Throttling centrifugal pump suction is not a good practice that may lead to pump cavitation. We may have the same effect by throttling the pump discharge. We must first of all that understand the job of a centrifugal pump is to deliver the volume rate required by the system.technically speaking, the pump curve meets the system curve. When we throttle the pump suction pressure we are actually controlling the flow-rate delivered by the pump in which we can also achieve the same effect by throttling at the pump discharge. That is why a good practice is to install flow control at the discharge of the pump.
Centrifugal pumps trip is normally triggered by current due to higher power requirement. Increasing pump suction pressure but the flow rate is maintained the same by controlling at the pump discharge will not increased the pump power.We must also understand that pump power is proportional to pump head and flow-rate but inversely proportional to pump efficiency.When pump suction increases the net effect is to increase the discharge pressure accordingly resulting in increasing the system flow rate as simply explained by Bernoulli equation.The pump is then responded by delivering the system flow requirement this increases the pump power accordingly such that it triggered the pump tripping current.
Hope the above comments triggered your though. We may be able to solve the problem if you can provide more detailed data such as pump suction and discharge pressure and the corresponding flow-rate and most important t is the pump performance curve.
Best regards from S. Ahmad.