Power system transmission and distribution technology to the development of high voltage, large capacity, long distance, but also to promote the continuous development of high voltage switches. With a different period of development of power system, manufacturing enterprises will produce different off performance of high voltage switch to meet the needs of the power system, at the same time, the match of the operating mechanism of the development and application will have a significant impact. Due to the increase of operating power, the large capacity high voltage switch will be used to match the hydraulic operating mechanism. Therefore, how to do a good job and design a new type of hydraulic mechanism has become a major issue.
Discussions and we should pay attention to several cases of the hydraulic operating mechanism design as many designers generally focus on whether the system to meet the mechanical movement characteristic and disconnect, energy comprehensive utilization, and some minor aspects is easy to be neglected, many problems easily ignored in the initial design personnel, now according to the hydraulic mechanism of years design experience and actual discovery problem is presented.
1. Problems Should Be Paid Attention To In Design Of Hydraulic System
Selection of motor power
The formula of motor power is usually chosen:
N = P1 Q/η
P1: Pressure required to operate the system load;
Q: Flow rate of oil pump plunger;
η: Volumetric efficiency
Design and calculation of the maximum working pressure of hydraulic system:
P1 = F/ A
F: Maximum load force;
A: Hydraulic cylinder action area.
The pressure as a safety valve set pressure, thus ignoring the pipeline along the way loss and control valve system of local loss. Especially when the pipeline is longer or system memory in the greater resistance of the control valve or the synchronous valve, pressure loss is can not be ignored. Otherwise, actual pressure cylinder of a simply not up to the actual required, and the motor as power calculation is not accurate and not work reliably, thereby leading cause fever, resulting in the decrease of insulation capability and burn out, so the choice of the motor power should be according to the formula
N = (P1 + △P) Q/η
P: The pressure loss in system
P = P1 + P
When we were designing a product in our company, due to the neglect of the hydraulic system pressure loss, just according to the normal pressure consider the load of the working cylinder, calculate the motor power is relatively small, and simply with smaller power of the motor is working pressure, the motor running time is too long, lead to the oil pressure cannot establish suitable condition, near the heating of the motor, the consequences are from about 30% of the motor burned out, there is no damage to the motor insulation
Ability also drops. After the re calculation, select the appropriate motor replacement, after several twists and turns to ensure the reliable use of users.
2. Filter Flow Selection
The working capacity of the filter is determined by the effective filtration area, the performance of the filter, the viscosity of the oil, the pressure difference before and after filtration, and the content of solid particles in oil.
Whether the normal work flow filter selection in relation to the hydraulic system, individual designers to choose the filter flow, because the choice is not suitable, just choose the is about 2 times the normal work flow, work as the filter is satisfied that the sewage capacity is small, easily blocked, resulting in the work flow is reduced. Therefore, the design should choose the filter flow of 3 to 5 times the normal flow of work, so that the filter pollution capacity increased, and the service life of the filter is extended.
3. Selection Of Air Filter Flow
Due to the high voltage switch used in hydraulic mechanism in debugging the prototype stage and began construction of pressure, hydraulic pump and shrill noise, also heat pump, check the pump suction port does not leak, no clogging of the suction strainer, at first thought is the pump itself quality doesn’t pass, connecting damage 2 oil pumps, after careful analysis, accident found the root cause of is air filter is chosen too small, the air cleaner to fuel tank ventilation flow rate is less than the pump suction flow. So in the choice of air filter, should pay attention to the ventilation flow should be at least greater than the pump oil absorption. Especially the multi pump system should pay attention to this problem.
