JPS61187693A - Method of controlling recirculating flow rate - 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 recirculation flow rate control method for preventing a nuclear reactor scram even if a recirculation system becomes abnormal.

[Background of the invention]

In nuclear power plant recirculation systems, protection against failure modes can be broadly classified into two types. One is protection for the recirculation system components, and the other is protection against adverse effects on the plant caused by abnormalities in the recirculation system, but the former protection function is sufficiently satisfactory. The reality is that this is the case.

However, the latter poses a risk of causing a reactor scram. Motor-driven generator (
MG) Depending on the abnormality around the set, the recirculation flow rate increases rapidly, which may cause the neutron velocity in the reactor to increase and lead to a reactor scram.

Until now, the only work related to the latter protection function was published in Japanese Unexamined Patent Publication No. 5
3-90591 and Japanese Unexamined Patent Publication No. 54-62490, but both have insufficient protection functions. This is because in the former case, fail-safe operation is performed only in response to an abnormality in the recirculation flow rate control device. In addition, although the latter method aims to improve stability by limiting the range of change in the recirculation flow rate, it is not possible to immediately deal with sudden increases or decreases in the recirculation flow rate in abnormal situations. be.

[Purpose of the invention]

An object of the present invention is to provide a recirculation flow rate control method that effectively prevents reactor scram and output fluctuation even if an abnormality occurs in the recirculation system.

[Summary of the invention]

For this purpose, the present invention provides a method for detecting an abnormality when an abnormality is detected based on the deviation between the current applied to the recirculation flow regulating pump motor from the variable frequency power supply equipment and the rotational speed corresponding to the output frequency of the variable frequency power supply equipment. In this case, the recirculation system is controlled to be on the fail-safe side.

[Embodiments of the invention] The present invention will be explained below with reference to FIGS. 1 to 6.

First, a system configuration of an example of a BWR nuclear power plant recirculation flow rate control system according to the present invention will be described. FIG. 1 shows its configuration. According to this, the drive motor 12 is rotated at a predetermined rotational speed by a three-phase AC power supply via a drive motor shield breaker 17, and its output shaft is rotated via a fluid coupling 11 to drive a variable frequency generator 8. It has become. Therefore, under the control of the recirculation flow control device 121, the scoop tube operator 18
When the amount of hydraulic fluid in the fluid coupling 11 is controlled via the variable frequency generator 8, a power generation output with a variable frequency is obtained from the variable frequency generator 8.

By driving the recirculation pump 2 via the pump motor 3 by this generated output, the cooling water within the nuclear reactor 1 is circulated to control the reactor output. In this case, the ratio (V, #) between the output voltage V of the variable frequency generator 8 and its frequency f is controlled by the voltage regulator 14 so as to be constant. The number N is determined by the speed detector 7.

Further, the voltage V is obtained by the instrument transformer 4, and based on this, the V/f control section 15 controls the thyristor section 1.
6, while the three-phase alternating current from the thyristor section 16 is applied to the field coil 9 via a rectifier 13 and a field breaker 10.

Here, we will explain the recirculation flow rate control device 21 that controls the scoop pipe operating device 18.The mode of control thereof can be roughly divided into automatic control and manual control, but the automatic/manual switch 23 is In the case of 1-manual control, which is switched according to the mode of control, the main controller 22 generates the rotation speed set value in an up-and-down manner based on the increase command signal U and the decrease command signal. This is output as the automatic/manual switching s23 output.

On the other hand, in the case of automatic control, the turbine control device i! At step 20, the deviation between the target generator output and the actual generator output is determined, and this is output as the rotation speed setting value from the automatic/manual switch 23 via the proportional integrator 24. . The rotation speed setting command value from the automatic/manual switch 23 is then sent to a low value selector 27, an adder 28, a limiter 29,
By applying this to the motor in the scoop tube operating device 18 via the proportional integrator 30 and the function generator 31, the rotation speed N of the variable frequency generator 8 is controlled to follow the rotation speed setting command value. That's it.

FIG. 2(a) shows various devices arranged around the scoop tube operating device.

Although no particular explanation is required regarding this, a brief explanation of the scoop tube operating device 18 is as follows.

