For the past several years a transformer is used for creating a neutral. Thus, converting a 3 wire distribution system to a 4 wire distribution system. The transformer which is used is called a zig zag transformer. In a zig zag transformer there is no secondary winding.
As we already knew that in the star connected system, the common connection point acts as a neutral. Hence, in a delta connected power supply system, there is no neutral point so a zig zag transformer grounding is used.
Zig Zag Transformer Basics:
The symbol used for zigzag representation is shown as:
We can see that there are a total of 6 coils used in a zigzag transformer and per limb there are 2 coils. Out of the 2, one of the coil of each limbs are connected together to form a star connection.
Zig Zag Transformer Connection:
The connections for a zig zag transformer are shown in the figure as following:
The zigzag transformer connections are basically setup on a core type transformer as shown in the following diagram:
We can see clearly that each limb of a core have 2 coil winding’s. The flux which is produced by the 2 coils, have the equal number of turns and will oppose each other and cancel each other’s effect.
During the normal system operation or when there is no fault, the winding’s of the zigzag transformer are connected in such a way that the magnetic flux in the three winding’s will cancel each other, and a negligible amount of current will flow in the neutral.
During the unusual system operation or having a fault in a system i.e. if there is a faulted phase, a single line to ground fault occurs, then the magnetic flux in the coils of a zigzag transformer is not equal.
Hence, a zero sequence current will flow through all the winding’s of the transformer, and at the neutral they will add up.
We can also connect the system or load neutral to the neutral of the transformer winding’s. If we ground the neutral, the connection is called grounded neutral connection.
The zig zag transformer advantages and disadvantages are:
- Due to the composition of a zigzag transformer, it is more effective for the grounding purposes rather than star type transformer because of the reason that it’s internal winding impedance is less. Hence more effective for the grounding.
- Zigzag transformer is probably the least costly method that we can use it as a high impedance grounding system.
- They are rarely used for the commercial or industrial purposes because they are more expensive to manufacture as compared to the conventional star connected transformers because they use more coil winding as compared to others.
Zig Zag Transformer Application:
The possible applications of zigzag transformer are:
- Most commonly, the zigzag transformer is used as a grounding transformer in a delta connected power supply system or in ungrounded star system.
- The zig-zag transformer are used for harmonic cancellation. They reduce the 3rd harmonics in the distribution system.
- If we are working with a 3-phase system and we need a neutral for grounding or if we want to supply neutral to the 1-phase ungrounded power system, a zigzag connection is a better choice.