Entries by psgweb

Seconds From Disaster – Overspeed Devices

A full loss of generator load can cause the operating speed of a turbine (steam or combustion) to go from normal to catastrophic in a matter of seconds. The electrical load can be lost from generator failure or from external sources such as hurricanes, floods or ice storms downing power lines. Basically, the generator load […]

Set IGVs for Maximum Efficiency

Have your combustion turbines been losing power after overhauls? There are many factors which can affect power production, but the IGV settings are one area that even the OEM can overlook. We recently helped a plant with three GE Frame 6B gas turbines that had lost power over successive overhauls. Units 1 and 2 had […]

Measure the Cause, Not the Symptom

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 […]

The Ugly Effects of Water in Lube Oil

Free and emulsified water are the two most harmful conditions in a lubricating system. The incompressibility of water overrides the hydrodynamic oil film that protects bearings, leading to excessive wear. As little as one percent water in oil can reduce the life expectancy of a journal bearing by as much as 90 percent. Water will […]

Rotor Axial Position Sensor

It’s an average day in the powerhouse, and suddenly the turbine starts squealing. As you’re running around trying to find the cause, the turbine gives a terrific shudder and shuts down. What you will soon discover is that the thrust bearing reached its limit of wear, sending the blades crashing into the diaphragms. This disaster […]

Why Is My Generator Rotor Vibrating?

Generator rotor imbalance can come from a number of different sources, i.e. coupling misalignment, component non-concentricity, rubbing, oil issues, bearing, and journal issues. Each has unique characteristics. Thermal sensitivity has its own recognizable characteristics. If you are unable to operate your Turbine Generator at high field current or VARs because of exceedingly high vibration, your […]

D11 Issues – Cracks in the HP/IP Shell

At STUG 2015, 50% of users of the GE D11 Steam Turbine reported cracking issues in the HP/IP shell, especially the N2 packing gland and shell fit. These cracks create the potential for forced shutdowns and relatively long outage cycle times. Operators can mitigate this potential through a more rigorous NDE of the gland and […]

Why Valve Freedom Testing is Critical

At STUG 2015, a survey revealed that 43% of D11 combined cycle users perform valve freedom testing on a daily basis, while 38% perform it on a weekly basis. The potential accumulation of deposits is a little more critical in these high temperature units, but exercising valves is important on any unit. For instance, on […]

Why is a Clean Generator a Happy Generator?

A generator is susceptible to four categories of aging factors which reduce the overall service life of the machine: 1) Mechanical aging; 2) Thermal aging; 3) Electrical aging; 4) Environmental aging. Simply stated, a dirty (contaminated) generator causes environmental aging. A few of the more common contamination elements include oil, water, dirt, dust, carbon, and […]

How 0.002” Can Ruin a Turbine

Steam turbines can reliably run for 30, 40 years or more. However everything wears and eventually fits, finishes and tolerances become unacceptable. For instance, the rabbet fit on the coupling faces of a three bearing machine will eventually become loose and in need of repair. This defect can cause misalignment, abnormal vibration levels and undue […]