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On a stup down transformer what does the xo symbol mean?
On a step down transformer XO symbol denotes the secondary split phase grounding point. This is also where the neutral of the three wire secondary is connected. The transformer connection is known as a single phase - three wire - with one secondary winding.
Why is star connection used in a three phase transformer?
The power of all three phases can be transmitted on three conductors.A star connection, as opposed to a delta, provides a grounding reference. Also, for ground faults on the secondary (assuming no delta third winding, or source third winding) will be a direct ratio similar to phase faults, instead of 57%. Another reason is to avoid the inherent phase shift involved in a delta/star configured transformer.Another AnswerA 'star-connected' secondary is the standard European connection for a three-phase distribution transformer, as it provides a line voltage of 400 V together with a phase voltage (i.e. line to neutral) of 230 V.
How do you take a single phase output by giving 2phase input in transformer?
You are not really connecting two phases to the primary of the transformer; you are connecting one phase. In delta configuration, each phase is actually the connection of two legs, AB, BC, and CA. Even though you are connecting two legs to the transformer, there is only one phase involved. In star configuration, however, each phase is the connection of one leg to neutral, AN, BN, and CN. In star, you would only use one of AN, BN, or CN to connect to the transformer's primary winding. Star configuration is preferred, and is actually used in the transmission/distribution system, because in delta, loss of one leg takes out two phases. Star configuration, however, would not be preferred if your local distribution was based on a non-centered neutral, such as a quadraplex connection providing split phase simultaneously with three phase. (120/240-240/3) The neutral in that case is not at the center of the star triangle - it would be at the center of one of the phase pairs.
Why earthing transformer is zigzag connection?
A zigzag transformer is used in connection with 3 phase and is made up of 6 coils connected in a "Y" manner. Each leg of the "Y" is made up of a coil on a different phase leg of the transformer. The neutral formed by the zigzag connection is very stable. 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. Many times this type of transformer or auto transformer, lends itself very well for establishing a neutral for an ungrounded 3 phase system. Many times this type of transformer or auto transformer will carry a fairly large rating, yet physically be relatively small. This particularly applies in connection with grounding applications. The reason for this small size in relation to the nameplate KVA rating is due to the fact that many types of grounding auto transformers are rated for 2 seconds. This is based on the time to operate an overcurrent protection device such as a breaker. Zigzag transformers used to be employed to enable size reductions in drive motor systems due to the stable wave form they present. Other means are now more common, such as 6 phase star.
Voltage across Neutral and earth for a 3 phase auto transformer?
A grounded neutral will be at earth potential. A floating neutral will be at a voltage dependent upon the voltage imbalance between phases, and the design of the transformer.
