Nuclear-grade rotating speed overspeed protection system

Abstract

The invention relates to the technical field of nuclear power plant steam-driven pump electric overspeed protection systems, in particular to a nuclear grade rotating speed overspeed protection system which comprises three rotating speed sensors used for monitoring the rotating speed of a steam turbine and three nuclear grade rotating speed relays composed of circuits without single-chip microcomputers. The output ends of the three nuclear-grade rotating speed relays are correspondingly connected with the three input ends of a two-out-of-three module respectively, the input end of each nuclear-grade rotating speed relay is correspondingly connected with a rotating speed sensor, and the output end of the two-out-of-three module is connected with a protection execution module. Only a pure hardware circuit is adopted to carry out overspeed early warning and protection on the steam turbine of the steam-driven auxiliary feed pump of the nuclear power plant, and the problems of safety, stability and real-time performance in the operation process of the steam-driven auxiliary feed pump of the nuclear power plant are thoroughly solved on the premise that a single chip microcomputer and software program control of the single chip microcomputer are not needed.

Description

Technical Field

[0001] The invention relates to the technical field of electrical overspeed protection systems for pneumatic pumps in nuclear power plants, and in particular to a nuclear-grade rotational speed overspeed protection system. Background Art

[0002] The pneumatic auxiliary feedwater system (ASG) is a specialized safety feature in nuclear power plants. In the event of an incident in the normal feedwater system, the ASG is activated to remove residual heat from the reactor core. The ASG pump is typically a horizontal multi-stage centrifugal pump, integrally integrated with the steam turbine and supplied by the main steam system. The operating characteristics of this pump are regulated by the turbine's main steam valve differential pressure controller, allowing it to operate at a rated speed of 6,000 to 11,000 rpm. To ensure the pump's safe operation and prevent runaway accidents, overspeed warning and overspeed protection are required.

[0003] The existing mechanical overspeed protection system for this type of pneumatic auxiliary feedwater pump has low accuracy, poor warning and protection effects, and requires on-site operation and data reading. During testing, the turbine speed must be actually increased to the overspeed value, which causes significant damage to the blades, damage to the equipment, and cavitation. Therefore, an overspeed warning and protection system built using a single-chip microcomputer is currently commonly used to improve the accuracy of judging overspeed in pneumatic auxiliary feedwater pumps, so as to be able to predict and take protective measures in a timely manner. However, the operation of this overspeed warning and protection system is mainly controlled by the software program within the single-chip microcomputer, which has the following disadvantages:

[0004] 1) Stability issues

[0005] 1-1) Program Crash Risk: Software programs within the MCU may crash for various reasons. For example, a bug in the program could cause a pointer error, potentially accessing an illegal memory address. This can occur when the program attempts to read or write to an unallocated or released memory location. For example, in the MCU control program for an overspeed protection system, a pointer error could prevent speed acquisition and control instructions from being sent properly, leading to uncontrolled device speed.

[0006] 1-2) Memory Leakage: Memory leaks occur when a software program fails to properly release memory after dynamic memory allocation. Over time, available memory resources gradually decrease. For example, the microcontroller control program for an overspeed protection system must continuously process sensor data and store alarm records. A memory leak could prevent the system from properly storing new alarm information, ultimately leading to system failure.

[0007] 1-3) Software aging: Software programs that run for extended periods of time may experience software aging. Due to internal logic errors or resource management issues, system performance gradually degrades over time. For example, after a long period of operation, the microcontroller control program for an overspeed protection system may accumulate undetected minor issues, leading to slower device response and reduced production efficiency.

[0008] 2) Limited real-time performance

[0009] 2-1) Difficulty Scheduling Complex Tasks: When a microcontroller needs to handle multiple tasks simultaneously, such as data acquisition, data processing, and device control, the software program's task scheduling can become complex. Without an efficient task scheduling algorithm, task response delays can occur. For example, the microcontroller in the speed overspeed protection system for a steam-assisted feedwater pump must handle both real-time data acquisition from the steam turbine and real-time control of other equipment within the steam-assisted feedwater pump. If the software program fails to prioritize tasks appropriately, the speed overspeed protection system may be delayed, preventing it from providing timely warnings and protection.

[0010] 2-2) Interrupt processing delay: The MCU software program may also experience a delay in responding to external interrupts. External interrupts are a way for an external device to request MCU service, such as a button press or sensor trigger. If the interrupt service program is not designed properly or the priority of the main program task being executed is too high, the interrupt response may not be timely. For example, in an overspeed protection system, when a worker hears an alarm and wants to perform a protection operation by pressing a button, or when the system automatically triggers a protection action through a sensor, an interrupt request will be generated. If the MCU software program is processing other complex data tasks at this time, it may delay the activation of the protection measures, resulting in unpredictable consequences.

