Large steam driven turbines require a constant flow of lubricating oil to the bearings to maintain balance, reduce friction, wear and maintenance.

Customer profile

250 MW power generating utility produces electricity by steam generation through large steam turbines.

Application description

Large rotating turbines require continuous lubrication during operation. The oil not only lubricates the bearings, but also aides in removal of heat generated by the high speed turbine shaft.
Hot oil (250°F) is moved from the turbine oil sump to an oil cooler reservoir tank. The oil is cooled to 100°F, filtered and reused in the turbine bearing holders.
The oil inventory for the lubrication system is critical. Vertical narrow surge tanks with interior recirculating cooling lines do not provide room for interior mounted instruments, plus the oil moves quickly through the cooling process. Sensors need to ignore density and viscosity changes for accurate level measurement.
Previous instruments used were remote pressure transmitters with long capillary tubes. The main problem was that response time was too slow.

Solution

Endress+Hauser recommended theLiquicap M FMI 51 capacitance probe. Due to space limitations, the system was installed in a stilling well (see diagram on back page).

Measurement results

The Liquicap M from Endress+Hauser was a perfect solution. The system didn’t require any special settings and the output followed the fast changing oil levels without incident.
Instrument description
The FMI51 is a top mounted compact
capacitance level 2-wire transmitter. Available in rod or cable versions and 4 to
20 mA HART® or PFM electronics, the Liquicap M is ideal in many industries.
Process connections include threaded (1/2” up to 1-1/2”), flanged (1” to 6”) or Tri-clamp. Designed specifically for liquids, the measuring ranges for the Liquicap are up to 13 feet for rod probes and 72 feet for cable.

Measuring principle

Capacitance level measurement systems take advantage of the dielectric constant in all materials to determine changes in level.
A capacitor is no more than a pair of conductive electrodes, or plates, with fixed spacing and a dielectric (process material) between them. In the most common applications, the probe element (a metal rod or cable) serves as the active plate, while the process vessel serves as a ground plate. When “empty space” or air in the vessel is replaced by the process material, the capacitance electronics register the change in capacitance. This change is converted to an electrical signal and used to provide an output for continuous level. Continuous level measurement can be accomplished with the right probe configuration and electronics.