JPS6099908A - Device for changing over operation of pump - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a pump operation switching system, and more particularly to a pump operation switching device in an emergency for a pump system having a standby pump.

[Background of the invention]

Pumped water systems are used in all industries. Although there are many different types of water transmission systems, water supply systems and various circulating water systems are important for power plants, and when these systems trip, it is often necessary to shut down the power plant. Therefore, in preparation for the tripping of the operating pump due to unforeseen circumstances, the pump configuration usually includes a backup pump to provide redundancy.

A water supply system is generally constructed as shown in Figure 1.

From the water tank 1, it passes through the suction main pipe 2 and reaches the pump group. In this example, there are three pumps, 3a, 3h, and 3c, each with a capacity of 50% of the rated water flow rate, and 2 pumps at all times.
It is driven by a machine. The other pump is a standby pump, which is activated immediately and used in place of the trip pump when the regular pump trips for some reason.

On the pump discharge side, check valves 4a and 4J'C are respectively provided on the pump discharge side piping to prevent the pump flow rate from flowing backward. After passing through the check valve, the water is again sent to the water receiving tank 6 via the common main pipe 5.

Flow rate control methods for water transmission systems can be divided into methods in which the system flow rate changes depending on the plant output, and methods in which the flow rate is always constant. Typical examples of the former include water supply systems for thermal power and nuclear couplants.

The latter applies to various other water supply systems. In the former case, it is necessary to ensure a minimum pump flow rate at low flow rates. For this reason, the recirculating water pipes 7a, 7b are connected between the pumps 3a, 3b, 3c and the check valves 4a, 4b, 4c.
, 7c was installed.

Its flow rate is controlled by recirculation valves 13a, 8b, 8c and returned to water tank 1. In order to ensure the minimum pump flow rate, this recirculation valve is controlled by a control system in which it opens when the pump passing flow reaches a predetermined flow rate (Wmlnl) and closes at a second predetermined flow rate (Wmin2). be exposed.

In the above-described pump configuration, one of the pumps serves as a standby pump, and an interlock is installed to automatically start the pump immediately when the regular pump system trips in an unexpected situation. A transient change in the pump flow rate when such an event occurs is shown in FIG. 2. That is, pump 3
When pump 3b trips at time t1 and pump 3C starts at time t2 during a and 3b operation, the flow rate Ws of pump 3b rapidly decreases, and the flow rate WA of pump 3a rapidly increases. Because We is generated by starting pump 3C, WA decreases, and WA and W.

have the same flow rate. During this time, the system flow rate WFw decreases significantly. When such a trip event occurs, the pump 3a, which serves as the residual pump, has a transiently excessive flow rate, which exceeds the bon-plan-out flow rate and puts the pump in a dangerous state. This is because when an excessive flow rate occurs, the pump suction pressure decreases, lowering the pump's effective suction head, and when it becomes equal to the required net suction head, cavitation occurs and normal operation of the pump becomes impossible.

The above is a case where the pump system is a single pump group, but in water supply systems for thermal power plants and nuclear power plants, two to three groups of pumps are used. Here, an example of three groups is shown in FIG. In other words, condenser 19 yori, low pressure condensate yi! 7”
high pressure condensate pump 12a to the condensate demineralizer via loa, 10b, and IOC.

The pressure is further increased by 12b and 12C, and the turbine-driven water supply pumps 13a and 13b and the motor and drive water supply pump 14a
, 14b, the water becomes high pressure, and is supplied to the nuclear reactor 16 via the feedwater heater 15. In the case of group 2, condensate demineralizer 1
1 and a high pressure condensate pump 12a.

12b and 12C are removed, and the low pressure condensate pump 10a.

10b, IOC and water pump 13 ar 14 b+1
58.15b and the feed water heater 15 only.

In the water supply system composed of the above-mentioned 2nd group and 3rd group pumps, the low pressure condensate pumps 10a and 10 which are the most upstream pump group
b. When an IOC trips, a method is adopted in which the number of downstream pumps corresponding to the trip pump is forcibly stopped, the upstream backup pump is automatically started, and then the downstream backup pump is automatically started. Ru. A detailed explanation of this example is given in Japanese Patent Application No. 51-117173, so it will be omitted here. The problems in this case are: - During the above pump trip, the backup pumps are started one after another, so (1) the power supply voltage decreases (2) the water supply flow rate decreases for a long time, causing the reactor water level to decrease, etc. .

