Ground fault protection is a type of equipment that can be used to protect against the effects of ground faults. According to the National Electrical Code, ground fault relays are required to be installed in certain areas.
There are two benefits that ground fault protection for an electrical grid can offer. There are two types of ground fault protection, known as restricted and unrestricted.
First, let’s quickly define Ground fault protection.
Normal unbalanced currents and ground fault currents are two different phenomena. When there is a ground fault, the current travels along the grounding path, while with single-phasing or unequal loading on all three phases, the fault current travels only along the neutral path.
Whether a system is grounded solidly or through impedance determines how many wires are used for ground fault protection.
Unrestricted Ground Fault Protection
In many cases, a hybrid system that safeguards against both ground and phase faults is used. For a system with a high number of load points, like a distribution network, an unrestricted ground fault protection scheme is typically implemented. Ground fault protection and phase fault protection are shared at the incoming feeder in this type of network. All MV switchgear feeders share the same Phase and Ground fault protection.
Since ground protection for the entire system was what was needed, rather than for each piece of equipment separately, a restricted earth fault protection was unnecessary. It is not practical or advised to use restricted ground fault protection for each individual feeder, so this scheme is typically used for LV and MV systems.
Connecting Methods for Unrestricted Ground Fault Protection: This type of protection is used for three-phase, three-wire or four-wire systems, as depicted in the following diagrams.
In this setup, you can choose from three different connections. The scheme chosen is determined by the level of protection required and its monetary cost.
Restricted Ground Fault Protection
When we only need to safeguard the circuit in a small space, we can employ this safeguard. Restrictive ground fault protection systems do not pick up on faults originating from the outside world.
Generators, transformers, and other similar circuits can all benefit from this equipment protection scheme. If there are problems with the machinery outside of the protected area, this system can isolate it.
Protection for Three-phase Four Wire Systems:
In this plan, too, you can choose between three different links. The scheme chosen is determined by the level of protection required and its monetary cost.
These configurations are identical to the ones described above with the addition of a neutral wire. Please find below the connection diagrams.
1. Only Ground fault protection
2. Three over current and one Ground fault combined protection
3. Two over current and one Ground fault combined protection
Protection for Three-phase Three Wire Systems:
1. Only Ground fault protection
As can be seen in the diagram below, a single ground fault relay serves all three phases in this configuration.
This article explains in depth the Restricted Earth Fault Protection Scheme for transformers.
2. Three over current and one Ground fault combined protection
As can be seen in the figure below, this configuration uses three overcurrent relays for each phase in addition to a single ground fault relay for all three circuits.
3. Two over current and one Ground fault combined protection
As can be seen in the diagram below, this configuration makes use of a single ground fault relay for all three phases in addition to two overcurrent relays connected in two phases.
Note : Keep in mind that in numerical relays, all these safeguards are provided by a single relay. Elements of the R, Y, and B phases, as well as the ground, are present.