- The Siemens V20 is for sure not the cheapest VFD on the market, if you are tight on budged.
- High overload or low overload is set upon drive commissioning. Usually it is done by software package Starter (not sure for V20). Anyway you would need a communication adapter for PC<->VFD which is usually high cost. With mount on panel BOP you can't do anything. I have already spent two weeks the first time with BOP and throw it away (Sinamics G120 inverter).
- The overload capability is a short time overload. The VFD can deliver very high overcurrent for very short time, or not so high overcurrent but longer time period. The processor accumulates these overloads and when it's enough it trips into an error.
- The start of the motor with VFD does not cause any overload situation, since you can adjust the ramping time. The current will be proportional to the acceleration and it can be controlled. The overload itself can be caused by material congestion or the need of fast speed change (high acceleration/deceleration) .
- What you should look in the table is the rated power, and rated current.
Q: What is the motor rated current, voltage. What is the desired frequency of the motor. Is it still 50Hz (nominal motor speed rpm) or it will change, since you are thinking to change the reduction ratio?
EDIT:
The drive has to output the torque:
\$M_{mot}=J\cdot\alpha + M_{load} \$, where \$\alpha\$ is the acceleration. If you set ramping time enough large, then the torque needed for mass acceleration is enough small. The motor will have to output mostly the required load torque. Which in your case (extruder): \$M_{load} \propto \Omega\cdot F\$ where \$\Omega\$ is the speed and \$F\$ is the material friction. Note that when using VFD vs. star/delta starting, the induction motor "knee" characteristics is quasi eliminated using VFD. The term quasi is referring at possibility of the VFD to stay within the window of the characteristics where the slip is small.
Starting the motor with heavy load, would require that frequency of the inverter doesn't escape to much from actual motor speed. If so, then you have almost identical problem like with star/delta starter. I would suggest you to use a different type of inverter, that has the capability of Vector control. This is Sinamics G120.
I have done an application, that compresses the material with VFD. The motor is spinning very fast until it begins to compress the material, the final speed is approx 20Hz. The VFD self adapts the frequency so that outputs rated current. It's an G120 inverter, but there are many other manufacturers like Mitsubishi, Omron, Yaskawa,... that have vector drives.
EDIT2:
I have checked the Siemens catalogue, well the V20 series is very basic inverter for pumps, conveyors...it is switching PWM at 2kHz.
MY application consisted in material compressing with vector control G120. The toughest test to compress the material to insane small dimension, so that inverter went in overload error. The tensioning is done with screw lead and nut, so when the inverter stopped due to overload the material wasn't released. After a while the machine was forced to repeat further compression. Therefore: the material was already compressed, the required starting torque was well above the nominal torque. The motor moved and then tripped again into error. This is a proof that with sensorless vector control the motor was able to start turning even in overloaded condition. Of course it stopped very soon, since further moving increased the required torque even more, but you shouldn't be worried to use sensorless vector control to start the motor heavy loaded. But if even this is not good enough, then a reserve plan is to use an encoder feedback for speed (if the VFD can accept the encoder mount).
Check prices for power module PM240-2 30kW (6SL3210-1PE26-0UL0) + control unit CU240E-2 (6SL3244-0BB12-1BA1). Additionally you need 24VDC PSU + USB cable (I used my phone cable, but I ended with micro USB connector ripped off the control unit). Software package: Starter alone (it's free, I think) + BOP panel for information. Presumably you don't need the braking chopper, so there is also a cheaper alternative to PM240-2, it's PM230 (6SL3210-1NE26-0UL0), but it is older, bulkier and not necessarily cheaper than PM240-2.
Similarly check Mitsubishi A700 FR-A740-00570-NA inverter. It has the possibility to hook an encoder. The Siemens would need a control module CU250S-2 instead of CU240-2 for the possibility of an encoder mount.
Maybe Lenze series 8400, Hitachi SJ700D-220 HFEF3, ....There are many of them. You should ask for local dealers and opinions. The final price won't be low (3 to 4 times higher than Sinamics V20), so any good dealer won't hesitate to contact you and give the best price.