star delta connection

In Star-connection, the voltage applied to each winding of transformer is "phase voltage" but in Delta-connection the voltage applied to each winding of transformer is "Line voltage" i.e. "1.73*phase voltage". In economic point of view it may be a good reason. I think it is not a common rule to have star-connection for HT side and delta-connection for LT side.

At HT side & LT side of what ?

Do you refereeing to Transformer ?

If , yes, Not at all , such preference for HT side Star and delta LT side.

why HT side star and LT side delta for transformer is prefered?

If the Transmission lines are 3wire system, considering the cost of conductor and supporting spars, primary of Transfomer should be in Delta connection. If we connect in star, neutral will be floting.The secondry of Transformer to be in Star position, since we required single phase voltage (ph & Ne) for our equipments.Hence it is preferable Delta/Star Transfomer on our distribution side.The other alternative with vector differance are depands on voltge,purpose & application.

I personally feel that you are completely right with the savings in cable cost and support costs made by transmitting high voltages only over 3 wires to a delta connection, it makes sense to me.

Also the need for a star connection at the substation where most often the lower single phase to neutral voltages are also generally needed.....

It comes to me as extremely plausible is all I can say.....

Firstly, which article or book you read this statement "star for HT and delta for LT"?

If using star on HT, insulation requirement will be less compared to delta. This needs comment from experts.

I do believe that what he meant was for the transmission line side High Tension and for the other Low or Lower tension....it works for me.

Its an old type of terminology I believe and I am old, younger persons might not have been exposed to these names/acronyms before....

You said:-

This needs comment from experts.

I agree.

In my experience, it's been Delta primaries and Wye Secondaries.

The Delta is more convenient for transmission, the Wye, with it's

neutral, and dual voltage availability. more flexible in use.

I don't quite agree, it depend in which section of power grid you're thinking about. In the transmision line when voltage need to be stepped down so primary is star, secondary is delta (transformation ration = 1/√3), and 30º shift between primary and secondary is made to allow path of third harmonic current in delta connection, to provide sinusoidal flux.

In distribution, delta/star is prefered, because it provide power flexibility line and phase voltage. Also prefer for safety protection purpose, such as TT or TN connection made.

So both Y-Δ and Δ-Y are preferable.

But Y-Y or Δ-Δ connection are not prefered as 30º shift are impossible to make.

In EHT the primary has to be with concern and co ordinated with Licensee for relay protection co ordination between out going from Licensee and at receiving at consumer.

It can not be thumb rule for star or delta as primary / secondary OR HT or LT side , and vector also depend on the type of connected secondary for phase displacement between primary and secondary

Normally HT is connected delta, LT is connected star so that ground faults and third order harmonics on the secondary will not be reflected into the primary

How ??????

With cables internal to the transformer...

If this is not the answer you were seeking, it is better to rephrase your question I think.

Normally HT is connected delta, LT is connected star so that ground faults and third order harmonics on the secondary will not be reflected into the primary

The statement given above by you as LT connected star so that ground fault and third harmonics on the secondary will not be reflected in to primary .,

How ?????

Hope, is clear

Star Delta is better for the motor and the levels off the peak power.

What do you mean by HT and LT?

Jan

This has already been asked and answered, see posts #5 & #6.....

All replies seem valid so far, overlooked so far is that a three phase delta system can suffer a casualty of one transformer, assuming separate transformers for each phase, and continue to deliver 3 phase power, at 2/3 the power rating of the network, this configuration is called open delta.

As stated the advantage of star or Wye networks is the ability to supply two different voltages though the phase to phase voltage is not twice the voltage of the phase to neutral voltage, it is the sine of 120 degrees 1.732 times the phase to neutral voltage due to the 120 degree phase displacement.

A question for engineers/ mathematicians, is the sine of 120 degrees and the square root of three the same number, and can you prove it. Took me forty years to get an answer.

Shipboard electrical practice governed by IEEE 45 is to provide all three phase circuits (120 volt also) as delta configuration with no connection to the ships hull except through ground detection devices. Wye networks neutral must be connected to the ships hull through a current monitoring device capable of withstanding the maximum energy that can be delivered by the source. Wye networks, or center tapped single phase transformers are used very little in shipboard practice, and only where absolutely necessary.

As a related matter, the ship that I am on now has a diesel electric propulsion system, four diesel alternators provide ships power for hotel load and propulsion I am able to start, parallel and load/ unload generators as the load demands. A curious arrangement exists in the propulsion control system.

A three phase full wave rectifier produces six pulses of DC current per cycle.

On this ship each propulsion motor is supplied through a transformer with one delta connected primary, and two secondaries, one secondary is connected delta, the other Wye. the two secondaries are connected to individual SCR controllers, the variable voltage DC output of the SCR controllers are paralleled to operate the propulsion motors. The 60 degree phase shift from delta to Wye produces DC pulses 30 degrees out of phase with the DC pulses from the delta secondary SCR's providing twelve pulses of DC during each AC cycle, thus reducing the filtering required, and thus noise (Electrical as well as audible) from the propulsion system.

Regards CEKM

on star side Vl=sqrt(3)Vn

and for delta Vl=Vn....so with same winding and excitaion we got more line voltage thats why star is preffered on Hv side.

Normally HT is connected delta, LT is connected star so that ground faults and third order harmonics on the secondary will not be reflected into the primary

The statement given above by you as LT connected star so that ground fault and third harmonics on the secondary will not be reflected in to primary .,