Design of zig zag earthing transformer in an 11kv system ralphchristie electrical 6 dec 07 09. 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. A zigzag transformer functions to provide a grounding source for ungrounded power systems as shown in the following 1line and 3line sketches. Zigzag grounding transformers are more common than a grounded wye delta transformer because they are smaller in size. 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. Design of delta primary transposed zigzag secondary dtz. Each core leg of the zig zag transformer has two coils wound on it. Design of zig zag earthing transformer in an 11kv system. Effective grounding zigzag transformer mike holts forum. The block allows you to provide an artificial neutral in an ungrounded threephase power system. This article will the address the use of the zig zag transformer.
The second coils are then all tied together to form the neutral and the phases are connected to the primary coils. 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. The current trend in wind farm designs is toward the wye connected primary with a delta secondary. Groundingzigzag transformers quality transformer and. They are mostly used to obtain a ground connection in a delta circuit. The zig zag transformer is typically the least costly of the above three transformers mentioned. In the case of three phase transformer windings, three forms of connection are possible. Each phase, therefore, couples with each other phase and the voltages cancel out. The common portion of an autotransformer low voltage is the common winding, and the remainder is the series winding. Zig zag grounding transformers are more common than a grounded wye delta transformer because they are smaller in size. Grounding transformers are used for obtaining a grounded neutral on three phase, threewire systems, providing a return path for zero sequence current generated.
File sharing on the engtips forums is outsourced to. Earthing transformers, neutral earthing transformers. The earthing transformer block models a threephase zigzagconnection earthing or grounding transformer. Earthing transformers neutral earthing transformers. 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. Grounded wye grounded zigzag transformer connection. If there is a zero sequence impedance of transformer, the power and leakage impedance rating of the transformer may be calculated. A zigzag transformer is used for providing grounding on the transformer. The grounding transformer is commonly referred to by this connection type, the zigzag transformer. Comments about the use of a zigzag transformer to reduce the.
We performed a shorted secondary test on the zig zag transformer which gave us a transformer impedance of zo. You can use the zigzag transformer in two winding transformer applications, where you obtain voltage transformation and isolation with the zigzag feature. From this we calculated the transformer reactance for 60 hz x60. The most common connection used in grounding transformers is the zig zag connection. The zigzag connection is also called the interconnected star connection. If there is a zero sequence impedance of transformer, the power and leakage impedance rating. 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. Pdf zigzag transformer some new applications with a. 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.
The most common connection used in grounding transformers is the zigzag connection. In addition, impedance values of each transformer must be within 7. This article will the address the use of the zigzag transformer. Calculate required resistance value at secondary side rsec. 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. We performed a shorted secondary test on the zigzag transformer which gave us a transformer impedance of zo.
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. 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. Threephase earthing transformer in zigzag configuration. In this paper, an electrical model of a threephase transformer connected in grounded wye grounded zigzag configuration is developed, based in the common. The zigzag transformer contains six coils on three cores. The grounding transformer is one of most important equipment in power energy system. I have a utility requesting effective grounding for a system behind a grounded wye grounded wye distribution transformer. Custom dry type zig zag transformers zig zag transformers are a special purpose three phase transformer used in power systems. The zigzag transformer has been used some years ago for creating a neutral, thereby converting a three wire distribution system to a fourwire system. 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. A zigzag transformer is more efficient than a grounded wyedelta transformer. The primary and secondary windings of a transformer can be connected in different configuration as shown to meet practically any requirement. This connection has some of the features of the y and the. Three phase transformer winding configurations and.
If the earthing current has to be limited under fault conditions, a suitable resistor can be placed in zig zag neutral terminal. Calculate size of neutral earthing transformer netexcel. Zigzag transformers used to be employed to enable size reductions in drive motor systems due to the stable wave form they present. Pdf design of delta primary transposed zigzag secondary. Even though this type of transformer connection is not useful in transforming power, it has many features needed in todays power generation systems. The artificial neutral creates a lowimpedance path for the zerosequence current and highimpedance path for the positivesequence current.
A zigzag transformer is a specialpurpose transformer with a zigzag or interconnected star. The dtz transformer is constructed with delta connection in primary winding and the three transposed windings at the different core legs of secondary winding. Pdf zigzag transformer is only used as a grounding transformer in a three phase delta connected power supply system. What exactly is the purpose of a zigzag transformer. Calculate required grounding resistor value at primary side rp.
A zig zag can provide a relatively lowimpedance path to ground. Together these make up the high voltage side of the transformer. 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. Three phase transformer winding configurations and differential relay compensation pdf. The zigzag transformer is a special type of 3 phase transformer. Zag grounding transformer a pv facility with 1 mva inverter total ac nameplate is interconnected to a. The first coil on each core is connected contrariwise to the second coil. Analysis of zigzag transformer applying in the threephase four. I believe both would fall under the general category of impedance grounding. A properly applied zigzag transformer keeps the neutral current local, eliminates triplen harmonics zerosequence currents from the phase currents.
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. Each core leg of the zigzag transformer has two coils wound on it. It provides insulation between the ground and the component so that the component may not be affected by the fault currents. Wyeg and ngrs used with wyeg elta, although im not sure of the exact reasons behind that. Zigzag transformer winding mc5w electrical 6 oct 04 23. Calculate neutral earthing transformer xr ratio calculate fault current through neutral single line to ground fault if calculate rating of neutral earthing. This can take the form of either a grounding transformerzigzag transformer or a neutral ground reactor. The zigzag transformer can be combined with either star or delta connections in twowinding transformer, in this application only the deltazigzag winding is used. 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. Both the 3phase and singlephase loads may be supplied with the rated.
The factor that influences how is share the neutral current is the impedance of the paths. Calculate neutral earthing transformer secondary current. Each zigzag grounding bank would still have to be protected by overcurrent relays 51 as shown in figure 12 or differential relays. 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. When a ground fault occurs on one phase, the zigzag transformer will provide the return path to groun.
The simulation results show that a the zigzag transformer can effectively attenuate the neutral current and zerosequence harmonic currents on the utility side. Zigzag transformer some new applications with a note to energy efficiency article pdf available in international journal of power and energy conversion 63. With the zigzag transformer, you typically insert a resistor between the neutral point and ground to limit ground fault current on the system. Other means are now more common, such as 6 phase star. I generally see zigzag transformers used with wyeg. Applications of zigzag transformers to reduce harmonics in. This paper describes the modeling of zigzag grounding transformer wound core type with varying degrees of complexity. The goal of installing a zigzag transformer is to share the neutral current. Neutral earthing transformer is having zig zag interstar winding to achieve the required zero phase impedance. This application note is focusing on using transformer turn ratio measurements for diagnostic purposes. The zigzag transformer is typically the least costly of the above three transformers mentioned. 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. Zigzag grounding transformers post glover resistors. It can be order as a custom three phase unit or as 3 individual single phase units.