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Motor start time
There are many variables that will govern the run up time of the motor. It's not uncommon to start the motor/pump of this rating DOL provided you've ensured that the voltage drop at the bus from where it is fed is within the limits. We presume, you've carried out the motor starting study with your other base load ON and established the Voltage drop at the bus.
Ideally, the actual run up time will be based on motor characteristics and on whether you are starting it on load or else. The motor manufacturers shall be able to provide you with the typical datasheet for the motor as well as the pump. I mean, for the equipment as a whole. Typically, at this rating and with a back pressure of feed water, i would imagine it to be in the region of 1 to 11/2 minutes. Get in touch with in good pump manufacturer and he shall be able to give you the guideline numbers based on the identically rated equipment that he may have supplied in the recent past.
One thing to consider is capacitors on the terminal of the motor to provide adequate PF correction. This will also shorten the start time and reduce the voltage sag as the capacitors supply reactive support.
SEL makes a great motor protective relay, SEL-710 that has thermal learning for specific motor application.
Motors will pull up to 13x FLA for the 1st half cycle of start and then drop to 6x fla for the rest of the start. A motor that is driving a centrifugal pump needs to be started with the discharge of the pump closed if it has a control valve. This reduces the load on the motor, allows the pump to produce its rated Dp without flow of boiler feed water.
The wk2 of the driven load and the torque curve of the motor should be compatible.
You can go back to the motor manufacturer and have them do the calculation for you. The calculation is in IEEE STD 112. You will need to provide a load speed vs torque curve. You will also need to provide the inertia of the pump with water. Tell them it is DOL and any Short Circuit Limit or inrush limit. They basically have an integration calculation based on the difference in torque between what the motor provides and the load requires. The difference is acceleration torque. They will use the average acceleration torque over a 10% (10 % is common but it could be another increment) change in speed change and the total inertia to calculate an incremental acceleration time. They will calculate these times from 0 to 10%, 10% to 20%, etc to 90% to 100%, and add them up (integrate). They will change the speed torque curve of the motor to accommodate the voltage drop, SC, or inrush limit. Please note: regardless of where you look up the calculation or go back to the motor manufacture, inform the motor manufacturer what you are doing. That size of motor is usually designed for a specific application. If you try to start with an excessive voltage dip or a high inertia, you may very easily damage the motor thermally even start a fire if your control equipment is not set properly.
Ideally, the actual run up time will be based on motor characteristics and on whether you are starting it on load or else. The motor manufacturers shall be able to provide you with the typical datasheet for the motor as well as the pump. I mean, for the equipment as a whole. Typically, at this rating and with a back pressure of feed water, i would imagine it to be in the region of 1 to 11/2 minutes. Get in touch with in good pump manufacturer and he shall be able to give you the guideline numbers based on the identically rated equipment that he may have supplied in the recent past.
One thing to consider is capacitors on the terminal of the motor to provide adequate PF correction. This will also shorten the start time and reduce the voltage sag as the capacitors supply reactive support.
SEL makes a great motor protective relay, SEL-710 that has thermal learning for specific motor application.
Motors will pull up to 13x FLA for the 1st half cycle of start and then drop to 6x fla for the rest of the start. A motor that is driving a centrifugal pump needs to be started with the discharge of the pump closed if it has a control valve. This reduces the load on the motor, allows the pump to produce its rated Dp without flow of boiler feed water.
The wk2 of the driven load and the torque curve of the motor should be compatible.
You can go back to the motor manufacturer and have them do the calculation for you. The calculation is in IEEE STD 112. You will need to provide a load speed vs torque curve. You will also need to provide the inertia of the pump with water. Tell them it is DOL and any Short Circuit Limit or inrush limit. They basically have an integration calculation based on the difference in torque between what the motor provides and the load requires. The difference is acceleration torque. They will use the average acceleration torque over a 10% (10 % is common but it could be another increment) change in speed change and the total inertia to calculate an incremental acceleration time. They will calculate these times from 0 to 10%, 10% to 20%, etc to 90% to 100%, and add them up (integrate). They will change the speed torque curve of the motor to accommodate the voltage drop, SC, or inrush limit. Please note: regardless of where you look up the calculation or go back to the motor manufacture, inform the motor manufacturer what you are doing. That size of motor is usually designed for a specific application. If you try to start with an excessive voltage dip or a high inertia, you may very easily damage the motor thermally even start a fire if your control equipment is not set properly.
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