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TechC@RE machinery breakdown EXPERIENCE FEEDBACK Steam turbine anti-motoring (reverse power) Rotor damage risk Return of power Mechanical repair of steam turbine Start of acceptance test Black out on public network Turbine running as a synchronous motor 15 days 5 days 2 hours 20 minutes Mechanical damage to turbine Breakdown duration: 1 month Steam turbine are used to drive synchronous alternators for electricity production. TURBINE DAMAGE TO TURBINE GENERATOR GENERATOR ELECTRICAL CURRENT ELECTRICAL CURRENT Motoring can happen when a turbine’s steam supply is lost whilst the generator is still coupled to a network (or operated in parallel with another generator). The generator will then become a synchronous motor and will actually drive the steam turbine with the potential for significant mechanical damage. A reverse power protection device should be inserted within the generator protection scheme, in compliance with Institute of Electrical and Electronics Engineers standard IEEE C37.102-2006 – Guide for AC Generator Protection (Section 4.5.5). This document is © AXA Matrix RC – March 2015Version For further information or specific questions contact: [email protected] Steam turbine anti-motoring EXPERIENCE FEEDBACK Facts 1. A large paper mill has a steam turbo-generator connected to the public network or can be operated in island mode. 2. In order to increase its power output, the steam turbo-generator was refurbished/ upgraded in 2012. 3. T he upgrade focused on mechanical components, as the electrical components were overhauled/ upgraded some years earlier by another contractor. 4. During re-commissioning; the sequence of power disconnection and power reconnection to the public network induced motoring of the steam turbine. Total loss amount: several millions euros (shaft, bearings, blades, packing seals) Main causes Lack of bearings lubrication causing significant wear/vibration to rotor shaft and thermal stresses Generator running as synchronous motor Client agreement on testing without environment analysis Lack of formalized procedures for testing protection systems on re-start up/commissioning. Aggravating factors Operator waited more than 15 minutes before calling an electrical technician to open the main generator breaker. Lack of a dedicated electrical technician during the commissioning/test procedures. Suggested recommendations Annual testing of reverse power (anti-motoring) protection. It should provide backup for sequential tripping schemes. Control the presence of safety chains, test safety valves, surge valves on steam supply, pressure/ level devices on lubrication system, bearing temperature, over speed protection, vibration monitoring, earth fault, loss of field, over voltage/current instrumentation, including anti-motoring. Annual testing and calibration is recommended. Operators should be trained on identifying generator motoring conditions and on subsequent shutdown/isolation procedures. This document is © AXA Matrix RC – March 2015Version For further information or specific questions contact: [email protected] oxygenemultimedia.fr - Photos : Shutterstock, © 2000 Geothermal Education Office, NRC Failure of protection relay on anti-motoring chain (partially wired)