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| DSH 201A
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| Characteristics of D.C. electric circuits for verifying normal operation and making and breaking cap ...; K8 u1 L# h+ Z0 @
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| Generality
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8 ?9 @, K# ^& W, i+ W/ r p1 j1 NTo reach an acceptable test reproducibility, when verifying normal operation and making and breaking capacity, it is recommended that the test circuit has the following characteristics:
C5 l5 h8 n2 ]. a- y% ]+ B- Voltage drop
* R: M; F- v' y; Q. e7 UThe maximum voltage drop which should not be exceeded, when passing from noload( F) Q- f5 Q. c) z
to load condition, is 5% of the rated voltage.
% W6 ^4 E; M! ^- Voltage ripple value6 x. I6 x; H7 ?
The supply voltage ripple, at no-load condition, should not exceed 5%.
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0 k% k/ Z1 o* [+ S5 i- Percentage ripple is given by r% = Vac/Vdc x 100, where Vac is the RMS value of the superimposed a.c. voltage and Vdc is the d.c. voltage.
/ i+ A& Q, }% xA simple way to evaluate the ripple is to use an oscilloscope, whose input is selected in a.c. for the measurement of Vac and in d.c. for the measurement of VDU.
, B1 `) v: f' W6 p: x- The limitation of the ripple, which occurs, in practise, in rectifying converters, may be obtained choosing appropriately a rectifying bridge.. i0 o& v- c0 @& L
- The use of a three-phase rectifying bridge, which gives a theoretical ripple of about 4,2%, complies with this recommendation.1 y t# x& T# H) F" B5 A5 G& c: Z
- Recovery voltage& D5 |1 T2 r; I9 r
Test circuit, where:+ p* [) L4 J& v2 _" G5 t# i
- E is the supply voltage at no-load condition;
n ^( c r$ a: r; u- Li is equivalent to the different self-inductances of the supply as well as the stray inductances of the rest of the test circuit;- q7 x2 H- Y7 n
- Cp is the stray capacitance of the circuit;
$ F0 d" p) }) p4 Y" D- @- Rp is the parallel damping resistance.
. K& M4 j6 l3 {" ]8 D6 e! x: YNeglecting the parallel damping resistor, Rp, the parameters Li and Cp should be adjusted so as to obtain:# t. G. l& C0 v9 [
- Li = 2·10-3 H ± 25%, and5 V; B, r. J5 g+ n h4 K
- Cp = 50 mF ± 25%.& f6 [6 ?* T4 t+ n2 O, n
NOTE - Adopting the above mentioned parameters, all CTL Laboratories will get approximately
7 W4 P9 R" s4 O4 m- the same time constant T = Li / Ri = 2·10-3 / Ri;
! {! F0 O. [& w& l6 t" B6 B- the same oscillatory frequency fo = 1 / 2· (Li Cp)1/2 500 Hz.
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