That is, FIG. 2(b) schematically shows its internal configuration, which basically consists of a motor 32 that is a rotation-stopping cylinder. Motor 32 is normally a recirculation flow control bag! 21 to a rotational position according to the rotational speed command value from 21, and the amount of hydraulic fluid in the fluid coupling 11 is controlled via the lever attached to the output shaft 35 and the scoop pipe 19. . However, in certain cases, a locking operation is performed and the output shaft 35 is placed in a state where it cannot rotate. Figure 2(c)
As shown in the figure, the contact 37 is opened during the lock operation, but
As a result, the attraction of the spring 34 by the excitation coil 33 that had been excited until then is released, and the spring 34 increases its frictional force and comes into contact with the flange portion 36 attached to the output shaft 35. be.

Note that the reference numeral 38 indicates a field.

Now, to explain the present invention in detail, the present invention locks the rake pipe operator when an abnormality is detected based on the deviation between the current I to the pump motor and the rotation speed N of the variable frequency generator. The drive motor breaker switching operation, field breaker switching operation, and runback operation are to be performed.

As shown in Figure 1, the current to the pump motor 3 is connected to a current transformer 5.
Therefore, the rotation speed N can be obtained from the speed detector 7,
The system protection device 6 controls the above operations by comparing the deviations of I and H with various set values. The above operations will be explained below in order of decreasing influence on plant operation.

(1) Lock operation of scoop pipe operator This is for so-called fail-safe operation.

By locking the scoop pipe in that position when the deviation between the The circulating flow rate is controlled to be approximately constant or as much as possible.This operation is specifically performed by opening the contact point 37 mentioned above.

(2) Runback Operation This operation is a fail-safe operation in which the recirculation flow rate is reduced to the lowest controllable flow rate. Specifically, in FIG. 1, the contact 26 is closed and the runback rotation speed setting command value from the setting device 25 is outputted from the low value selector 27 as the rotation speed command value. As a result, the frequency f in the MG upper set is rapidly reduced to the lowest frequency, and the recirculation flow rate also decreases accordingly. However, control of the recirculation system is still ongoing.

(3) Drive motor breaker disconnection operation (MG upper set trip operation) This operation is a fail-safe operation, and the recirculation flow rate is M
It is reduced to almost zero only by the G set inertia (excluding natural circulation in the furnace).

Specifically, this is an operation performed by opening the drive motor breaker 17.

(4) Field breaker cutting operation This operation cuts off the current of the MG upper set.
The recirculation flow rate is rapidly reduced to zero only by the inertia of the pump motor 3.

This operation is specifically performed by opening the field breaker 10, and the response is better than in case (3) above.

All of the above operations are fail-safe operations to prevent a reactor scram, and one of the operations is selected depending on the severity of the abnormality. Therefore, the operation setting value is the smallest in case (1), and (
Case 4) is the largest.

Now, to explain the principle of protection by the system protection device, a pump motor as an induction motor generally has characteristics as shown in FIGS. 3(a) and 3(b).

I-N... (1) T-
N... (2) However, T
is the pump motor torque.

Therefore, formula (3) holds true from formulas (1) and (2).

T-I (3) On the other hand, torque T is expressed as the sum of two types of components.

TvT, 10TLL... (4)
However, T is the torque required for constant rotation of the pump (-1
, ), and Tg is the torque (ac ILαα) required for acceleration/deceleration of the pump (α: generator acceleration).

Therefore, the following relationship holds true from equations (3) and (4).

ToeIaeI, +ILwK, N+, <-(5) However, K1. K is a constant.

Therefore, the deviation between N and N can be expressed as:

T- to 3N=,,...
・(6) However, K3. K4 is a constant.

The system protection device performs a protection operation based on this equation (6), and FIG. 4 shows the configuration of an example of the system protection device. As shown in the figure, the deviation between I and N is determined as an absolute value by the adder 39, and this is compared with a set value in each of the monitoring relay circuits 40 to 43. In this case, the monitoring relay circuits 40 to 43 are for determining the start timing of the scoop pipe operator lock operation, runback operation, MG set drip operation, and field breaker trip operation, respectively. The magnitude relationship between the set values for each is as described above.

By the way, in the illustrated circuit configuration, for example, the deviation is extremely large, and when the field breaker trip operation is performed by the monitoring relay circuit 43, it is as if other operations are performed in parallel. In reality, only the field breaker trip operation is performed. That is, each operation has a priority order, and when two or more operations are performed, only the operation with the highest priority is performed. In this example, the four types of operations described above are possible, but it is not necessary to perform all the operations, and it is sufficient to perform the necessary operations depending on the specifications of the plant.

