The neutral point grounding method in a power system is a critical technical decision that affects safety, power supply reliability, equipment protection, communication interference, and overvoltage control. It also has significant economic implications, including infrastructure investment and operational costs. Choosing the right grounding method involves both technical and economic considerations.
In systems where the neutral point is not grounded or where an arc-suppression coil is used, there are several advantages: high power supply continuity, better safety for personnel and equipment, minimal communication interference, and lower initial investment. These methods are typically more suitable for smaller systems with low single-phase capacitive current (within regulatory limits), simple network structures, and stable operating conditions. However, it's important to note that as the power grid expands, the capacitive current may increase. Therefore, regular measurements should be conducted, and if the current exceeds allowable levels, the grounding method should be adjusted accordingly.
When a resistor is used to ground the neutral point, one of the main benefits is reduced overvoltage, which allows for lower insulation levels in cables, thereby saving on infrastructure costs. This method is particularly effective in cable-based distribution networks, where transient faults are less common. However, in overhead line systems, where most single-phase faults are temporary, this method can lead to unnecessary tripping, increasing operational disruptions. For such systems, a resistor grounding approach may not be the best choice unless the fault current is limited to below 1000A and the capacitive current reaches at least 150A.
From a safety perspective, resonant grounding—using an automatic tracking compensated arc suppression coil—is considered superior. It effectively limits the impact of single-phase ground faults and is increasingly becoming the preferred method in modern power systems. This technique works well in both overhead and cable-based networks, as well as hybrid systems. For example, in Berlin, even with a fault current reaching up to 4000A, resonant grounding is still employed. The use of thyristor-controlled, automatic tracking compensation arc suppression coils, which combine controllable reactors and power electronics, is gaining popularity due to their enhanced performance and adaptability.
In the Hai'an Power Grid, the neutral points of 10kV and 35kV systems are primarily ungrounded. Only a few substations in the southern suburbs and the 35kV system have traditional arc suppression coils, but these are rarely used now due to low capacitive currents and difficulties in adjustment. Recently, the new city 10kV system has adopted automatic tracking compensation arc suppression coils, and plans are underway to implement similar technology in the southern suburbs to improve system reliability and safety.
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