Views:174 Author:Site Editor Publish Time: 2020-11-03 Origin:Site
Generally, the power system operates under balanced conditions, all devices carry normal load current, and the bus voltage is also within the specified limits. If the system fails, the line fault indicator will work. If the electrical fault current exceeds the interruption rating of the protection device, the consequences can be catastrophic. It may pose a serious threat to human life, and may cause personal injury and extensive equipment damage.
1). Convert the system to a reference value: Convert the system to a unit system based on the same reference value.
2). Failure type: Determine the type of failure to be analyzed, such as the short circuit to ground, the short to voltage, the electrical outlet short circuit, etc.
3). Construct a sequence network: The system converted from step 1 draws a sequence network for each positive and negative sequence and zero sequence network.
4). Make a fault sequence network diagram: Take a fault-free sequence network, and modify and interconnect according to the types of electrical shorts to generate a fault sequence network diagram.
5). Manual calculation: Manually calculate the sequence current and voltage in the case of a fault.
6). Convert per-unit value to three-phase current and voltage: Convert the per unit value we calculated in step 5 into three-phase current and voltage that can be actually used and intuitively understood.
7) Calculation of faults on the low-voltage side of the transformer: Calculate the faults that occur on the low-voltage side of the transformer.
1). Weather conditions
Weather factors that usually cause overhead power distribution system failures include lightning strikes, snow on transmission lines, heavy rain, high-speed winds, earthquakes, salt pollution on overhead lines and conductors, floods and fires near electrical equipment, etc. Environmental conditions can cause the short circuit and earth fault, interrupt power and damage electrical equipment.
2). Equipment failure
Electrical equipment such as machines, motors, generators, transformers, cables, reactors, and switchgear can cause electrical failures including short circuit and overloading. These failures may be caused by malfunctions, aging and degradation, insulation failures of cables and windings, and failures caused by high switching. These faults can cause a large current to flow through the device or equipment, thereby further damaging it.
3). Human error
Electrical failures are also caused by human error, such as selecting incorrect equipment or equipment level, forgetting metal or conductive components once coupling or maintenance is performed, and switching circuits under maintenance below its level. The classic example is where maintenance personnel inadvertently isolate. After the maintenance work is completed, the instrument is connected through a safety ground clamp. When the device is re-energized to resume use, a ground short circuit fault occurs.
4). Fire smoke
The fire smoke under the overhead electric line is composed of fine particles, causing sparks between the lines or between the conductors of the insulator. This arc will cause the insulator to lose its insulation due to high voltage. Hot air in a flame has a much lower insulation strength than air at close to temperature.
At Chaobo, our goal is to interrupt the fault current as soon as possible by achieving good coordination between protection equipment and precise trip settings to minimize interference to upstream equipment.