Application of the hottest servo proportional valv

Application of servo proportional valve in hydraulic turbine governor

hydraulic turbine governor is a proprietary equipment used to directly control the speed of hydraulic turbine generator set in hydropower plant. It controls every link of generator set, such as normal startup, no-load, combination, load increase and decrease, normal shutdown, etc. its working performance directly affects the normal operation of generator set, The operation of large capacity units also affects the safety and stability of power system. In 1990, the power department of the former Ministry of energy and the science and Technology Department of the China Electricity Council conducted an investigation on the failure of 134 turbine governors in 40 hydropower plants. The investigation results showed that the failure rate of turbine governors in operation was amazing, with a total of 827 failures, of which the failure rate of hydraulic control cabinet accounted for 61.1%; In the total failure rate, the failure caused by the electro-hydraulic converter of the hydraulic control cabinet accounts for 45%. Therefore, it is particularly important to solve the reliability problem of the electro-hydraulic converter in the hydraulic control cabinet

from the pure mechanical centrifugal pendulum of the governor in the early days to various electro-hydraulic converters later, such as nozzle baffle type, annular spray type, biconical type, jet pipe type electro-hydraulic converters, they have made considerable improvements in terms of the design of the working principle of the product itself and the production and processing technology, so that the dynamic and static characteristics of the governor products have been greatly improved, Basically, it can meet the general requirements of hydropower plant operation. However, judging from the higher requirements for hydropower plants to achieve "unattended" (few people on duty), there is obviously a certain gap. Therefore, according to the prompts to enter the main page of the experimental program, we must explore new methods to further improve the quality of the component. 1. Application of servo proportional valve in governor according to the requirements of hydropower plants to realize full-automatic operation of units and "unattended" (few people on duty), Nari electric control company, after long-term investigation and test, first proposed and officially adopted the scheme of servo valve as the electro-hydraulic conversion component of hydraulic control cabinet of hydraulic turbine governor in China in 1994, that is, the servo valve converts the electrical signal input by the cabinet into flow output signal, Through a servo cylinder (developed by Nari electric control company and patented by the state), the flow signal is converted into displacement signal output, so as to complete the control of the hydraulic regulator cabinet of the governor. Its control principle is shown in Figure 1. Figure 1 control principle it can be seen from Figure 1 that in the large closed loop formed by the electric cabinet, main servomotor and displacement transmitter, the servo proportional valve first forms a small closed loop with the electric cabinet. During the control process, the CPU in the electric cabinet is always monitoring the motion state of the servo proportional valve spool and making corresponding adjustments, thus further improving the control accuracy of the servo proportional valve. 2. Characteristics of servo proportional valve (1) compared with electro-hydraulic converter, servo proportional valve has greater improvement in anti jam ability. The electromagnetic operating force of the pilot control stage of the servo proportional valve is many times higher than that of the electrohydraulic converter commonly used in the past, and the maximum value is 5 kg. Generally, the electromagnetic operating force of the pilot control stage of the electrohydraulic converter is usually less than 0.5 kg, the maximum value is not more than 0.75 kg, and some are even less than 0.1 kg, which makes it difficult to overcome its own static friction. According to the field experience, the pilot control part of the electro-hydraulic converter is the most prone to jam; The small electromagnetic operating force of the pilot control stage is one of the most important reasons for card issuing. Therefore, the enhancement of the anti jam ability of the servo proportional valve is very important to improve the reliability of the governor

(2) the matching accuracy of servo proportional valve is completely at the same level as that of servo valve (electro-hydraulic converter). The precision fitting parts inside the servo proportional valve completely adopt the processing technology of the servo valve. The radial fitting clearance and axial overlap tolerance between the spool and the valve sleeve of each servo proportional valve are achieved through the single grinding of each spool and valve sleeve. The spool and valve sleeve of the same servo proportional valve are not interchangeable, and its fitting accuracy is completely at the same level as that of the servo valve. Therefore, its dynamic characteristics and static characteristics are not lower than those of previous electro-hydraulic converters. This can be seen from the following partial parameters of the servo proportional valve: the maximum working pressure is 315 bar; Rated flow（ Δ P=35 bar)40 L／min； Hysteresis ＜ 0.2%; Reverse return difference ＜ 0.1%; Response time signal changes 0 ~ 100% <10 ms; Temperature drift <1% Bei（ Δ T=40℃)； Leakage (at 100 bar) 1.1 L/min

(3) strong oil resistance. The pilot control stage of servo proportional valve adopts the structure of simple slide valve cooperation, which does not require high accuracy of oil quality, usually less than 25 μ This is mainly because there is no small orifice in its internal flow channel that is easily blocked. One of the most common failures of general electro-hydraulic converters is that the small oil injection orifice is blocked, that is, Kobe Steel Co., Ltd. has participated in the final industry insiders said that the poor anti oil ability of several aluminum exhibitions has led to control failure

(4) it is convenient to optimize the structural design of pilot valve and main pressure distribution valve. Compared with other solenoid valves with the same diameter, the new type of channel structure design of servo proportional valve has a lot of increase in excess flow under the same pressure difference; Using it to directly control the servo cylinder can make the piston core of the servo cylinder have a linear relationship with the input flow within the range of ± 15 mm displacement. This feature is convenient to optimize the structural design of pilot valve and main pressure distribution valve to a great extent

(5) it has high reliability. Because the pilot stage of the servo proportional valve adopts the moving iron structure, the connecting wire of its electromagnetic coil will not break or fall off due to the action of the electromagnetic core, thus improving the reliability. 3. On site use of servo proportional valve. The hydraulic regulator cabinet of hydraulic turbine governor using servo proportional valve developed by Nari electric control company has operated safely and stably in various hydropower plants since the first prototype was put into operation in Sichuan Ying4 raw material Xiuwan hydropower plant in 1994. During this period, only four times showed that the servo proportional valve was switched to other control modes due to failure. After inspection, these four failures were all caused by the internal oil hole of the hydraulic manifold block not being cleaned completely, resulting in the transportation of iron filings at the soft edge of the intersecting hole