As a solution to the above problem, the above-mentioned patent application No. 51-1171
73 proposes setting a second state where the analog state quantity that is a trip factor is on the safer side than the trip level, and activating the standby machine when the analog state quantity that is a trip factor reaches the second state. ing. This method is excellent in that it only requires starting and tripping of the relevant pump group, and does not affect other pump groups, and changes in water supply flow rate, pump suction pressure, etc. are small. However, if the rate of change in the analog quantity that is the cause of the trip is rapid, there may be a time delay between the startup of the standby unit and the trip of the corresponding pump, and the occurrence of the pump flow rate of the standby unit. Pong suction pressure may decrease. If the rate of change of the analog quantity is still slow, the standby unit will start up in advance and then
A pump trip will occur after a period of time.

[Purpose of the invention]

An object of the present invention is to provide a solution in which almost no fluctuations in flow rate or pressure occur when switching bongs at the trip level, regardless of the magnitude of the rate of change of the analog value of the trip factor.

[Summary of the invention]

The present invention provides that many of the causes of pump operation in emergencies such as pump trips or flow rate reductions are plant state quantities having analog values, and these are more severe for pumps or plan ICs than predetermined state quantities. This was done based on the fact that the IJ knob and flow rate are reduced when the pump goes to the non-safe side (non-safe side), and the time when the analog signal reaches the trip level is estimated from the rate of change of the analog signal.
The purpose is to start the backup pump when the time required to start the backup pump and the time to reach the trip level match.

FIG. 4 shows trip factors for a turbine-driven water pump. Factors that reduce the pump trip and flow rate include the factor that reduces the water supply flow rate of 1 and the individual trip factor of 2. Among these, A1 applies to all water supply pumps, and there is no need to start up the standby unit. There are 52 factors that require activation of the backup pump, and these are the factors that are the subject of this application. These include low pump inlet flow rate, low bong suction pressure, normal bearing oil, normal control oil, and high thrust protection device pressure.

[Embodiments of the invention]

An embodiment of the invention is shown in FIG. This figure is an interlock diagram applied to a motor-driven water supply pump.

The switch 101 is mounted on a control panel (not shown) and can be manually operated by a person.

Can be set to automatic off as desired. Various interlocks are incorporated between switch 101 and motor-driven water pump breaker 1050. 103a to 103d are OR circuits;
104a-104C4tAND circuit. Therefore, to start the stop pump, either turn the switch 101 to the on position, or switch 101 is in the automatic position with the remaining cut 112 and the M-4FP is activated while the M-RFP-A (motor-driven water pump-A) is stopped. - If B trips, or
When the conditions within the dashed line, which is the part of the present invention, are satisfied,
Even if drive permission conditions such as the M-RFP-A inlet valve are fully open are met, the circuit breaker 105 is turned on and the pump is started.

On the other hand, the interlock for stopping the pump can be set by turning the switch 101 to the OFF position, or by setting the water level in the reactor as shown in Figure 4.
fG, 1 water supply flow rate reduction factor and M-R, FP-A
If any of the independent trip factors of the normal image plane 2 with low nail receiving pressure is established, the breaker 105 is opened and the pump trips.

Next, the present invention will be described. Motor driven pump (M
-I'tFP) is a turbine driven pump (T-RFP)
is a standby pump while it is in operation, and it is necessary that the predicted advance activation conditions for one of the two T-RFPs be met. That is, the OR output 103C of the predicted advance activation condition satisfaction 108 of T-RFP-A and the establishment of the predicted advance activation condition 103 of T-RFP-H is used as the OR condition 103 for pump activation.
This is done by putting it in a.

Although it is possible to assemble a circuit using analog circuits to satisfy the predictive advance activation condition, here, we will explain using a program flowchart using a digital computer, which is advantageous for calculating the four arithmetic operations. This flowchart is shown in FIG. First, signal acquisition is performed periodically, and the type of signal corresponds to the analog signal of the single trip factor shown in Figure 4. Next, engineering unit conversion is performed and it is determined whether the trip level has been reached. If the trip level has been reached, the following process is skipped and a process is performed in which it is assumed that the backup pump predicted advance activation condition is satisfied. If the trip level has not been reached, rate of change calculation is performed. The rate of change is calculated using, for example, a linear regression method.

Here XI: Analog signal (current value) xl-1:
// (previous value) The noise component of the rate of change is removed, and the accuracy of the rate of change is further improved.

Next, when the rate of change is greater than a predetermined value and the sign of the rate of change is toward the non-safe side, the trip time is estimated. FIG. 7 shows the transient changes in this case. The current moment is 1. Then, tgT, which will cause a pump trip after tIIT(s) from the current time, can be determined from the current value (XI) of the analog signal and the rate of change ΔX/Δt using the following equation.