[0011] 3) Low security

[0012] 3-1) Code is vulnerable to cracking: If adequate encryption measures are not implemented for the software program within the MCU, the code can be easily cracked. Hackers could potentially obtain the control code for the steam turbine (or overspeed protection system) within the MCU software program through reverse engineering, thereby controlling the operation of the steam turbine (or overspeed protection system), causing significant damage to the nuclear power plant.

[0013] 3-2) Data Security Risks: Without appropriate security mechanisms in place during data processing and storage by the microcontroller, data could be stolen or tampered with. In the overspeed protection system, if the operating data of the pneumatic auxiliary feedwater pump is not stored and transmitted in an encrypted manner, it could be illegally accessed. Some hackers could even gain access to and control data from other related devices by invading the microcontroller system within the overspeed protection system. This overspeed protection system, built using a microcontroller, could potentially lead to data leaks in nuclear power plants and pose significant security risks.

[0014] In summary, nuclear power plants have a very high safety level. If a problem arises in the microcontroller software of the overspeed protection system, the stability, safety, and real-time performance of the equipment will be greatly reduced, which is very likely to lead to a major accident. Therefore, how to completely avoid the above problems while ensuring the safe operation of the pneumatic auxiliary feedwater pump has always been a pressing problem for those skilled in the art. Summary of the Invention

[0015] The purpose of the present invention is to address the corresponding deficiencies in the existing technology and provide a nuclear-grade speed overspeed protection system, which only uses pure hardware circuits to implement overspeed warning and protection for the turbine of the nuclear power plant's pneumatic auxiliary feedwater pump. Without the need for a single-chip microcomputer and its software program control, it completely solves the safety, stability and real-time problems during the operation of the nuclear power plant's pneumatic auxiliary feedwater pump.

[0016] The purpose of the present invention is to adopt the following scheme to achieve:

[0017] A nuclear-grade speed overspeed protection system includes three speed sensors for monitoring steam turbine speed and three nuclear-grade speed relays composed of circuits that do not include a single-chip microcomputer. The output ends of the three nuclear-grade speed relays are respectively connected to the three input ends of a three-choose-two module. The input end of each nuclear-grade speed relay is respectively connected to a speed sensor. The output end of the three-choose-two module is connected to a protection execution module. The nuclear-grade speed relay has the function of presetting a speed overspeed alarm threshold and an overspeed fault clearance threshold, and the function of comparing the speed sensor output signal with the speed alarm threshold. This enables the three-choose-two module to control the protection execution module based on the overspeed judgment signals output by the three nuclear-grade speed relays.

[0018] Preferably, the nuclear-grade speed relay includes a speed signal sampling and conditioning module, an overspeed action value setting module, an overspeed comparison module and an overspeed isolation output module, the output end of the speed signal sampling and conditioning module and the output end of the overspeed action value setting module are respectively connected to the input end of the overspeed comparison module, and the output end of the overspeed comparison module is connected to the input end of the overspeed isolation output module;

[0019] The speed signal sampling and conditioning module is used to collect the real-time speed signal output by the speed sensor, filter out interference signals, protect the circuit from interference, and condition the signal required for subsequent comparison;

[0020] The overspeed action value setting module is used to determine the reference signal of the speed action value and the return value, and to preset the speed overspeed alarm threshold and the overspeed fault release threshold;

[0021] The overspeed comparison module is used to perform hysteresis comparison on the output signal of the speed signal sampling and conditioning module and the output signal of the overspeed action value setting module;

[0022] The overspeed isolation output module is used to amplify the signal after the overspeed comparison, thereby driving the relay of the output control unit to open and close, thereby realizing isolation of the overspeed output signal.

[0023] Preferably, the speed signal sampling and conditioning module includes a protection unit, a filtering unit, and a conditioning unit:

[0024] The protection unit is used to prevent external interference signals from being introduced into the system, or excessive current / voltage from damaging the circuit;

[0025] The filtering unit is used to filter the high-frequency noise and low-frequency noise of the pulse signal;

[0026] The conditioning unit is used to condition the signal to make it more accurate and stable;

[0027] The overspeed action value setting module includes a reference unit, an action value setting unit, and a return value setting unit:

[0028] The action value setting unit is used to set the action value as the speed overspeed alarm threshold;

[0029] The return value setting unit is used to set the return value as the overspeed fault release threshold;

[0030] The reference unit is used to generate a reference signal to provide a reference for the action value setting unit and the return value setting unit to set the threshold;

[0031] The overspeed comparison module includes an overspeed action comparison unit and an overspeed return comparison unit:

[0032] The overspeed action comparison unit is used to compare the output signal of the speed signal sampling and conditioning module with the action value output by the action value setting unit;

[0033] The overspeed return comparison unit is used to compare the output signal of the speed signal sampling and conditioning module with the return value output by the return value setting unit;

[0034] The overspeed isolation output module includes a drive amplifier unit and an output control unit including a relay:

[0035] The driving amplifier unit is used to amplify the signals output by the overspeed action comparison unit and the overspeed return comparison unit;

[0036] The output control unit is used to electrically isolate the side low voltage of the protection system from the high voltage of the main circuit.

