Pär Holmberg

Some inequalities related to the analysis of electricity auctions

Most balancing markets of electric power are organized as uniform-price auctions. In 2001, the balancing market of England and Wales switched to a pay-as-bid auction with the intention of reducing wholesale electricity prices. Numerical simulations of an electricity auction model have indicated that this should lead to decreased average prices. In this article we prove two inequalities which give an analytic proof of this claim in the same model.

Discussion of "A wide-band lumped circuit model of eddy current losses in a coil with a coaxial insulation system and a stranded conductor"

This paper presents a wide-band lumped circuit model of eddy current losses in a coaxially insulated coil. The wide frequency range of the model is achieved by means of dual and extended Cauer circuits, equivalent circuits used for eddy current modeling. The complete lumped circuit reproduces the expected response well. However, because of resonances in the coil, the model cannot be experimentally verified for higher frequencies than 5 kHz. The parameters of the lumped circuit are mainly acquired from field calculations and aggregate the eddy current losses In the stranded conductor of each tum. The aggregate considers the contact resistance between the strands. The eddy current model can be used as a part of a complete model of the coil intended for e. g. lightning impulse simulations, as the winding is discretised into short pieces. The results of the paper are of special interest for coaxially insulated electric machines, such as the commercially available Powerformer and Dryformer.

A wideband lumped circuit model of the terminal and internal electromagnetic response of rotating machine windings with a coaxial insulation system

The polyphase model can be used to simulate the terminal and internal electromagnetic response of, for example, Powerformer/spl trade/: a new power generator. The circuit parameters are based on geometrical and material data. The slot leakage is modeled by means of a reluctance circuit, which is coupled to the electric circuit by means of winding templates. The capacitive current and its losses in the outer semiconducting layer of the cable are modeled with a simplified version of an RC model that has been used previously for other coaxially insulated windings. The eddy current losses were neglected; however, it is presented how they can be included in the model. The simulated frequency and transient response of the lumped circuit is compared with measurements on an 11-MVA/45-kV, 600-r/min hydro Powerformer. With exception of the damping, the agreement is good, qualitatively, up to 100 kHz.