Requirements for grounding resistance of electrical devices
Abstract: requirements for grounding resistance of electrical devices, power equipment with non directly grounded neutral point of high-voltage power equipment, grounding resistance of its grounding device, low-voltage power equipment, etc.
key words: requirements for grounding resistance of electrical devices Untitled Document 3.1 grounding resistance of its grounding device for power equipment with non directly grounded neutral point of high-voltage power equipment, It shall meet the requirements of the following formula: a) the grounding device shared by high-voltage and low-voltage power equipment R ≤ 120/I, where R - the maximum grounding resistance considering seasonal changes, Ω; I - ground fault current for calculation, a. The grounding resistance shall not be greater than 4 Ω. When the total capacity of power equipment such as transformers operating in parallel does not exceed 100kVA, the grounding resistance should not exceed 10 Ω. b) The grounding device only used for high-voltage power equipment, R ≤ 250/i, and the grounding resistance should not exceed 10 Ω. In the power whose neutral point is grounded through the arc suppression coil, the value of grounding fault current is taken according to the following provisions: for the grounding device of the substation or power equipment equipped with arc suppression coil, the calculated current is equal to 1.25 times the sum of the rated current of each arc suppression coil of the same power connected to the same grounding device. For the grounding device of substation or power equipment without arc suppression coil, the calculated current is equal to the maximum possible residual current value when the power interrupts the largest arc suppression coil, but it shall not be less than 30A. The method is as follows: 3.2 low voltage power equipment the grounding resistance of the grounding device of low voltage power equipment shall not exceed 4 Ω. When the total capacity of generators, transformers and other power equipment operating in parallel with the same grounding device does not exceed 100kVA, the grounding resistance should not be greater than 10 Ω. Terminals of main and branch lines of overhead lines and every 1km along the line; At the entrance of cables and overhead lines to buildings, pen lines shall be repeatedly grounded (except those not more than 50m away from the grounding point). The grounding resistance of repeated grounding shall not be greater than 10 Ω. In the power where the grounding resistance of the grounding device of power equipment is allowed to reach 10 Ω, the grounding resistance of each repeated grounding device shall not exceed 30 Ω, but the repeated grounding shall not be less than three places. (1) All exposed conductive parts of TT system protected by the same protector shall be connected to the common grounding electrode of these parts together with its protective conductor. When several protective appliances are used in series, the above requirements apply to all exposed conductive parts protected by each protector. The following conditions shall be met: RA × IA ≤ 50V, where ra - sum of resistance of protective conductor and grounding electrode of exposed conductive part, Ω; IA - current for automatic action of protective appliance, a. A foreign investment transaction of 394billion yuan has been announced but not completed. When the protective appliance is a residual current protector, IA is the rated residual operating current I △ n. for the purpose of selectivity, the S-type residual current protector can be used in series with the ordinary residual current protector. In order to obtain the selectivity of S-type residual current protector, the operation time of residual current protector is allowed to not exceed 1s in the distribution circuit. When the protective appliance is an overcurrent protective appliance, it should take one of the following two: for the appliance with inverse time limit characteristics, IA should be the current that ensures automatic action within 5S, a, or the appliance with instantaneous characteristics, IA should be the minimum current that ensures instantaneous action, a. (2) It system in it system, the device should be insulated from the ground or grounded through a large enough impedance. The grounding point is either the neutral point of the system or an artificial neutral point. If the zero sequence impedance is high enough, the artificial neutral point can be directly grounded. When there is no neutral point, a phase conductor can be grounded through an impedance. Therefore, when a single fault occurs to the exposed conductive part or to the ground, the fault current is small, and it is not necessary to cut off the electricity. 1. It is not necessary to cut off the crystalline material source. However, measures should be taken to avoid harmful pathophysiological effects when the human body touches different conductive parts at the same time when there are two faults at the same time. Exposed conductive parts shall be grounded separately, in groups or collectively. The following conditions shall be met: RA × ID ≤ 50V, where ra - grounding electrode resistance of exposed conductive part, Ω; ID - fault current when the first fault with negligible impedance occurs between the phase conductor and the exposed conductive part, a. The value of ID takes into account the influence of leakage electricity on the continuous development of new product flow and the total grounding impedance of the device
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