1. Single-phase grounding creates overvoltage
Generally, the grid and equipment operation management should be strengthened to reduce the occurrence of ground faults. The transformer should be inspected and maintained frequently to keep it in a healthy state. Preventive tests should also be carried out regularly to avoid single-phase grounding failure due to insulation breakdown. The power supply line should pay attention to improve the quality of erection, reasonably select the conductor section and the span, and the trees under the corridor should be cut down regularly so that the line channel meets the technical specifications. It is strictly forbidden to build houses, plant trees, and quarry stones near the lines to prevent grounding faults from breaking the lines.
2. Overloading of load
A shunt reactor can usually be used, and the no-load line is cast and cut according to a certain procedure to limit the overvoltage generated by the long line capacitance effect. A fast demagnetization system is employed on the motor side to limit generator rotor acceleration and armature response.
3. Resonance forms overvoltage
The duration of the resonant overvoltage is related to the characteristics of the loop itself. Therefore, the resonance operation that may be caused by the specific grid should be avoided as much as possible, or measures should be taken to destroy the resonance conditions, such as using a harmonic elimination device. For the resonance caused by the electromagnetic voltage transformer, a small resistor can be connected to the secondary opening triangle to destroy the resonance; or a voltage of 15kV, 50w or so can be grounded in the high voltage neutral point of the voltage transformer to limit the flow. The current of the point of the point avoids the ferromagnetic resonance of the voltage transformer due to magnetic saturation.
4. Intermittent arc forming overvoltage
The arc suppression coil is usually grounded at the neutral point of the grid. The inductance of the arc suppression coil is used to compensate the capacitance current flowing through the grounding point, so that the existence time of the arc is shortened, and the number of reignitions is reduced, thereby suppressing the overvoltage of the high amplitude.
5. Switching overvoltage generated by small inductive load
This type of overvoltage is generated based on the interception of the circuit breaker. Because of its small energy, it is usually suppressed by a lightning arrester.
6. Breaking overvoltage generated by capacitive load
Such overvoltage is generated on the basis of re-ignition of the circuit breaker by limiting the rise of the fracture recovery voltage to reduce the re-ignition path, thereby suppressing the generation of such overvoltage. The measures are: parallel resistance in the circuit breaker breaking device, can play a damping role, or use a vacuum circuit breaker that does not generate arc re-ignition. In addition, frequent switching operations should be minimized during capacitor operation.
7. Overvoltage generated by the operation of the no-load long line
It is usually used with a closing resistor circuit breaker, or a special device to judge when the voltage across the circuit breaker is the lowest, or to try to eliminate and weaken the residual voltage of the line.
In addition, transformers or lines running in the power grid are equipped with metal oxide surge arresters for protection (even if they are not out of operation during the off-peak season), which can limit the line overvoltage and eliminate the overvoltage caused by transformer and line no-load switching. The drop fuses that control the branch should be changed to three-phase linked on-column oil-less circuit breakers to avoid non-full-phase operation.
Test items
The performance indicators are tested using a dedicated Ethernet test instrument, and the test results of these performance indicators can also evaluate whether the LAN system meets the acceptance requirements. From GBT21671-2008 "Ethernet-based LAN System Acceptance Evaluation Specification", it can be understood that LAN can also judge performance by measuring performance indicators such as network throughput, transmission delay, and packet loss rate. The Ethernet tester is a rugged test platform suitable for field use. It has a complete Ethernet test function, dual optical ports and dual electrical ports, Ethernet service interface module, HST-3000 supports multiple data stream tests. Including 10/100/1000M Ethernet link traffic generation and troubleshooting, it can test electrical and optical port links up to 1Gbit/s. Due to the limitation of various conditions in the acceptance inspection, point-to-point or routing network testing can be supported for routine testing of switches.
The problem
The overall characteristics of modern test instruments are high reliability, high performance and high applicability. Therefore, the gap between domestic test products and foreign products is reflected in this aspect. Although some domestic testing equipment is close to the international advanced level in certain performance indicators, there are generally few products with comprehensive equipment performance indicators that meet international standards. In addition, most of the domestic test instruments are common specifications, which cannot meet the test work in some special environments. Low-level automated testing is also a common problem. [3]
Switch test technology
Nowadays, switches put forward new requirements on the performance of switches based on application requirements. There have been new developments in comprehensive network services, security, and intelligence. Protocol testing is a basic switch testing technology. The network protocol is to improve the efficiency of testing and the effectiveness of communication to ensure the rules of communication. In the era of increasing network communication, network protocols are also indispensable. The basic requirements of network protocols are correct functions, good interoperability and superior performance. The initial prototype of protocol testing is software testing, and the main categories are black box testing, white box testing and gray box testing.
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