EMC-PARTNER CDN2000-06-25 User Manual page 11

respect, the resulting transient voltage and current in HV busbars are characterised by a fundamental
oscillation frequency that depends on the length of the circuit and on the propagation time.
The oscillation frequency ranges from about 100 kHz to a few megahertz, depending on the influence of the
parameter mentioned above and the length of the busbars, which may vary from some tens of meters to
hundreds of meters. In this respect, the oscillation frequency of 1 MHz may considered respective of most
situations, but 100 kHz has been considered appropriate for large HV substations.
The repetition frequency is variable and a function of the distance between the switching contacts. The
minimum repetition frequency in respect of each phase, is twice the power frequency. The repetition rates
selected, 40/s and 400/s represents therefore a compromise, taking into account the different duration of
the phenomena, the suitability of the different frequencies considered and the problem related to the energy
to which the circuits under test are subjected.
Impedance of the test generator
For testing the input/output ports of measuring relays, the selection of the 200 Ohm impedance is a
compromise. This takes into account that the characteristic impedance of cables used for this purpose
(twisted pairs) has a value ranging from 120 to 150 Ohm in the frequency range above 100 kHz and for a
length of the order of 100 m.
Relevant standards:
IEC 605-4, IEC 605-22-1, IEC 61000-4-18, IEC834-1, VDE 435 Teil 303, ANSI/IEEE C37.90.1
Damped oscillatory wave
Generator
S
C L
Rd
Rs
Cb U
CDN2000-06-25 coupling decoupling network
Voltage at no load
U
100%
T1 = rise time 75 ns
10 to 90 %
T = oscillation period
10 µs for 0,1MHz
1 µs for 1MHz
50%
t
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