phineascage
Member
- Location
- Gaffney, SC
Hi,
This is my first post here. I’ve read and gained lots of useful information from this forum over the years and for that I’m grateful. I’ve tried finding help for a current problem I’m having here and on other websites but can’t seem to nail down what I’m dealing with. I’m looking for some troubleshooting advice on a 3 phase 2S1W type motor problem. The motor is operated by three contactors. One contactor supplies line voltage to T1, T2, &T3 for Low speed while the other two contactors are open. For High speed another contactor supplies line voltage to T6, T4, & T5 and the third contactor shorts T1, T2, & T3. This motor is used to operate a cooling tower fan in a power plant type facility. It is a three cell cooling tower and generally all cells are in operation. In the warmer months all three cell fans will operate in high speed. My problem is that one fan continuously draws abnormally high current while operating in high speed. While in low speed the current is below FLA and appears normal. The motor nameplate information is below:
High: 460VAC / 250HP / 290FLA / 1.15SF / 1790RPM / 2 SPD 1 WDG Variable Torque
Low: 460VAC / 62HP / 100FLA / 1.15SF / 890RPM / 2 SPD 1 WDG Variable Torque
Below are some of the tests I’ve performed thus far:
High speed current to problem fan motor:
T6 - 329.2A
T4 - 327.6A
T5 - 324.1A
Low speed current to problem fan motor:
T1 - 89.2A
T2 - 91.2A
T3 - 90A
High speed current to other normally operating fan motor:
T6 - 274.9A
T4 - 287.1A
T5 - 275.7A
Output high speed voltage to problem motor at bottom of contactor:
T6, T4, & T5 – All roughly 480VAC
High speed voltage to problem motor at leads in junction box:
T6, T4, & T5 – All roughly 476VAC
High speed voltage to ground for problem motor at leads in motor junction box:
274.4V
274.2V
273.4V
Uncoupled motor from gear box and ran motor unloaded. Recorded motor current:
High Speed:
T6 - 191.1A
T4 - 198.1A
T5 - 191.9A
Low Speed:
T1 - 80.8A
T2 - 81.8A
T3 - 81.6A
High speed shorted connection current to problem fan motor:
T1 - 161.9A
T2 - 154A
T3 - 156.6A
High speed shorted connection current to other normally operating fan motor:
T1 - 135.5A
T2 - 136.6A
T3 - 139.4A
Interestingly this motor was recently repaired having new bearings and rotor work done. An insulation resistance and HiPot test were done at the motor shop and both indicated good motor windings. The motor shop report indicated that in High speed unloaded the motor current was at an average of 152A and when operated unloaded at our site the High speed current is roughly 45A higher. All connections have been checked for looseness and corrosion and nothing found. The High speed motor conductors are individual sun resistant 600V, 500kcmil wires. There are two splices in two different phase 500kcmil wires that I have found. I have viewed both splices with a Fluke IR camera and saw nothing warm leading me to believe they are OK. The Low speed and High speed shorted conductors are a sun resistant direct burial 90C 600V, three conductor and ground 2AWG jacketed cable. When this motor is operating in high speed the three conductor cable is showing very warm with our IR camera, naturally since it has about 30A higher flow than the 2AWG is rated for. I have found some cracked insulation on the individual 2AWG conductors in the motor junction box and sealed these up with silicone high voltage tape and super 33. The cracked insulation could be due to the excessive heat that the motor is experiencing over an extended period of time as from what I’ve been told this has been and ongoing problem for years.
We are not experiencing any breaker or overload trips just hot conductors and a motor which I believe are contributing to a reduced motor life. I have talked to our contact at the motor shop several times and he has run out of ideas and is now suggesting sending the motor in for winding replacement. I’m not convinced the motor is at fault and have my suspicions of the motor conductors since the motor shop unloaded high speed current differed significantly from what was measured at the plant site. If anyone on this board has any suggestions to what I should look at next it would be most appreciated. I apologize for the long winded description, I just wanted to give as much info up front as I could.
Warm regards,
Michael
“What do electricians chant to meditate? Ohm….”
