Relationship Between Fixed and Variable Speed Pump

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Contromatix Participant Join Date: May 2009 Location: Burkina Faso - West Africa Posts: 1	Relationship Between Fixed and Variable Speed Pump 01/25/2010 1:37 AM
	We have a tailings pump system which pumps tails to our tails dams.There is 2 pumps, one being a fixed speed and one a variable speed.The variable speed is last in line to control the level in the tank.The problem we have is when the variable speed is running and we try to start the fixed speed, it trips on over current.The question is : should the variable speed be firts in line or last.The pumps are both idendical in size, kilo watt and pulley rating. The only way we are able to start the fixed speed pump is to open the suction valve < 10% and slowly openning as the pump current stabelize.
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Kaisan Power-User Join Date: Nov 2009 Posts: 296 Good Answers: 27	#1 Re: Relation ship between fixed and variable speed pump 01/25/2010 4:18 AM
	Most centrifugal pumps trip on overcurrent because the flow is too high. For this reason they would normally be started against a closed or partially opened discharge valve. They should never ever be started with a partially open suction valve, it should always be 100% open. What is probably happening is that your variable speed drive pump is running slower than the fixed speed pump and therefore has a lower differential head. When you start the fixed speed pump, it is trying to start up with high flow due to the low head in the system and this is causing too high a load on the motor. Ensure that the head is high enough to reduce the starting load on the pump to what is acceptable for your motor. (Or throttle the discharge valve for startup and then open immediately the motor is up to speed). __________________ I have no special talent. I am only passionately curious. Albert E
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MalcolmK Power-User Join Date: Jul 2008 Location: UK Posts: 205 Good Answers: 50	#2 In reply to #1 Re: Relation ship between fixed and variable speed pump 01/26/2010 12:36 PM
	GA. I suppose the 2nd pump is required as the first is at full speed and not meeting demand. So the VFD is at full speed (50Hz) and another solution is to disconnect VFD from pump 1 and connect d-o-l and reconnect VFD to pump 2 and bring this to a level where it can add to pump 1. In my experience, its better to have both on VFD to balance the head and share the load better, you only have one VFD so there are always some compromise to be made in control __________________ Something new every day!
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