The importance of grounding in the DC-distribution network with its types is also discussed in a deep sense. Furthermore, the protection systems implemented for AC microgrid, high voltage DC-transmission, DC microgrid are also compared, and it is impartial to declare that protection of DCMGs is still regarded as an open issue for future studies.
It should be noted that none of the grounding schemes provides the FRT capability under LL faults. The paper presents a comprehensive review on the topic of DC grounding systems. The existing grounding strategies for DC-systems are comprehensively reviewed, and their structures, implementation, and principle of performance are discussed.
Fig. 1. Ungrounded DC system, (a) unipolar system, and (b) bipolar system. The term of grounded in DC-grids is referred to a system in which at least one conductor or a point (usually the mid- point of VSC DC-link or one of the positive or negative poles of DC grid) is intentionally grounded [14, , ].
Grounding configurations utilized in DC networks are detailed, and their advantages and limitations are compared in terms of; personnel and equipment safety, fault detection capability, fault ride-through capability and minimizing stray current induced corrosion.
Resistive Grounded System; Using a resistor in the grounding system effectively attenuates the amplitude of common-mode current, stray current, and short circuit fault current. Using a proper resistance value makes this grounding scheme a suitable choice for DC traction systems, AC drive applications, and also LVDC grids.
In a network with solidly grounded AC grid, solid grounding of the non-isolated DC bus creates a permanent fault. Hence, AC grid network with solidly grounded neutral, preclude the possibility of solid grounding of the DC bus, unless the network is electrically isolated using an isolation transformer, as in Fig. 8 (a).