FIG. 5 shows an example of a system protection device in which the set values in each monitoring relay circuit are variable in accordance with the rotational speed N. When the number of rotations N is small, the protection operation is performed with a sufficient margin, and when it is large, the protection operation is performed with a small margin. This fifth
Assuming that the setting values in each of the monitoring relay circuits 40 to 43 shown in the figure are the same as in the case of FIG. 4, the function generator 4
4 outputs the output and uses an adder 45 to appropriately increase or decrease the deviation from the adder 39. In other words, the smaller the rotation speed, the smaller the deviation, and the larger the rotation speed, the larger the deviation.Other than this, the situation is the same as in the case of FIG. 4. As a result, the acceleration rate can be set corresponding to the rotational speed N, and abnormality detection can be performed according to the operating state of the plant. This kind of control is performed because, for example, the pump motor acceleration during 5.0% operation may naturally have a different setting value for abnormality detection than that during 100% operation. It is supposed to be.

Finally, a recirculation flow rate control system for a BWR type nuclear power generation plant will be described in the case where a stationary variable frequency power supply equipment using a thyristor circuit is used as the variable frequency power generation equipment.

Of course, the present invention can also be applied to such a control system. As shown in FIG. 6, the three-phase AC power from the breaker 51 is connected to a rectifier fi
! It is rectified by 50 and then converted into a three-phase alternating current power source with variable frequency by an inverter 49 under the control of a gate pulse generation circuit 48 and then supplied to the pump motor 3. In this case, the rotation speed N is determined by a frequency detector 46 from the output of the instrument transformer 4. System protection device 6 has current I and rotational speed N
However, the protective operation corresponding to the drive motor breaker tripping operation or the field breaker tripping operation is performed by tripping the breaker 51, and the rake tube operator locking operation and runback operation are performed. The corresponding operation is performed by controlling the gate pulse generation circuit 48 in a predetermined manner.

〔Effect of the invention〕

As explained above, according to the present invention, by monitoring the deviation between the pump motor supply current and the actual generator rotation speed, reactor scram and output fluctuation can be effectively prevented even if an abnormality occurs in the recirculation system. It has the effect of

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a system configuration of an example of a recirculation flow rate control system for a BWR type nuclear power generation plant according to the present invention, and FIG.
Figures (a), (b), and (c) are diagrams showing the peripheral arrangement, internal configuration, and partial electric circuit of the scoop tube operating device, respectively. Figures 3 (a) and (b) are A diagram showing the current and torque characteristics with respect to the rotation speed of the pump motor, Fig. 4,
FIG. 5 is a diagram showing a configuration example of a system protection device according to the present invention, and FIG. 6 is a system diagram of an example of a recirculation flow control system of a BWR nuclear power plant equipped with stationary variable frequency power generation equipment. FIG. 3 is a diagram showing the configuration. 2... Recirculation pump, 3... Pump motor, 4...
- Instrument transformer, 5... Current transformer, 6... System protection device, 7... Speed detector, 8... Variable frequency generator, 10... Field breaker, 11.・Fluid coupling, 1
2... Drive motor, 17... Drive motor breaker,
18... Rake pipe operator, 20... Turbine control device, 21... Recirculation flow rate control device, 26... Contact (
for runback operation), 39.45...Adder, 40~
43... Monitoring relay circuit, 44... Function generator, 4
6... Frequency detector, 47... Stationary variable frequency power generation equipment, 48... Gate pulse generation circuit, 49...
Inverter, 51... Breaker (for protective operation).

Claims (1)

[Claims] 1. In a nuclear power plant recirculation system, when a recirculation pump is driven via a pump motor by the output from a variable frequency power supply equipment, the current to the motor and the output frequency of the equipment are controlled. After detecting the rotational speed, the deviation between the current and the rotational speed is determined, and based on the results of comparing the deviation with various set values, the system is installed around variable frequency power supply equipment to put the recirculation system in a fail-safe state. A recirculation flow rate control method characterized by controlling. 2. The recirculation flow rate control method according to claim 1, wherein the various set values are set according to the rotation speed.