Aircraft Maintenance Technology

MAR 2018

The aircraft maintenance professional's source for technological advancements, maintenance alerts, news, articles, events, and careers

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AIRLINE HOW TO ENHANCE GENERATOR PERFORMANCE Using the right high performance capability (HPC) turbine oil can help airlines overcome maintenance challenges By Ed Barnes ED BARNES, FIELD ENGINEER FOR AVIATION Lubricants at ExxonMobil, talks about the top reasons for unplanned generator reliability issues and how HPC oils can help airlines overcome maintenance challenges. In the demanding, competitive aviation marketplace, fleets are constantly seeking ways to boost revenue and keep downtime to a minimum. If severe enough, a single maintenance issue has the potential to delay or ground a flight, creating a financial burden for air- lines and frustrating passengers eager to get to their next location. Generator failure (i.e., integrated drive generators (IDG), variable frequency generators and variable frequency starter generators) is one important maintenance challenge faced by airlines. Not surprisingly, generator maintenance and unplanned removals can be incredibly costly; however, using the right high performance capability (HPC) turbine oil can help airlines overcome these challenges. Outlined below are key causes for unplanned generator removals and maintenance. Also included are benefits of HPC oils, underscoring how they can help promote reliability of essential aircraft components. 1. DIODE FAILURE A diode, which is a semiconductor device allowing electricity to flow in one direction, can fail if a turbine oil does not have adequate electrical conductivity. The fluid friction between the rotating generator components and the lubricant can generate static electrical charges on different parts of the generator during operation. These electrical charges need a path to dissipate, either through the air around the generator — if the ambient humidity is high enough — or through the lubricant. To dissipate through the lubricant, there must be adequate electrical conductivity. If the ambient humidity is too low and the lubricant lacks sufficient conductivity, the charge will be strongly separated, which may result in a powerful electrical discharge that causes permanent damage to diodes in the generator control circuitry. The risk of insufficient conductivity is the highest when oil is fresh and the temperature is below freezing. Also, it's important to note that there are significant differences in electrical conductivities between turbine oils. In fact, there are some turbine oils on the market that have low conductivity. In contrast, a modern HPC oil, like Mobil Jet™ Oil 387, offers higher electrical conductivity, which can minimize the risk of diode failures and delayed flights. 2. CORROSION AND FILTER PLUGGING Turbine oils can be exposed to harsh conditions in a generator, such as extreme temperature ranges. On occasion, this can cause the lubricant's base oil to undergo oxidation. During oxidation, the fluid develops a high total acid number (TAN), causing corrosion and potentially, the failure of non-ferrous components in the generator. IDG DIODE failures compromise generator control circuitry and sensors. EXXONMOBIL

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