Mechanical characteristic test of high-voltage switch

The mechanical characteristic test of the switch is an important test for the action characteristics of high-voltage switches. The experimental data includes the opening/closing time, opening/closing speed, rigid closing speed, rigid opening speed, three-phase different period time, three-phase action sequence, three-phase bounce time (vacuum switch), opening distance of the fracture, dynamic contact stroke and overtravel of the high-voltage switch.
1、 The relationship between switch contact stroke, opening distance, and overtravel, and how to adjust contact stroke A=fracture opening distance L+overtravel S; among them, contact stroke A is related to the output of the switch mechanism and the crank arm, where the output of the mechanism is fixed and cannot be adjusted. By adjusting the crank arm connecting rod, the contact stroke of the three-phase switch can be adjusted. The break distance L refers to the distance between the moving contact and the stationary contact of the switch in the open state, which can be adjusted by adjusting the length of the output crank arm. It reflects the breaking ability of the switch and can be verified through high-voltage withstand voltage testing; And the overtravel S is the contact distance between the moving and stationary contacts (if it is a vacuum switch, it is the compression amount of the contact pressure spring after the contact between the moving and stationary contacts), which can be adjusted by adjusting the crank arm connecting rod of the switch body and the crank arm screws at various fracture points. It reflects the quality of the contact between the moving and stationary contacts after the switch is closed, and can be verified by conducting a contact resistance test.
The first thing we need to do before conducting various experiments is to measure the opening distance and overtravel to ensure that they meet the technical requirements. If they do not meet the requirements, adjustments must be made.
2、 If the closing and opening power are determined (i.e. the length of the opening and closing spring is constant):
1. The relationship between opening and closing time and opening distance travel
The time from the opening time, that is, the time from the contact of the moving and stationary contacts to their separation, reflects the amount of overtravel (contact stroke), that is, the amount of contact between the moving and stationary contacts. If the opening time is long, the overtravel of the switch (the amount of contact between the moving and stationary contacts or the compression of the contact pressure spring) will be larger, and vice versa, it will be smaller. The closing time refers to the time it takes for the dynamic and static contacts to come into contact from the open state to the moment of initial contact. It reflects the opening distance of the switch. If the closing time is longer, it indicates that the distance between the dynamic and static contacts of the switch in the open state is larger, otherwise it is smaller.
From the above relationship, we can see that the opening time and closing time are two opposite quantities: the longer the closing time, the stronger the breaking ability of the L large switch, and the shorter the opening time, the better the closing of the S small switch, resulting in poor contact and higher contact resistance; If the closing time is short, L will be small, and the breaking ability of the switch will be poor. If the opening time is long, S will be large. After the switch is closed, the contact between the moving and stationary contacts is good, and the contact resistance will be small. If the length of the opening and closing time of phases A, B, and C is reflected on each phase of the switch, that is, the order of opening and closing of the three phases, that is, the phase with shorter closing time closes first, with smaller opening distance and larger overtravel (contact stroke), resulting in longer opening time and later separation; The longer the closing time, the larger the opening distance and the smaller the overtravel (contact stroke), and the shorter the opening time, the earlier the separation. This principle is also a magic weapon for us to adjust the switch for different periods. In principle, the smaller the three-phase different period, the better, that is, the ideal state is to open and close the switch at the same time when the different periods are zero. However, it is difficult to achieve in practice, sometimes even exceeding the standard range by a lot, which requires us to make on-site adjustments.
Summary: According to the above magic weapon, when the opening and closing of the switch are not synchronized, adjust the Z-large and Z-small phases based on the middle value of time to reduce different periods. When the closing is not synchronized and biased, adjust the closing time Z-large phase or Z-small phase (adjust whichever phase deviates greatly from the middle value, adjust which phase or two phases at the same time) to reduce or increase its opening distance, thereby shortening or increasing the time to keep the different periods of the three phases within the standard value range; (Opening is exactly the opposite of closing). Sometimes there is a situation of rebellion, where the closing time is too long (or too short) and the phase opening time is also too long (or too short), which indicates that the mechanism is stuck. Proper lubrication of the transmission part of the mechanism is sufficient.