'1IT= (XI Xrt)/(ΔX/Δt) (S
)...(2) Here:
(Constant value) Next: Has the preliminary pump start time reached or not? 18T≦TPI+ (Conditions for preliminary pump start are met)
...... (3) Here・TP [+: Standby pump startup time (constant value) T
Strictly speaking, P6 differs depending on conditions such as the motor power supply voltage, pump load system pressure, flow rate, etc., but it can be set as a constant value using a calculated value under normal operating conditions or an actual measured value. There is no practical problem.

In this way, if formula (4) is satisfied, the preliminary pump prediction activation condition is satisfied, and the activation condition 108 in FIG. 4, which is the interlock of the backup pump M-RFP, is activated, and the 2M-RFP is Start automatically. In this way, the backup pump is activated before time TP8 reaches the trip level, and that time is a time with high prediction accuracy that approaches the trip level no matter what the rate of change of the analog signal of the trip factor is. This enables switching operation during pump trips, reducing fluctuations in system flow rate and transient changes in various quantities such as pump suction pressure due to switching operation.

The change in system flow rate according to the present invention is disclosed in Japanese Patent Application No. 51-11717.
3, and the change in flow rate obtained by implementing the present invention is as shown in FIG. 8.

That is, the two backup pumps are started at time t, / and their flow rate W. When W increases, the flow rate of other pumps decreases somewhat, but since the pump trips at time t21, its flow rate W11 decreases.

From this point on, WA=Wc and the original flow rate returns.

During this time, the system flow fff WF increases slightly due to the preliminary activation of the backup pump, but returns to the original system flow rate due to the decrease in the flow rate of the trip pump, and fluctuations in the system flow rate become extremely small.

The above description has mainly been given using nuclear reactor feed water pumps as an example, but the operational performance of other systems can be significantly improved by adopting this switching device. In other words, taking as an example the condensate purification system which is now being adopted in some of the subordinate couplants, the condensate purification system has a configuration as shown in Fig. 9. That is, condensate from the turbine 208 enters the first hot well 201, is pumped out by the condensate purification pumps 203a to 203c, and the water purified by the condensate demineralizer 205 is returned to the second hot well 202. A head tank 207 is installed in the return pipe to the system, and a hydrostatic head is applied to the system pressure. The head tank head is provided with an overflow line 209 that allows overflow. In this system, condensate purification pump 203
In the conventional system, two machines are operated at all times, and the trip takes precedence.

When one pump trips, the standby pump starts and the pump operation is successfully switched, but if two pumps trip at the same time, the pump back pressure decreases and a large amount of pump flow occurs during the start-up process of the standby pump. Therefore, the pump load torque is morph driven! (l1lJ) The engine may become unable to start if the engine speed exceeds the current limit. Therefore, when two pumps trip at the same time, the current practice is to stop the backup pumps instead of starting them.

When the present invention is applied to a condensate purification system, the standby pump starts up in advance even when two pumps trip, without causing the inability to start as described above. By combining this with lowering the flow rate setting to match the capacity, it is possible to continue operating the system, making a significant contribution to improving plant utilization.

〔Effect of the invention〕

As described above, according to the present invention, not only is it possible to switch the pump operation with less fluctuation in system flow rate and pressure, but also the plant utilization rate is improved, and the effect is enormous.

[Brief explanation of the drawing]

Figure 1 is a general configuration diagram of the water supply system, Figure 2 is a diagram of the transient characteristics of the flow surface at the time of IJ tube (pumps according to the prior art), Figure 3 is a diagram of the water supply system of an atomic couplet consisting of three pump groups, Figure 4 is a diagram showing the factors of IJ tube and flow rate reduction, Figure 5 is a start/stop interlock block diagram of the motor-driven water supply pump according to the present invention, and Figure 6 is a predicted advance of the backup pump of the present invention. Flowchart of calculations for processing startup conditions - Figure 7 is a diagram explaining the preliminary function of the present invention, Figure 8 is a transient characteristic diagram when switching pump operation according to the implementation of the present invention, Figure 9 is a condensate purification system FIG. 101=-, X one, 103 a to 103 d-
OR circuit, 1048-104 C=・AND circuit, 10
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Claims (1)

[Claims] 1. In a system having at least one standby pump, the time up to a pump trip is calculated moment by moment based on the rate of change of an analog signal that causes the operating pump to trip, and the standby pump is A pump operation switching device characterized in that the backup pump is started in advance when the former is /J% shorter than the latter with a preset starting time. 2. In claim 1, the signal for which the advance starting condition is satisfied is a manual starting signal, an automatic starting signal along with other preliminary pump trips, etc. A pump operation switching device characterized by automatically starting a pump under permitted reliability. 36% In the scope of claim 1: When the analog signal reaches a trip level, the trip pump is tripped at that point. A pump operation switching device characterized by: