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An increasing number of electricity market employing some form of spot pricing. However, limited experience of the behavior of spot prices exists. This paper introduces and investigates one particular aspect of pricing behavior observed in the New Zealand spot market, known as 'Price Inversion.' Spot prices are generally calculated using some form of OPF or power-flow software. The phenomena of price inversion is investigated using the dc power-flow implemented in the New Zealand spot market, and using a full ac power-flow. Price inversion is shown to be dependent on the physical characteristics of the power system. The economic implications of price inversion are also discussed. Index Terms--Ac power-flow, dc power-flow, nodal pricing, price inversion, spot pricing.

This paper describes a modular algorithm for solution of power systems containing active nonlinear devices such as power converters. The solution is a unified real-valued Newton method allowing simultaneous solution of electrical and nonelectrical variables. The algorithm is demonstrated using the reduced equivalent of a real power system which includes both load-flow busbars and a large uncontrolled rectifier. The solution process is fast, robust and exhibits excellent convergence.

Large-current, low-voltage applications such as aluminium smelters use diodesaturable reactors or thyristor-based rectification to control the DC current. Transformer on-load tap-changers are also used to minimise the steady-state reactive power requirements. This paper describes a new double-group, two-quadrant thyristor-based concept suitable for high current, where several thyristor and insulated gate bipolar transistor bridges are paralleled. By using a combination of leading and lagging firing angles, high power-factor is maintained and supplying bridges via phase shifting transformers enables continuous high-pulse operation. The theory is verified by EMTDC simulation. [ABSTRACT FROM AUTHOR]

A three-phase converter configuration, with each phase consisting of a series chain of H-bridges has become a popular multilevel solution for STATCOM application. Such a configuration, however, is not suitable for HVDC transmission. A new concept, where the series chain of H-bridge cells is used to derive a multilevel voltage reinjection waveform, is described in a companion paper. Its application to HVDC transmission is discussed in this paper and extensive use is made of EMTDC simulation to verify its steady-state and dynamic behavior. [ABSTRACT FROM AUTHOR]

A new multilevel configuration is proposed for use in voltage source conversion of large power and voltage ratings; it consists of the standard double bridge converter and a series chain of H-bridges, each connected to a capacitor. The H-bridge chain is connected between the middle node of the dc capacitors and the neutral point of the two main bridges. The new reinjection configuration provides all the features of the previously proposed multilevel reinjection schemes with a considerably reduced number of switches (that only increases in direct proportion to the converter dc voltage rating) and acts as a dynamic voltage balancer for the main bridge switches. Extensive simulation is carried out to verify the steady state waveforms and the dynamic behavior with reference to the STATCOM application. [ABSTRACT FROM AUTHOR]

Knowledge of the process noise covariance matrix Q is essential for the application of Kalman filtering. However, it is usually a difficult task to obtain an explicit expression of Q for large time varying systems. This paper looks at an adaptive Kalman filter method for dynamic harmonic state estimation and harmonic injection tracking. The method models the system as a linear frequency independent state model and does not require an exact knowledge of the noise covariance matrix Q. As an alter- native, the proposed adaptive Kalman filter switches between the two basic Q models for steady-state and transient estimation. Its adaptive function allows for the resetting of the Kalman gain to avoid Kalman filter divergence problems under steady-state and allow fast tracking of system variations in transient conditions. Simulation results on the 220 kV network of the lower South Island of New Zealand are presented to validate this approach. [ABSTRACT FROM AUTHOR]

A new STATCOM configuration is described in this paper that combines the advantages of the diode clamped, dc. voltage reinjection VSC and soft switching concepts. The new scheme uses asymmetrical switches instead of diodes in a common clamping switching circuit for the three-phases of the converter bridges. Detailed analysis is provided of the steady state output voltage and current waveforms. It is shown that this configuration provides very low distortion levels with greatly simplified auxiliary switching arrangements and reduced switching losses. [ABSTRACT FROM AUTHOR]

Isozyme analysis of L-alanine:2-oxoglutarate aminotransferase (ALT) in maize indicates that there are three genes encoding this enzyme activity. Two of the gene products interact with each other to form heterodimers, while the third gene product does not interact with the other two. Another isozyme that appears after gel electrophoresis and ALT staining is shown to be glutamate dehydrogenase-1. Anaerobic treatment does not result in increased ALT levels, indicating that the previously reported increase in alanine levels caused by this treatment may be due to increases in the level of pyruvate, a substrate of ALT.