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

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DSH 201A / X# F- ^. ]" ?- i( q- ]; o

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

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Generality

. k- K. p0 G! h" J( ZTo 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:
7 A2 }7 W4 R; r( T7 i% h- Voltage drop
# l( @) q" n" e, K; t1 k# M$ q0 TThe maximum voltage drop which should not be exceeded, when passing from noload
to load condition, is 5% of the rated voltage.
; n9 k& E( ~. j9 ~- Voltage ripple value
1 P, y5 @% O7 L8 P. R7 s" X/ MThe supply voltage ripple, at no-load condition, should not exceed 5%.
' m( ~, \9 h6 G/ X, wNOTES:
" i' b0 g" Z/ f4 u2 x. j$ G- 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.
- ]0 n- g) u  S4 ^6 J: L- d# a( B  AA 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.
1 z% R, x1 i0 [' R- The use of a three-phase rectifying bridge, which gives a theoretical ripple of about 4,2%, complies with this recommendation.
- Recovery voltage
$ J* {& N# _2 i! r- `Test circuit, where:
& \$ u$ E, J! w- E is the supply voltage at no-load condition;
- Li is equivalent to the different self-inductances of the supply as well as the stray inductances of the rest of the test circuit;
- J8 o( X9 ~+ O( O* @- L+ ~- Cp is the stray capacitance of the circuit;
- Rp is the parallel damping resistance.
Neglecting the parallel damping resistor, Rp, the parameters Li and Cp should be adjusted so as to obtain:
- Li = 2·10-3 H ± 25%, and
- Cp = 50 mF ± 25%.
NOTE - Adopting the above mentioned parameters, all CTL Laboratories will get approximately
; j5 B, e  f1 z, k- 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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