A first-stage overspeed protection system for a hydropower station

Abstract

The present invention relates to the overspeed protection technology of hydropower generating units, and discloses a first-stage overspeed protection system for a hydropower station and its control method, which solves the problem that the traditional first-stage overspeed protection scheme does not consider the self-failure of the governor PLC, which may cause the first-stage overspeed protection to fail to act correctly. In the present invention, the important signal "main distributor fails to act" that constitutes the first-stage overspeed protection system is not determined by the governor PLC and given, but a control circuit is formed by an electronic time relay, a hard pressure plate, and a trip locking relay for the microswitch signal directly from the governor main distribution valve body, the guide vane position signal, and the unit speed signal, and a serious fault signal of the governor body is added to the first-stage overspeed protection logic to improve the first-stage overspeed protection logic of the hydropower station.

Description

Technical Field

[0001] The present invention relates to the overspeed protection technology of hydropower generating units, and specifically relates to a first-stage overspeed protection system for a hydropower station and its control method. Background Art

[0002] The water turbine generator units of a hydropower station generally operate at the rated speed. In the event of an accident, the speed may become too high, causing serious damage to the units. Usually, three-stage overspeed protection is set for the water turbine generator units: the first-stage overspeed protection is set at 115% of the rated speed (the specific speed setting is determined according to the calculation results of the hydropower station's regulation and protection), and if a failure occurs where the main servo valve of the governor refuses to move, it will act on the emergency shutdown solenoid valve; the second-stage overspeed protection is set at 140% of the rated speed (the specific speed setting is determined according to the calculation results of the hydropower station's regulation and protection), and it acts on the emergency shutdown solenoid valve; the third-stage overspeed protection is a pure mechanical overspeed protection that directly acts on the governor's hydraulic circuit to close the guide vanes.

[0003] Generally, in large and medium-sized hydropower stations, each unit will be equipped with a set of local control unit (LCU) for the unit. The local control unit of the unit uses a PLC as the core control element, and the unit control process and the waterwheel protection logic are realized by it. Usually, to ensure the safety of the unit, in addition to the waterwheel protection in the PLC of the unit LCU, an independent waterwheel protection PLC will be additionally set up to shut down the unit when the unit LCU cannot operate normally, so as to achieve dual protection and ensure the safety of the unit. In the PLC in the unit LCU and the waterwheel protection PLC, independent first-stage overspeed protection programs for the water turbine generator unit are respectively set.

[0004] Due to the microswitch set on the main servo valve body of the governor, the signal generally given is actually a "main servo not moving in the closing direction" signal, which is not equivalent to the "main servo refusal to move" signal. In the current conventional design scheme, one of the input conditions for constituting the first-stage overspeed protection, the "main servo refusal to move signal", is given by the governor PLC device after comprehensive judgment. That is, the governor PLC device gives the "main servo refusal to move signal" to the PLC of the unit LCU and the independent waterwheel protection PLC after comprehensive judgment.

[0005] It can be seen that the first-stage overspeed protection logic of the water turbine generator unit in the existing scheme is too dependent on the PLC device of the governor. In the case of abnormal increase in the unit speed, if the governor PLC fails and does not correctly give the "main servo refusal to move" signal, it will cause the first-stage overspeed protection of the unit to fail to act correctly, resulting in a further increase in the unit speed and causing the accident to expand. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: to propose a first-level overspeed protection system for a hydropower station and a control method thereof, so as to solve the problem that the first-level overspeed protection scheme in traditional technology does not take into account the fault of the speed regulator PLC itself, which may cause the first-level overspeed protection to fail to operate correctly.

[0007] The technical solution adopted by the present invention to solve the above technical problems is:

[0008] A primary overspeed protection system for a hydropower station comprises a first control circuit, wherein the first control circuit comprises a main pressure regulating valve body, an electronic time relay, a speed measuring device, a guide vane travel switch, a trip lockout relay and a first protection hard pressure plate; a micro switch signal of the main pressure regulating valve body is delayed by the electronic time relay, and the delayed micro switch signal is connected in series with a unit speed signal output by the speed measuring device and a guide vane position signal output by the guide vane travel switch to an input end of the trip lockout relay; and an output end of the trip lockout relay is connected to a unit LCU and a waterwheel protection PLC.

[0009] As a further optimization, the system also includes a second control loop, which includes a speed regulator control cabinet and a second protective hard pressure plate. When the speed regulator body has a serious fault, the speed regulator control cabinet gives a "speed regulator serious fault signal", and the tripping lockout relay is energized, directly triggering the first-level overspeed protection.

