This can take the form of either a grounding transformerzigzag transformer or a neutral ground reactor. Pdf zigzag transformer some new applications with a. The artificial neutral creates a lowimpedance path for the zerosequence current and highimpedance path for the positivesequence current. Neutral earthing transformer is having zig zag interstar winding to achieve the required zero phase impedance. This article will the address the use of the zig zag transformer. Zigzag grounding transformers post glover resistors. Zigzag grounding transformers are more common than a grounded wye delta transformer because they are smaller in size. Regardless of the configuration, star, delta or zigzag, the measurements are normally made phase to phase and comparisons are made to the estimated ratios defined by the transformer template voltages and configuration. In terms of installation, do we just need to tie the a, b, c phases of the zigzag to the distribution transformer secondaries and then ground the derived neutral of the. We performed a shorted secondary test on the zig zag transformer which gave us a transformer impedance of zo. Wyeg and ngrs used with wyeg elta, although im not sure of the exact reasons behind that. It provides insulation between the ground and the component so that the component may not be affected by the fault currents. In the case of three phase transformer windings, three forms of connection are possible. A zigzag transformer is more efficient than a grounded wyedelta transformer.
The zig zag transformer has been used some years ago for creating a neutral, thereby converting a three wire distribution system to a fourwire system. Zigzag transformer some new applications with a note to energy efficiency article pdf available in international journal of power and energy conversion 63. Calculate size of neutral earthing transformer netexcel. Winding 2 zigzag r2 l2 the resistance and leakage inductance of the windings 2 of the singlephase transformers used to implement the primary winding of the zigzag phaseshifting transformer. Grounding transformers are used for obtaining a grounded neutral on three phase, threewire systems, providing a return path for zero sequence current generated. The goal of installing a zigzag transformer is to share the neutral current. Analysis of zigzag transformer applying in the threephase four. Zag grounding transformer a pv facility with 1 mva inverter total ac nameplate is interconnected to a. Each zigzag grounding bank would still have to be protected by overcurrent relays 51 as shown in figure 12 or differential relays. The most common connection used in grounding transformers is the zigzag connection. Effective grounding for pv plants srcw00101 3 p a g e due to their simplicity and cost effectiveness, grounding banks are widely used to provide effective grounding in three phase three wire systems. Transformer a has an impedance of 4%, transformer b which is to be parallel to a must have an impedance between the limits of 3. Each core leg of the zig zag transformer has two coils wound on it.
The delta primary transposed zigzag secondary dtz transformer has been designed and used to reduce the bad impacts of the harmonic in the distribution power system. A zigzag transformer is used for providing grounding on the transformer. Each core leg of the zigzag transformer has two coils wound on it. Zig zag grounding transformers are more common than a grounded wye delta transformer because they are smaller in size. From this we calculated the transformer reactance for 60 hz x60. You can use the zigzag transformer in two winding transformer applications, where you obtain voltage transformation and isolation with the zigzag feature. Comments about the use of a zigzag transformer to reduce the. The grounding transformer is commonly referred to by this connection type, the zigzag transformer. Three phase transformer winding configurations and differential relay compensation pdf. File sharing on the engtips forums is outsourced to.
Both the 3phase and singlephase loads may be supplied with the rated. The zigzag transformer is a special type of 3 phase transformer. The dtz transformer is constructed with delta connection in primary winding and the three transposed windings at the different core legs of secondary winding. The block allows you to provide an artificial neutral in an ungrounded threephase power system.
I generally see zigzag transformers used with wyeg. Each phase, therefore, couples with each other phase and the voltages cancel out. Together these make up the high voltage side of the transformer. Groundingzigzag transformers quality transformer and. The earthing transformer block models a threephase zigzagconnection earthing or grounding transformer. Earthing transformers, neutral earthing transformers. Earthing transformers neutral earthing transformers. Effective grounding zigzag transformer mike holts forum. What exactly is the purpose of a zigzag transformer. The factor that influences how is share the neutral current is the impedance of the paths. We performed a shorted secondary test on the zigzag transformer which gave us a transformer impedance of zo. The primary and secondary windings of a transformer can be connected in different configuration as shown to meet practically any requirement.