This is my first post here. I’ve read and gained lots of useful information from this forum over the years and for that I’m grateful. I’ve tried finding help for a current problem I’m having here and on other websites but can’t seem to nail down what I’m dealing with. I’m looking for some troubleshooting advice on a 3 phase 2S1W type motor problem. The motor is operated by three contactors. One contactor supplies line voltage to T1, T2, &T3 for Low speed while the other two contactors are open. For High speed another contactor supplies line voltage to T6, T4, & T5 and the third contactor shorts T1, T2, & T3. This motor is used to operate a cooling tower fan in a power plant type facility. It is a three cell cooling tower and generally all cells are in operation. In the warmer months all three cell fans will operate in high speed. My problem is that one fan continuously draws abnormally high current while operating in high speed. While in low speed the current is below FLA and appears normal. The motor nameplate information is below:
High: 460VAC / 250HP / 290FLA / 1.15SF / 1790RPM / 2 SPD 1 WDG Variable Torque
Low: 460VAC / 62HP / 100FLA / 1.15SF / 890RPM / 2 SPD 1 WDG Variable Torque
Below are some of the tests I’ve performed thus far:
High speed current to problem fan motor:
T6 - 329.2A
T4 - 327.6A
T5 - 324.1A
Low speed current to problem fan motor:
T1 - 89.2A
T2 - 91.2A
T3 - 90A
High speed current to other normally operating fan motor:
T6 - 274.9A
T4 - 287.1A
T5 - 275.7A
Output high speed voltage to problem motor at bottom of contactor:
T6, T4, & T5 – All roughly 480VAC
High speed voltage to problem motor at leads in junction box:
T6, T4, & T5 – All roughly 476VAC
High speed voltage to ground for problem motor at leads in motor junction box:
274.4V
274.2V
273.4V
Uncoupled motor from gear box and ran motor unloaded. Recorded motor current:
High Speed:
T6 - 191.1A
T4 - 198.1A
T5 - 191.9A
Low Speed:
T1 - 80.8A
T2 - 81.8A
T3 - 81.6A
High speed shorted connection current to problem fan motor:
T1 - 161.9A
T2 - 154A
T3 - 156.6A
High speed shorted connection current to other normally operating fan motor:
T1 - 135.5A
T2 - 136.6A
T3 - 139.4A
Interestingly this motor was recently repaired having new bearings and rotor work done. An insulation resistance and HiPot test were done at the motor shop and both indicated good motor windings. The motor shop report indicated that in High speed unloaded the motor current was at an average of 152A and when operated unloaded at our site the High speed current is roughly 45A higher. All connections have been checked for looseness and corrosion and nothing found. The High speed motor conductors are individual sun resistant 600V, 500kcmil wires. There are two splices in two different phase 500kcmil wires that I have found. I have viewed both splices with a Fluke IR camera and saw nothing warm leading me to believe they are OK. The Low speed and High speed shorted conductors are a sun resistant direct burial 90C 600V, three conductor and ground 2AWG jacketed cable. When this motor is operating in high speed the three conductor cable is showing very warm with our IR camera, naturally since it has about 30A higher flow than the 2AWG is rated for. I have found some cracked insulation on the individual 2AWG conductors in the motor junction box and sealed these up with silicone high voltage tape and super 33. The cracked insulation could be due to the excessive heat that the motor is experiencing over an extended period of time as from what I’ve been told this has been and ongoing problem for years.
We are not experiencing any breaker or overload trips just hot conductors and a motor which I believe are contributing to a reduced motor life. I have talked to our contact at the motor shop several times and he has run out of ideas and is now suggesting sending the motor in for winding replacement. I’m not convinced the motor is at fault and have my suspicions of the motor conductors since the motor shop unloaded high speed current differed significantly from what was measured at the plant site. If anyone on this board has any suggestions to what I should look at next it would be most appreciated. I apologize for the long winded description, I just wanted to give as much info up front as I could.
Warm regards,
Michael
“What do electricians chant to meditate? Ohm….”