High-voltage circuit breakers equipped with hydraulic operating mechanisms have a large operating parameter that is affected by temperature. The influence of temperature on the opening characteristics of the circuit breaker is analyzed, and a structure for changing the return path is proposed. The method of installing the throttle valve to compensate for the decrease of the speed of the circuit breaker opening at low temperature is due to the vast territory of China, as the power system. The high-voltage circuit breaker of the important protection device has a large temperature change in the working environment. Generally, the working temperature of the circuit breaker is between -4 (TC~4 (TC), so the temperature change will have an important impact on the opening characteristics of the circuit breaker. The ultra-high voltage circuit breaker is equipped with a hydraulic operating mechanism. This paper mainly analyzes the air pressure type. 3 匕 circuit breaker.
1 Influence of temperature change on the circuit breaker For the compressed air SFs circuit breaker equipped with hydraulic operating mechanism, the opening characteristic is mainly determined by the hydraulic mechanism and the arc extinguishing chamber. The temperature has a greater impact on the hydraulic system. The schematic of the hydraulic mechanism is shown.
For the circuit breaker with hydraulic mechanism, the quality of the motion system is fully attributed to the piston, and the equation of motion for the circuit breaker opening process is as follows: hydraulic cylinder without rod cavity pressure; 'for the hydraulic cylinder without rod cavity actual The area of ​​action; the total mass of the piston that is naturalized to the hydraulic working cylinder; -Y is the piston stroke of the hydraulic working cylinder; t is the movement time; it is the reaction force of the compression chamber; it is the friction force; 'is the hydraulic buffering force. The reaction force 5 of the compressor chamber, the friction force 6, and the hydraulic buffer force are less affected by the temperature, so the influence on the opening can be neglected. The rod chamber, ie the high pressure chamber pressure, is generally taken as the accumulator output pressure. Since the accumulator is pre-filled with nitrogen, the gas pressure is greatly affected by the temperature, and the temperature change will affect the pressure of the high pressure chamber.
The hydraulic cylinder has no rod chamber pressure 6: the pressure loss coefficient of the road; the ratio of the oil speed to the moving piston speed dA'/dt in the pipelines on the high pressure oil side and the low pressure oil side is the pressure of the low pressure tank, and is generally taken as atmospheric pressure. Since the working medium of the hydraulic mechanism is hydraulic oil, the kinematic viscosity of the hydraulic oil has a function relationship with the temperature. The hydraulic loss in the formula (2) is related to the kinematic viscosity, so the temperature change will affect the rodless chamber pressure.
1.1 Accumulator output pressure and temperature change relationship Accumulator is a kind of use of nitrogen as a medium to store energy, and return energy to the hydraulic system device in the form of effective work. The accumulators used in the switch hydraulic mechanism are mostly piston type, and the hydraulic oil and nitrogen are separated by the piston. The pressure of the hydraulic oil and nitrogen on both sides of the piston is inversely proportional to the area of ​​the piston on the side where they are located. Therefore, it is only necessary to consider the relationship between the pressure and temperature changes on the nitrogen side during the analysis.
Since the volume of the hydraulic oil is little affected by the temperature, the volume of nitrogen in the accumulator can be considered as a constant value when the circuit breaker has no output. According to the van der Waals equation, the relationship between nitrogen temperature and pressure at a given initial volume can be determined.
The van der Waals equation is: temperature); K is the volume of nitrogen in the accumulator (determined); the mass of nitrogen is W is the gas constant; the molar mass of nitrogen; a, b is the gas pressure and volume correction factor.
For a certain volume of accumulator, the pressure-temperature relationship can be obtained by using equation (4), and the relationship between the temperature and the rod cavity pressure of the hydraulic cylinder is obtained.
1.2 The effect of temperature change on the rodless chamber pressure can be seen from equation (2). The rodless chamber pressure is mainly the pressure loss on the low pressure oil side, and the pressure loss on the low pressure oil side is the path loss and partial pressure loss, where the partial pressure The loss is not sensitive to temperature changes, so the temperature change mainly affects the pressure loss along the path. The pressure loss along the path is: A/pressure loss along the path; Z is the length of the hydraulic pipe; c/ is the diameter of the hydraulic pipe; Frictional resistance coefficient; P is the hydraulic oil density; "is the liquid flow velocity. Among them: the temperature change will affect the kinematic viscosity v. For the 1st aviation hydraulic oil commonly used in the switch hydraulic mechanism, the empirical formula of the viscosity-temperature relationship is: (8) Only applicable to 30C-150TC, and the ambient temperature of the circuit breaker is -3 (TC~50X:, and because the length of the pipe in the sf6 circuit breaker is shorter, the pressure loss along the path is smaller, so due to the temperature The change in pressure caused by the change is not obvious, and the effect of temperature is mainly to make the pressure of the accumulator change greatly.
2 Simulation analysis -20C and 401: For the compressed air 110kV SF6 circuit breaker used in 151: volume 25L, rated pressure 258MPa accumulator, the speed of the split and the maximum speed of the circuit breaker are different as shown in Table 1 The sub-divided speed and the maximum speed temperature CC) The sub-divided speed (m/s) The maximum speed (m/s) is shown in Table 1. As the temperature drops, the breaker's split speed and maximum speed decrease. This will seriously affect the breaking of the circuit breaker.
3 Compensation for the splitting speed of the opening at low temperature In the existing circuit breaker design, the method of heating the hydraulic oil to increase the oil temperature at low temperature compensates for the lowering of the opening speed at low temperature, but this method is troublesome in use. And need to consume power.
From the analysis of the rodless chamber pressure in the equation of motion of the circuit breaker, it can be known that by adjusting the pressure loss coefficient of the return line of the hydraulic mechanism of the circuit breaker, the speed of the breaker can be changed, that is, increasing the pressure loss coefficient can reduce the pressure. Dividing the speed and reducing the pressure loss coefficient can improve the speed of the circuit breaker. Using this principle, a new speed compensation method is proposed in this paper, that is, a manual throttle valve R is installed in the return line.
The principle of the compensation method is as follows: when the ambient temperature is low, the opening degree of the throttle valve R is increased, and the pressure loss coefficient of the return passage is lowered. At this time, although the output pressure of the accumulator is decreased due to the decrease of the ambient temperature, When the return oil circuit structure is changed, the pressure loss coefficient is lower than that of the original circuit breaker when the return oil circuit is in this state, thereby compensating for the decrease of the speed of the branching due to the temperature drop, and ensuring that the circuit breaker is opened with the required speed characteristics. When the temperature is high, the opening degree of the throttle valve is adjusted to increase the pressure loss coefficient of the return line, and the opening speed of the opening due to the temperature rise is restricted. The minimum opening degree of the throttle valve shall be such that the opening speed of the circuit breaker at the high temperature is not higher than the difference, that is, the pressure loss coefficient of the returning oil circuit when the throttle valve is at this opening degree is the same as before the speed compensation device is not used, so as to ensure The circuit breaker is reliably broken. In the specific implementation, the solenoid valve can be used to send a signal through the control cabinet to adjust the opening of the throttle valve.
(Finish)
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