An agitator is essentially a centrifugal load. This means that the power-to-speed ratio is typically a square function. In most agitators, the actual relationship between torque and density is:
Torque = (Shaft Power) * (Fluid density) * (Shaft speed)^2 * (Impeller diameter)^5 / (2 * pi)
There are too many variables to analyze, so you would have to put more detailed information, as for example, location of the panel, number of I/O cabinets, quantity and type of PLC and quantity of modules, type of MCC, type and quantity of cubicles, same for the drives, if they are soft starters they may occupy more space, type of mountings for the electrical and PLC components, etc.
If there is no need for a variation of speed, the Soft Starter is the ideal solution. Soft Starting solutions will enable a reduction in equipment size, reduced demand on the electrical network, zero harmonics (after starting), reduced maintenance on equipment, user friendly configuration and set up.... and a great commercial offer. Although the starting conditions can be very harsh (High Inertia), from units in new projects, through replacement of DOL starting and gears to replacement of slip ring motor starting with Soft Starters.
Motor model, rated power, rated voltage, rated current and motor connection mode;
Motor basic parameters and motor drive load type;
Installation site condition and cabinet color;
Soft start is used for three main reasons:
First, with a very fast output voltage rise time the charging current of the output capacitors (C × dV/dt) can trip your overcurrent circuit or at the very least, cause excessive component stress.
The decision-making process for selecting a custom machine builder depends on a lot of factors, but I would say the most important is expertise in applications similar to that being quoted. No custom machine builder has equal expertise in every area. Most of the machine builders I have worked with specialize in certain genres, i.e. packaging, automotive, robotics, test and measurement, pharmaceutical/medical devices, process, etc.
It depends on load, every electrical/electronic hardware has capacitance inductance, to transfer the current from power supply to another machine need these parasitic capacitances to charge which then acts as local load as it provides a discharge path for those charges accumulated in those contact capacitances & inductance. I told this because the delay very much depends on current & parasitic reactances offered by them which ultimately decides the charging time & discharging time.
When the motor load is light, the soft starter working at energy-saving conditions, PF switch to Y position, under the current feedback action, the soft starter reduces the motor voltage automatically, to reduce excitation component of the motor current. Thereby improving the power factor of the motor (COS∮). If the contactor in bypass state, this feature cannot works. TPF switch provides energy saving features with two reaction times: normal speed and slow speed. The soft starter operation in energy saving state automatic (In normal and slow speed), saving 40% energy in no-load and 5% with load.
A few years ago I had to find root cause of Mosfets failing in an inverter bridge. There were 4 low power devices all in a tiny TSOP-8 package. Part of a module for powering an LCD monitor. The failures were random, but in the range of a few thousand ppm during the system burn in. Peculiar thing was that it was always one pair that got burnt out - the right arm of the bridge.
It depend on your load characteristic for example you can use soft starter for centrifugal pumps, fan...where Moment (N.m) directly proportional to speed (rpm). Soft starter will reduce your start up current by reduce stator voltage when start up motor. Typically, it start with 60% nominal voltage. So it should not use for flit, lathe...which need more/most moment when start-up.
Although both devices falls under reduced voltage starting method, but soft starter can not vary the frequency. Soft starter just helps to lower the starting current and smoother the start up. Whereas AC drive inverter its much more intelligent and it has all the functions of soft starter.
If the money is not an issue and proper investigation of application, I will consider AC drive inverter instead Soft starter.
Rotor current will be directly proportional to torque and stator current. In affect you could measure the stator current and calculate the approx rotor current. Measuring the rotor current directly with standard instruments will give errors as you are in affect measuring the current at whatever the slip frequency is.