[0037] Preferably, the protection unit of the speed signal sampling and conditioning module includes an overcurrent protection circuit and / or a limiting circuit.

[0038] Preferably, the filtering unit of the speed signal sampling and conditioning module includes an RC filtering circuit and / or an RC differentiating circuit.

[0039] Preferably, the conditioning unit of the speed signal sampling and conditioning module includes a level conversion circuit, or / and a logic gate circuit, or / and a monostable multivibrator circuit, or / and a frequency-voltage conversion circuit.

[0040] Preferably, the reference unit of the overspeed action value setting module includes a voltage reference circuit and / or an active crystal oscillator circuit.

[0041] Preferably, the action value setting unit of the overspeed action value setting module includes a programmable frequency divider calculator or a precision resistor voltage divider circuit for setting the action value;

[0042] The return value setting unit of the overspeed action value setting module includes a programmable frequency division calculator or a precision resistor voltage divider circuit for setting the return value.

[0043] Preferably, the overspeed action comparison unit of the overspeed comparison module includes a voltage comparator for comparing action values, or a frequency signal comparison digital circuit;

[0044] The overspeed return comparison unit of the overspeed comparison module includes a voltage comparator for comparing return values, or a frequency signal comparison digital circuit.

[0045] Preferably, the driving amplification unit of the overspeed isolation output module includes a triode amplification circuit and / or a MOS tube amplification circuit.

[0046] The beneficial effects of the present invention are as follows:

[0047] A nuclear-grade speed overspeed protection system includes three speed sensors for monitoring steam turbine speed and three nuclear-grade speed relays composed of circuits that do not include a single-chip microcomputer. The output ends of the three nuclear-grade speed relays are respectively connected to the three input ends of a three-choose-two module. The input end of each nuclear-grade speed relay is respectively connected to a speed sensor. The output end of the three-choose-two module is connected to a protection execution module. The nuclear-grade speed relay has the function of presetting a speed overspeed alarm threshold and an overspeed fault clearance threshold, and the function of comparing the speed sensor output signal with the speed alarm threshold. This enables the three-choose-two module to control the protection execution module based on the overspeed judgment signals output by the three nuclear-grade speed relays.

[0048] The nuclear-grade speed relay includes a speed signal sampling and conditioning module, an overspeed action value setting module, an overspeed comparison module and an overspeed isolation output module. The output end of the speed signal sampling and conditioning module and the output end of the overspeed action value setting module are respectively connected to the input end of the overspeed comparison module, and the output end of the overspeed comparison module is connected to the input end of the overspeed isolation output module.

[0049] The speed signal sampling and conditioning module is used to collect the real-time speed signal output by the speed sensor, filter out interference signals, protect the circuit from interference, and condition the signal required for subsequent comparison;

[0050] The overspeed action value setting module is used to determine the reference signal of the speed action value and the return value, and to preset the speed overspeed alarm threshold and the overspeed fault release threshold;

[0051] The overspeed comparison module is used to perform hysteresis comparison on the output signal of the speed signal sampling and conditioning module and the output signal of the overspeed action value setting module;

[0052] The overspeed isolation output module is used to amplify the signal after the overspeed comparison, thereby driving the relay to open and close, realizing electrical isolation of the overspeed output signal, isolating the side low voltage of the protection system from the high voltage of the main circuit, so that the high voltage of the main circuit cannot interfere with the side low voltage of the protection system.

[0053] In this way, it is possible to use only a nuclear-grade speed relay composed of pure hardware circuits to implement overspeed warning and protection for the turbine of the nuclear power plant's pneumatic auxiliary feedwater pump. Without the need for a single-chip microcomputer and its software program control, the safety, stability and real-time problems of the nuclear power plant's pneumatic auxiliary feedwater pump during operation can be completely solved.

[0054] Preferably, the speed signal sampling and conditioning module includes a protection unit, a filtering unit, and a conditioning unit. The protection unit is used to prevent external interference signals from being introduced into the system, or excessive current / voltage from damaging the circuit; the filtering unit is used to filter the high-frequency noise and low-frequency noise of the pulse signal; the conditioning unit is used to condition the signal to make the signal more accurate and stable. The conditioning unit includes a level conversion circuit, or / and a logic gate circuit, or / and a monostable multivibrator circuit, or / and a frequency-voltage conversion circuit. The level of the pulse signal is converted into the level signal required for subsequent digital processing through level conversion. The logic gate circuit and the monostable multivibrator can also be used to tune and adjust the precise output pulse. Finally, the frequency signal can be converted into a DC voltage signal through the frequency-voltage conversion circuit for subsequent comparison, etc.

