—————— SM 32 ——————
38-GB
3. SELECTION OF THE SM-32 CONVERTER
The SM32 converter has to be chosen so that the sum of the inverter DC-link currents,
both for class 1 and 2, is lower or equal to the corresponding ones stated in chapter 2.6.1.
3.1. DIP-SWITCHES AND JUMPER
On R-SM3-L Card
S1.1-4 Selection of the delay for thyristor disabling during mains dip.
S2.1-3 Selection of the undervoltage threshold.
S3.1-4 Selection of the capacitors precharge time
S4 - S5 Selection of the AC mains frequency: 50 or 60 Hz
CV Selection of the ML signal function
3.2. USE OF S1 SWITCH
If the system functioning allows a limited dip voltage value of the DC-LINK, (a condition
obtainable by handling the DC-LINK with a suitable software or with additional external
capacitors) it is possible, during a mains dip with a maximum duration time of 10mS, to
prevent the thyristor switching off, of the SM-32, during the detection of the voltage drop
(repeating then the precharging sequence once the voltage is restored).
The disadvantage of such function is obviously the presence of a high current inside the
SM-32 once the voltage is restored. For this reason it is necessary to take appropriate
countermeasures by checking the decreasing slope of the DC-LINK voltage during the
mains dip. Therefore, knowing the value of the connected capacitors and the maximum
current supplied by the SM-32, it is possible to calculate the maximum “mains dip” bearable
by the converter itself.
Example:
Calculate the maximum “mains dip” bearable by a converter size 185A, whose mains
choke has the following values: 0.148mH 173 rated A and 350A of saturation current.
The converter supplies 8 inverters AMV32- 4011 (the internal capacitors value of each
inverter is equal to 470μF); using an oscilloscope, it has been stated that during a normal
functioning, in case of a mains dip, the DC-LINK discharges 70V after a 3-mS mains dip.
The aim is to state whether such “mains dip” can be overcome without the precharging
phase.
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