Why vector group of SUT is chosen as Yn-Yo-Yo?

Why vector group of SUT is chosen as Yn-Yo-Yo?
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1 Answer

Answer :

To facilitate momentary paralleling of SUT with UT on 6.6kV buses.  
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Related questions

What is the vector group of GT, UT, SUT?

Description : What is the vector group of GT, UT, SUT?

Last Answer : Yd11 Dy1 Yy0 

What are the protections for SUT?

Description : What are the protections for SUT? 

Last Answer : a) Over current protection for phase and earth fault b) Differential protection c) HV and LV restricted earthfault protection  d) HV side directional back up over current protection for phase ... protection f) Over fluxing protection g) Buchholz and high oil, winding temperature protection. 

Why UT, SUT secondary is rated for 6.9kV where as bus voltage is 6.6kV?

Description : Why UT, SUT secondary is rated for 6.9kV where as bus voltage is 6.6kV? 

Last Answer : The no load secondary 6.9kV voltage level adequately takes into account voltage drop during loaded condition to cater station buses at 6.6kV level. 

Why twin secondary SUT?

Description : Why twin secondary SUT? 

Last Answer : As per is, the rating single secondary power transformer is limited to 25MVA (6.6 kV) or 40 MVA (11 kV), in order to limit the 3 phase symmetrical fault level with in 26-40 kA (contribution from grid and local machines) 

Why REF is provided in the LV side of SUT and UT?

Description : Why REF is provided in the LV side of SUT and UT? 

Last Answer : The LV sides of the two transformers are earthed through the resistance. This will limit the flow of current in case of LV earth fault. Hence the differential protection may not act for a LV earth fault. Hence ref protection is provided. 

Why the neutral is earthed through earthing resistance in case of UT and SUT?

Description : Why the neutral is earthed through earthing resistance in case of UT and SUT? 

Last Answer : This is done to limit the earth fault current.  

During unit operation, can we parallel UT & SUT continuously?

Description : During unit operation, can we parallel UT & SUT continuously?

Last Answer : No, due to switchgear limitation.  

During unit operation, can we parallel 2 SUT?

Description : During unit operation, can we parallel 2 SUT? 

Last Answer : No, due to switchgear limitation. 

What is the coverage of differential protection for SUT?

Description : What is the coverage of differential protection for SUT?

Last Answer : Covers from 230 kV bushing to 6.6 kV breaker end.  

What is E/F current limit for SUT and UT?

Description : What is E/F current limit for SUT and UT?

Last Answer : 400a limited by 10 ohms resistor.  

Purpose of standby E/F protection in SUT/UT?

Description : Purpose of standby E/F protection in SUT/UT? 

Last Answer : Back up for LV winding, LV neutral CT- CDG 12 – resistance earthing – relay set high time delay to discriminate with LV feeder and trip transformer if sustained E/F, also protects neutral earthing resistor.

Why REF is now is used for HV side also in GT/SUT?

Description : Why REF is now is used for HV side also in GT/SUT?

Last Answer : The E/F setting of differential is poor.  

X and y are points on the side LN of the triangle LMN , such that LX = XY = YN . Through X, a line is drawn parallel to LM to meet MN at Z. -Maths 9th

Description : X and y are points on the side LN of the triangle LMN , such that LX = XY = YN . Through X, a line is drawn parallel to LM to meet MN at Z. -Maths 9th

Last Answer : Here, △XZM and △XZL are on the same base (XZ) and lie between the same parallels (XZ || LM). ∴ ar(△XZL) = ar( △XZM) Adding ar(△XZY) on both sides , we have ar(△XZL) + ar(△XZY) = ar(△XZM) + ar(△XZY) ⇒ ar(△LZY) = ar(quad.MZYX)

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Description : X and Y are points on the side LN of the triangle LMN such that LX = XY = YN. -Maths 9th

Last Answer : Given X and Y are points on the side LN such that LX = XY = YN and XZ || LM To prove ar (ΔLZY) = ar (MZYX) Proof Since, ΔXMZ and ΔXLZ are on the same base XZ and between the same parallel lines LM and XZ. ... get ar (ΔXMZ) + ar (ΔXXZ) = ar (ΔXLZ) + ar (ΔXYZ) => ar (MZYX) = ar (ΔLZY) Hence proved.

X and y are points on the side LN of the triangle LMN , such that LX = XY = YN . Through X, a line is drawn parallel to LM to meet MN at Z. -Maths 9th

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X and Y are points on the side LN of the triangle LMN such that LX = XY = YN. -Maths 9th

Description : X and Y are points on the side LN of the triangle LMN such that LX = XY = YN. -Maths 9th

Last Answer : Given X and Y are points on the side LN such that LX = XY = YN and XZ || LM To prove ar (ΔLZY) = ar (MZYX) Proof Since, ΔXMZ and ΔXLZ are on the same base XZ and between the same parallel lines LM and XZ. ... get ar (ΔXMZ) + ar (ΔXXZ) = ar (ΔXLZ) + ar (ΔXYZ) => ar (MZYX) = ar (ΔLZY) Hence proved.

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Last Answer : UT and SUT are getting paralleled at 6.6 kV bus. Hence they should have voltage of same phase relationship. This is achieved by assigning different vector group to the transformers. 

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