Analysis and selection of neutral grounding mode i

Analysis and selection of distribution neutral point grounding mode

the neutral point grounding mode of power system is a comprehensive technical subject involving many aspects of power system. It not only involves the safety and reliability of electricity itself, the selection of overvoltage insulation level, but also has an important impact on communication interference and personal safety

2 comparison of different grounding methods of neutral point

(1) the jaws of the power distribution experimental machine with ungrounded neutral point include mutual encouragement and support of internal system hardware. The R & D institutions and graphene production and utilization enterprises jointly undertake R & D projects and scientific and technological achievement transformation projects. The neutral point ungrounded mode, that is, the neutral point is insulated from the ground, has simple structure, convenient operation, does not need any additional equipment, saves investment, and is suitable for the long radial or tree shaped power supply network of rural 10KV overhead lines. In the operation of this grounding method, if a single-phase grounding fault occurs, the current flowing through the fault point is only the capacitive current of electricity to ground, and its value is very small. It is necessary to install an insulation monitoring device, so that the single-phase grounding fault can be found in time and handled quickly, so as to avoid the fault developing into a two-phase short circuit, resulting in a power failure

when a single-phase grounding fault occurs in a neutral ungrounded system, its grounding current is very small. If it is a transient fault, it can generally automatically extinguish the arc, and the voltage rise of the non fault phase is not large, which will not damage the symmetry of the system. It can continuously supply power with faults for 2h, so as to obtain the troubleshooting time, and relatively improve the reliability of power supply

(2) the neutral point is grounded through the traditional arc suppression coil. The neutral point is grounded through the arc suppression coil, that is, an inductive arc suppression coil is connected between the neutral point and the earth. When a single-phase grounding fault occurs in the system, the inductive current of the arc suppression coil is used to compensate the grounding capacitive current, so that the current flowing through the grounding point can be reduced to the range of self arc extinguishing. Its characteristic is that when the line is single-phase grounded, Inspect the surface of the plate according to the regulations, and wrinkles and floating bulges begin to appear. It is specified that the electricity can operate for 2h with single-phase grounding fault. For medium voltage power, due to the compensation of grounding current, single-phase grounding fault does not develop into phase to phase fault. Therefore, the power supply reliability of neutral grounding through arc suppression coil is much higher than that of neutral grounding through small resistance

(3) the neutral point is grounded through resistance. The neutral point is grounded through resistance, that is, a certain resistance is connected between the neutral point and the earth. The resistance and the system capacitance to the ground form a parallel circuit. Because the resistance is an energy consuming element, it is also a capacitive charge release element and a resonant voltage resistive element, which has certain advantages in preventing resonant overvoltage and intermittent arc grounding overvoltage. In the neutral point resistance grounding mode, the resistance value of the resistance is generally selected to be small. When the system is single-phase grounded, the current flowing through the grounding point is controlled at about 500A, and some are controlled at about 100A. The zero sequence protection action is started by the current flowing through the grounding point to cut off the fault line

3 automatic tracking and compensation arc suppression coil

automatic tracking and compensation arc suppression coil can be roughly divided into turn adjustment type, air gap adjustment type, capacitance adjustment type, DC bias adjustment type, thyristor adjustment type, etc. according to the different methods of changing inductance

(1) turn adjustable automatic tracking compensation arc suppression coil. The turn adjustable arc suppression coil is to extract the tap from the winding according to different turns, and switch with the on load tap changer to change the number of turns connected, so as to change the inductance. Due to the slow adjustment speed, the turn adjustment type can only work in the pre tuning mode. In order to ensure that there are more agreements in transportation, logistics, ports, customs clearance and other aspects than at the same time, the small residual current must be operated near the resonance point

(2) adjustable air gap automatic tracking compensation arc suppression coil. The air gap inductor divides the iron core into upper and lower parts, the lower part of the iron core is fixed on the frame with the coil, and the upper part of the iron core is used as a motor to change the reactance value by adjusting the size of the air gap. It can automatically track, stepless and continuously adjustable, safe and reliable. Its disadvantage is that the vibration and noise are relatively large, and measures should be taken to control the noise in the structural design. This kind of device can also share the grounding transformer and adjustable inductance, making the structure more compact