Neutral Connected to Earth in Transformer

Neutral Connected to Earth in Transformer

For a single phase transformer , The neutral is necessary in order to give current a return path .

Coming to three phase type systems , There will be star connection and Delta connections (There are Scott connections and some other types too but del and star are primary ) . In delta connections the phase voltage and line voltages are same and hence we employ delta connected transformers only on Low voltage side . While in star connected transformers phase voltage is 1,73 times lower than line voltage . The voltage ratings of a transformer depends on the phase voltage ratio (example:- insulation basically ) . So hence we employ star connected transformers usually on High voltage sides.

Now coming to the question . In a three phase connected system you don’t necessarily need a neutral as mostly 3 phases are balanced . But there is a concept of magnetizing current and 5th and 7th harmonics due to which an unbalance can happen . And also most of the equipment's we use nowadays are non linear devices Also due to some fault there can be unbalance . So usually relays are there for those connections . but as safety for high voltages we usually use 3 phase 4 wire systems .

Note :- Provision of neutral connection is only in star connected windings . This is one of the reasons too for employing high voltage sides with star connected windings .

As you know that at our homes we have single phase supply. So basically what we do is we take one phase of transformer and a neutral(which is common for all phases) and we connect it to our homes at the mains.

Let’s say we have 230 V AC phase to neutral supply(all phase to neutral 230 V AC). Now if the neutral is not earthed then its possible that there might be some induction in neutral wire so it will be at some potential wrt earth. Now this induction is totally random and might not be same for neutral everywhere so it will create an imbalance in supply which can damage the equipment's. Also since the neutral is not earthed and it is at some potential wrt earth you might get electrocuted by that little induced voltage.

So that's why neutral is earthed to keep it at zero potential to maintain the balance of supply as well as for safety of personnel using equipment's.

The neutral of a STAR connected three phase transformer is the non-active side of three coil voltages.

The three LINE Voltages do not use the neutral, yet are symmetrically dispersed in a circular arrangement relative to that point.

The requirement, in order that the technical integrity of the system is guaranteed, is to NOMINATE one of the FOUR as the reference. The aim is to construct an arrangement that protects against accidental connection of any one of these four to earth, which would result in chaos.

The most common of all connections is the conductive planet. The one upon which people stand and to which lightning is attracted in order to produce fertilizer as well as restoring the electrical balance of the local environment. What better choice than the neutral to become the protector of the electrical system, and of it's people.

Multiple earth neutrals threaten the stability of the system in order to protect against another difficulty. A broken neutral return. Neutral in a three phase star winding of a transformer is grounded mainly for three reasons:

(1) It provides a path for triplen harmonics i.e. third, nineth, fifteenth harmonics.

(2) It provides a path for zero sequence currents.

(3) It facilitates detection of earth faults.