JPS6146676B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement of a variable frequency power supply device for a recirculation pump used for reactor power control in a nuclear power plant.

(Prior art) Conventional reactor output control in boiling water nuclear power plants involves two systems: one that changes the ratio of control rods in the reactor, and the other that uses a recirculation pump to change the flow rate of coolant in the core. There are two systems. Among these changes, the coolant flow rate can be changed by changing the frequency of the variable frequency wave power supply device, which is the power source of the induction motor for driving the recirculation pump, which is directly connected to the recirculation pump, by approximately 20 to 95%. This is done by changing. Since this variable frequency power supply device has a large capacity of about 4000 to 6000 kW, a motor generator with a fluid coupling is often used as a device that changes the frequency significantly. The configuration of the variable frequency power supply device that adopts this fluid coupling is the commercial frequency power supply (50 or 60
The induction motor is rotated at a constant speed (Hz), and this mechanical output is used to drive a synchronous generator via a torque transmission device using a fluid coupling to generate electrical output. Therefore, in order to make the voltage of the synchronous generator correspond to the rotation speed of the synchronous generator, a separate exciter, field breaker, disconnector, etc.
An excitation circuit consisting of an automatic voltage regulator, etc. is provided. The power of the reactor is increased by increasing the flow rate of the recirculation pump, i.e. increasing the pump speed;
It is reduced by reducing the flow rate of the recirculation pump, i.e. by reducing the pump speed. Therefore, the reactor output is proportional to the output frequency or load current of the variable frequency power supply. Conventionally, as a protection device for such a variable frequency power supply device, an overcurrent relay is provided in the main circuit of a synchronous generator to detect short circuits and overloads in the circuit and take appropriate protective action. In general, overcurrent relays, such as thermal type and induction disk type, have operating characteristics that are not affected by changes in frequency, that is, the frequency characteristics are flat, and the detection set point is The current value is such that the motor does not operate at the maximum output, that is, at the maximum rotation speed.

(Problem to be Solved by the Invention) However, since the overcurrent relay has a detection set point that is equal to or higher than the maximum current value required by the load and has a flat frequency characteristic, Abnormal conditions in the small current area cannot be detected and protected. Abnormal conditions include, for example, poor contact due to wear of the brushes of the synchronous generator's slip ring, insufficient field due to failure of the automatic voltage regulator, or overload of the synchronous generator due to overexcitation and low synchronous generator. There is a short circuit between the generator at output and the induction motor main circuit for driving the recirculation pump.

Although such an abnormal condition does not exceed the electrical and mechanical strength of the synchronous generator or the pump drive induction motor, if operation is shifted to a high output range without knowing this abnormal condition, the abnormal condition will expand. This would lead to a major accident, requiring the reactor to be shut down and repaired for a long period of time.

The present invention was made in view of the above circumstances, and
The purpose of this is to change the overcurrent detection set point according to changes in the rotational speed of the synchronous generator, so that abnormal conditions in the circuit can be quickly detected even in the low output or low rotational speed region of the synchronous generator. It is an object of the present invention to provide a variable frequency power supply device for a recirculation pump that can prevent the expansion of recirculation pumps.

[Structure of the invention]

(Means for Solving the Problems) A variable frequency power supply device for a recirculation pump according to the present invention provides a variable frequency power supply device for a recirculation pump that controls the flow rate of coolant in a nuclear reactor to control output. At the power supply, a protection device is provided in which the overcurrent detection set point changes with speed in response to varying load currents as the speed of the recirculation pump changes from the recirculation pump speed signal and the drive motor current signal.

(Function) The variable frequency power supply device for a recirculation pump of the present invention compares and calculates the current of an induction motor for driving a recirculation pump that drives a recirculation pump of a nuclear reactor and the speed signal of the recirculation pump using an operational amplifier. In addition to outputting a signal when there is a mismatch, an overload detection point is set as the speed changes using the recirculation pump speed signal, and the current of the induction motor for driving the recirculation pump, which changes due to speed changes, is related to the operating speed. It properly detects and protects against overloads and short-circuit accidents in the main circuit, as well as abnormal overcurrents such as failures in the excitation circuit.

