The zig zag transformer used for earthing of delta connected transformer. The problem is that the 11 kV delta no longer has an earth reference point. Thus far we have looked at the construction and operation of the single-phase, two winding voltage transformer which can be used increase or decrease its secondary voltage with respect to the primary supply voltage. Transformer Star and Delta Configurations Symbols are generally used on a three phase transformer to indicate the type or types of connections used with upper case Y for star connected, D for delta connected and Z for interconnected star primary windings, with lower case y, d and z for their respective secondaries. A three phase transformer has three sets of primary and secondary windings.
They can also be used to isolate, suppress harmonics, derive neutrals through a zig-zag grounding arrangement, and reregulate voltage. As discussed later, it is important to identify and isolate a ground fault in a system, particularly if the system has long cable networks. When transformers are used to provide three or more phases they are generally referred to as a Polyphase Transformer. The problem is that the 11 kV delta no longer has an earth reference point. Here, We install zigzag units near loads that produce large triple harmonic currents. The windings trap the harmonic currents and prevent them from traveling upstream, where they can produce undesirable effects.
The second coils are then all tied together to form the neutral and the phases are connected to the primary coils. Normally, phase overcurrent relay settings are much higher than earth fault settings. In the star-star arrangement Yy , wye-wye , each transformer has one terminal connected to a common junction, or neutral point with the three remaining ends of the primary windings connected to the three-phase mains supply. Therefore, this type of transformer, or in some cases an auto transformer, lends itself very well for establishing a neutral for an ungrounded 3 phase system. These winding halves interconnect to obtain a zigzag arrangement.
The number of turns in a transformer winding for star connection is 57. The voltage balance across the capacitors in the three phases is disturbed. In case of an earth fault in the secondary of transformer B, the earth fault is reflected in the primary side also. Hence, the purpose of a zigzag transformer is to provide a return path for earth faults on delta connected systems. If You find this content in any other site,it makes the page you are viewing an infringement of the copyright. Maybe you can write an article on how these things work, and if there is anything special about them.
Here we discuss only the techniques of achieving some connection. That is the input and output voltages for the windings are the same. Many times this type of transformer or auto transformer will carry a fairly large rating, yet physically be relatively small. Then the secondary side of the transformer supplies a line voltage, V L of about 35v giving a phase voltage, V P of 20v at 0. This is based on the time to operate an over current protection device such as a breaker. If one or more phases fault to earth, the voltage applied to each phase of the transformer is no longer in balance; fluxes in the windings no longer oppose.
The content in is for personal, non-commercial use only. The transformer primary or secondary can be connected in zig-zag. Zigzag transformers used to be employed to enable size reductions in drive motor systems due to the stable wave form they present. Thus, a sensitive earth fault protection can be provided. Three Phase Transformer Construction We have said previously that the three-phase transformer is effectively three interconnected single phase transformers on a single laminated core and considerable savings in cost, size and weight can be achieved by combining the three windings onto a single magnetic circuit as shown.
The Delta connection on the primary side is the most ideal connection. The combinations of the three windings may be with the primary delta-connected and the secondary star-connected, or star-delta, star-star or delta-delta, depending on the transformers use. The shell-type five-limb type three-phase transformer construction is heavier and more expensive to build than the core-type. We rarely use zigzag configurations for typical industrial or commercial use, because they are more expensive to construct than conventional wye-connected transformers. Clearly b1 should be connected to a3 and not the other ways. Transformers for high voltage operation with the star connections has the advantage of reducing the voltage on an individual transformer, reducing the number of turns required and an increase in the size of the conductors, making the coil windings easier and cheaper to insulate than delta transformers.
In the table of groups we also included transformer zig-zag connections. Therefore, spurious operation of upstream protection is avoided. With the zigzag connection, the currents in the two halves of the windings on each leg of the transformer flow in opposite directions, avoiding saturation. Five-limb cores are generally used for very large power transformers as they can be made with reduced height. The first coil on each core is connected contrariwise to the second coil on the next core.
Zigzag transformers used to be employed to enable size reductions in drive motor systems due to the stable wave form they present. N is the virtual neutral, which does not exist physically in delta side, but found geometrically from the diagram. In the obsence of grounded neutral, voltages of healthy would increase line to line voltage level, stressing the insulation connected to equipment. The first coil on each core is connected contrariwise to the second coil on the next core. He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. As with the conventional delta or wye winding configuration transformer, a standard, stand-alone transformer containing only six windings on three cores can also be used in zigzag winding connection, such transformer sometimes being referred to as a zigzag bank.
With negligible current in the neutral under normal conditions, engineers typically elect to under size the transformer; a short time rating is applied. If yes, how can it be done? Each phase, therefore, couples with each other phase and the voltages cancel out. With negligible current in the neutral under normal conditions, providing the defective load will be automatically disconnected in a fault condition, an undersized transformer may be used only as short-time rating is required i. We rarely use zigzag configurations for typical industrial or commercial use, because they are more expensive to construct than conventional Star connected transformers. With the neutral grounded, during a phase-to-ground short fault, a third of the current returns to the fault current, and the remainder must go through two of the three phases when used to derive a grounding point from a delta source. A shell-type transformers core materials, electrical windings, steel enclosure and cooling are much the same as for the larger single-phase types.