transformer sizing for starting motor.pptx

Sizing transformer

1. T R A N S F O R M E R M V A S I Z I N G U S I N G E T A P B y W aqar H u ss a i n Electrical Dept.

2.  In ower s stems transformer is one of man devices whose proper size is critical to the design of a power delivery system.  ETAP has com lied the information contained on standards ANSI – IEEE C57, IEC 60076-2 and IEC 60726 into a program that can easily determine the proper size of a power transformer

3.   r i n h f ll w i n f r E T A P k i n n i for trafo MVA sizing     Altitude    Type (dry or liquid fill)  Expected future growth  Short circuit requirement (trafo impedence and BIL)

4.   The two winding transformer MVA sizing calculation sizes the following  parameters of a transfomer  Rated MVA  Maximum MVA  Percentage impedance Maximum MVA is 1.25 times the rated MVA for ONAN – ONAF trafo.

5. . Transformer Loading   This section allows you to find the operating load ca cu a e rom oa ow ana ys s or connec e load to this transformer and then use either load for sizin ur oses   Also you can manually enter the loading for the transformer While sizing transformer based on connected load, spares can also be included

6. . Load Variation  Growth Factor – For allowance for future growth. Growth transformer. If “Use growth factor for max MVA” is checked, then it is used for calculating the max MVA  Load Factor – is 100 % if the transformer carries required load continuously all the time

7. . Installation  ETAP adjusts the calculated required Rated MVA b a s e d o n t r a fo ’ s a l t i t u d e v a l u e . F o r e x a m l e f o r L i u i d Immersed Forced Air Cooled trafo, the MVA rating is derated by factor 0.5 % for every 330 ft above 3300 .  Ambient Temp. ETAP adjusts the required Rated MVA

8. . Im edance  B a s ic I m u l s e L ev e l B I L L i m i t - E T A P u t i l i z e s t h i s value for determining the trafo minimum impedance according to ANSI – IEC standards  Limit Short Circuit kA – If this option is checked, then ETAP calculates % impedance based on short circuit ,

9. .   Larger size, Required size or smaller size

10.    Type (Liquid fill or Dry) , …  Class (ONAN, ONAN-ONAF, OFAF etc …)    Primary Winding kV rating 

11.    One of the factors to be considered while sizing a trafo is the voltage drop on start.  According to IEEE Brown Book, the voltage at terminals of starting motor should not fall below 80% of rated voltage for typical NEMA design B motors  T h i s v o l t a g e d r o p i s p r o p o r t i o n a l t o t h e r e g u l a t i o n o f t r a f o d u r i n g m o t o r s t a r t  The voltage drop at trafo secondary (regulation) during motor start is inversely proportional to trafo short circuit kVA and directly proportional to motor starting kVA  The Transformer MVA Sizing Module of ETAP does not take into account this factor. The regulation of trafo can be checked by Motor Starting Study on ETAP

12.   A roximate   volta e   dro   on   the   transformer   secondar   can   be   calculated   by   the   following   formula Where =   P   =   Peak   Load   on   trafo in   kVA other   than   largest   Motor   S   =   Short   circuit   capacity   of    trafo in   kVA

13. UCH2 Unit Auxiliary Transformer sizing using ETAP

14.   – Standard: IEC Type: Liquid Fill Sub type: mineral oil ass:  - emp. r se: Primary V = 14.5 kV Sec. V = 6.6 kV

15. –  Plant ETAP model a e v n a d l u o a p t e e r a c o t i n g n e l o c t e a d d o n a transformer Unit Auxiliary transformer to be sized Lum 1 of 13869 kVA represents the UCH2 operating BOP load other than 1 No. circulation water pump motor. The lump load contains all and loading factors of  different loads

16.    Based on Operating  rans ormer oa , growth factor (for max MVA or ONAF) and 28 degree C ambient tem . , the recommended size by ETAP is 20-25 MVA at ONAN-ONAF  Here worst case load is considered for GT, HRSG , by HET. (This load is included as “lump 1” in ETAP model)

