System neutral grounding refers to the intentional connection of the neutral point of a power system to the earth or ground. The neutral point is the common reference point in a three-phase electrical system.
There are three main types of system neutral grounding:
- Solid or Solidly Grounded System: In this type of grounding, the neutral point of the power system is directly connected to the earth with a low impedance connection. The grounding impedance is typically very low, allowing high fault currents to flow during a fault condition. This type of grounding provides effective fault current path and is commonly used in low-voltage systems.
- Resistance Grounding: Resistance grounding involves connecting a resistor between the neutral point and the ground. The resistor limits the fault current magnitude, typically to a relatively low value, while still allowing detection of the fault and protection coordination. The resistor provides some level of fault current limiting and is commonly used in medium-voltage systems. It helps reduce the damage caused by fault currents and allows for selective tripping of protective devices.
- Reactance Grounding: Reactance grounding, also known as impedance grounding, involves connecting an inductor or reactor between the neutral point and the ground. The reactor limits the fault current and provides a level of impedance to the fault current path. This type of grounding is mainly used in high-voltage systems and provides a compromise between solid grounding and resistance grounding.
The choice of system neutral grounding depends on various factors, including the system voltage level, fault current magnitude, equipment sensitivity, safety requirements, and the specific application. Each type of grounding has its benefits and considerations, and the selection should be based on a thorough analysis of the electrical system and its requirements.
The neutral grounding method affects the system’s behavior during fault conditions, including the magnitude of fault currents, voltage stability, protection coordination, and safety considerations. Therefore, it is essential to consult with electrical engineers and adhere to relevant standards and regulations when designing and implementing the system neutral grounding scheme.