4. Valve Before And After The Pressure Difference
When using the throttle valve or pressure reducing valve in the system, when the valve before and after the pressure P2 P1/ > 315, easy to produce cavitation phenomenon, the performance of the valve noise, the system vibration and seriously shorten the service life of the valve
5. The Smooth Flow Of The Oil Drain Pipeline Of The Pressure Relay
Pressure relay is switch hydraulic mechanism often speak of the pressure switch, structure, mechanical and electrical equipment is composed of two parts, in the mechanical part is mainly composed of a piston, a spring, a safety valve, electrical parts is mainly micro switch component. Pressure relay need to discharge oil pipeline, the pipeline should not have any resistance, also should not and large flow valve components of the oil return common line, otherwise due to pressure fluctuations and other reasons, the pressure relay easily mistaking signal and does not move. Pressure relay adjustment of a product range is 25 ~ 27 MPa, less than 25 MPa when the pump starts to run, higher than 30 MPa when the safety valve leakage, the pump stops running. But because of the pressure relay drainage pipeline design is not appropriate, the pressure relay often false signal. Low-voltage sometimes 26 MPa, high pressure sometimes 2615 MPa, signal and lower, sometimes greater than 27 MPa signal, cause misunderstanding to run, so the pressure relay leakage oil pipeline must be smooth, in order to make the normal work
6. Oil Pump Oil Drain Pipe Routing
CY pump output shaft end sealing bearing compressive stress only 0.2 MPa, once the leaks oil pipeline processing is undeserved, the choice is too thin, there will be damaged seal, from the end of the output shaft appear the phenomenon of large-scale hydraulic oil splash, design for oil pipeline relief, first choosing the diameter to the right. Secondly, line as far as possible the use of less pressure loss of the valve.
7. Properly Designed Sealing Device
Hydraulic transmission is to rely on the volume of the seal to establish the pressure, transmission efficiency. Seal failure, in the zone pressure leakage and pressure loss, lower volumetric efficiency of heat to the system, sometimes oil leakage also soiled equipment (high voltage switch hydraulic system does not allow leakage), in the negative pressure area caused by vacuum suction; sealing over, although can prevent oil leakage, but increased friction intensified seal wear and shorten the life span. Therefore must be properly designed sealing device.
Sealing performance is good or bad is related to many factors, groove size is not correct; contact surface roughness is too low; sealing the gap value had great; improper use and maintenance; assembly rough and seals use unreasonable etc. will be causing leakage, the leakage problem from many aspects to analyze. In the selection of a seal, in addition to ensure good performance, must also have a longer life span period, in order to correctly select the required seal must familiar with the form and characteristics of various sealing, the sealing properties of the material and the use conditions (such as: work pressure, working environment temperature is high or low, part of the motor speed, lubrication, etc.) after comprehensive consideration.
Sealing device quality directly affects the work quality of hydraulic system:
(sealing device that is including: sealing, groove, a retainer ring and a supporting ring relevant parts are combined to form the sealing mechanism).
Therefore, the sealing device should have a basic requirement:
1) working pressure has good sealing performance, and with the increase of pressure can automatically improve the sealing performance, that is, there is no significant increase in the leakage under high pressure.
2) sealing device for the friction of the moving parts to be small, friction coefficient
To be stable, so as to avoid the movement of the phenomenon of stagnation or uneven movement of the card.
3) the wear is small, the working life is long.
4) manufacturing is simple, low cost, easy to install and maintenance.
8. Avoid Hydraulic Shock
In the hydraulic system, the hydraulic oil pressure caused by some kind of reason suddenly rises abruptly at a certain instant, which forms a very big pressure peak. The instantaneous pressure peak of the hydraulic shock is several times higher than that of the normal pressure, which is easy to cause the malfunction of the hydraulic equipment and affect the normal operation. My company in a hydraulic mechanism is a new and improved, due to the oil pressure of the high-pressure oil leads directly to the pressure relay without damping measures, to suppress the end of, causing the pressure relay micro switch repeatedly moves up and down, originally thought is a problem of pressure relay, after the careful analysis, instead of the pressure relay leading to the middle of the high-pressure oil pipeline increased buffer device. Finally, the problem was solved.
The above points are the author’s experience in the design of hydraulic system, for the peer discussion, in order to attract attention in the design. Of course, there will still be a lot of problems in the actual design, which requires high voltage electrical manufacturing industry counterparts to jointly solve the progress, to ensure that the design of the high voltage switch hydraulic system to further improve.