DSH 201A Characteristics of D.C. electric circuits for verifying normal operatio

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DSH 201A

Characteristics of D.C. electric circuits for verifying normal operation and making and breaking cap ...

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Generality

& ^6 B% S" w# YTo 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:
; U- Y6 i# y( r7 q- ^8 i- Voltage drop
1 \& @. d6 G8 Y8 i: t2 d" mThe maximum voltage drop which should not be exceeded, when passing from noload
to load condition, is 5% of the rated voltage.
) I. N! ?6 Q# ?/ N6 [# w- Voltage ripple value
The supply voltage ripple, at no-load condition, should not exceed 5%.
NOTES:
! \) G7 Y! t/ h+ ^( g9 b8 q- 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.
A 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.
- The limitation of the ripple, which occurs, in practise, in rectifying converters, may be obtained choosing appropriately a rectifying bridge.
0 V/ ?# w& F) [  p" N2 ]- The use of a three-phase rectifying bridge, which gives a theoretical ripple of about 4,2%, complies with this recommendation.
- Recovery voltage
Test circuit, where:
0 M) m/ o# b4 l, D( @- E is the supply voltage at no-load condition;
! V; c1 e# h# J- Li is equivalent to the different self-inductances of the supply as well as the stray inductances of the rest of the test circuit;
4 h: u6 O9 @# m$ m1 w, D- Cp is the stray capacitance of the circuit;
  Q- \+ j4 G: \8 j$ l- Rp is the parallel damping resistance.
Neglecting the parallel damping resistor, Rp, the parameters Li and Cp should be adjusted so as to obtain:
+ m7 X% d$ P* z; G2 s1 h* K- Li = 2·10-3 H ± 25%, and
- Cp = 50 mF ± 25%.
: I# g& _1 B3 I. gNOTE - Adopting the above mentioned parameters, all CTL Laboratories will get approximately
+ N* f' v; E; x/ ~- the same time constant T = Li / Ri = 2·10-3 / Ri;
- the same oscillatory frequency fo = 1 / 2· (Li Cp)1/2  500 Hz.

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