Elimination of Transformer Inrush Transients John Brunke

					Elimination of Transformer
   Inrush Currents When
Energizing Unloaded Power
       Transformers
         John H. Brunke
    Presentation Outline
 Basics of transformer inrush transients
 Three phase transformer core flux
  transients based on model studies
 New controlled closing strategies
 Statistical performance
Transformer Core
 Characteristics
       Flux



                   Current


                   1




          2
Energizing a Transformer
Transformer Inrush Current
    4000




                Time 0.05 ms/div
     0.0




    Amperes

    4000
Optimal controlled closing
Three Phase Transformers
Core Flux - No residual
Prospective and Dynamic Flux
      0.80     Flux, zero residual




      0.0    42.0     46.0    50.0   54.0      58.0

                                            Time ms1




      Flux
      kVs
     -0.80
Three phase residual flux




                Time 3 ms/div
Core flux with residual flux
                        Core flux, EMTP Study
                800




                  0.0
                                                Time 6 ms/div



                 Vs
                -800
Prospective and Dynamic Flux
   0.80         Flux, residual 0%, -70%, 70%
                     B          C           A




   0.0
              42.0       46.0       50.0   54.0        58.0

                                                  Time ms




   Flux kVs

   -0.80
Prospective and Dynamic Flux
 800




   0.0
                  Time 6 ms/div



  Vs
 -800
        Closing Strategies
   Rapid closing strategy
    – Requires detailed transformer data and
      look up table
   Delayed Closing strategy
    – Generalized approach
   Three phase strategy
    – Limited to high residual flux scenarios
Verification - Laboratory Tests
                                                     Rapid Closing Strategy

       . 8       0       0        0                  A       P       h   a   s       e       F   l u   x




                     0       . 0
                                                                                                               T   i m   e   2   0   . 5   m   s   / d   i v



             V           s
     - . 8       0       0       0

       . 8       0       0        0                  B       P       h   a   s       e       F   l u   x




                     0       . 0
                                                                                                               T   i m   e   2   0   . 5   m   s   / d   i v



             V           s
     . 8     0       0       0

      . 8    0       0        0                      C       P       h   a   s       e       F   l u   x




                     0       . 0
                                                                                                               T   i m   e   2   0   . 5   m   s   / d   i v



             V           s
    - . 8    0       0        0


                         2    0
                                                     N   e       u   t r a       l       C   u    r r e    n       t




                 0           . 0
                                                                                                               T   i m   e   2   0   . 5   m   s   / d   i v



             A           m         p   e   r e   s
                 - 2          0
Verification - Laboratory Tests
          Delayed Closing Strategy


 .8000




   0.0



                                 Time 6 ms/div
  Vs
 -.8000
Effect of Closing Error
              Model Study Results, Peak Inrush Current for a 70%
                   Residual as a Function of Closing Angle

                      3500
Peak Inrush Current




                      3000
                      2500
     Amperes




                      2000
                      1500
                      1000
                       500
                         0
                       -500 0   5         10          15      20
                      -1000

                                    Closing Time ms
        Prestrike
 800.


 400.


 0.0
                    Time 2 ms/div


-400.

kV
-800.
      Statistical Studies
 Benchmarks - linear bias runs with
  statistical pole span 1000 studies/run
 Controlled studies - 200 studies/run 0.5,
  1.0, 1.5, 2.0 ms timing error ranges
   Statistical Performance

CLOSING TIME            LEVEL EXCEEDING         PERCENT
SCATTER, 3 SIGMA        2% AMPERES              REDUCTION FROM
                                                UNCONTROLLED 2%
                                                LEVEL
0.5                    62                       98%
1.0                    140                      95.3
1.5                    350                      88.3%
2.0                    620                      79.3
Table 5.3. The improvement in performance using controlled closing with a
70% residual flux. .
Transformer Model
       Effect of Capacitance




               Time            Time



Flux
                      Flux
                                 State of the Art
                      Peak Inrush Current as a Function of Opening
                                          Time

                      1200
Peak Inrush Current




                      1000
     Amperes




                       800

                       600                                           Model
                                                                     Moraw
                       400

                       200

                        0
                             0      0.2   0.4   0.6    0.8     1

                                 Opening Time over One Power
                                       Frequency Cycle
                          Delayed Performance
                          Peak Inrush Current (2% Probability of occurrence)as a
                                    Function of Closing Time Scatter
                          800


                          700
Worst Phase Peak Inrush




                          600
   Current Amperes




                                                                                   70,-70,0
                          500                                                      0,0,0
                                                                                   0,-70,70
                          400                                                      0,70,-70
                                                                                   0,35,-35
                          300
                                                                                   70,-40,-30

                          200


                          100


                           0
                                0    0.5       1        1.5      2        2.5

                                    Closing Time Scatter (3 sigma) ms
   Three Phase Performance
              Peak Inrush Current as a Function of Closing Time
                                   Scatter

                   1200
Worst Phase Peak




                   1000
 Inrush Current
    Amperes




                   800
                                                                        0,-70,70%
                   600
                                                                        0,-35,35%
                   400                                                  0,-.5,.5

                   200

                     0
                          0       0.5     1      1.5     2        2.5

                              Closing Time Scatter (3 sigma) ms
Rapid Closing Performance
                           Peak Inrush Current (2% Probability of occurrence) as a
                                      Function of Closing Time Scatter
                          700


                          600
Worst Phase Peak Inruch
   Current Amperes




                          500


                          400
                                                                                     70,0,-70%
                                                                                     0,-70, 70%
                          300


                          200


                          100


                           0
                                0    0.5       1        1.5       2        2.5

                                    Closing TIme Scatter (3 sigma) ms
          Conclusions
 It is possible, by considering residual
  flux together with the appropriate
  closing strategy, to eliminate
  transformer inrush currents in most
  transformer configurations
 With consideration of breaker closing
  scatter, a reduction of typically 90% of
  worst, can be achieved

				
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posted:4/3/2011
language:English
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