Jiangsu Starlight Electricity Equipments Co.,Ltd. Guide: When the unit system has a ground fault, because the capacitive current is 90 ° ahead of the voltage, when the capacitive current at the fault point crosses zero and extinguishes the arc at the first half wave, the voltage applied to the fault point is just the peak value. If the capacitive current is too large and the air is free seriously, it is very easy to re break down the fault point. This re ignition is sometimes unavoidable.
However, repeated reburning will lead to grid voltage oscillation and intermittent arc over-voltage. This overvoltage is characterized by long time, high amplitude, large energy and lack of effective means for protection. Under the action of such overvoltage for a long time, the arrester will accelerate aging and even damage. Therefore, measures should be taken to avoid the occurrence of such overvoltage, and resistance grounding protection should be provided for diesel generator set. Let's follow Jiangsu Starlight Electricity Equipments Co.,Ltd. to learn about three different resistance grounding methods.
The resistance range of resistance grounding mode is divided as follows:
High resistance: ＞ 500 Ω, ground fault current ＜ 10~15A;
Medium resistance: 10 ～ 500 Ω, 15A ＜ ground fault current ＜ 600A;
Low resistance: ＜ 10 Ω, ground fault current ＞ 600A.
1. High resistance grounding.
High resistance grounding is generally used for generator circuits with single-phase grounding fault requiring an instantaneous shutdown of 125MW or above. The purpose of high resistance grounding is mainly to avoid intermittent arc grounding overvoltage when the generator stator winding is in single-phase grounding fault, and to reduce the burn degree of grounding fault current on the iron core as far as possible.
2. Medium resistance grounding.
Medium resistance grounding is mainly used for the power grid mainly composed of cables, including urban power grid, power plant, industrial and mining enterprises and public facilities distribution network. The external insulation of the cable is solid, and the wire core is in direct contact with the atmosphere, so the probability of single-phase grounding fault is greatly reduced. In addition, once the fault occurs, the insulation performance cannot be recovered automatically, so the fault should be quickly removed. Before fault removal, it is required that no intermittent arc over-voltage occurs. The condition is that the resistive current at the fault point shall not be less than the capacitive current of the power grid, which is the main basis for selecting the resistance value. On this premise, it is hoped that the resistance value is not too large to ensure the sensitivity of relay protection. It is also hoped that the resistance value will not be too small to avoid excessive grounding fault current and some problems in low value grounding mode.
3. Low resistance grounding.
Low resistance grounding is only used to connect the power grid with a large number of high-voltage motors. Because the single-phase grounding current is too large, the following problems will occur:
(1) Easy bypass and others.
(2) It endangers the safety of personnel and equipment.
(3) Resistors have large volume, many consumables and high price.
(4) Misoperation of differential protection of main transformer may be caused.
Therefore, the use of low resistance grounding shall be limited.
Jiangsu Starlight Electricity Equipments Co.,Ltd. is one of the earliest manufacturers of generating sets in China. It has first-class testing equipment, advanced production technology, professional manufacturing technology, perfect quality management system, and strong R&D technical strength. It can provide 3KW-2500KW various specifications of universal, automatic, four protection, automatic switching, low noise and mobile, etc., high-quality, low-energy generating sets to meet all customers' power needs, and can also meet users' different voltages and different Frequency requirements, as well as the parallel-connected power supply system of multiple units, use excellent talents to build excellent enterprises, create excellent products, create excellent services, and strive to build excellent domestic enterprises. For more product details, please contact us with firstname.lastname@example.org.