[0055] The overspeed action value setting module includes a reference unit, an action value setting unit, and a return value setting unit. The action value setting unit is used to set the action value as the speed overspeed alarm threshold; the action value setting unit includes a programmable frequency division calculator or a precision resistor voltage divider circuit for setting the action value; the return value setting unit is used to set the return value as the overspeed fault release threshold; the return value setting unit includes a programmable frequency division calculator or a precision resistor voltage divider circuit for setting the return value.

[0056] The reference unit is used to generate a reference signal to provide a reference for the action value setting unit and the return value setting unit to set the threshold. The reference unit includes a voltage reference circuit and / or an active crystal oscillator circuit. The voltage reference circuit generates the reference voltage required by the subsequent circuit, or the active crystal oscillator circuit provides a high-frequency reference signal for the subsequent circuit. The present invention uses the signal generated by the reference unit to provide a reference for the action value setting unit and the return value setting unit.

[0057] The present invention employs a hysteresis comparison for overspeed protection of steam turbines. When the turbine speed exceeds the set action value, an overspeed signal is output to reduce the speed of the pneumatic pump. When the speed drops to the action value, the overspeed fault state remains until the speed drops to the return value, at which point the overspeed fault state is resolved. Therefore, the set action value should be greater than the return value. After the action value is set by the action value setting unit, an action value threshold signal is actually output. Similarly, after the return value setting unit is set, a return value threshold signal is actually output.

[0058] The overspeed comparison module includes an overspeed action comparison unit and an overspeed return comparison unit. The overspeed action comparison unit includes a voltage comparator for comparing the action value, or a frequency signal comparison digital circuit, for comparing the output signal of the speed signal sampling and conditioning module with the action value output by the action value setting unit; the overspeed return comparison unit includes a voltage comparator for comparing the return value, or a frequency signal comparison digital circuit, for comparing the output signal of the speed signal sampling and conditioning module with the return value output by the return value setting unit.

[0059] In this way, the actual speed signal will be compared with the action value threshold signal and the return value threshold signal in the overspeed comparison module, and finally the overspeed comparison module will output an overspeed control signal to determine whether the turbine is overspeeding.

[0060] The overspeed isolation output module includes a drive amplifier unit and an output control unit including a relay. The drive amplifier unit includes a transistor amplifier circuit and / or a MOS tube amplifier circuit, which is used to amplify the signals output by the overspeed action comparison unit and the overspeed return comparison unit; the output control unit includes a relay, which is used to electrically isolate the side low voltage of the protection system from the high voltage of the main circuit.

[0061] The overspeed isolation output module of the present invention can improve the driving capability of the overspeed control signal output by the overspeed comparison module, so that the overspeed isolation output module can better achieve electrical isolation through the relay, thereby improving the reliability of overspeed protection control.

[0062] The advantages of the present invention are as follows:

[0063] ① The present invention uses only pure hardware circuits to implement overspeed warning and protection for the steam turbine of the nuclear power plant's steam-driven auxiliary feedwater pump. Without the need for single-chip microcomputer and its software program control, it can solve the safety, stability and real-time performance issues during the operation of the nuclear power plant's steam-driven auxiliary feedwater pump, fully meet the safety level requirements of the nuclear power plant, and directly avoid various problems caused by the use of single-chip microcomputer control;

[0064] ② The circuit performance of the present invention is stable and reliable, with high control accuracy, which is far superior to traditional mechanical overspeed protection systems and overspeed protection systems composed of single-chip microcomputers.

[0065] Glossary

[0066] Speeding: A manifestation of exceeding the maximum operating speed. When the speed of the power machinery increases, the overspeed protection fails, the speed is out of control, and exceeds the speed limit. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 It is a structural schematic diagram of the present invention;

[0068] Figure 2 Schematic diagram of the structure of the nuclear-grade speed relay in the present invention;

[0069] Figure 3 Schematic diagram of the circuit principle of the reference unit in an embodiment of the present invention;

[0070] Figure 4 Schematic diagram of the circuit principles of the action value setting unit and the return value setting unit in an embodiment of the present invention;

[0071] Figure 5 Schematic diagram of the circuit principle of the overspeed action comparison unit and the overspeed return comparison unit in an embodiment of the present invention;

[0072] Figure 6 Schematic diagram of the circuit principle of the three-choose-two module in an embodiment of the present invention. DETAILED DESCRIPTION