17. U C H 2 L O A D F L O W A T 3 D I FF E R E N T U N I T A U X . T R A F O R A T I N G S – W O R S T C A S E L O A D I N G 16 ‐ 20   MVA   trafo 20 ‐ 25   MVA   trafo 25 ‐ 31.5   MVA   trafo %   Z   =   10,   X\R   =   22.2 %   Z   =   10,   X\R   =   22.2 %   Z   =   10,   X\R   =   22.2 Trafo   Input   kVA 16198 16046 15932 Trafo   Output   kVA 15217 15286 15339 – Increase in trafo output kVA as trafo rating is increased. ? Decrease in trafo input kVA as trafo rating is increased. ? Trafo % Z is taken rated trafo, ETAP performs Load flow at ONAN rating  20 % of the lump   model is static as contant at 10 %   regulation at trafo sec. the static load consumes more k V A

18. ETAP MOTOR START STUDY AT 3 DIFFERENT TRAFO R A T I N G S – N O R M AL C A S E L O A D I N G M o t o r   S t a r t i n g   A n a l y s i s For   Circulation   Water   Pump   Motor Load   Flow   before     M o t o r s t a r t Trafo   Input   MVA Load   Flow   at     M o t o r s t a r t   Motor   start   (steady   state) 16 ‐ 20   MVA   trafo %   Z   =   8,   X\R   =   22.2 . . . 20 ‐ 25   MVA   trafo %   Z   =   8,   X\R   =   22.2 20 ‐ 25   MVA   trafo %   Z   =   10,   X\R   =   22.2 13.655 21.345 15.333 13.632 20.865 15.277 If Normal loading is considered . , the sizing module recommends 16 – 20 M V A t r a f o

19. ETAP MOTOR START STUDY AT 3 DIFFERENT TRAFO R A T I N G S – N O R M AL C A S E L O A D I N G … . . C O N T D Motor   Starting   Analysis Motor   Terminal   Pump   Motor Trafo   sec.   Voltage   at   Motor   Start   Motor   Terminal     16 ‐ 20   MVA   trafo %   Z   =   8,   X\R   =   22.2 20 ‐ 25   MVA   trafo %   Z   =   8,   X\R   =   22.2 ‐ %   Z   =   10,   X\R   =   22.2 Start State 88.35% 92.09% 98.38% 90.34% 94.18% 99.49% 88.35% 92.09% 98.38% Motor Rated Voltage: Please note that the motor rated voltage is 6.3 kA where as the MV bus and trafo sec. rated voltage is 6.6 kV As per IEEE Standard 399-1997, IEEE Recommended Practice for Industrial and Commercial Power System Analysis (Brown Book), the Voltage at terminal of Motor during starting shall not fall below 80 % of rated voltage. Hence this condition is satistfied for all the three d iff e r e n t t r a f o r a ti n g s For ONAN – ONAF rated trafo, ETAP performs Motor Start at ONAN r a t i n g  

20. C AL C U L A T I O N O F T R A F O S E C . V O L T A G E A T M O T O R S T A R T U S I N G F O R M U LA …… C O M P A R I S O N calculated   using   ETAP T r a f o s e c .   V o l t a g e   a t   M o t o r   S t a r t   Formula Motor   Starting   Analysis   Pump   Motor 16 ‐ 20   MVA   trafo %   Z   =   8,   X\R   =   22.2 88.35% 87.36% 20 ‐ 25   MVA   trafo %   Z   =   8,   X\R   =   22.2 90.34% 89.89% 20 ‐ 25   MVA   trafo 88.35% 87.35%  Almost same results using  formula and ETAP, confirms the validity of the formula used in UCH2 trafo sizing  calculations   =   ,   =   . Starting kVA of motor = Full Load kVA x 6 = 11412 kVA Peak load on trafo excluding motor load = 13869 kVA