They are mostly used to obtain a ground connection in a delta circuit. Grounding transformers are used for obtaining a grounded neutral on three phase, threewire systems, providing a return path for zero sequence current generated by the loads in the system or by the fault currents. The zigzag transformer has been used some years ago for creating a neutral, thereby converting a three wire distribution system to a fourwire system. Each leg of a grounding transformer carries onethird of the neutral current and has linetoneutral voltage. This article will the address the use of the zigzag transformer. Zig zag transformer offers low impedance path to zero sequence components under fault conditions so it can be perfectly used as earthing transformer with and earthing reference. The zigzag transformer can be combined with either star or delta connections in twowinding transformer, in this application only the deltazigzag winding is used. Calculate neutral earthing transformer xr ratio calculate fault current through neutral single line to ground fault if calculate rating of neutral earthing. Pdf zigzag transformer is only used as a grounding transformer in a three phase delta connected power supply system. Zigzag transformer winding mc5w electrical 6 oct 04 23.
Where and why do we use grounding transformer zigzag. The transformer being referred to by this article is called grounding transformer or earthing transformer in europe and the article should be named accrdingly to avoid confusion to readers. Applications of zigzag transformers to reduce harmonics in. Other means are now more common, such as 6 phase star. A grounding bank uses either a zigzag or wyedelta transformer which represents a high impedance. It can be order as a custom three phase unit or as 3 individual single phase units.
Threephase earthing transformer in zigzag configuration. Design of zig zag earthing transformer in an 11kv system. If the earthing current has to be limited under fault conditions, a suitable resistor can be placed in zig zag neutral terminal. The most common connection used in grounding transformers is the zig zag connection. This application note is focusing on using transformer turn ratio measurements for diagnostic purposes. This example discusses the use of the zigzag transformers in power systems to provide a high impedance ground system for the delta connected or ungrounded.
This is the purpose of the earthing transformer, which could consist of a zig zag winding, or a twowinding star delta transformer where the star winding of correct voltage supplies an accessible neutral point when connected to the supply system. The second coils are then all tied together to form the neutral and the phases are connected to the primary coils. The common portion of an autotransformer low voltage is the common winding, and the remainder is the series winding. In this paper, an electrical model of a threephase transformer connected in grounded wye grounded zigzag configuration is developed, based in the common. Comments about the use of a zigzag transformer to reduce. It is used as a grounding transformer, creating a missing neutral connection from an ungrounded 3phase system to permit the grounding of that neutral to an earth reference point. With the zigzag transformer, you typically insert a resistor between the neutral point and ground to limit ground fault current on the system. Even though this type of transformer connection is not useful in transforming power, it has many features needed in todays power generation systems. Grounded wye grounded zigzag transformer connection. A properly applied zigzag transformer keeps the neutral current local, eliminates triplen harmonics zerosequence currents from the phase currents. If there is a zero sequence impedance of transformer, the power and leakage impedance rating. Design of delta primary transposed zigzag secondary dtz. If there is a zero sequence impedance of transformer, the power and leakage impedance rating of the transformer may be calculated.
The zigzag connection is also called the interconnected star connection. Custom dry type zig zag transformers zig zag transformers are a special purpose three phase transformer used in power systems. Three phase transformer winding configurations and. In addition, impedance values of each transformer must be within 7. This paper describes the modeling of zigzag grounding transformer wound core type with varying degrees of complexity. Most grounding transformers use zigzag windings but it is not the only configuration used. Calculate required resistance value at secondary side rsec. A zig zag can provide a relatively lowimpedance path to ground. The grounding transformer is one of most important equipment in power energy system. When a ground fault occurs on one phase, the zigzag transformer will provide the return path to groun. Pdf design of delta primary transposed zigzag secondary. The zig zag transformer is typically the least costly of the above three transformers mentioned.
Pdf zigzag transformer some new applications with a note to. Design of zig zag earthing transformer in an 11kv system ralphchristie electrical 6 dec 07 09. A zigzag transformer is a specialpurpose transformer with a zigzag or interconnected star. Zigzag grounding transformers specification for zigzag grounding transformers scope this specification covers design, manufacture and testing of low or mediumvoltage zigzag grounding transformers for use with neutral grounding resistors ngr for installation indoors or outdoors onto a concrete pad or power transformer. A zigzag transformer functions to provide a grounding source for ungrounded power systems as shown in the following 1line and 3line sketches. A zigzag transformer may also be used to rebuild a balanced 3phase load voltage by isolating the faulty phase from the load. The zigzag transformer is typically the least costly of the above three transformers mentioned. Calculate neutral earthing transformer secondary current. Zigzag transformers used to be employed to enable size reductions in drive motor systems due to the stable wave form they present. The first coil on each core is connected contrariwise to the second coil.
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