﻿152 
  The 
  Use 
  of 
  Shunts 
  and 
  Transformers. 
  

  

  cent, 
  as 
  against 
  2*7 
  per 
  cent, 
  by 
  experiment, 
  and 
  the 
  phase- 
  

   displacement 
  works 
  out 
  at 
  *57°* 
  which 
  agrees 
  with 
  the 
  

   experimental 
  value. 
  The 
  agreement 
  between 
  calculation 
  and 
  

   experiment 
  is 
  not 
  always 
  therefore 
  very 
  close, 
  but 
  this 
  is 
  

   probably 
  due 
  to 
  the 
  difficulty 
  of 
  determining 
  the 
  core 
  induc- 
  

   tion. 
  In 
  a 
  current 
  transformer 
  the 
  magnetic 
  leakage 
  may 
  be 
  

   quite 
  comparable 
  with 
  the 
  main 
  working 
  flux, 
  owing 
  to 
  the 
  

   small 
  value 
  of 
  the 
  latter, 
  and 
  hence 
  the 
  distribution 
  of 
  flux 
  in 
  

   the 
  core 
  is 
  very 
  irregular. 
  The 
  mean 
  value 
  of 
  the 
  induction, 
  

   however, 
  as 
  calculated 
  by 
  formula 
  27, 
  agrees 
  very 
  fairly 
  with 
  

   the 
  experimental 
  value, 
  being 
  1575 
  as 
  against 
  1565 
  in 
  case 
  

   VII., 
  and 
  1345 
  as 
  against 
  1385 
  in 
  case 
  VI. 
  Calculations 
  have 
  

   not 
  been 
  made 
  in 
  other 
  cases, 
  as 
  the 
  induction 
  densities 
  are 
  

   too 
  low. 
  

  

  The 
  statement 
  on 
  p. 
  144 
  that 
  a 
  non-inductive 
  secondary 
  

   circuit 
  should 
  give 
  a 
  better 
  ratio 
  than 
  an 
  inductive 
  one 
  of 
  the 
  

   same 
  impedance, 
  is 
  amply 
  borne 
  out 
  by 
  comparing 
  curves 
  V. 
  

   and 
  VI. 
  The 
  advantage 
  of 
  a 
  low 
  induction 
  density 
  is 
  also 
  

   manifest. 
  

  

  Calculations 
  of 
  P.D. 
  ratio 
  and 
  phase-displacement 
  show 
  an 
  

   agreement 
  within 
  *1 
  per 
  cent, 
  in 
  the 
  ratio 
  and 
  *01° 
  in 
  the 
  

   displacement, 
  which 
  is 
  sufficient 
  for 
  most 
  purposes. 
  The 
  

   theory 
  is 
  in 
  each 
  case 
  confirmed. 
  

  

  Tests 
  made 
  with 
  instrument 
  transformers 
  of 
  various 
  makers 
  

   have 
  in 
  no 
  case 
  shown 
  anything 
  like 
  such 
  good 
  results, 
  and 
  

   the 
  writer 
  is 
  of 
  opinion 
  that 
  these 
  results 
  represent 
  nearly 
  the 
  

   best 
  that 
  can 
  be 
  obtained 
  without 
  using 
  some 
  special 
  alloy 
  of 
  

   low 
  core-loss, 
  and 
  also 
  of 
  high 
  permeability. 
  In 
  view 
  of 
  the 
  

   importance 
  which 
  magnetic 
  leakage 
  assumes 
  in 
  current 
  trans- 
  

   formers, 
  the 
  secondary 
  current 
  nearly 
  always 
  lags 
  20° 
  to 
  30°, 
  

   and 
  the 
  magnetizing 
  current 
  is 
  therefore 
  nearly 
  as 
  important, 
  

   as 
  the 
  core 
  loss-current. 
  

  

  Fig. 
  11 
  (PI. 
  IV.) 
  gives 
  the 
  relation 
  between 
  A 
  c 
  and 
  A 
  ni 
  and 
  is 
  

   consequently 
  the 
  locus 
  of 
  the 
  end 
  of 
  the 
  no 
  load 
  vector 
  A 
  for 
  

   various 
  inductions. 
  This 
  vector 
  is 
  therefore 
  over 
  a 
  con- 
  

   siderable 
  part 
  of 
  the 
  range, 
  at 
  about 
  45°, 
  and 
  consequently 
  

   the 
  best 
  ratio 
  should 
  be 
  obtained 
  with 
  a 
  secondary 
  circuit 
  

   leading 
  by 
  about 
  45°. 
  In 
  fig. 
  12 
  a 
  curve 
  is 
  given 
  for 
  

  

  the 
  relation 
  of 
  ? 
  to 
  " 
  l 
  which 
  is 
  of 
  use 
  in 
  working 
  out 
  the 
  

  

  P.D. 
  ratio 
  and 
  phase-displacement. 
  

  

  Figs. 
  13 
  and 
  14 
  show 
  curves 
  of 
  ratio 
  and 
  phase-displace- 
  

   ment 
  for 
  three 
  current 
  transformers 
  made 
  by 
  Messrs. 
  I0vorett& 
  

  

  * 
  The 
  curves 
  for 
  current 
  ratio 
  and 
  phaae-displacemenl 
  appeared 
  in 
  

   the 
  'Electrician' 
  (lac. 
  cit.), 
  but 
  in 
  case 
  VI. 
  the 
  phase-displacement 
  was 
  

   unfortunately 
  given 
  with 
  reversed 
  sign 
  

  

  