6 is determined to have tripped by the pump operating condition determination circuit 14 determines. The reactor feedwater pump control system 15 then outputs a setting change instruction to the maximum flow limit setting circuit 15A that limits a maximum value of a rotational speed instruction for each of the reactor feedwater pumps 10 driven by the adjustable speed motors with variable frequency power supply systems 9. Upon receipt of the instruction, the maximum flow limit setting circuit 15A changes the maximum flow limit value from the design flow 110% (flow obtained by three low-pressure condensate pumps 6) to the run out flow 86.8% that is operational only for a short-time transition (flow obtained by two low-pressure condensate pumps 6). The rotational speeds of the reactor feedwater pumps 10 are thus reduced, which causes the feedwater flow to decrease. This eliminates the flow unbalance between the low-pressure condensate pumps 6 on the upstream side and the pumps on the downstream side (the high-pressure condensate pumps 7, the high-pressure drain pumps 13 and the reactor feedwater pumps 10 driven by the adjustable speed motors with variable frequency power supply systems 9), thereby preventing a cavitation operation.

Subsequently, when the pump operating condition determination circuit 14 detects a start-up of the standby low-pressure condensate pump 6, the reactor feedwater pump control system 15 outputs a setting return instruction to the maximum flow limit setting circuit 15A. Upon receipt of the instruction, the maximum flow limit setting circuit 15A changes the maximum flow limit value from the run out flow 86.8% (flow obtained by two low-pressure condensate pumps 6) to the design flow 110% (flow obtained by three low-pressure condensate pumps 6). The rotational speeds of the reactor feedwater pumps 10 accelerate, causing the feedwater flow to increase. The control thus moves to a normal operation state. Consequently, the plant feedwater flow can be quickly ensured, and the decrease in water level of the steam generator 1 can be suppressed.

According to the first embodiment of the reactor feedwater pump control system of the present invention described above, when any of the condensate pumps 6 is tripped, the decrease in feedwater flow of feedwater supplied to the steam generator 1 can be minimized to suppress the decrease in water level of the steam generator 1. In addition, the operating condensate pumps 6 can be prevented from continuing a run out operation as well.

Further, according to the first embodiment of the reactor feedwater pump control system of the present invention described above, the time period of the sequence from tripping to a recovery of a normal state can be shortened as follows. When it is detected that one of the plurality of low-pressure condensate pumps 6 has been tripped, the reactor feedwater pump control system 15, which controls the rotational speed of the reactor feedwater pumps 10 driven by the adjustable speed motors with variable frequency power supply systems 9, executes the control for tripping. The maximum flow limit value for the rotational speed control instruction is given to each of the reactor feedwater pumps 10 to thereby change from the design flow to the run out flow. After it is detected that the standby low-pressure condensate pumps 6 has started, the reactor feedwater pump control system 15 executes the control for returning to return the maximum flow limit value from the run out flow to the design flow. Thus, the time required can be shortened from the tripping of one of the plurality of low-pressure condensate pumps 6 to the control for returning that starts up the standby low-pressure condensate pumps 6 to return the feedwater flow to a normal rate.

In this embodiment, a contact signal of the breaker is used as a signal to indicate start-up of a standby low-pressure condensate pump 6, which is used as a signal for returning the maximum flow limiter to the normal settings. However, the present invention is not limited to this. For example, each of the low-pressure condensate pumps 6 may be provided with a rotational speed detection means, and the signal detected by the rotational speed detection means may be output to the pump operating condition determination circuit 14 of the reactor feedwater pump control system 15. Alternatively, the discharge side of each of the low-pressure condensate pumps 6 may be provided with a pressure detection means for detecting the pump discharge pressure. The signal detected by the pressure detection means may be output to the pump operating condition determination circuit 14 as with the above. Further, the start-up of the standby pump may be determined by comparison operation of these values and a set value(s) derived from pump start-up characteristics. Determining the start-up of the standby pump on the basis of the pump start-up characteristics enables to ensure a substantial control time for the control for tripping of the reactor feedwater pumps 10. Consequently a risk where the low-pressure condensate pumps 6 operate beyond the run out flow can be reduced.

Second Embodiment

A second embodiment of the reactor feedwater pump control system of the present invention will be described below with reference to the accompanying drawings. FIG. 4 is a characteristic chart illustrating the operation where a standby pump does not start up even required upon tripping of a condensate pump in the second embodiment of the reactor feedwater pump control system of the present invention. In the description referring to FIG. 4, reference numerals that are same as those shown in FIGS. 1 to 3 represent similar parts. Therefore the detailed description thereof will be omitted.