[0010] In addition, the present invention also provides a control method for the primary overspeed protection system of the hydropower station, which comprises:

[0011] When the main pressure regulating valve is abnormal, the main pressure regulating valve body provides a signal that "the main pressure regulating valve does not move in the closing direction";

[0012] The signal of "the main pressure regulating valve does not move in the closing direction" is delayed by the time relay;

[0013] At the end of the delay, if the guide vane of the unit is opened above no-load and the unit speed exceeds the first-level overspeed protection speed threshold, the trip lockout relay will be energized, triggering the first-level overspeed protection in the unit LCU and waterwheel protection PLC, and starting the shutdown process.

[0014] As a further optimization, the delay time of the time relay is set according to the actual guide vane closing rule of the speed regulator, and is not greater than the travel time from the guide vane fully open position to the guide vane no-load position.

[0015] As a further optimization, the control method further includes:

[0016] When the speed governor body has a serious fault, the speed governor control cabinet will give a "speed governor serious fault signal", the tripping lockout relay will be energized, directly triggering the first-level overspeed protection in the unit LCU and waterwheel protection PLC, and starting the shutdown process.

[0017] As a further optimization, when the governor control cabinet gives out a "severe governor failure signal" and the unit speed exceeds the first-stage overspeed protection speed threshold, the trip locking relay is energized, triggering the first-stage overspeed protection in the unit LCU and the waterwheel protection PLC, and starting the shutdown process.

[0018] The beneficial effects of the present invention are as follows:

[0019] (1) By using the microswitch signal of the main distribution body and delaying it with a time relay, and then connecting in series with the guide vane opening signal and the signal of excessive speed, the logic of the main distribution refusal to operate is realized, starting the shutdown process in the first time, and avoiding the problem of the failure of the first-stage overspeed protection caused by the governor body failure.

[0020] (2) By adding the severe governor failure signal to improve the first-stage overspeed protection logic of the hydropower station, the unit is shut down as early as possible when the governor has a severe failure, avoiding the rapid increase of the unit speed caused by the inability to adjust the guide vane opening.

[0021] (3) By using the trip locking relay to improve the anti-interference ability of the circuit and enhance the protection action speed.

[0022] Therefore, the present invention overcomes the problem of the failure of the first-stage overspeed protection of the hydropower station caused by the governor body failure, and has the advantages of simple and clear circuit, clear logic, low cost, strong anti-interference ability and fast response time. By improving the first-stage overspeed protection logic of the hydropower station, the operation safety of the unit is further improved, the risk of excessive unit speed is reduced, and the damage to each component of the unit and the hydraulic structure of the power station at high speed can be avoided. Description of the Drawings

[0023] Figure 1 It is the schematic diagram of the first-stage overspeed protection system of the hydropower station in the embodiment of the present invention. Detailed Embodiments

[0024] The present invention aims to propose a first-stage overspeed protection system for a hydropower station and its control method, solving the problem that the traditional first-stage overspeed protection scheme does not consider the self-failure of the governor PLC, which may cause the first-stage overspeed protection to fail to act correctly. Its core idea is that the important signal "main distribution refusal to operate" that constitutes the first-stage overspeed protection system is not determined and given by the governor PLC, but a control circuit is formed by an electronic time relay, a hard pressure plate, and a trip locking relay for the microswitch signal directly from the governor main distribution valve body, the guide vane position signal, and the unit speed signal, and a severe governor body failure signal is added to the first-stage overspeed protection logic to improve the first-stage overspeed protection logic of the hydropower station.

[0025] The trip blocking relay adopted in the present invention has the characteristics of strong anti-interference ability, fast operation time, stability and reliability. After tripping, the relay is in a self-holding state and needs to be manually reset to release the self-holding. The contacts of the trip blocking relay are respectively connected to the unit LCU and the waterwheel protection PLC, and act to start the accident shutdown process.

[0026] Embodiment:

[0027] As Figure 1 shown, the first-stage overspeed protection system of the hydropower station in this embodiment includes a first control loop and a second control loop. The first control loop includes a main distribution valve body, an electronic time relay, a speed measurement device, a guide vane travel switch, a trip blocking relay, and a first protection hard pressure plate; the second control loop includes a governor control cabinet and a second protection hard pressure plate; in the first control loop, the microswitch signal of the main distribution valve body is delayed by the electronic time relay, and the delayed microswitch signal, the unit speed signal output by the speed measurement device, and the guide vane position signal output by the guide vane travel switch are connected in series (i.e., form a "logical AND") to the input end of the trip blocking relay; the output end of the trip blocking relay is connected to the unit LCU and the waterwheel protection PLC.