(Example) An example of the present invention will be described below with reference to the drawings.

Figure 1 is a diagram of the recirculation system of a boiling water reactor, which consists of a variable speed recirculation pump 15.
The cooling water 24 which is the coolant of the nuclear reactor 21 is
Recirculation pump suction pipe 25A and discharge pipe 25B
circulate through. The discharge pipe 25B and the circulating water pass through the jet pump 23, circulate through the reactor core 22, and control the reactor output. The recirculation pump 15 is driven at a variable speed by a recirculation pump drive induction motor 16 which is directly coupled to the shaft. Speed control of the induction motor 16 for driving the recirculation pump is performed by changing the output frequency of the synchronous generator 14. This frequency can be controlled by changing the slippage of the fluid coupling 13 directly connected to the induction motor 12.
The rotational speed of the synchronous generator 14 directly connected to the output side of the fluid coupling 13 is changed to change the output frequency. The electrical output of this synchronous generator 14 is connected by a power cable 17 to an induction motor 1 for driving the recirculation pump.
Power is transmitted to 6.

Further, in addition to the fluid coupling 13, the induction motor 12 has an AC exciter 2 and a permanent magnet generator 1 directly connected to each other, and is started by turning on the shield breaker 11. The output of the permanent magnet generator 1 is the synchronous generator 14
An automatic voltage regulator is installed so that the secondary voltage of the instrument transformer 7 provided in the power cable 17 of the main circuit of Nono and the output voltage of the speed detection generator 8 directly connected to the synchronous generator 14 are in a constant ratio. 6, and becomes the field voltage of the field circuit 9 of the AC exciter 2. The output of the AC exciter 2 is full-wave rectified by a rectifier 3, passes through a field switch and disconnector 4, and becomes the field voltage of the field circuit 5 of the synchronous generator 14.

The load current of the induction motor 16 for driving the recirculation pump is proportional to the output of the recirculation pump 15, that is, the frequency (or rotation speed) of the synchronous generator 14, and is represented by (1).

I=K・F...(1) where I: Load current F: Frequency or rotation speed of the synchronous generator K: Proportionality constant Figure 2 is a block diagram of the protection device, and the synchronous generator 14
The load current flowing into the induction motor 16 for driving the recirculation pump is detected by a current transformer 18 provided in the power cable 17, converted to a DC voltage by a full-wave rectifier 50, and outputted as a second signal e(I ), the protective device 60
It becomes the input of the variable resistor R11 of the operational amplifier 51. On the other hand, a voltage proportional to the rotation speed of the speed detection generator 8 directly connected to the synchronous generator 14 is a second signal e(F).
This becomes the input to the variable resistor R12 of the operational amplifier 51. Variable resistor R11, R of operational amplifier 51
12 and the feedback resistor R13 to obtain equation (2).

K ₁ = R ₁₁ / R ₁₂ = e(I)/e(F) ...(2) where K ₁ : Ratio of load current signal to frequency signal R ₁₁ : Load current signal input resistor R ₁₂ : Frequency signal input resistor e(I): Voltage proportional to load current I e(F): Voltage proportional to frequency F The output voltage _e1 of the operational amplifier 51 is expressed by equation (3).

e ₁ =-(R ₁₃ /R ₁₁・e(I)−R ₁₃ /R ₁₂・
e(F))...(3) Therefore, if the variable frequency power supply device is normal and the ratio of load current I to frequency F satisfies the relationship expressed by equation (2), the output voltage _e1 will always be zero.

The output voltage of the speed detection generator 8 further becomes the input signal of the operational amplifier 52, and the amplification factor K ₁ .
Adjust variable resistors R ₂₁ and R ₂₂ so that K ₂ is obtained.