[0073] like Figures 1 to 2As shown, a nuclear-grade speed overspeed protection system includes three speed sensors for monitoring the speed of a steam turbine, and three nuclear-grade speed relays composed of circuits that do not include a single-chip microcomputer. The output ends of the three nuclear-grade speed relays are respectively connected to the three input ends of a three-choose-two module, and the input end of each nuclear-grade speed relay is respectively connected to a speed sensor. The output end of the three-choose-two module is connected to a protection execution module; the nuclear-grade speed relay includes a speed signal sampling and conditioning module, an overspeed action value setting module, an overspeed comparison module and an overspeed isolation output module. The output end of the speed signal sampling and conditioning module and the output end of the overspeed action value setting module are respectively connected to the input end of the overspeed comparison module, and the output end of the overspeed comparison module is connected to the input end of the overspeed isolation output module; the input end of the speed signal sampling and conditioning module serves as the input end of the nuclear-grade speed relay, and the output end of the overspeed isolation output module serves as the input end of the nuclear-grade speed relay. The output end serves as the output end of the nuclear-grade speed relay and is connected to the input end of the three-choice-two module; the speed signal sampling and conditioning module includes a protection unit, a filtering unit, and a conditioning unit, which are used to protect the signal output by the speed sensor, filter out interference signals, and condition the signal required for subsequent comparison; the overspeed action value setting module includes a reference unit, an action value setting unit, and a return value setting unit, which are used to obtain reference signals for the speed action value and return value; the overspeed comparison module includes an overspeed action comparison unit and an overspeed return comparison unit, which are used to perform hysteresis comparison on the output signal of the speed signal sampling and conditioning module and the output signal of the overspeed action value setting module; the overspeed isolation output module includes a drive amplification unit and an output control unit including a relay, which is used to amplify the signal after the overspeed comparison, thereby driving the relay of the output control unit to open and close, thereby realizing isolation of the overspeed output signal.

[0074] For example, the output end of the speed sensor 1 is connected to the input end of the protection unit of the speed signal sampling and conditioning module in the nuclear-grade speed relay 1, the output end of the protection unit is connected to the input end of the filter unit, the output end of the filter unit is connected to the input end of the conditioning unit, the output end of the conditioning unit is connected to the input end 1 of the overspeed action comparison unit, and is also connected to the input end 1 of the overspeed return comparison unit;

[0075] At the same time, the output end of the reference unit of the overspeed action value setting module in the nuclear-grade speed relay 1 is connected to the input ends of the action value setting unit and the return value setting unit at the same time; the output end of the action value setting unit is connected to the input end 2 of the overspeed action comparison unit, and the output end of the return value setting unit is connected to the input end 2 of the overspeed return comparison unit;

[0076] The output ends of the overspeed action comparison unit and the overspeed return comparison unit are both connected to the input end of the drive amplifier unit of the overspeed isolation output module, and the output end of the drive amplifier unit is connected to the input end of the relay output unit (i.e., the output control unit including the relay). Finally, the output end of the relay output unit is connected to the input end 1 of the three-choose-two module.

[0077] Similarly, the connection relationship between the speed sensor 2 and the speed sensor 3 and the nuclear-grade speed relay 2 and the nuclear-grade speed relay 3 can be obtained respectively.

[0078] like Figures 3 to 6 As shown, according to the above content, the following examples are made:

[0079] During operation, the speed signals output by each speed sensor are pulse signals of a certain frequency. Conventional signal sampling and conditioning modules can be used to receive the output signals of the speed sensors. Therefore, the speed signal sampling and conditioning module in this embodiment can be composed of a conventional limiter circuit (protection unit), an RC filter circuit (filtering unit), and a level conversion circuit (conditioning unit). Of course, in order to maximize the signal sampling and conditioning effects, other circuits can be added to the various functional units of the speed signal sampling and conditioning module, such as adding an overcurrent protection circuit or an overvoltage protection circuit to the protection unit, so that the speed signal sampling and conditioning module can smoothly and accurately transmit the speed signal of the speed sensor to the overspeed comparison module.

[0080] In order to achieve high precision of overspeed protection, it is necessary to set the overspeed action value and return value with high precision. Before setting the overspeed action value and return value with high precision, it is also necessary to provide a reference signal for the setting of the action value and return value through the reference unit.

[0081] The overspeed action value setting module of this embodiment is as follows Figure 3 As shown, the reference unit includes a voltage reference circuit and an active crystal oscillator circuit. First, a three-terminal adjustable output linear regulator integrated circuit module LM117 is used as an adjustable linear regulator U2 (LDO) to form a voltage reference circuit. A 5V power supply is generated from a 15V power supply to power the active crystal oscillator circuit. The output voltage of the third pin of the chip LM117 is 5V. The specific calculation formula is as follows:

[0082] Vout=1.25×(1+R14 / R13)

[0083] Where Vout is the output voltage of the third pin of the chip LM117. Substituting R13 = 0.47Ω and R14 = 1.4Ω into the above formula, we can know that Vout = 5V.

[0084] The crystal oscillator in the active crystal oscillator circuit outputs a square wave with a frequency of 4MHz and a duty cycle of 50%. This signal is converted by an N-channel enhancement mode field effect transistor (MOSFET) BS170 to produce a 4MHz square wave signal with a high level of 15V and a low level of 0V. This signal is then inverted by a NOT gate (CD40106BF3A) and fed into a frequency divider circuit for processing. This signal is divided by a dual binary counter (CD4520BF3A). In this embodiment, the two binary up-counters in the CD4520BF3A are cascaded to form an eight-level divide-by-two frequency divider, a cascaded circuit in traveling wave mode (a 4MHz signal divided by eight levels yields 4MHz, 2MHz, 1MHz, ..., 15.625kHz). Here, a jumper cap is used to select a 2MHz reference clock signal output by the active crystal oscillator circuit.