In the first embodiment, it was assumed that a standby pump started up when one of the plurality of low-pressure condensate pumps 6 tripped. Meanwhile in this embodiment, it is assumed that the standby pump would not start up even when one of the plurality of low-pressure condensate pumps 6 is tripped. The turbine facility, the reactor feedwater pump control system 15 and the like are configured similarly to those disclosed in the first embodiment.

In FIG. 4, it is presumed that the pump operating condition determination circuit 14 determines one of the plurality of low-pressure condensate pumps 6 to be tripped. The reactor feedwater pump control system 15 then outputs a setting change instruction to the maximum flow limit setting circuit 15A that limits a maximum value of a rotational speed instruction for each of the reactor feedwater pumps 10 driven by the adjustable speed motors with variable frequency power supply systems 9. On receipt of the instruction, the maximum flow limit setting circuit 15A changes the maximum flow limit value from the design flow 110% (flow obtained by three low-pressure condensate pumps 6) to the run out flow 86.8% (flow obtained by two low-pressure condensate pumps 6) that is operational for only a short-time transition. The rotational speeds of the reactor feedwater pumps 10 are thereby reduced, which causes the feedwater flow to decrease.

After this, if the standby low-pressure condensate pump 6 does not start, the two low-pressure condensate pumps 6 would continue to operate in the run out flow. This may cause overload tripping due to exceeding of an allowed operation time. In addition, if all of the low-pressure condensate pumps 6 trip, a flow unbalance occurs between the low-pressure condensate pumps 6 on the upstream side and the pumps on the downstream side (the high-pressure condensate pumps 7 and the reactor feedwater pumps 10 driven by the adjustable speed motors with variable frequency power supply systems 9). The pumps may be damaged because of cavitation operation.

Therefore, for example, when a start-up signal is not accepted for five seconds after commandant, the pump operating condition determination circuit 14 determines that the standby low-pressure condensate pump 6 would not start up. The reactor feedwater pump control system 15 outputs a further setting change instruction to the maximum flow limit setting circuit 15A. On receipt of the instruction, the maximum flow limit setting circuit 15A changes the maximum flow limit value from the run out flow 86.8% (flow obtained by two low-pressure condensate pumps 6) to the design flow 73.3% (33.3×2×1.1; flow obtained by two low-pressure condensate pumps 6). This prevents the overload tripping which occurs when operation time of the low-pressure condensate pumps 6 exceeds an allowed time. Cavitation operation caused by the decrease in suction pressure of the reactor feedwater pumps 10 driven by the adjustable speed motors with variable frequency power supply systems 9 can also be prevented.

According to the second embodiment of the reactor feedwater pump control system of the present invention described above, the same effects as those of the first embodiment can be achieved. Further, along with those effects, even if a standby low-pressure condensate pump 6 would not start up when required, overload tripping in the continuously operating low-pressure condensate pumps 6 and the cavitation operation of the reactor feedwater pumps 10 can be prevented.

Third Embodiment

A third embodiment of the reactor feedwater pump control system of the present invention will be described below with reference to the accompanying drawings. FIG. 5 is a characteristic chart illustrating the operation where a standby pump would not start up even when a condensate pump is tripped in the third embodiment of the reactor feedwater pump control system of the present invention. In the description referring to FIG. 5, reference numerals that are same to those shown in FIGS. 1 to 4 represent similar parts. Therefore the detailed description thereof will be omitted.

The second embodiment discloses the example in which the standby pump would not start up even when one of the plurality of low-pressure condensate pumps 6 is tripped. This embodiment discloses another example of the operation in which the standby pump would not start as well. The turbine facility, the reactor feedwater pump control system 15 and the like are configured similarly to those disclosed in the first embodiment.

In FIG. 5, when the pump operating condition determination circuit 14 determines that one of the plurality of low-pressure condensate pumps 6 has been tripped, the reactor feedwater pump control system 15 and the maximum flow limit setting circuit 15A operate in a same manner as the operation disclosed in the second embodiment. After the pump operating condition determination circuit 14 determines that the standby pump would not start up, the maximum flow limiters of the reactor feedwater pumps 10 are further changed to the design flow obtained by the two operating low-pressure condensate pumps 6.