[0028] When the governor is in normal operation, since the speed generally does not exceed 105% of the rated speed, the first control loop will not conduct under normal circumstances. When the main distribution valve has an abnormality (such as the main distribution getting stuck due to an oil circuit blockage), the main distribution valve cannot act correctly. At this time, the output contact of the time relay will conduct after reaching the set time. At this time, if the unit's speed rises above 115% of the rated speed due to load rejection or other situations, and the guide vane opening will be above the no-load opening due to the incorrect action of the main distribution valve, the first control loop will conduct, the trip blocking relay will be energized, and the first-stage overspeed protection will be triggered. The first protection hard pressure plate set in this loop should be in the input position during normal operation, and should be switched on or off as appropriate during the commissioning and testing of the unit.

[0029] The design of the second control loop takes into account the serious faults of the governor body in order to be able to close the unit as soon as possible and reduce the damage; the "governor serious fault signal" is given by the governor control cabinet, and this loop will conduct when the governor has serious electrical control faults, double-set controller failures, etc. When this signal appears, it means that the governor has lost the normal control of the guide vane opening and cannot normally adjust the unit speed. After this loop conducts, the trip blocking relay will be energized and directly trigger the first-stage overspeed protection. The second protection hard pressure plate set in this loop should be in the input position during normal operation, and should be switched on or off as appropriate during the commissioning and testing of the unit, or when the governor is switched to the manual operation mode.

[0030] In the above solution, the "governor serious fault signal" directly triggers the first-stage over-speed protection. This method improves the safety of the unit and reduces the protection action time, but at the same time increases the risk of protection malfunction. In specific implementation, to reduce the possibility of protection malfunction, the "unit speed exceeding 115% of the rated speed signal" can also be connected in series after the "governor serious fault signal", that is, the first-stage over-speed protection of the unit is triggered only when both the "governor serious fault signal" and the "unit speed exceeding 115% of the rated speed signal" are satisfied.

[0031] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A control method for the first-stage over-speed protection system of a hydropower station, which is applied to the first-stage over-speed protection system of a hydropower station. The first-stage over-speed protection system of the hydropower station includes a first control loop and a second control loop. The first control loop includes a main distribution valve body, an electronic time relay, a speed measurement device, a guide vane travel switch, a trip blocking relay, and a first protection hard pressure plate. The micro-switch signal of the main distribution valve body is delayed by the electronic time relay, and the delayed micro-switch signal, the unit speed signal output by the speed measurement device, and the guide vane position signal output by the guide vane travel switch are connected in series to the input end of the trip blocking relay. The output end of the trip blocking relay is connected to the unit LCU and the waterwheel protection PLC. The second control loop includes a governor control cabinet and a second protection hard pressure plate. The second protection hard pressure plate is in the inserted position during normal operation. When the governor body has a serious fault, the governor control cabinet gives a "serious governor fault signal", the trip blocking relay is energized, and the first-stage over-speed protection is directly triggered. It is characterized in that This control method includes: When the main distribution valve is abnormal, the main distribution valve body provides a "signal that the main distribution valve does not act in the closing direction". The "signal that the main distribution valve does not act in the closing direction" is delayed by the time relay. At the end of the delay, if the unit guide vane is at an opening above no-load and the unit speed exceeds the first-stage over-speed protection speed threshold, the trip blocking relay is energized, triggering the first-stage over-speed protection in the unit LCU and the waterwheel protection PLC and starting the shutdown process.

2. A control method for the first-stage over-speed protection system of a hydropower station as described in claim 1, It is characterized in that The delay time of the time relay is set according to the actual guide vane closing law of the governor and is not greater than the stroke time from the fully open position of the guide vane to the no-load position of the guide vane.

3. A control method for the first-stage over-speed protection system of a hydropower station as described in claim 1 or 2, It is characterized in that This control method further includes: When the governor body has a serious fault, the governor control cabinet gives a "serious governor fault signal", the trip blocking relay is energized, directly triggering the first-stage over-speed protection in the unit LCU and the waterwheel protection PLC and starting the shutdown process.

4. A control method for the first-stage over-speed protection system of a hydropower station as described in claim 3, It is characterized in that When the governor control cabinet gives a "serious governor fault signal" and at the same time the unit speed exceeds the first-stage over-speed protection speed threshold, the trip blocking relay is energized, triggering the first-stage over-speed protection in the unit LCU and the waterwheel protection PLC and starting the shutdown process.

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