Hi,

Currently, we have 2 identical motor blowers with 1 header. There is a significant difference in ampere between the 2 motors. The first motor is around 20A and the second motor is around 30A. We do not have a pressure or flow transmitter to monitor the performance of the blower. Our analysis is the check valve on the first motor is not fully opened which causes the ampere to decrease, hence increasing the current of the second motor to cover up the decreasing flow on the first motor blower. Is our analysis correct? Thank you.

 

why is your check valve not fully opened?

 

We do not have the justification on the state of check valves, so it just our initial hypotesis. We suspect the check valve is not fully opened because there is no debris on the outlet of the blower.

 

the power will be proportional to the mass flow for low pressure blowers

 

I had a similar situation once, with a similar set-up. It turns out the set screw of one of the blower motor-to-fan couplings was loose, allowing the motor to run at rated speed while the blower fan was not running at rated speed. A little thread-lock fluid before we re-tightend the set screw was all it took to fix the problem. We had checked the three-phase starter contactors, the voltage/current draws, the check valves, the single orifice controlling flow. All good--until we used a non-contact tachometer to check the speed of the blower itself. (Of course, the coupling was underneath a safety guard/cover that was tight up against the blower fan housing so we couldn't really see the blower fan shaft as it was turning until we (finally) removed the cover.) The Company lost a LOT of money because of the unavailability of the machine--all for a 1/8-th inch set screw and our assumption that the problem was not the simplest mechanical problem while we checked every OTHER possible cause for the fan not running at rated speed and preventing a machine start.

It's all good to analyze the situation before taking action to try to determine the best and most likely cause of the problem before starting investigation. But have you considered if the coupling bolt/screw had loosened and how easy it is to verify if it's tight or has loosened. There should be more than one criteria for prioritizing troubleshooting activities.


I'm not saying the problem is a loose coupling bolt/screw, but it's a possibility for most mechanical motor-blower configurations. That OFTEN gets overlooked, because anything that has wires on it is automatically suspect when troubleshooting equipment these days.

Yeah?

 

I forgot to ask: WHEN DID THIS PROBLEM START?

After a maintenance outage?

After the motor or the blower was replaced?

After the discharge manifold was removed and replaced?

 

Hi WTF,

Thank you for sharing. Our motor blower does not have a coupling so I think we can eliminate this possibility.
We did not know when exactly the problem started since we took the ampere measurement reading once per month. On May 2022, 88TK-1 current is 26A and 88TK-2 is 26A. On June 2022, 88TK-1 is 26A and 88TK-2 increase to 33A. On July 2022, 88TK-1 decrease to 20A and 88TK-2 stay on 33A. There is no maintenance on the any of the motor or the blower between May - July 2022. We are confused why this is happened in the first place.

 

I'm sorry I forgot to mention that on October 2023, we swapped the check valves on 88TK-1 and 88TK-2. The results are 88TK-1 current is decrease to 20A and 88TK-2 current is stay on ~33A.

 

Please, can you post clear photos of one or both of the exhaust frame blowers, and in particular the "interface" between the output shaft of the motor and the input shaft of the blower?

ALSO, can you post a clear photo of one of the exhaust frame blower motor nameplates?

Okay, so it doesn't seem to be the check valve(s). AND, the problem seems to have stayed with 88TK-1 when the check valves were replaced. (Interesting this discrepancy was apparently first noted in July of 2022 and this post appeared in January of 2024, after some troubleshooting was done in October 2023.) It seems the site takes motor readings periodically. What were the two motor currents before July 2022--where they nearly equal, or slightly different?

When I was asking about maintenance outages, I was speaking specifically about gas turbine maintenance outages not exhaust frame blower maintenance (though exhaust frame blower maintenance is often during a gas turbine maintenance outage). Depending on the location of the exhaust frame blowers/motors sometimes they have to be removed to perform the maintenance (older GE-design Frame 6 heavy duty gas turbines had the exhaust frame blowers/motors mounted on the roof, so if the roof had to be removed for maintenance the exhaust frame blowers/motors had to be removed (and reinstalled).