As mentioned above, overload tripping of the continuously operating low-pressure condensate pumps 6 and the cavitation operation of the reactor feedwater pumps 10 can be prevented. However, the required feedwater flow required by the steam generator 1 and the feedwater flow supplied to the steam generator 1 by the reactor feedwater pumps 10 remains unbalanced. This may lead to plant tripping due to a decrease in water level of the steam generator 1.

Therefore, after the pump operating condition determination circuit 14 determines that the standby pump would not start up, the reactor feedwater pump control system 15 outputs a power changeover instruction from the steam generator power changeover demand circuit 15B to the steam generator automatic power regulator 100. On receipt of the instruction, the steam generator automatic power regulator 100 decreases the output of the steam generator 1 down to a level lower than or equal to the design flow available from the operating low-pressure condensate pumps 6. Consequently, the required feedwater flow for the steam generator 1 decreases. Balance can be achieved between the required feedwater flow for the steam generator land the feedwater flow supplied to the steam generator 1 from the pumps: the low-pressure condensate pumps 6, the high-pressure condensate pumps 7, the high-pressure drain pumps 13 and the reactor feedwater pumps 10. This prevents plant tripping which is caused by the decrease in water level of the steam generator 1.

According to the third embodiment of the reactor feedwater pump control system of the present invention described above, the same effects as those of the second embodiment can be achieved. Along with those effects, even if the standby low-pressure condensate pump 6 would not start up when required, plant tripping due to the decrease in water level of the steam generator 1 can be prevented.

Fourth Embodiment

A fourth embodiment of the reactor feedwater pump control system of the present invention will be described with reference to the accompanying drawings as below. FIG. 6 is a characteristic chart illustrating the operation in which a standby pump would not start up even when a condensate pump is tripped in the fourth embodiment of the reactor feedwater pump control system of the present invention. In FIG. 6, reference numerals that are same to those shown in FIGS. 1 to 5 represent similar parts. Therefore the detailed description thereof will be omitted.

The third embodiment discloses the example in which the standby pump would not started up even when one of the plurality of low-pressure condensate pumps 6 is tripped. This embodiment discloses still another example of the operation in which the standby pump would not start up. The turbine facility, the reactor feedwater pump control system 15 and the like are configured in a manner similar to that disclosed in the first embodiment.

In FIG. 6, when the pump operating condition determination circuit 14 determines that one of the plurality of low-pressure condensate pumps 6 has been tripped, the reactor feedwater pump control system 15, the maximum flow limit setting circuit 15A and the steam generator power changeover demand circuit 15B operate in a manner similar to that disclosed in the third embodiment. After the pump operating condition determination circuit 14 determines that the standby pump would not start up, the maximum flow limiters of the reactor feedwater pumps 10 are further changed to the design flow obtained by the two operating low-pressure condensate pumps 6. The power of the steam generator 1 is decreased down to a level lower than or equal to the design flow available from the low-pressure condensate pumps 6 which are continuously operating.

This enables operation to be continued in this plant output state. However, the operation capacity of each one of the pumps which constitute a feedwater supply system differs from the others. To be more specific, while the number of the operating low-pressure condensate pumps 6 is two, the number of the operating high-pressure condensate pumps 7 and the number of the operating reactor feedwater pumps 10 are each three. If the operation is transient, no problem arises. However, in the case where operation continues, operation by three pumps should be shifted to operation by two pumps.

Therefore, after the pump operating condition determination circuit 14 determines that the standby pump would not started up, the reactor feedwater pump control system 15 outputs a power changeover instruction from the steam generator power changeover demand circuit 15B to the steam generator automatic power regulator 100, and stops one of the high-pressure condensate pumps 7 and one of the reactor feedwater pumps 10. Consequently, the operation capacity per pump is balanced among the operating low-pressure condensate pumps 6, the operating high-pressure condensate pumps 7 and the operating reactor feedwater pumps 10. At the same time, the required feedwater flow required by the steam generator 1 can be balanced with the feedwater flow supplied to the steam generator 1 from the pumps: the low-pressure condensate pumps 6, the high-pressure condensate pumps 7, the high-pressure drain pumps 13 and the reactor feedwater pumps 10. This makes it possible to prevent plant tripping caused by the decrease in water level of the steam generator 1.

According to the fourth embodiment of the reactor feedwater pump control system of the present invention described above, the same effects as those of the first to third embodiments can be achieved.