[0085] In this embodiment, the action value setting unit and return value setting unit in the overspeed action value setting module are both programmable divide-by-N counters (CD4059AM) (i.e., divide-by-N down counters), which can be programmed to divide by any value between 3 and 15999. This counter output has TTL drive capability. The CD4059AM counter in this embodiment is packaged in a 24-pin surface mount package, rated for an operating temperature range of -55°C to +125°C, and an operating voltage range of -0.5V to +15V.

[0086] The 16-bit encoding input pin connected to the counter CD4059AM is connected with a 22K resistor A09-233FP (i.e. Figure 4 R6, R7, R8, R9) in the 4-bit encoding input pin are pulled down to GND, and a 16-bit BCD encoder RTE1600G4 (i.e. Figure 4 Manually determine the encoding value by using S7-S10, S30-S33 in the counter, and set the mode value (MODE) through the pins Ka, Kb, and Kc of the counter CD4059AM.

[0087] In this embodiment, the two sets of frequency counters are respectively set with encoders to set the action value and return value. Since the reference clock signal fosc output by the active crystal oscillator circuit is 2MHz, the frequency of the reference clock input to the programmable N frequency counter CD4059AM is 2MHz. The method of setting the action value and return value is as follows:

[0088] If you need to set the action value (i.e. speed overspeed alarm threshold) n1 to 9240r / min, then:

[0089] Overspeed frequency threshold = n1 / 60 = 9240 / 60 = 154Hz. Further calculation yields the corresponding encoder value: 2MHz / 154Hz = 12987. Therefore, the setting value for the 16-bit encoder of Action Value 4 is C987, and the corresponding output signal is 4059OUT1.

[0090] The return value (i.e., the overspeed fault release threshold) can be set as 90% of the action value, that is:

[0091] Return value n2 = n1 × 90% = 8322 rpm. Similarly, when return value n2 is 8322 rpm, return frequency = n2 / 60 = 8322 / 60 = 138.7 Hz. Further calculation yields the corresponding encoder value: 2 MHz / 138.7 Hz = 14420. Therefore, the setting value for the 16-bit encoder in return value group 4 should be E420, resulting in an output signal of 4059OUT2.

[0092] After the action value and return value are set in the overspeed action value setting module, the action value setting unit and the return value setting unit respectively output the action value threshold signal 4059OUT1 and the return value threshold signal 4059OUT2 to the overspeed action comparison unit and the overspeed return comparison unit of the overspeed comparison module, and compare them with the real-time speed signal in the overspeed comparison module (obtained by the speed sensor).

[0093] In this embodiment, the overspeed action comparison unit and the overspeed return comparison unit in the overspeed comparison module are implemented by a dual D-type flip-flop integrated circuit CD4013BF3A (ie, a frequency signal comparison digital circuit) to compare signals.

[0094] The CD4013BF3A dual D-type flip-flop integrated circuit consists of two identical, independent data-type flip-flops. Each flip-flop has independent data, set, reset, and clock inputs, as well as Q and / Q outputs. The flip-flops are housed in a 14-pin dual-in-line ceramic package and are rated for operation over an ambient temperature range of -55°C to +125°C and a 3V to 18V operating voltage range.

[0095] This embodiment uses two dual D-type flip-flop integrated circuits (CD4013BF3A) and one quad-channel, two-input OR gate (CD4071BF3A). Dual D-type flip-flop integrated circuit D5 consists of flip-flops D5A and D5B, while dual D-type flip-flop integrated circuit D7 consists of flip-flops D7A and D7B. The overspeed action comparison unit primarily includes D5A, D7A, and D4A. The overspeed return comparison unit primarily includes D5B, D7B, and D4B.

[0096] The clock signals input to flip-flops D5A and D5B are both real-time speed signals output by the speed signal sampling and conditioning module. After passing through inverter CD40106BF3A (not shown in the figure), the input clock signals are fed into each CLOCK pin. Flip-flops D5A and D5B employ a normally low data input, D. Their two outputs, Q1 and Q2 (i.e., pins 1 and 13 of dual D-type flip-flop integrated circuit D5), are connected to data inputs D1 and D2 of dual D-type flip-flop integrated circuit D7, respectively (data input D1 corresponds to pin 5, and data input D2 corresponds to pin 9). The output of dual D-type flip-flop integrated circuit D5 serves as the data input of dual D-type flip-flop integrated circuit D7. The action value setting unit and return value setting unit output action value threshold signals 4059OUT1 and return value threshold signals 4059OUT2, respectively. These signals are connected through OR gates to the reset SET pins of flip-flops D5A, D7A, D5B, and D7B, respectively.