_K1・_K2 = _R22 / _R21 ...(4) Here, _K2 : Expected current I required by the load at frequency F
Overload current rate that the synchronous generator and induction motor can withstand R ₂₁ : Frequency signal or rotational speed signal input resistor R ₂₂ : Feedback resistor The output signal e ₂ of the operational amplifier 52 is expressed by equation (5).

e ₂ =K ₁・K ₂・e(F)=・R ₂₂ /R ₂₁・e(F) ...(5) Output signal e ₁ of operational amplifier 51 and operational amplifier 52
The calculation of equation (6) is performed so that the output signal e ₂ of is turned into the output signal e ₃ of the operational amplifier 53.

e ₃ =-(e ₂・R ₃₃ /R ₃₂ +e ₁・R ₃₃ /R ₃₁ )
...(6) Here, R ₃₁ : Abnormal current signal adjustment resistor R ₃₂ : Overload current setting signal adjustment resistor R ₃₃ : Feedback resistor To set the operational amplification factor to 1, R ₃₁ = R ₃₂ = If R _{is 33} , then the equation (7) is obtained.

e ₃ =−R ₂₂ /R ₂₁・e(F)+(R ₁₃ /R ₁₁ e(I)−R ₁₃ /R ₁₂・e(F)) ……(7) Therefore, the synchronous generator 14 If the circuit is normal
e ₃ <0. When this output signal _e3 becomes a positive voltage, the comparator X54 operates and its output contact 54a
works.

FIG. 3 is a block diagram of a protection device 61 of another embodiment, in which an operational amplifier 55 is added to the protection device 60 shown in FIG.
By adding an operational amplifier 56 and a comparator Y57 and setting the overcurrent amount of the operational amplifiers 52 and 55 differently, it is possible to create a two-stage setting in which the comparator Y57 issues an alarm and the comparator X54 performs a trip. .

In addition, FIG. 4 shows another embodiment of the protection device 6.
In the configuration diagram of 2, the operational amplifier 58 has a simple configuration, and the signal input resistor R of the operational amplifier 58
Adjust 71 and R72 as shown in equation (8).

R71/R72= _K1・_K3 ...(8) Here, _K1 : Ratio of load current signal to frequency signal during normal operation _K3 : Ratio of expected current to withstand load current R71: Resistance for inputting load current signal R72: Frequency signal input resistor Further, the output voltage _e5 of the operational amplifier 58 is expressed by equation (9).

e ₅ =-(R73/R71e(I)-R73/R72e(F)) =-R73/R71(e(I)-R71/R72e(F)) =-R73/R71(e(I)-K ₁・K ₃・e(F))……(9
) As a result, if the circuit of the synchronous generator 14 is normal, the output voltage e ₅ is always >0 and the comparator Z59 is inactive.

Next, the effect will be explained. In FIG. 2 of one embodiment, the amount of mismatch between the output frequency F of the synchronous generator 14 and the load current I is calculated by the operational amplifier 51,
The operational amplifier 52 calculates the amount of overload current that will cause the main circuit of the synchronous generator 14 to become abnormal at that frequency, and if this amount of mismatch exceeds the amount of overload current,
The output voltage _e3 of the operational amplifier 53 becomes a positive voltage,
Activate comparator X54. This output contact 54a trips the shield breaker 11 and the field shield breaker 4 of the variable frequency power supply shown in FIG. 1, and also issues an alarm. FIG. 5 is a characteristic diagram at this time, where the solid line 63 is the load current characteristic of the induction motor 16 for driving the recirculation pump when there is no circuit failure, and the dotted line 6
4 is the detection setting characteristic of the protection device 60. According to the present invention, the detection set point automatically drops as indicated by the dotted line 64 as the frequency F decreases, so when an abnormal current as indicated by the two-dot chain line 65 occurs, the current I
Since detection and protection can be performed at point a before reaching point b and point c, where is 100%, accidents can be kept to a minimum range. For example, if the overcurrent is 50%, the comparator X54 will operate when the load current at a certain frequency reaches 50% or more of the appropriate load current required at that frequency.

FIG. 6 is a characteristic diagram of the two-stage setting of the other embodiment shown in FIG.
The dash-dotted line 67 is characteristic of the trip detection set point. By using such a two-stage setting, when an abnormality occurs, instead of immediately tripping the recirculation pump 15, a warning of the abnormal condition is first issued, and then the recirculation pump 15 is tripped after confirming that it continues to expand, thereby reducing the response and repair time. It is possible to improve the operation rate of nuclear power plants.

