Damper cage loss reduction and no-load voltage THD improvements in salient-pole synchronous generators

Abstract

Salient-pole synchronous generators (SG) have a long history of utilization as reliable power generation systems. Important aspects of such generators include a high power-to-weight ratio, high efficiency and a low cost per kVA output [1]. Another critical aspect is the requirement for very low harmonic content in the output voltage. Hence, it is very important to be able to model and predict the no-load voltage waveform in an accurate manner in order to be able to satisfy standards requirements, such as the permissible total harmonic distortion (THD). Also, at steady-state conditions, parasitic voltages are induced in the damper bars which lead to a current flow with associated power losses and an increase in temperatures. This paper deals with an in-detail analysis of a 4 MVA SG, whose operation is studied and compared with experimental results for validation purposes. The same platform is then used to propose innovative solutions to the existing design and operational challenges of the machine aimed at reducing ohmic loss in the damper cage and improving the output voltage THD, without reverting to disruptive techniques such as rotor and/or stator skewing.

A hybrid analytical-numerical approach for the analysis of salient-pole synchronous generators with a symmetrical damper cage

“…The vector voltage equation related to the equivalent circuit of a generic electrical machine is shown in (1), where the hypothesis of linear characteristics for all of the magnetic materials is assumed.…”

“…Although wound-field synchronous generators (SGs) have been extensively studied over the years, the design and analysis of such machines is presently attracting attention again due to the ever-increasing power quality and efficiency requirements [1] and the improvements in the potential of the analysis tools available, such as powerful computing and accurate modelling resources. In this context, particular focus has recently been given to the damper winding usually embedded in the rotor of salient-pole SGs.…”

Analysis of salient-pole synchronous generators operating in single-phase condition

“…Due to the importance of the damper cage during the 1θ operation, particular focus is given to the modeling of this additional rotor winding. In fact, in order to consider potential skin effects into the damper bars ensuing from the stator slot harmonics, each bar is modelled as a solid conductor, as suggested by [8] and [9]. The FE model is coupled to the in-built electrical circuits in the FE software, representing the stator phases, the rotor field winding and the damper cage.…”

“…1. The calculations related to the mmf drops and thus those relevant to the evaluation of the necessary Ampere-turns are given in (5)- (9), where the Ampere's law is applied along the main flux line shown in Fig. 1.…”

Analysis, Modeling, and Design Considerations for the Excitation Systems of Synchronous Generators

“…Sizing equations have been extensively studied and applied for the design of electrical machines [16][17][18][19][20][21] in a wide range of applications [22][23][24]. However, with recent advancements in computational resources, numerical techniques such as FE [25][26][27][28][29] are often preferred to analytical methods due to the complexity and non-linearity of the studied problems. Recently, more innovative optimization techniques, employing GAs have been shown capable to further improve electrical machines' performance [30,31].…”