Each time the closing operation is performed, the closing spring stores the opening spring for the next opening (this is the advantage of the spring mechanism opening). Energy distribution For the circuit breaker, the opening operation is very important. The spring energy is mainly reflected in the lifting, compression and loss of the spring. During arcing, the pull-up energy is as large as possible and remains stable. For example, when a 145kV three-phase asymmetric current of 40kA is broken, the energy required for pulling up is 1/3 of the total energy. At the end of the opening, part of the pulling energy is used to overcome the gas resistance, and part of Loss in system friction. In the same example, for a compressed gas circuit breaker, 2/3 of the total energy is used to overcome the gas resistance during the opening operation.
In a modern design known as a self-extinguishing arc-break circuit breaker, the total energy of the trip is derived in part from the expansion of the gas due to arcing. The self-energy size varies depending on the amount of breaking current. This means that a flexible design must be used to meet the speed requirements during arcing.
Performance, Limitations, and Possible Improvements Currently, spring mechanisms are used in applications ranging from a few hundred joules to more than 10,000. The entire field covers a voltage range of 550 to 800 kV. At present, although it has been considered to be low in consumption and highly reliable. However, many manufacturers are still making further improvements in the areas of low cost and high reliability.
There are several drawbacks in the existing design: (1) Tension-related defects: The spring mechanism includes several moving parts related to the entire kinetic energy. Most parts of the mechanism must transmit large torques and pressures. This means that these components must be of high quality and also have high inertia defects. For small circuit breakers, a certain range of inertia contributes to the stability of the system from transient to static process transitions. However, when applied in a high-pressure system, it is very important to reduce the inertia of the motion system. (eg from 72kV to 800kV) Due to the large mass of moving parts in the circuit breaker, the powerful spring can provide 12000J of energy and the internal system's kinetic energy is also very high.
(2) Defects related to arc thermal effect: In the self-extinguishing circuit breaker, the responsibility of the circuit breaker is the large current fault caused by the breaking line and the small capacitive current caused by the breaking of the no-load line. The thermal effects in the case are quite different. The solution to the current problems is to use an operating mechanism with self-adjusting function. The advantage of this operating mechanism is that it can adjust the transmission of the required energy according to the different requirements of the type of breaking fault.
The technology shows a 145kV/40kA porcelain column breaker system. The key component is a hybrid drive mechanism that has been given. This system will be discussed below. Test device diagram for hybrid drive (1) Energy storage unit This is a key part of the system. The energy stored in the capacitor bank must meet the operational requirements for completing an O-C-O. The reason for choosing this mechanism is that the capacitor bank has high reliability under the conditions of a high voltage substation. Switching equipment is usually required to operate normally without an auxiliary power supply and to store for a long time at a storage temperature of -50 ° C to 55 ° C. Since electrolytic capacitors cannot withstand such storage conditions, a high failure rate will result during service. Therefore, electrolytic capacitors cannot be used in such systems.
Due to the high insulation capacity of the film capacitor, the rated DC voltage of the high-energy capacitor can exceed 1kV. The energy stored in the capacitor is proportional to the square of the rated voltage of the capacitor. The capacity of the capacitor bank and the cost of the capacitor bank should be optimized at the same time as the operating voltage should be as high as possible. A disadvantage of IGBT electronics is that the price is more expensive as the voltage level increases.
Another disadvantage of the motor is that during the sequential operation of the O-C-O, the last trip operation should enable the motor to run at full speed, but the residual voltage across the capacitor may not meet this requirement.
The residual voltage across the capacitor cannot meet the voltage requirements for full motor operation after the first trip operation. The voltage Vmotor required for full motor operation, the initial voltage across the capacitor Vbank, the total energy required for the O-C-O operating cycle, and the required minimum capacity Cbank can be expressed by the following equation: motorbankocobankVWC22=Assumption :Vbank=800V, Vmotor=450V, get: μF/Joule57. 4=ocobankWC The above formula shows that the choice of components and the determination of their ratings should be treated as if the system cost and reliability are valued. The energy storage unit stores energy in the capacitor bank. Therefore, the energy storage unit is related to the discharge system.
(2) Motor motor is also an important component. When selecting, the key is to choose a motor with low inertia, high speed, high torque and precise control over a wide speed range. In practice, few motors can meet this requirement. The low inertia and high torque performance can be achieved by designing two opposing rotors, which is equivalent to two motor systems. One is a small radius, the rotor is long, the other is a large radius and the rotor is short. The brushless motor belongs to the first case. The rotor size is made smaller by the method of embedding the permanent magnet. It is obvious that the longer the rotor, the greater the torque. The stator is caused to generate a rotating magnetic field by dedicated electronic equipment.
Flat rotor motors are of the second type. The rotor coil is very flat. A large radius is used to obtain a large torque. This design optimizes the coupling of both the rotor coil and the stator magnet. This type of motor is a conventional type of shunt motor and has its unique advantages when used as a servo motor. In addition, due to the low internal inductance of the rotor, it is possible to have a low time constant that makes fast control a reality.
(3) Energy unit The function of the energy unit is to transfer the DC voltage and DC current required by the motor. The capacitor bank is the provider of the DC voltage required for the power unit.
Performance A comprehensive test was conducted in the laboratory in order to compare the differences between the behavior predicted by the simulation and the results obtained by the measurement-related system. The simulation result is a mathematical model that can describe the system very accurately. We can rely on estimating the sub-parameters in the system instead of using direct measurements to get the system sub-parameters.
The overall performance of the hybrid drive mechanism can be described as shown. The figure shows the speed characteristics of the circuit breaker obtained in three different situations and the stroke characteristics of the moving contact of the circuit breaker. These characteristic curves differ from one another due to the different delays from the closing position of the closing position (measuring the opening delay by software).
The horizontal curve shows the breaking of the main contact, and its maximum speed value is basically independent of the parameter dispersion. This means that the required contact speed during the arcing time is always sufficient. Therefore, the system can output the required torque within a prescribed time.
Additional test tests have shown that this operating mechanism compensates for variations in the parameters injected in the circuit breaker system while maintaining a constant stroke characteristic. It is assumed that these variables already include all possible deviation factors, whether it is machining errors or initial arc energy due to different currents or other factors.
Conclusion The hybrid drive mechanism can be used in tank circuit breakers, porcelain column circuit breakers and circuit breakers in GIS switchgear with a wide voltage range. When the switch button is activated, the smooth operation of the operating mechanism can reduce the pressure applied to the mechanism itself and the circuit breaker. The hybrid drive mechanism can improve the technical performance of the circuit breaker, especially when the mechanism action time is dispersed, the system can automatically adjust the appropriate stroke curve is very meaningful. At the same time, this technique will cause a significant advancement in circuit breaker breaking technology if the stroke curve is brought to the same characteristic curve as the initial current energy by electronic adjustment.
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