DSH 201A Characteristics of D.C. electric circuits for verifying normal operatio
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Characteristics of D.C. electric circuits for verifying normal operation and making and breaking cap ...
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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
The 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.
- Recovery voltage
Test circuit, where:
- 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;
- 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
- 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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