amit291977,
It's obvious that English is not your native language so some of what you posted is unclear to us, but I will attempt to address some of your issues as well as further explain the other's questions.
As I perceive your question, you have a total of 1110kW of connected load on your switchboard, with the 3 x 315kW + 1 x 165kW motors being started DOL. You want to know what will happen if you have some of the loads connected and you attempt to start the remaining one (or more). Your initial scenario implies that you have 315kW connected and want to add in another 315kW motor. But actually, a worse scenario is that you have 795kW connected and attempt to add the final 315kW motor. So there is one problem; you need to be more clear about what your worst-case scenario is.
The point others were making is that nobody can answer that question anyway with the information you have provided. Voltage is irrelevant in this situation, what matters is the available current capacity of your system. With 1100kW that can be connected, that means you will have approximately a 1400kVA potential load on whatever transformer you have feeding power to the switchboard. Without knowing the capacity of that transformer, there is no way to begin to predict what will happen when you add a motor. For example, if your transformer is rated for only 2000kVA, attempting to start that final 315kW motor when you have already loaded that transformer with 994kVA means that your voltage will drop considerably. That means that ALL of the existing motors will lose torque, which may cause them to become overloaded, just at the time you are attempting to add in that final motor. The result may be that everything fails. On the other hand, if you have a transformer rated for 10,000kVA, adding a second or 3rd or 4th motor when others are already running will not likely have any noticeable effect.
