September_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 1 9 1 9 housing (Fig. 1). The rotor and stator are the most highly stressed components. Three primary fluids used to cool a gen- erator rotor and stator during operation are air, hydrogen, and water. The rotor consists of a forged machined steel al- loy shaft packed with insulated copper conductors and dressed with a retain- ing ring (Fig. 2). The stator mainly con- sists of electrical-steel laminations (the core) and insulated bundled copper strands (stator bars) as shown in Fig. 3. Radiography, a nondestructive ex- amination (NDE), or testing (NDT), meth- od provides an interpretable image of the component offering a reliable way to assess generator component integ- rity. In some instances, NDE can enable life assessment of certain generator components. The results can provide engineers with a reliable, quantifiable view of internal defects and discon- tinuities that can be detrimental to material and component service life. Radiographic techniques can lead to shorter outage durations by enabling noninvasive inspection of insulated R adiographic inspection techniques have been developed for differ- ent applications in various indus- trial fields including medical, airport security, cargo scanning, oil and gas, aerospace components, and manufac- turing quality control. Siemens Ener- gy has used radiography in common inspection applications such as corro- sion allowance inspection, weld integri- ty, blocked cooling passages in various components, and now has developed a technique to inspect electric generator components without the need of strip- ping insulation. Continual changes in market con- ditions with the ramp up of renewable energy and varying strategies to pro- duce more electrical power while min- imizing cost of maintenance and repair has created an ever-increasing strain in electrical-generation equipment. Cus- tomers expect faster, cost-effective, more reliable inspection methods that minimize the impact of electrical pow- er generation and increase efficiency and profitability. Radiography inspec- tion of electrical generators offers an alternative to common inspection methods, which can help meet those expectations. Electric power companies sched- ule outages to minimize the impact on the electrical grid and increase profit- ability by balancing power demand and supply. The energy industry is being re- shaped as a result of not only advanc- es in renewable energy, but also due to changes in investment strategies for the power-management market. The industry more often is seeing a delay in decisions to service and/or replace equipment. Executives may be hesitant to make significant investments due to regulatory and tax-structure chang- es and may instead focus on devising strategies to maximize outcomes in the prevailing political environment [1] . The electrical grid is under con- stant stress due to changes in pow- er demand and unexpected additions of power supply. On the demand side, energy loads, such as those of an elec- tric-arc furnace for example, can have a severe impact in the power train at the nearest power plant. On the sup- ply side, continual additions of variable power such as from wind turbines and solar panels create fluctuations, which can result in accelerated aging of elec- trical generators, particularly those op- erating during peak cycle times. KEEPING ELECTRIC GENERATORS OPERATING RELIABLY Four major components of elec- trical generators (for brevity in this ar- ticle) are the exciter, rotor, stator, and Fig. 1 — Electrical generator consisting of exciter housing (left) and stator, rotor, and housing (right). Fig. 2 — Generator rotor. Fig. 3 — Generator wound stator with rotor in place.