2. Opening and closing speed
The opening and closing speed of high-voltage switches is crucial. When the opening and closing power (opening and closing spring) is well done, its size is determined by the opening and stroke and time. The key is the speed of just closing and just opening, which directly reflects the closing and opening ability of the switch. If the opening and closing time of the switch is constant, the opening distance and stroke are constant, and the speed can be calculated using the following formula:
V=x/t=Δx/Δt=dx/dt
Where V is speed, x is travel, and t is time
The average speed v of opening and closing is the ratio of the contact stroke (opening distance) to the opening and closing time, and the initial opening and closing speed V (t) is the ratio of the stroke Δ x of the moving and stationary contacts when they are just separated (closed) to the time Δ t.
Summary: As can be seen from the above, the speed of switch action is reflected in time (t), because each distance (x) is fixed. Therefore, as long as the closing and opening time (t) is qualified, the average speed is also qualified. The speed of just closing and just opening is greater than the average closing and opening speed, so the closing and opening speed meets the requirements, and the speed of just closing and opening can also meet the requirements. Acceleration cannot be directly measured and is an indirect quantity. It is obtained by measuring the ratio of Δ x to Δ t. Due to the limitations of on-site test conditions and the different forms of moving contacts of various switches, it is difficult to measure the speed of the switch's opening and closing. Generally, only the opening distance stroke (meeting technical requirements) and the opening and closing time are measured. As long as several quantities meet the requirements, the speed of opening and closing can be tested on site (except in special cases).
3、 When the travel distance, opening distance, and overtravel are constant
Previously, we analyzed the relationship between various distance quantities and time in the switch characteristic test. The prerequisite for our analysis is that the opening and closing power of the switch is constant. Now, we will analyze the relationship between the opening and closing time of the spring mechanism switch and the opening and closing power when the total stroke of the switch moving contact is constant. That is to say, the distances between the switches are within the standard range, and the opening and closing time of the switches can only be achieved by adjusting the closing power, which is very helpful for us to deal with some faults.
1. Opening and closing time and speed
In principle, the shorter the opening time, the faster the opening speed, the better. As the opening speed directly affects the speed of the recovery of the dielectric strength between the contacts after the current crosses zero, if the recovery speed of the dielectric strength between the contacts is less than the recovery voltage after the arc is extinguished, it will cause arc reignition. In order to prevent arc reignition and shorten the arc ignition time, the opening speed must be met. The magnitude of the opening speed mainly depends on the elasticity of the opening spring, which is the length of the spring when the elasticity coefficient is constant. But in reality, this is not the case. The shorter the opening time and the faster the opening speed, the more severe the opening bounce vibration caused, and the more severe the overshoot. This can lead to more severe vibration and compression of the switch tube bellows, which can easily cause premature damage to the bellows and air leakage. The vibration of the gearbox is also greater, which can easily cause damage to components. At the same time, it cannot meet the requirements of closing time and speed. Therefore, it is sufficient to be able to disconnect within the specified time, usually less than 60 milliseconds.
The requirements for the closing time and closing speed of the switch are relatively lower than those for the opening. As long as there is a certain closing time and speed, efforts should be made to minimize the electrical wear and tear caused by pre breakdown of the contacts during the closing process, and to avoid contact welding. Therefore, there is no need to require a too high closing speed, because a too short closing time and a too fast closing speed not only increase the closing power of the operating mechanism, but also increase the closing impact on the switch tube, greatly reducing its service life. Therefore, as long as the requirements are met, smooth closing is generally required to be less than 100 milliseconds.
