The oil systems (hydraulic and lubrication) of a turbine are critical not only for normal operation but also during power outages. Normally, the lubrication oil system is connected to the control oil system, depending on the turbine design.

Bearing lubrication oil is maintained at approximately 40⁰C (104⁰F) as this is an optimum temperature for the oil. Increasing the temperature of the oil above this temperature will reduce its lubrication and cooling abilities, which may lead to damage of the bearing and turbine components.

Lubrication and control oil systems are normally low pressure, high volume systems. The generator bearings, turbine bearings, turbine control valves, gearbox oil sprayers, coupling oil feeds, and other turbine components, may all use a common oil system.

The bearing oil system is connected to a trip valve, so that in the event of a supply failure (reduction in oil pressure), the turbine will trip/stop. Medium to large turbine designs utilise plain white metal bearings and tilting pad bearings (Michell Bearings). Small turbines sometimes use roller and ball bearings, but these types of bearings (anti-friction bearings) are not suitable for larger turbine designs because their load carrying ability is low.

Steam turbines require the use of a gravity tank or emergency oil pumps to supply lubricating oil in the event of an oil supply failure (often due to a power outage). A gravity tank (or tanks) is installed at the top of the power plant building and oil is constantly circulated through the tank to maintain the desired level. Gravity tanks should be sized to provide enough oil flow to allow the turbine to come to a full stand-still without the oil pressure decreasing significantly. However, a gradual turbine stop would require a large amount of oil and a correspondingly large gravity tank. To circumvent this problem, direct current (DC) electrically driven emergency lubrication oil pumps are used. The power to rotate the DC pumps is taken from batteries (flooded lead acid type typically), which operate independently of the main electrical bus board; this ensures the pumps will operate even if a power outage occurs. It is very important that a turbine’s emergency lubrication DC pumps are tested periodically, failure to operate when needed will most likely lead to significant damage of a turbine’s components.

Flooded Lead Acid Batteries

Condenser condensate pumps (extraction pumps) are critical for the safe operation of a condensing steam turbine; these pumps are used to return condensate from the condenser back to the deaerator via boiler feedwater heaters. It is important to constantly monitor the condenser condensate level, as too much condensate in the condenser hotwell may lead to several problems:

1. High level - a reduction in condenser efficiency due to some of the heat exchanger surfaces being submerged by condensate.

2. High level - poor control concerning maintaining of the condensate close to saturation temperature.

3. High level - in extreme cases, condensate may enter the low-pressure turbine(s); this is more a problem for condensers installed on an axial plane with the turbine, not for turbines which have the condenser installed beneath them.

4. Low level – cavitation within condensate pumps may occur. Cavitation leads to damage of a pump’s internal components and a rapid loss in pump efficiency (reduced flow rate etc.).