WHAT HAPPENS TO THE CURRENT DRAW OF 88TK-1 WHEN 88TK-2 IS STOPPED? AND WHAT HAPPENS TO THE CURRENT DRAW OF 88TK-1 WHEN 88TK-1 IS STOPPED? (Depending on the machine, one exhaust frame blower/motor can be stopped without affecting turbine operation; some machines will automatically lower load when one exhaust frame blower/motor stops, and some will initiate an automatic shutdown of the gas turbine if both blowers/motors stop running. It would be necessary to see the programming/configuration of your machine's turbine control system to understand how the machine at your site is programmed. But, this test could be performed when the machine is shut down, by first starting both blowers/motors and noting the current draws of both motors, and then cycling one blower/motor OFF, checking the current draw of the other motor, re-starting the blower/motor that was stopped and stopping the other blower/motor and checking the current draw of the running blower/motor, then re-starting the stopped blower/motor and checking the current draws of both motors again.)

HOW OLD ARE THE EXHAUST FRAME BLOWER MOTORS AND BLOWERS?

ARE YOU MEASURING ALL THREE PHASE CURRENTS OF BOTH 88TK-1 AND 88TK-2? (Sorry; I have to ask because I'm not there and I don't know how you are checking the phase currents of the motors.)

HAVE YOU USED A NON-CONTACT THERMOMETER (INFRARED HEAT DETECTOR) TO CHECK THE CONTACTOR OF 88TK-1 AND 88TK-2, AS WELL AS THE TERMINALS WHERE THE MOTOR LEADS ARE CONNECTED? IF SO, DID YOU NOTE ANY HOT, OR COLD, SPOTS ON THE CONTACTOR TERMINALS OR WHERE THE MOTOR LEADS ARE TERMINATED?

DO YOU HAVE A NON-CONTACT TACHOMETER TO CHECK THE SPEED OF THE TWO EXHAUST FRAME BLOWER MOTORS--AND THE TWO BLOWER IMPELLERS?

HAVE YOU OPENED THE JUNCTION BOX ON 88TK-1 TO SEE WHAT IT LOOKS LIKE INSIDE?

IS IT A LOT OF WORK TO SWITCH THE MOTOR LEADS TEMPORARILY IN THE MOTOR CONTROL CENTER/MOTOR STARTER BUCKETS?

Electric motors, even three-phase electric motors, are pretty simple things. They are going to produce torque in proportion to the load on the output shaft, so if the load on the output shaft is low the motor load will be low, and vice versa. Electric motors are also subject to wear and aging as well as degradation of stator windings and rotor issues. Most electric motor repair facilities will have someone who has experience with troubleshooting and fixing electric motor problems.

So, there's some ideas for things to try and what might possibly be the problem. It's NOT likely the problem is caused by the turbine control system, and, again, most electric motor repair shops have at least one person who might be able to suggest some troubleshooting ideas. But, don't overlook anything in your troubleshooting--troubleshooting is often a process of elimination, meaning that one has to have a list of possible causes then prioritize that list to select the most likely causes (INCLUDING loose terminals, bad starter contacts, and poor motor lead terminations) and just start working through the prioritized list until the cause is eventually identified, and resolved. Yes, this seems like a simple problem--and it may well turn out to be simple. And you may already have done some of the steps/ideas, but you didn't tell us if you did, and more importantly you didn't tell us what the results of the troubleshooting were. Each step needs to be done methodically and logically and completely taking into account how the testing is performed because poor testing can often fail to identify a problem (and it's kind of embarrassing to have someone come to site to help with troubleshooting and have them find something simple that was already supposedly checked... ask me how I know this...).

We can't help you if you don't answer the questions above. The reason there are many steps and suggestions is because we don't know anything except what you tell us, and you haven't really told us very much, so we either have to say we don't know what the problem, or we can suggest multiple things to try (which we did) and hope the problem becomes evident with good testing. Don't assume anything.

Best of luck!