Types of Vector Groups for Transformers

I could be wrong but this sounds suspiciously like a homework question.

pl refer Fizerald and kingsley 's Electrical machines

hey first i want to describe the general information abt the vector groups

The vector group of a polyphase power transformer indicates its windings' configurations and the difference in phase angle between them.

The phase windings of a polyphase transformer can be connected together internally in different configurations, depending on what characteristics are needed from the transformer. For example, in a three-phase power system, it may be necessary to connect a three-wire system to a four-wire system, or vice versa. Because of this, transformers are manufactured with a variety of winding configurations to meet these requirements.

Different combinations of winding connections will result in different phase angles between the voltages on the windings. This limits the types of transformers that can be connected between two systems, because mismatching phase angles can result in circulating current and other system disturbances.

The vector group provides a simple way of indicating how the internal connections of a particular transformer are arranged. In the system adopted by the IEC, the vector group is indicated by a code consisting of two or three letters, followed by one or two digits. The letters indicate the winding configuration as follows:

D: Delta winding, also called a mesh winding. Each phase terminal connects to two windings, so the windings form a triangular configuration with the terminals on the points of the triangle.

Y: Wye winding, also called a star winding. Each phase terminal connects to one end of a winding, and the other end of each winding connects to the other two at a central point, so that the configuration resembles a capital letter Y. The central point may or may not be connected outside of the transformer.

Z: Zigzag winding, or interconnected star winding. Basically similar to a star winding, but the windings are arranged so that the three legs are "bent" when the phase diagram is drawn. Zigzag-wound transformers have special characteristics and are not commonly used where these characteristics are not needed.

III: Independent windings. The three windings are not interconnected inside the transformer at all, and must be connected externally

and inorder to know whether the transformers are leading or lagging that primary voltages and secondary voltages a simple technique is used .

In transformers like 1600,1250kva that in distribution t/f's generally DY11 is used in which primary side is delta which helps to nullify the odd harmonics and help to get pure sinuosidal and the secondary side is star in which neutral is mostly grounded and the 11 reprsents the leading condition.

and other information i will dicuss later

Dear Mam,

In DY- 11 vector group what is the meaning of 11.

It means that the LV winding voltage lags the HV winding voltage by 30 degrees.

The 11 typically means 11 o'clock on a standard clock. whenever you see a vector group like Dy11 ar Yd1 or Yd5 ... all you have to do is first FIX THE HV WINDING AT 12 o clock

now the 11 shows that it is behind 12 on the clock so you can say that the LV is lagging by....30 degrees

in Yd1, the lv windings is at 1 o' clock meaning it is ahead of 12 o clock by thirty degrees so it means that the LV winding leads the HV winding voltage by 30 degrees

in Yd5, the lv windings is at 5 o' clock meaning it is ahead of 12 o clock by 150 degrees so it means that the LV winding leads the HV winding voltage by 150 degrees

11 O'clock, ie. 30 degrees lag.

Nicely plagiarised from WikiAnswers...the place one should never trust for "real" answers.

http://wiki.answers.com/Q/How_we_select_a_transformer_by_vectorgroup

Dear Mam,

I have small doubt, the different transformer rating 11/ .415 kv Dyn11 and 6.6/0.415kv Dyn11, it can be possible to Synchronizayion?

hi srinivas,

power transformer and disrtibution transformer differences are:

POWER TRANSFORMER:

these are used in transmission network of power system only and the rating of these are generally greater than 1MVA

these are not directly connected to the consumers,so load luctations are very less

these are loaded fully during 24 hr's a day,so cu losses & iron losses takes place through out day

the specific weight i.e (iron weight)/(cu weight) is very less.

the average loads are nearer to full loaded or full load and these are deisgned in such a way that maximum efficiency at full load condition

these are independent of time so in calculating the efficiency only power basis is enough.

DISTRIBUTION TRANSFORMER:

these are used in disrtibution of the network and rating is lessthan 1MVA

these are directly connected to the consumer so load fluctions are very high

these are not loaded fully at all time so iron losses takes place 24hr a day and cu losses takes place based on load cycle

the specific weight is more i.e (iron weight)/(cu weight)

average loads are about only 75% of full load and these are desgned in such a way that max efficiency occurs at 75% of full load.

as these are time dependent the all day efficiency is defined in order to calculate the eficiency.

all day efficiency = (o/p in KWhr)/(i/p in KWhr) in 24 hrs which is always lessthan power efficinecy

the 11 means it leads by 30 degrees.

hey DY11 means the primary side leads the secondary side by 30 degrees or

the secondary side lags the primary by 30 degrees

the leading and lagging are relative terms with respective to windings

in general notation primary side is taken as reference but we can describe in any way by specifying the condtions

if conditons are not specified then it represents the first case.

It means it LAGS not LEADS. HV winding sits at 12 o'clock, 11 o'clock suggests that it LAGS by 30 degrees.