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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.
Is delta connection also called a star-star connection?
the delta has a higher voltage to ground on the B phase and is identified by the orange color for identification means so its easier to smoke equipment if not careful.hardly see delta connections anymore so old school and outdated. it just makes economic sense to use a star connection.On the above answer there should be no voltage to ground on a delta connection. All three phase coils are connected in series with each other and at no point in the delta are they grounded. Most of the commercial and industrial motor connections are connected delta. In installations where the motor inrush is above utility company specifications the Star- Delta connection is used. This limits the inrush current in the star configuration and then after a time delay connects the motor in a delta configuration. With delta systems the use of grounding lights are mandatory. These are used to detect if a phase grounds out. One phase and the motor can still be in operation, two grounds represent a short circuit and the system will trip.CommentThe second answer is not altogether correct... In the USA and Canada, it is common practise for one phase of the delta-connected secondary windings of a three-phase transformer bank, to have an earthed (grounded) centre tap. With each phase providing 240 V; the centre-tapped phase then provides a combination of 240 V line-to-line together with two 120-V line-to-neutral (earth) voltages which is the standard supply method for residences in North America. The point of common connection between the two remaining phases is termed the 'high leg' of that particular transformer connection, having a potential of 208 V with respect to earth (although this is not used). To summarise, this method provides a 240-V three-phase supply, combined with a single-phase 240/120-V supply, which is useful for small businesses (e.g. garages) which might need to operate three-phase motors.However, the second answer is perfectly true for the UK (and, possibly, elsewhere in Europe) where residences are supplied with just one voltage (230 V) -unlike North America- and delta-connected supplies are relatively unusual.
When is a motor in star or delta connection?
Star (or wye) connection is where each of the three phases has a fourth conductor, neutral, as its current return. Current flow in this configuration is phase to neutral, which is also grounded back at the distribution center. There will be five total connections, phase A, B, and C, neutral, and (protective earth) ground. Delta connection is where each of the three phases uses the prior phase as its current return. Current flow in this configuration is phase to phase, and there is no neutral, though there is still a ground. There will be four total connections, phase A, B, and C, and (protective earth) ground.
What is the difference between star delta and wye delta?
With a delta connection, picture a triangle. Each side of the triangle is a transformer or motor winding. Call the 3 corners of the triangle A, B, and C. There are only 3 wires except for a safety ground, which has no connection to, nor is any part of, the power transmission service lines.but for the star connection take our triangle above and use your wire cutters (literally) to cut the triangle apart at the corners. rearrange the three sides (transformer or motor windings) to form a Y. Where the three sides join in the centre, connect a fourth wire. Call this wire "neutral". Call the three ends A, B, and C. Connect the 3 supply service lines to A, B, and C.
Why delta connections used in overhead transmission lines?
There are essentially 2 types of connections for a 3 phase AC transmission lines Star and Delta , Star is a 4 wire connection with each phase supplying potential with respect to a common ground wire , while delta is 3 wire connection with any single phase at one given time acting as a ground , for transmission reducing one wire makes a lot of cost difference hence it is favored