2. The relationship between opening and closing power
The requirement for closing power is to provide sufficient power to achieve the closing of the switch, and its magnitude should not be less than the sum of the opening power and the closing buffer energy (if it is a vacuum switch, there is also overtravel elasticity; if it is a plug-in joint, there is also contact resistance). The requirement for the opening power is to provide sufficient energy to ensure that the switch can reliably open at a certain speed within the specified time. From the above, it can be seen that the magnitude of the opening power determines the magnitude of the closing power (energy of the energy storage spring), while the opening power is determined by the energy of the opening spring. The opening and closing energy springs are pre installed at the factory, and in our actual work, we can only adjust the closing power by adjusting the length of the energy storage spring, thereby adjusting the closing time and closing energy. Adjust the length of the opening spring to simultaneously change the opening time (speed) and closing time (speed). At the same time, adjusting the length of the energy storage spring and the opening spring ensures smooth closing. Actual case analysis:
（1） After the outdoor 110 kV sulfur hexafluoride switch is closed, the energy of the closing spring cannot be released. The closing cam must be pushed to the closing position by the energy storage motor during the energy storage process. At this time, the spring energy is released, and the switch is closed again in place. After adjusting the closing spring and appropriately relaxing the opening spring, the switch can be closed normally.
（2） A 110 kV coal mine substation has an indoor combination electrical switch. After the switch is closed, there is no position indicator, and the red and green lights, as well as the energy storage indicator light of the switch, do not light up. The energy storage motor has been idling for a while, and the overheating protection has started, causing the energy storage motor to be powered off. After investigation, there was no indication on the switch opening and closing indicator board, and manual tripping was not possible. The switch refused to move. After supplying the energy storage power source, the energy storage motor keeps idling and does not store energy. After inspection, the ratchet wheel of the energy storage mechanism cannot reach the teeth of the transmission wheel, and only half of the transmission wheel has gears. After analysis, it was found that the switch did not have enough closing power, the switch could not be closed in place at once, the closing spring could not be released, and because only half of the transmission wheel had teeth, the ratchet of the energy storage mechanism could not reach the teeth when the switch was not closed in place. This prevented the switch from being closed through the energy storage mechanism, resulting in the switch refusing to move (unable to close or trip) after being closed halfway, and the energy storage motor idling. After tightening the length control screw of the closing spring and adding a gasket to the opening spring, the switch action was normal.
（3） Within a few seconds after closing the switch on the 10 kV column, a "clack" sound was heard again. The reason for this was that the closing power was not sufficient after closing, and the energy storage spring could not be released after closing. The switch could not be closed in place at once. During the energy storage process, the energy storage motor pushed the closing cam to the closing position, and then the sound of the energy storage spring being released was heard again, which was the normal energy storage of the switch.
The above three cases are typical cases where the switch cannot be closed at once due to insufficient closing power, and can only be closed twice through energy storage of the energy storage motor. We only need to stretch the closing spring or replace it with a new one to achieve one-time closing. The above-mentioned faults may cause minor damage to the closing coil, and if the energy storage gear is a half toothed disc (only a part of the energy storage gear has teeth), it may cause damage to the energy storage motor. In severe cases, if the switch is closed with a large load, the contact resistance is high due to improper closing, and the contact instantly heats up, causing severe contact burning or gas thermal expansion, leading to switch explosion. If a fault is encountered during the closing process (closing at the fault point), it may cause the switch to refuse to move, resulting in a leapfrog trip and expanding the scope of the accident, and other serious consequences.
Summary: When installing, debugging, and conducting mechanical characteristic tests, as long as the opening and closing times are within the specified range, we do not adjust the mechanism and do not compare the relationship between the opening and closing times. Although the opening and closing actions of the switch were flexible during the new installation and debugging, the above phenomenon appeared after a period of operation. Therefore, when conducting mechanical characteristic tests, we should pay attention to the analysis of the opening and closing time data. If the requirements are met, the opening time should not be too short, and the closing time should not be too long. Based on my years of summary and analysis, the closing time is approximately 1.5 to 2 times the opening time. This proportional relationship is reasonable and reliable. If it exceeds this range, the length of the opening and closing spring should be adjusted appropriately. Because the opening time is too short and the closing time is too long, it indicates that the spring force of the opening spring is large, the effective closing power is small, and the closing time is longer. After the equipment is running, the opening and closing springs are always in a stretched state. In addition, some factors in the selection of switch energy storage springs cause premature fatigue of the springs, resulting in insufficient spring force and insufficient closing power. This leads to insufficient closing power, causing the switch to not be reliably closed in place at once, resulting in accidents such as component damage, mechanism refusal to move, or equipment explosion.