We are operating 2 frame 6 B DLN-1 machine (Only Gas fuel) in middle east for meeting out power requirements in process plant. The ambient temp remains above 40 Deg C. The accessory compartment temperature as per GE is 60 Deg C. The ambient temperature of this motor shown as per manual as 40 Deg C.

Thermal imaging was done and temperature is around 60° C during day hours and on the running equipment the temperature reach 90 - 100° C
which cause overheating of cables, windings, cooling fan of motors. Acc cooling fan motor 88 BA 1 & 2 has burnt 3 times in a span of 2 years. The fan of motor is non metallic and gets melted. The motor is EX Motor and its protection EEx e II T3.

I like to know is it normal to have acc compartment temp 60 Deg C and on the running equipment the temperature reach 90 - 100° C or any flue gas ingress.

88BA1 &2 cooling fan of motor is it non metallic generally? (Pl note the fan 88BA 1 & 2 is metallic. The cooling fan of motor is non-metallic.)

Is there alternative motor meeting the same specification?

Is it advisable to shift the motor outside the compartment out side the acc compartment keeping fan inside and having a sealing to protect the CO2 flooding system effectiveness?

 

I would say that even a high-temp plastic motor cooling fan is probably not the best for the application. Can you obtain metal fans from the motor manufacturer? Or source them from another vendor by shaft dimension and mounting method? These are probably being operated in a lead-lag configuration, and I wonder if the fan is melting on the fan that is running or the one that is not running.

Further, since the fans are probably operated in a lead-lag configuration have you tried running both of the fans at the same time to see what effect that has (after 10 or 20 minutes)?

As for compartment temperatures during normal operation, DLN compartments do get very warm. Which has always seemed a little odd to me since the flame temperature is much lower when being operated in Pre-Mix Steady State. You didn't mention if the units are operated mostly in Premix Steady State or Lean-Lean, or which combustion mode.

There should be dampers or louvers, some probably gravity-operated. I have seen many cases where during the original installation or after a maintenance outage the dampers were installed incorrectly and air flow did not open them. I've also seen incorrect damper weights used the gravity-operated dampers.

I've also seen latched dampers become unlatched during operation and close. Some newer units have limit switches on the dampers, but I've seen some latched damper limit switches improperly set up without inversion masks and close to alarm contacts and when the dampers closed but not fully closed there was no alarm.

You need to find the 'Heating & Ventilation' Piping Schematic (P&ID) and have a look at all the directions of air flow through the dampers, and then make sure all of the dampers are properly installed and open or opening when the fans are running. Also, you need to make sure there is no obstruction on the fan suction or discharge.

Lastly, many of the centrifugal fans (we don't know what kind fan it is) have reverse tangential centrifugal fan blades, which means that if you look at the fan blades you will think they should rotate in one direction, but should actually rotate in the opposite direction. When rotated in the wrong direction, they will not move very much air, and will, in fact, the motors will draw excessive current. I have seen people install new, higher-rated thermal overload elements in the motor starters thinking they weren't properly rated to solve the TOL alarm problem, when the real problem was that the motors were running in the wrong direction.

Some of the fan enclosures had direction of rotation arrows painted on the outside, but those usually get painted over before or during commissioning. NEVER trust a direction of rotation arrow on a motor unless you personally verify it is correct. The driven device should always have a direction of rotation arrow.

So, I suggest you also take a clamp-on ammeter and measure the current being drawn by the motor once you confirm all of the dampers are installed correctly, open or opening when the fans are in operation, and any latched dampers are in the open position. If the current being drawn is higher than the motor nameplate, then it's a good bet the fan is rotating in the wrong direction (presuming it is a centrifugal fan). Swapping two motor lead phase wires at the motor starter, re-starting the motor and re-measuring the current draw would be one indication. If the current decreases and the air flow increases through the compartments, then it's a safe bet the motor was being rotated in the wrong direction. If the current increases and the air flow through the compartment decreases, then the motor was probably rotating in the proper direction to begin with.

If you are confident the motor is rotating the fan in the proper direction and the dampers are all installed and open and working correctly, then, I'd say you should contact the packager of the unit (GE or BHEL or whomever) for more assistance with the problem.

But, you should first check to make sure everything is installed and working correctly and then when you ask the turbine packager you can provide all of the information and results you have obtained and probably get a faster response.

Write back to let us know what you find out.

 

Another issue you have with the motor running in an environment over 40 degC is that the motor temperature rating (T3) is only valid if the ambient temperature is below 40 degC. The fact that the motor is burning out means that it a possible source of ignition in the current operating conditions.

What is the T rating of the flammable material?

Bruce.

 

*As mentioned in orginal thread, the melting is the fan for motor cooling attached to motor, not the 88BA2 fan which is metallic. Since it is an explosion proof motor, the fan used for cooling of motor is non metallic. We are looking for an alternative to plastic fan which preliminary is the root cause. Fan gets melted, affects the cooling of motor and motor winding gets damaged. If you can suggest any alternative material to plastic for fan of motor that can be used in explosive atmosphere and can bear this high temperature we wish to proceed for it. The skin temperature of motor goes up to 95 deg c and ambient around fan 60 Deg C .

*We will observe the compartment temperature after starting 2 fans and come back to you.

*Operation is in Premix steady state only.

We had already referred 'Heating & Ventilation' Piping Schematic (P&ID), direction flow etc has been checked. Also we had measure the motor load of 88BA2 and cross checked with second frame 6B machine running. Minor current imbalance is observed in the range 4.8 to 5.2 amps. Vibration has been monitored.

 

AK... can you provide the 3 phase-to-phase voltages as well as the 3 line-currents?

Also you might want o substitute a fan made of alumininum, for the plasic fans!

Regards, Phil Corso

 

concerned that you have a motor inside the acc. cabinet, and their is no mention of the cabinet being purged.

in closed control cabinets (without rotating equipment or fans) we found it necessary to air purge the cabinet with instrument air to limit heat build up. With your motor on the inside, the heat build up will be severe.

Put the motor outside. and make sure you have a vent for any heat build up. Most of our projects were designed for 70C heat mid-day insolation on control cabinets. Sun shields were also required.