[0097] When the speed signal is less than 154Hz, the output signal D7_Q1 of trigger D7A is high. When the real-time speed signal is greater than 154Hz, the output signal D7_Q1 of trigger D7A is low. When the real-time speed signal is less than 138.7Hz, the output signal D7_Q2 of trigger D7B is high. When the real-time speed signal is greater than 138.7Hz, the output signal D7_Q2 of trigger D7B is low.

[0098] In this way, the overspeed control signal can be obtained through the overspeed comparison module, and driven and amplified by the overspeed isolation output module using a transistor amplifier circuit, thereby driving the relay of the output control unit to open and close, thereby realizing electrical isolation of the overspeed output signal. While providing one overspeed judgment signal for the subsequent three-choose-two module, the side low voltage of the protection system is isolated from the high voltage of the main circuit, so that the high voltage of the main circuit cannot interfere with the side low voltage of the protection system.

[0099] See also Figure 1 , through three nuclear-grade speed relays (i.e., nuclear-grade speed relay 1, nuclear-grade speed relay 2, and nuclear-grade speed relay 3), the three overspeed judgment signals generated are transmitted to the relays 041XR, 042XR, and 043XR of the three output control units for overspeed judgment of the turbine.

[0100] like Figure 6 As shown, when any two of the three overspeed signals exceed the speed limit, the three-choose-two logic circuit in the three-choose-two module determines the protection execution signal issued by the output control unit, ultimately driving the protection execution module to operate. In this embodiment of the three-choose-two module, relay 061XR serves as the overspeed three-choose-two relay. The control logic of this overspeed three-choose-two relay is as follows:

[0101] When the overspeed judgment signal 1 exceeds the speed overspeed alarm threshold, the contact of relay 041XR is closed, and the corresponding relays 011XR and 012XR are activated to connect the circuit;

[0102] When the overspeed judgment signal 2 exceeds the speed overspeed alarm threshold, the contact of relay 042XR is closed, and the corresponding relays 021XR and 022XR are activated to connect the circuit;

[0103] When the overspeed judgment signal 3 exceeds the speed overspeed alarm threshold, the contact of relay 043XR is closed, and the corresponding relays 031XR and 032XR are activated to connect the circuit;

[0104] When both the overspeed judgment signal 1 and the overspeed judgment signal 2 exceed the speed overspeed alarm threshold, 011XR and 021XR will be activated to make the overspeed three-to-two relay 061XR connect the circuit;

[0105] When both the overspeed judgment signal 1 and the overspeed judgment signal 3 exceed the speed overspeed alarm threshold, 012XR and 031XR will be activated to make the overspeed three-to-two relay 061XR connect the circuit;

[0106] When both the overspeed judgment signal 2 and the overspeed judgment signal 3 exceed the speed overspeed alarm threshold, 022XR and 032XR are actuated to make the overspeed three-to-two relay 061R connect the circuit;

[0107] That is to say, as long as two of the three overspeed judgment signals are greater than the speed overspeed alarm threshold, the turbine will be judged as overspeeding, and the overspeed three-to-two relay 061XR will immediately take action, making the circuit conductive and sending a signal to the protection execution module to issue an overspeed alarm and protect the turbine.

[0108] When the overspeed judgment signal 1 is less than or equal to the overspeed fault release threshold, the contact of 041XR is disconnected, and the corresponding relays 011XR and 012XR are activated to cut off the circuit;

[0109] When the overspeed judgment signal 2 is less than or equal to the overspeed fault release threshold, the contact of 042XR is disconnected, and the corresponding relays 021XR and 022XR are activated to cut off the circuit;

[0110] When the overspeed judgment signal 3 is less than or equal to the overspeed fault release threshold, the contact of 043XR is disconnected, and the corresponding relays 031XR and 032XR are activated to cut off the circuit;

[0111] When both overspeed judgment signal 1 and overspeed judgment signal 2 are less than or equal to the overspeed fault release threshold, 011XR and 021XR will operate to make the overspeed three-to-two relay 061XR disconnect the circuit;

[0112] When the overspeed judgment signal 1 and the overspeed judgment signal 3 are both ≤ the overspeed fault release threshold, 012XR and 031XR will operate to make the overspeed three-to-two relay 061XR disconnect the circuit;

[0113] When both overspeed judgment signal 2 and overspeed judgment signal 3 are less than or equal to the overspeed fault release threshold, 022XR and 032XR will operate to make overspeed three-to-two relay 061R disconnect the circuit;

[0114] That is to say, as long as two of the three overspeed judgment signals are less than or equal to the overspeed fault release threshold, the turbine will be judged as the overspeed state has been released, and the overspeed three-to-two relay 061XR will immediately take action to disconnect the circuit and send a signal to the protection execution module to release the alarm.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A nuclear-grade speed overspeed protection system, characterized in that: It includes three speed sensors for monitoring the speed of the steam turbine, and three nuclear-grade speed relays composed of circuits that do not contain a single-chip microcomputer. The output ends of the three nuclear-grade speed relays are respectively connected to the three input ends of a three-choice-two module. The input end of each nuclear-grade speed relay is respectively connected to a speed sensor. The output end of the three-choice-two module is connected to a protection execution module. The nuclear-grade speed relay has the functions of presetting a speed overspeed alarm threshold and an overspeed fault release threshold, and comparing the speed sensor output signal with the speed alarm threshold, so that the three-choice-two module can control the protection execution module according to the overspeed judgment signal output by the three nuclear-grade speed relays.

