# What is Zigzag Transformer ?

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### Zigzag Transformer

• Zigzag transformer is also known as the interconnected star connection. Zigzag transformer is a special purpose transformer.
• It is used in power system, zigzag connection has some of the features of the star(Y) and delta(∆) connections. this type of connection of transformer is not suitable for transforming power.
• Zigzag transformer has six coils in which three are outer coils and three are inner coils. Outer winding has known as Zig winding and inner winding has known as a zag winding. The zig winding of one phase is connected in series with the zag winding of another phase so it is called interconnected star winding.
• The primary coil on each core is connected in opposite direction to the secondary coil on the next core. If you need a neutral for grounding or for supplying single-phase line to neutral loads. this transformer working with a 3-wire, ungrounded power system. a zigzag connection may be the answer.
• Due to its Design, a zigzag transformer is more effective for grounding purpose. Because it has less internal winding impedance going to the ground than when using a star type transformer.
• We can use the zigzag transformer in two winding transformer applications. where we obtain voltage transformation and isolation with the zigzag feature.

Winding connection of zigzag transformer

primary coil is the outer coil and the secondary coil of the inner coil. Each coil has the same number of windings turns ,but they are wound in opposite direction. a1, b1 and c1 are outer coil and a2, b2 and c2 coil are inner coil.

1. coil a1 is connected to the coil c2 with opposite direction
2. coil b1 is connected to the coil a2 with opposite direction
3. coil c1 is connected to the coil b2 with opposite direction

The inner coil second terminals are connected together and connected to neutral terminal to pass the zero sequence current components.

Therefore, Zigzag connection used in power systems to eliminate the harmonic currents, due to opposite connection of winding coils. Here, you install zigzag units near loads that produce large triplet harmonic currents.  Zigzag transformer not only helps in protection, it also reduces the voltages stress under symmetrical fault conditions. Under normal system operation the both coil winding’s magnetic flux will cancel each other. so, only minor current will drawn in the in the neutral of the zigzag transformer.

1. Cost is less compared to Scott transformer.
2. There is no phase angle displacement between the primary and  secondary coil with this connection.
3. Provides low impedance to zero sequence currents.
4. It provides perfect isolation between ground and equipment.
5. Reduce Harmonic voltages and current.

Application

• Earthing transformer:- Zigzag transformer gives low impedance path to zero sequence components under fault conditions. so it can be used as earthing transformer. If the earthing current has to be limited under fault conditions. A suitable resistor can be placed in series with  neutral terminal of zigzag.
• hence, Zigzag connections are useful in special applications where conventional transformer connections aren’t effective. if system is subjected to unbalanced low voltage  then we can use zigzag connection.

If any query or suggestion about Zigzag connections please comment below or Email on sohal@electricalidea.com.

#### 1 COMMENT

1. I would like to see the analysis of short circuit currents when a zig-zag transformer is used.