.73 1.73
4.
By carefully evaluating these factors and referring
to earthing guidelines such those listed in
Table 4-1, MVDC system designers can select
the optimal earthing method balance safety,
reliability, and efficiency.
The general purposes earthing include:
§ Ensuring human safety.
§ Preventing electrical fires and arc accidents.
§ earthing system: The power line not
earthed, and only the conductive enclosure is
earthed.
§ Corrosion risks: Earthing designs should
minimize long-term exposure metallic
electrodes leakage currents, especially in
TT systems, where corrosion risks are higher.
§ Fault current management: High-resistance
earthing effective enhancing safety,
reducing stress equipment and limiting fault
current magnitudes. This directly influences
the insulation requirements cables and other
equipment.
For low voltage, IEC 60364-1 classifies earthing
systems into three types based the earthing of
the power lines (system earthing) and the earthing
of the enclosures electrical equipment the
consumer side [44]:
§ earthing system: The power line (system
earthing) and the conductive enclosure of
equipment are independently earthed at
separate points.5 2.7
Dielectric strength cable 1.
§ earthing system: The conductive enclosure
of equipment not earthed independently but
is connected the neutral point the power
line through protective conductor.
Considerations for designing MVDC earthing
systems include:
§ Transient overvoltage: The earthing method
affects the amplitude and duration transient
voltages during faults.
§ System application: The choice earthing
depends the system’s operational priorities,
such cost, safety, EMI considerations, and
continuity power supply.
§ Mitigating radiated and conductive
electromagnetic interference (EMI) and
minimizing electromagnetic compatibility
(EMC) issues.3 Earthing
Earthing and electrical protection are critical safety
considerations for any power system, including
MVDC operations.
§ Reducing equipment failures and minimizing
downtime.37
MVDC technologies and operational considerations
Table 4-1 Selection guidelines for various earth systems [45]
Characteristic High impedance IT
Earth fault current High Low Low
Arc flash hazard High Very low Very low
Transient overvoltage 2
