Inadequate Oil Supply: Measure the Cause, Not the Symptom

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This is Part Three of a three part series on steam turbine tips, discussing the challenge of inadequate oil supply.

Directly measuring bearing metal temperature is the most effective way to really determine if a bearing is running hot. 

Bearing oil drain temperatures are still being utilized on older machines.  By the time the bearing oil drain temperature has increased, the bearing may have already been compromised (wiped). PSG recommends that these older machines should have temperature probes (thermocouples or RTD’s) installed in the bearing Babbitt to properly monitor performance.

Inadequate Oil Supply - Part ThreeA two-level alarm is recommended (not automatic trip). Consequently, the first alarm should be set a few degrees above the highest temperature in the recommended normal operating range.  Operators should also closely monitor bearing temperature after the first alarm sounds.

Keep in mind that if the temperature rises abruptly and unexpectedly, the bearing may have been compromised and immediate action needs to be taken. Gradual temperature changes which trigger the alarm may be the result of other factors but are still a concern and should be thoroughly investigated.

The second alarm should be set at the maximum operating temperature of the bearing material.  Operators should manually trip the unit in a controlled manner as soon as possible after this second alarm sounds and determine the cause.

The critical temperatures for each of the two levels can be supplied by the manufacturer or recommended by PSG for your individual unit configuration. Different temperature ranges are recommended for Tilt Pad, Elliptical, Short Elliptical, and Thrust bearings.

Measuring drain oil temperature is too slow and too imprecise to effectively minimize your overall cost of maintenance. Taking all of this into consideration, the best practice is to retrofit your machine and save your bottom line.

Do you have questions about your steam turbine backup system? Contact PSG today to explore how we can provide support and maintenance options to help you avoid backup system problems.

Inadequate Oil Supply: Don’t Kill Your Turbine on Startup

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This is Part Two of a three part series on steam turbine tips, discussing the challenge of inadequate oil supply.

Your lube oil temperature needs to be lower at startup and shutdown than at full speed to reduce potential issues.

Your turbine’s rotor does not actually ride on the surfaces of its bearings. It rides on a thin film of oil between the rotor and the bearing. At high turbine speeds the rotor hydroplanes across the oil, eliminating contact with the Babbit of the bearing. The heat generated by the turbine decreases the viscosity of the oil and increases its “slipperiness”, which is important at high speeds.

Inadequate Oil Supply - Part TwoAs the rotor slows down, the oil needs to be more viscous to repel the force towards the bearing.

Failure to lower the lube oil temperature (and therefore increase viscosity) can result in light bearing wipes or smearing. These conditions would occur during turning gear operation, unit startup and unit coast down during shutdown.

The ideal lube oil temperature at these lower speeds is 90 degrees Farenheit. Of course, oil temperature can also be too cold on startup—similar to trying to start your car on a cold winter day. Operational personnel are ultimately responsible for maintaining this lower lube oil temperature by regulating water through the lube oil coolers.

Maintaining lube oil cooler cleanliness is also very important for turbine startups.  The tubes must be clean to allow the efficient transfer of heat. Also, as a best practice the bundles should be cleaned every two (2) years.  Lube oil coolers are the single most common area for contaminants to hide.

By following these tips, you can ensure the efficient startup of your turbine, as well as greatly reduce any potential operational issues or challenges.

Do you have questions about your steam turbine backup system? Contact PSG today to explore how we can provide support and maintenance options to help you avoid backup system problems.

Power Services Group (PSG) – the Best Alternative to the OEM for Alstom GT24 Gas Turbine Maintenance

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During the first half of 2017, PSG successfully performed a number of maintenance activities at combined cycle power plants with Alstom GT 24 Integrated Cycle System (ICS) turbine-generator equipment.  GT24 work executed by the PSG team for multiple customers throughout the continental U.S. and Latin America:

  • Generator field assembly and owner oversight
  • SSS clutch replacement
  • Bearing # 12 investigation and replacement
  • Owner Oversight during triple C-B-B-Inspection
  • Owner Oversight of HP and IP-LP rotor rework at OEM shop
  • GT 24 assembly supervision
  • Balancing and vibration engineering services

PSG’s leading Subject Matter Expert on Alstom GT 24 ICS equipment, Bob Fischer, comments “The demand for GT24 maintenance services is dramatically increasing as the OEM experiences a shortage of skilled and experienced resources and customers are looking for cost effective alternatives.   With the GT24 fleet reaching maturity, more owners are searching to reduce their OEM dependency.”

If you are interested in starting a discussion on how PSG can help you be successful with our gas turbine maintenance options, please visit our website to request more information, or email us direct at [email protected].

Inadequate Oil Supply: When a Backup isn’t a Backup

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This is Part One of a three part series on steam turbine tips, discussing the challenge of inadequate oil supply.

The International Association of Engineering Insurers has found that the loss of oil pressure causes the highest frequency of failure in steam turbines worldwide. 

Inadequate Oil Supply - Part OneMost of these steam turbine failures are caused by an unreliable backup system to maintain oil pressure to the bearings should the primary AC-driven lube oil pumps fail. These AC motors are powered by either the turbine’s output or the grid—causing a failure if the turbine or generator trips—or if there is an external outage.

Modern turbines have backup powered DC oil pumps mounted on the oil tank, which are triggered by a pressure switch in the event of a loss in oil pressure. With this in mind, it is very important to conduct tests with the AC and DC oil pumps during scheduled maintenance inspections to ensure that the DC pump engages as required.

Such tests can be referred to as cascade pump pressure inspections.  In addition, the tests will confirm the pressures when the DC oil pump will engage after the AC oil pump is actually turned off.

Another best practice is to verify backup batteries on a regular basis, when the unit is down, and mandatory tests should be performed before the unit is placed in operation after an overhaul.

Older turbines can use steam-driven pumps as backup. On these designs, a pressure regulator will sense the drop-in bearing oil pressure and turn on the steam supply to the blade wheel of the pump.  But while these pumps are usually very reliable, they still must be manually tested on a regular basis and after an overhaul.

Care must also be taken to not overspeed the pump or it will potentially cause internal component damage and may even completely destroy the pump.

Some older turbines use gravity lube oil tanks. These tanks are mounted above the unit on stands and are controlled by a check valve type of arrangement. In such cases, there are no pumps involved—gravity provides the bearings with sufficient lubrication in an emergency situation.  While less complicated than DC or steam powered backups, their operation must still be routinely checked.

The bottom line is, that a backup is not a backup unless it is reliable. And it can only be reliable if it is tested.

Do you have questions about your steam turbine backup system? Contact PSG today to explore how we can provide support and maintenance options to help you avoid backup system problems.

Power Services Group recently completed a 500 hour base bolt tensioning project

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Power Services Group recently completed a 500 hour base bolt tensioning project for 122 Siemens 2.3 megawatt wind turbines for a customer in Kansas. Consider Power Services Group for all of your wind turbine bolt tensioning needs.