In this paper polyphase transformer arrangements with reduced AVA capacities are presented for harmonic current reduction in high power rectifier utility interface systems. Based on the concept of an autotransformer, a proposed twelve-pulse redfier system is realized with a resultant kVA rating of 0.18P0 @U). In this arrangement the rectifier diodes each conduct for 120 degrees per cycle and thefiflh and seventh harmonics are absent from the utility input line current. In the second scheme an eighteen-pulse rectifier is realized with the AVA rating of 0.16P0 @U), rectifier diode conduction of 120 degrees per cycle andfiph, seventh, eleventh and thirteenth harmonic cancellation in the utility line currents. Additional applications for the proposed polyphase transformer arrangements include twelve and eighteen-pulse systems feeding multiple six-pulse nonlinear loah, such as ac motor drives, with an appropriate phase shifl, and this arrangement substantially reduces the utility line current harmonics. For example, it is shown that the fiflh and seventh harmonics generated by two separate six-pulse nonlinear loads are subtracted, and this contributes to reduced distortion. Simulation results verifiing the proposed concept are presented.

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Using the partial adjustment model of cash holding, we find that managerial ability is negatively related to adjustment speed of cash holdings toward the target, particularly when the firm has excess cash. We also find that the relation between managerial ability and cash holding adjustment speed is weaker in the presence of the internal capital market. Additionally, we provide evidence that firms with higher managerial ability are less likely to make inefficient investments when they have excess cash, implying that high-ability managers are willing to hold a large amount of cash to make timely investments.

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This paper proposes two new passive 24-pulse diode rectifier systems for utility interface of PWM ac motor drives. The first approach employs an extended delta transformer arrangement which results in near equal leakage inductance in series with each diode rectifier bridge. This promotes equal current sharing and improved performance.A specially tapped interphase reactor is then introduced with two additional diodes to extend the conventional 12-pulse operation to 24-pulse operation from the input current point of view. The proposed system exhibits clean power characteristics with 5th, 7th, llth, 13th, 17th and 19th harmonics eliminated from the utility line currents. The second scheme is a reduced kVA approach employing autotransformers to obtain 24-pulse operation. The kVA rating of the polyphase transformer in the second scheme is 0.18 Po @U). Detailed analysis and simulations verify the proposed concept and experimental results from a 208V, lOkVA rectifier system are provided.