2. The nuclear-grade speed overspeed protection system according to claim 1 is characterized in that: The nuclear-grade speed relay comprises a speed signal sampling and conditioning module, an overspeed action value setting module, an overspeed comparison module and an overspeed isolation output module, the output end of the speed signal sampling and conditioning module and the output end of the overspeed action value setting module are respectively connected to the input end of the overspeed comparison module, and the output end of the overspeed comparison module is connected to the input end of the overspeed isolation output module; The speed signal sampling and conditioning module is used to collect the real-time speed signal output by the speed sensor, filter out interference signals, protect the circuit from interference, and condition the signal required for subsequent comparison; The overspeed action value setting module is used to determine the reference signal of the speed action value and the return value, and preset the speed overspeed alarm threshold and the overspeed fault release threshold; The overspeed comparison module is used to perform hysteresis comparison on the output signal of the speed signal sampling and conditioning module and the output signal of the overspeed action value setting module; The overspeed isolation output module is used to amplify the signal after the overspeed comparison, thereby driving the relay of the output control unit to open and close, thereby realizing the isolation of the overspeed output signal.

3. The nuclear-grade speed overspeed protection system according to claim 2 is characterized in that: The speed signal sampling and conditioning module includes a protection unit, a filtering unit, and a conditioning unit: The protection unit is used to prevent external interference signals from being introduced into the system, or excessive current / voltage from damaging the circuit; The filtering unit is used to filter the high-frequency noise and low-frequency noise of the pulse signal; The conditioning unit is used to condition the signal to make it more accurate and stable; The overspeed action value setting module includes a reference unit, an action value setting unit, and a return value setting unit: The action value setting unit is used to set the action value as the speed overspeed alarm threshold; The return value setting unit is used to set the return value as an overspeed fault release threshold; The reference unit is used to generate a reference signal to provide a reference for the action value setting unit and the return value setting unit to set the threshold; The overspeed comparison module includes an overspeed action comparison unit and an overspeed return comparison unit: The overspeed action comparison unit is used to compare the output signal of the speed signal sampling and conditioning module with the action value output by the action value setting unit; The overspeed return comparison unit is used to compare the output signal of the speed signal sampling and conditioning module with the return value output by the return value setting unit; The overspeed isolation output module includes a drive amplifier unit and an output control unit including a relay: The driving amplifier unit is used to amplify the signals output by the overspeed action comparison unit and the overspeed return comparison unit; The output control unit is used to electrically isolate the side low voltage of the protection system from the high voltage of the main circuit.

4. The nuclear-grade speed overspeed protection system according to claim 2 or 3, characterized in that: The protection unit of the speed signal sampling and conditioning module includes an overcurrent protection circuit and / or a limiting circuit.

5. The nuclear-grade speed overspeed protection system according to claim 2 or 3, characterized in that: The filtering unit of the speed signal sampling and conditioning module includes an RC filtering circuit and / or an RC differentiating circuit.

6. The nuclear-grade speed overspeed protection system according to claim 2 or 3, characterized in that: The conditioning unit of the speed signal sampling and conditioning module includes a level conversion circuit, or / and a logic gate circuit, or / and a monostable multivibrator circuit, or / and a frequency-voltage conversion circuit.

7. The nuclear-grade speed overspeed protection system according to claim 2 or 3, characterized in that: The reference unit of the overspeed action value setting module includes a voltage reference circuit and / or an active crystal oscillator circuit.

8. The nuclear-grade speed overspeed protection system according to claim 2 or 3, characterized in that: The action value setting unit of the overspeed action value setting module includes a programmable frequency division calculator or a precision resistor voltage division circuit for setting the action value; The return value setting unit of the overspeed action value setting module includes a programmable frequency division calculator or a precision resistor voltage division circuit for setting the return value.

9. The nuclear-grade speed overspeed protection system according to claim 2 or 3, characterized in that: The overspeed action comparison unit of the overspeed comparison module includes a voltage comparator for comparing action values, or a frequency signal comparison digital circuit; The overspeed return comparison unit of the overspeed comparison module includes a voltage comparator for comparing return values, or a frequency signal comparison digital circuit.

10. The nuclear-grade speed overspeed protection system according to claim 2 or 3, characterized in that: The driving amplifier unit of the overspeed isolation output module includes a triode amplifier circuit and / or a MOS tube amplifier circuit.

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