edgarp
Member
- Location
- East Tennessee
We have a weird situation that has us scratching our heads...sorry for the long post and I hope I don't leave anything out.
System: Two 40 hp belt driven fan motors. Each motor has a normal and an emergency supply. Motor #1 starts and runs fine on both feeds - no problems at all.
Normal supply is about 30 feet from transformer. Emergency supply is from 600 feet away, but voltage drop doesn't appear to be a factor. A manual transfer switch changes from normal to emergency - double throw, 3 pole, 600V, 100A non-fusible.
On emergency power, motor #2 starts and runs every time. On normal, it starts every other time. The MCP (Cutler Hammer HMCP100R3) trips every other time, and once it is reset, the motor will start. Settings on the MCP have been adjusted up with no change - currently set at 600A. Everything in the combination starter is common to both feeds from the XFR switch.
We online (Baker) tested the motor with normal results, same on both feeds. MCP has been replaced. The guts of the manual transfer switch have been replaced with no change. Both motors start and run with same current and acceleration time, and voltage is within 5 volts on either supply. The power quality appears to be fine, tested with Fluke equipment.
All branch wiring has been meggered with good results. At one point the motor was reconnected for the wrong rotation and it started every time. That shouldn't significantly affect inrush, just running current I thought.
Every time we come up with an idea, it just doesn't add up since the motor starts and runs every time on one feed, and every other time on the other. Once the motor is running, it runs perfectly, just as motor #1 does. If we had a fault somewhere we believe tripping would be more random, but I have seen multiple starts and it is a definite pattern of every other time.
Has anyone ever seen anything like this? We believe the combination start is ok because it is common to both feeds, and we believe the motor is fine, as well as the transfer switch. Between engineers and electricians we have tons of experience, but like I said we are scratching our heads.
System: Two 40 hp belt driven fan motors. Each motor has a normal and an emergency supply. Motor #1 starts and runs fine on both feeds - no problems at all.
Normal supply is about 30 feet from transformer. Emergency supply is from 600 feet away, but voltage drop doesn't appear to be a factor. A manual transfer switch changes from normal to emergency - double throw, 3 pole, 600V, 100A non-fusible.
On emergency power, motor #2 starts and runs every time. On normal, it starts every other time. The MCP (Cutler Hammer HMCP100R3) trips every other time, and once it is reset, the motor will start. Settings on the MCP have been adjusted up with no change - currently set at 600A. Everything in the combination starter is common to both feeds from the XFR switch.
We online (Baker) tested the motor with normal results, same on both feeds. MCP has been replaced. The guts of the manual transfer switch have been replaced with no change. Both motors start and run with same current and acceleration time, and voltage is within 5 volts on either supply. The power quality appears to be fine, tested with Fluke equipment.
All branch wiring has been meggered with good results. At one point the motor was reconnected for the wrong rotation and it started every time. That shouldn't significantly affect inrush, just running current I thought.
Every time we come up with an idea, it just doesn't add up since the motor starts and runs every time on one feed, and every other time on the other. Once the motor is running, it runs perfectly, just as motor #1 does. If we had a fault somewhere we believe tripping would be more random, but I have seen multiple starts and it is a definite pattern of every other time.
Has anyone ever seen anything like this? We believe the combination start is ok because it is common to both feeds, and we believe the motor is fine, as well as the transfer switch. Between engineers and electricians we have tons of experience, but like I said we are scratching our heads.