Incidentally, the embodiments of the present invention each described the example in which one of the plurality of low-pressure condensate pumps 6 has been tripped. However, even when one of the plurality of high-pressure condensate pumps 7 is tripped, the maximum feedwater flow limiters are changed in like manner. FIG. 7 illustrates an example in which the maximum feedwater flow limiter is changed in a case where the standby pump starts up or would not started up when each of the low-pressure condensate pumps 6 or each of the high-pressure condensate pumps 7 has been tripped.

In addition, the embodiments of the present invention each described the example in which the present invention is applied to the power plant equipped with the condensate pumps having a two-stage configuration. However, the present invention is not limited to this. For example, the present invention can also be applied to a power plant equipped with condensate pumps having a one-stage configuration. Moreover, the examples in which each pump group is constituted of four pumps were described. However, the present invention can also be applied to an example in which each pump group is constituted of, for example, three or five pumps.

Furthermore, the embodiments of the present invention each described the example in which the present invention is applied to the power plant provided with drain-up by the drain pumps. However, the present invention is not limited to this. For example, even if the present invention is applied to a power plant in which drain is cascaded to a downstream feedwater heater, the same effects can be achieved.

Claims

1. A reactor feedwater pump control system provided with a feedwater supply system, the feedwater supply system comprising:

a plurality of condensate pumps disposed in parallel for boosting condensate water from a condenser;

a plurality of reactor feedwater pumps disposed in parallel for further boosting and supplying the condensate water to a steam generator; and

variable frequency power supply systems each for driving an electric motor of the reactor feedwater pump at an adjustable speed, the variable frequency power supply systems in the feedwater supply system receive frequency control instruction to thereby control the rotational speeds of the reactor feedwater pumps;

wherein:

the reactor feedwater pump control system includes:

control for tripping means for, when it is detected that one of the operating condensate pumps has been tripped, changing a maximum flow limit value for the frequency control instruction to the variable frequency power supply systems, in order to change a flow to the run out flow which is operational only for a short-time transition; and

control for returning means for, when it is detected that a standby pump for the condensate pump has started up, changing the maximum flow limit value from the run out flow to the normal operating flow.

2. The reactor feedwater pump control system according to claim 1, wherein:

the feedwater supply system includes pressure detection means for detecting discharge pressure of the condensate pumps; and

the reactor feedwater pump control system receives the discharge pressure of the condensate pumps from the pressure detection means, detects start-up of the standby condensate pump by comparison operation of the discharge pressure and pump start-up characteristics.

3. The reactor feedwater pump control system according to claim 1, wherein:

the feedwater supply system includes rotational speed detection means for detecting the rotational speeds of the condensate pumps; and

the reactor feedwater pump control system receives the rotational speeds of the condensate pumps from the rotational speed detection means, detects the start-up of the standby condensate pump by comparison of the rotational speeds and the pump start-up characteristics.

4. The reactor feedwater pump control system according to claim 1, wherein:

the reactor feedwater pump control system includes the control for tripping means, and control means for, when it is detected that the standby pump for the condensate pump has not started up, changing the maximum flow limit value from the run out flow to the normal operation flow obtained by condensate pumps that are continuously operating.

5. The reactor feedwater pump control system according to claim 4, wherein:

the reactor feedwater pump control system includes control means for, when it is detected that the standby pump for the condensate pump has not started up, outputting an

instruction to an automatic power regulator of the steam generator to request the automatic power regulator to decrease the power of the steam generator.

6. The reactor feedwater pump control system according to claim 5, wherein:

the reactor feedwater pump control system includes control means for, when it is detected that the standby pump for the condensate pump has not started up, changing the number of operating reactor feedwater pumps in such a manner that the number of operating reactor feedwater pumps becomes equivalent to the number of condensate pumps that are continuously operating.

7. The reactor feedwater pump control system according to claim 2, wherein:

the reactor feedwater pump control system includes the control for tripping means, and control means for, when it is detected that the standby pump for the condensate pump has not started up, changing the maximum flow limit value from the run out flow to the normal operation flow obtained by condensate pumps that are continuously operating.

8. The reactor feedwater pump control system according to claim 3, wherein:

the reactor feedwater pump control system includes the control for tripping means, and control means for, when it is detected that the standby pump for the condensate pump has not started up, changing the maximum flow limit value from the run out flow to the normal operation flow obtained by condensate pumps that are continuously operating.