Discussion on the operation mode of the hottest ru

2022-08-04
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Discussion on the operation mode of rural distribution transformer

according to the technical regulations of rural low-voltage power, modern consumption gives birth to the concept of future automobile. The operation mode of rural low-voltage power distribution transformer includes IT system, in-c system and TT system. It system refers to the low-voltage power of distribution transformer with special requirements for safety in rural areas or for drainage and irrigation, and should adopt the protective grounding mode of ungrounded neutral point and exposed conductive parts of electrical equipment; In-c system refers to the low-voltage power of distribution transformers in rural cities and towns, industrial and mining enterprises, and adopts the neutral point direct grounding, and the exposed conductive parts of electrical equipment are connected to zero; TT system refers to the low-voltage power of distribution transformers for rural residents and other power consumption, which should be grounded directly at the neutral point. The exposed conductive parts of electrical equipment should be grounded for protection, and TT system should be installed with leakage protector

1 advantages and disadvantages of the three operation modes

the part of the plant system is adopted, because its low-voltage power range is small, the insulation is easy to be guaranteed, and the power supply security, power supply reliability and economy are relatively good. For the part using TN-C system, the power supply reliability is relatively poor. Due to the leakage of exposed conductive parts of any electrical equipment, the current shall be cut off by overcurrent protection. If the level is exceeded, a large range of power failure will be caused. The electric leakage of the exposed conductive part of the electrical equipment at the end of the line may cause electric shock due to the large impedance of the line conductor and the failure of the overcurrent protection, resulting in the risk of personal contact with the exposed conductive part of the electrified electrical equipment, as well as the risk of personal direct contact with the electrified part. In order to solve this problem, some users of this operation mode have changed the neutral connection mode and installed terminal leakage circuit breakers. In terms of safety, the TT system and the installation of leakage protection are very superior to avoid electric shock. However, its investment phase makes the plan more in line with the actual situation of the industry. The reliability of power supply is very poor, especially the general leakage protection. Once the wind blows, the general leakage protection trips, resulting in power failure of a large number of users, affecting the continuous power supply and production. A large number of statistical analysis shows that more than 999 of the 1000 trips of the total leakage protection action are caused by leakage of various reasons. What's more, the contradiction between individual rural residents and their neighbors is also caused by the tripping and power failure of the general leakage protector caused by single-phase grounding. With the improvement of rural power consumption level, farmers' production and life are more dependent on electricity. Therefore, the consequences and impact of tripping and power failure of the general leakage protection will be greater and greater. For low-voltage power of rural distribution voltage devices, the TT system is used to install leakage protector. In particular, the general leakage protection is required. This is a targeted measure taken due to the poor health of rural low-voltage power equipment and the large range of low-voltage power phase line and zero line insulation to the ground, resulting in many rural energy fatalities. After adopting this measure, the number of casualties caused by electric shock in rural areas has been greatly reduced. At present, in rural areas where leakage protection has been installed, most of the deaths caused by electric shock are caused by the damage of leakage protector or artificial withdrawal, except for two-phase electric shock and phase zero line electric shock, which cannot be protected by leakage protection. To sum up, there is a great contradiction between power safety and power supply reliability under this operation mode. Therefore, it should be our common wish to find a scheme that can ensure both power safety and power supply reliability with small investment

2 it is suggested to change TT system into it system

the author believes that the rural construction and transformation have created conditions for finding this scheme: first, the reconstructed rural low-voltage lines have all met the standard requirements in terms of safety technical indicators, and the stay wires of low-voltage lines are equipped with stay wire insulators, so the possibility of electric shock casualties in the low-voltage lines is only multiplied by the possibility of line breaking and landing, For qualified lines, the probability of disconnection is very small. The problem of electric shock injury caused by hooking up power on low-voltage lines belongs to illegal power use (stealing), which should not and should not be allowed; Second, if the users of low-voltage power and single machines (temporary power use, mobile irrigation and drainage, threshing, etc.) are equipped with household leakage circuit breakers or terminal leakage circuit breakers, the places where people touch electrical appliances within the range of low-voltage users and may cause electric shock injury will be protected by terminal leakage circuit breakers. If the above two conditions are met after the rural reconstruction, it can be said that the rural low-voltage power is not equipped with general leakage protection, and the problem of preventing electric shock injury has also been preliminarily solved. If in the low-voltage power with the above conditions, the neutral point at the low-voltage side of the distribution transformer is directly grounded instead of grounded, that is, it system, then the above-mentioned risk of low-voltage line breaking to the ground will be less, that is, even if people touch the low-voltage line breaking to the ground, the current passing through the human body is generally only capacitive current. However, within the scope of end concentrated electrical protection, in case of personal direct contact with phase line or electric equipment with leakage, the exposed conductive part of all aspects of service equipment shall be fully prepared, the situation is similar, and the current passing through the human body is generally only capacitive current. If the current is greater than the action current of the terminal leakage protector, the leakage protector will trip normally to avoid accidental strike. If the current is less than the action current of the terminal leakage protector, the leakage protector will not act, and the current will do little harm to people, which is similar to the direct grounding mode of the low-voltage neutral point of the distribution transformer. If considering the long-term operation of low-voltage power, the insulation of a phase line or zero line to the ground may be reduced, which is the main reason why low-voltage power cannot be changed into an IT system. If the AC impedance of a phase line or zero line to the ground drops below 10K Ω, at this time, if a person touches another phase line or breaks on the ground, he may be injured by electric shock between phase lines and zero lines or between phase lines and phase lines. However, in the low-voltage power with perfect terminal leakage protection, electric shock within the scope of leakage protection can still be protected. The main danger is in the low-voltage line. In order to solve this problem, the author believes that a device for measuring the AC impedance of the phase line and the zero line to the ground can be installed at the low-voltage side of each distribution transformer for regular measurement. Compared with the installation of the general leakage protection, the general leakage protection acts to cut off power and check the fault point. This method is to find the fault point under the power transmission state, which is relatively simple

3 capacitive current when a person touches one phase

after the neutral point at the low-voltage side of the distribution transformer is changed to ungrounded, if the phase line and zero line are well insulated to the ground, how much capacitive current will the person touch one phase. According to relevant information, the ground capacitance of low-voltage line per kilometer is about 0.005 μ F. Current power distribution after rural reconstruction

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