Star-Delta Connection Overview

In this variety of electrical device affiliation, then primary is connected in star fashion whereas the secondary is connected in delta fashion as shown in Fig-1 below.

Star-Delta Connection

Key points

  • As Primary in Star connected
  • As Secondary in delta connected:
    Line voltage on Secondary facet = part voltage on the Secondary facet.
  • Secondary part Voltage = K X Primary part Voltage. =K X (Line voltage on Primary facet / √3)
  • Secondary part Voltage = (K/√3 ) X Line voltage on the first facet.
  • Line voltage on Primary facet = √3 X part voltage on Primary facet. So
  • Phase voltage on Primary facet = Line voltage on Primary facet / √3
  • Now Transformation Ration (K) = Secondary part Voltage / Primary part Voltage
  • Secondary part Voltage = K X Primary part Voltage.
  • There is s +30 Degree or -30 Degree part Shift between Secondary part Voltage to Primary part Voltage

Advantages of Star Delta Connection

  • The primary facet is star connected. thence fewer numbers of turns square measure needed. This makes the association economical for giant high voltage step down power transformers.
  • The neutral on the market on the first will be earthed to avoid distortion.
  • The neutral purpose permits each form of hundreds (single-phase or 3 phases) to be met.
  • Large unbalanced hundreds will be handled satisfactorily.
  • The Y-D association has no downside with third harmonic parts thanks to current currents in. it’s conjointly a lot of stable to unbalanced hundreds since the D part redistributes any imbalance that happens.
  • The delta connected winding carries third harmonic current thanks to that potential of neutral purpose is stable. Some saving within the value of insulation is achieved if the HV facet is star connected. however in observe, the HV facet is generally connected within the delta so the 3-phase hundreds like motors and single-phase hundreds like lighting hundreds will be equipped by cardinal facet exploitation three phases four-wire system.

Disadvantages of Star-Delta Connection

  • In this form of affiliation, the secondary voltage isn’t in section with the first. therefore it’s impracticable to work this affiliation in parallel with star-star or delta-delta connected the electrical device.
  • One downside related to this affiliation is that the secondary voltage is shifted by three hundred with relevance to the first voltage. this may cause issues once paralleling 3-phase transformers since transformers secondary voltages should be in-phase to be paralleled. Therefore, we tend to should concentrate on those shifts.
  • If secondary of this electrical device ought to be paralleled with secondary of another electrical device while not section shift, there would be a haul.


  • It is usually used for power to provide transformers. this sort of affiliation is usually used at the station finish of the cable. the most use with this affiliation is to step down the voltage. The neutral accessible in the first aspect is grounded. It may be seen that there’s a section distinction of 30° between primary and secondary line voltages.

  • Commonly utilized in a transformer, Y affiliation on the HV aspect reduces insulation prices the neutral purpose on the HV aspect may be grounded, stable with reference to unbalanced hundreds. As for instance, at the top of a cable. The neutral of the first winding is earthed.

    In this system, the road voltage magnitude relation is 1/√3 Times of electrical device turn-ratio and secondary voltage lags behind primary voltage by 30°. Also, third harmonic currents flow within the to administer a curved flux.

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