Ask Mr Turbine

Bearing Temperature

Bearing temperature monitor alarms should be set at fifteen degrees above normal operating termperature for your unit. It is important to be notified of a deviation from the norm rather than a deviation from some generically assigned number.

Grounding Brushes

Effective grounding of your turbine shaft is critical in eliminating shaft voltages that build up due to gas flow in your turbine. If your turbine has carbon brushes, a film has a tendency to form which effectively insulates itself from the shaft and may prevent effective grounding of shaft currents. Converting to a copper strap design provides a constant electrical contact. If your grounding system is not operating effectively, shaft currents can flow through your bearings causing babbitt deterioration. TGM can assist in the design and installation of this improved rotor grounding system.

Hydrogen System

The recommended cold gas operating temperature is 30C to 40C (86-104F). The alarm is usually set at 50C. Temperatures can be regulated by throttling the water to the hydrogen coolers. Colder hydrogen gas than desired can also affect unit vibration.

Oil Temperature Guidelines

1. Oil within the lube oil tank should be at a minimum of 130 degrees F.
2. Oil to the bearings should be kept at 115 degrees F (out of the lube oil coolers).
3. Satisfactory bearing outlet temperature (bearing oil drain) should be about 140 degrees F. Higher drain temperatures are allowable on larger units. When oil drain temperatures reach a high value such as 160 degrees, the unit needs to be closely monitored for potential bearing damage. Bearing metal temperature devices installed within the babbitt of the bearing provide a better means of monitoring the actual bearing performance.

Did You Know?

TGM’s man behind the scenes—Mr. Turbine—is available anytime for your turbine generator maintenance and repair questions. Mr. Turbine has over 30 years of experience in power generation, so you can expect more of TGM’s professional dedication, quality, and expertise. Just go to the Ask Mr. Turbine tab above. Fill out the form with your question and information, and Mr. Turbine will get back to you with a prompt and reliable answer.

Damage from Long-term Storage

Turbines that are going to be shut down for long periods of time should be prepared to prevent damage. A unit should be left on the turning gear, if possible. The steam to the unit should be eliminated. The drains should be kept open and clear. The result of not doing this can turn into major steam path repairs. The rotor blading can corrode or become pitted, diaphragm blading can become corroded or pitted, split lines and packing hooks become damaged, resulting in a loss of efficiency and potential failures.

Thermal Mass Imbalance

Some generator fields are subject to what is called a thermal mass imbalance condition. The thermal mass imbalance condition occurs when the windings grow during warm up at uneven rates. This causes changes in the balance of the rotating field. One way to counter this is changing the vars (up and down) as the unit is brought up. This changes the current across the field, warming it up evenly.