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

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DSH 201A ; U, j! {: Q* f0 b

Characteristics of D.C. electric circuits for verifying normal operation and making and breaking cap ... + F4 r1 F; d6 {

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Generality

To 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:
- Voltage drop
The maximum voltage drop which should not be exceeded, when passing from noload
to load condition, is 5% of the rated voltage.
- Voltage ripple value
. H, [9 f3 b4 U& CThe supply voltage ripple, at no-load condition, should not exceed 5%.
NOTES:
- 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.
- The use of a three-phase rectifying bridge, which gives a theoretical ripple of about 4,2%, complies with this recommendation.
4 E3 d' H7 S  s8 e- Recovery voltage
Test circuit, where:
- E is the supply voltage at no-load condition;
! _7 ^9 ^! B3 f/ T- Li is equivalent to the different self-inductances of the supply as well as the stray inductances of the rest of the test circuit;
. |( {* T% l7 j3 H- Cp is the stray capacitance of the circuit;
) E% c; P$ h4 U3 G+ n$ c- 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%.
1 J- \9 \! q6 \, E; J, y. MNOTE - Adopting the above mentioned parameters, all CTL Laboratories will get approximately
- the same time constant T = Li / Ri = 2·10-3 / Ri;
4 E$ ?  A5 z+ R1 L$ G' K- the same oscillatory frequency fo = 1 / 2· (Li Cp)1/2  500 Hz.


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