Also in FIG. 4, which is another example, if the abnormal current exceeds the normal load current, the output voltage e ₅
becomes <0, comparator Z59 operates and the fifth
Operation similar to the characteristics shown in the figure can be obtained.

In the above explanation, the voltage of the speed detection generator 8 is used as the frequency signal, but the voltage of the speed detection generator 8 is used as the frequency signal.
The output frequency of the synchronous generator 14 may be detected,
The rotation speed of the recirculation pump 15 and the recirculation pump 15
The same effect can be obtained by changing the discharge flow rate, differential pressure, etc. Further, as for abnormality detection of the variable frequency power supply device, not only overcurrent but also undercurrent can be detected using the same principle as the present invention.

Furthermore, the variable frequency power supply device of the above embodiment includes an induction motor 12 using a fluid coupling 13, a synchronous generator 14, and an induction motor 1 for driving a recirculation pump.
Although the description has been made using a motor generator having the configuration according to No. 6, it goes without saying that similar effects can be obtained using a power supply device using a stationary inverter.

〔Effect of the invention〕

As described above, according to the present invention, by inputting the parameters of load current and rotation speed, the overcurrent detection set point automatically moves to a predetermined position as the frequency changes. Since the current detection point is lower, it is possible to quickly detect and protect not only overloads and short circuits, but also abnormalities caused by slip ring brush wear, automatic voltage regulator failure, rectifier failure, etc. The scope of protection can be expanded. Furthermore, since it is possible to prevent small accidents from escalating into major accidents, this has the effect of shortening the reactor shutdown period, improving the operating rate, and further improving the reliability of nuclear power plants.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a variable frequency power supply device for a recirculation pump of a boiling water reactor according to the present invention, Fig. 2 is a block diagram showing one embodiment of the protection device, and Fig. 3 is another embodiment of the protection device. A configuration diagram showing an example of two-stage abnormality detection settings, Figure 4 is a configuration diagram showing other embodiments of the protection device, Figure 5 is a characteristic diagram of Figure 2, and Figure 6 is a characteristic diagram of Figure 3. It is a diagram. 12...Induction motor, 13...Fluid coupling, 14
... Synchronous generator, 16 ... Induction motor for driving recirculation pump, 17 ... Power cable, 18 ... Current transformer, 51, 52, 53, 55, 56, 58 ... Operational amplifier, 54, 57, 59...Comparator,
60, 61, 62...protective device.

Claims (1)

[Claims] 1. In a variable frequency power supply device for driving a recirculation pump electric motor that is installed in a recirculation system of a nuclear reactor and controls the flow rate of coolant in the reactor, A comparison operation is made between the first signal and a second signal proportional to the load current of the variable frequency power supply, and if this mismatch output signal exceeds a specified value, a trip and abnormality alarm signal is output for the variable frequency power supply. A variable frequency power supply device for a recirculation pump, characterized in that it is provided with a protection device that protects the recirculation pump. 2. The protection device includes a first computing unit that computes the amount of mismatch between the first signal and the second signal, and a second computing unit that computes the amount of overload of the variable frequency power supply device based on the second signal.
a third arithmetic unit that compares the output of the first arithmetic unit and the output of the second arithmetic unit;
2. The variable frequency power supply device for a recirculation pump according to claim 1, further comprising a comparator which outputs a trip or abnormal warning signal for the variable frequency power supply device based on the output of the arithmetic unit. 3. The protection device includes a first computing unit that computes the amount of mismatch between the first signal and the second signal, and a second computing unit that computes the amount of overload current of the variable frequency power supply device based on the second signal. and the output of the first arithmetic unit and the second arithmetic unit.
and calculating the overload current amount separately for the first level and the second level by comparing the outputs of A variable frequency power supply device for a recirculation pump according to claim 1, comprising a comparator for outputting an output. 4. Claim No. 4, wherein the protection device comprises a computing unit that computes the amount of mismatch between the first signal and the second signal, and a comparator that outputs a trip or abnormality alarm signal for the variable frequency power supply device based on the output of the computing unit. A variable frequency power supply device for a recirculation pump according to paragraph 1.