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A conventional six-winding, grounding transformer or zigzag bank, [1] with the same winding and core quantity as a conventional three-phase transformer, can also be used in zigzag winding connection. In all cases the first coil on each zigzag winding core is connected contrariwise to the second coil on the next core.
Provide a source of ground fault current during line-to-ground faults. Permit the connection of phase-to-neutral loads when desired. [2] Earthing transformer with a zig-zag. Grounding transformers most commonly incorporate a single winding transformer with a zigzag winding configuration, but may also be created with a (rare case) delta-wye ...
A special form of auto transformer called a zig zag is used to provide grounding on three-phase systems that otherwise have no connection to ground. A zig-zag transformer provides a path for current that is common to all three phases (so-called zero sequence current).
If the secondary is a delta winding, the ground may be connected to a center tap on one winding (high leg delta) or one phase may be grounded (corner grounded delta). A special purpose polyphase transformer is the zigzag transformer. There are many possible configurations that may involve more or fewer than six windings and various tap connections.
Parallel operations: All the transformers should have same phase rotation, vector group, tap setting & polarity of the winding. Ground fault Relay: A Dd transformer does not have neutral. To restrict the ground faults in such systems, we may use a zigzag wound transformer to create a neutral along with the ground fault relay.
Any Δ-Y (delta-wye) connected transformer may be used for the purpose. A nine winding transformer (a "zig zag" transformer) may be used to balance the phase currents of a delta connected source with an unbalanced load. Low-resistance grounding systems use a neutral grounding resistor (NGR) to limit the fault current to 25 A or greater.
Most grounding transformers use zigzag windings but it is not the only configuration used. Also, zigzag windings are used as configurations in many topographies of transformers: wye/zigzag, delta/zigzag, zigzag/zigzag, zigzag/delta, zigzag/wye, delta//zigzag/zigzag (dual secondary). Some of the types are more common than others, of course.
Yz5 is a relatively common connection for MV/LV transformers up to ~250 kVA, e.g. (p. 196) Grounding transformers for MV networks are often Ynd – while zigzag is better suited for the job, utilities often have a spare Yd in stock, and adapting them for the job turns out to be cheaper.