There are several different types of medium voltage earthing systems. These systems can be differentiated by using the neutral point connection method. They are different in the way that they operate and each of them has its own pros and cons. These earthing systems in medium voltage include the likes of:

The functioning of each differs from the other. They also have various applications. Let’s have a look at each system at a time:

In this one, there is no electrical connection between the earth and the neutral point except for the devices that are used for measurement or protection. There is high impedance inserted between the earth and the neutral point. There is no switching on occurrence of the first insulation fault. It is therefore important to carry out permanent insulation monitoring, show the first insulation fault and locate and clear the first insulation fault.

Pros and cons: The advantage of using this one is that it provides services by tripping only when the second fault occurs which is subject to the capacity of the network not leading to a high earth fault current which would be dangerous for people when the first fault occurs. It has its demerits. There is the risk of high internal over-voltages. Insulation monitoring is also compulsory as well as the presence of maintenance personnel who will be monitoring and locating the first fault during use.

It is also known as direct earthing. It has a connection between the earth and the neutral point. Upon first insulation fault occurrence compulsory switching must be done. It is significantly different from the above mentioned unearthed neutral.

Pros and cons: This system reduces risk of over-voltage occurring and also authorizes the use of equipment with a normal phase to earth insulating level. On the other hand, there is mandatory tripping upon occurrence of the first fault. The touch voltages developed are very high and this poses a high risk for the personnel while the fault lasts. Differential protection devices must be used so that the clearance time of the fault is as short as possible.

This system requires a resistor to be inserted between the neutral point and the earth. It is also known as limiting resistance earthing. Their operating technique is quite straightforward. Switching must be done upon the occurrence of the first fault.