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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.

The high-power self-commutated voltage-source converter (VSC) and current source converter (CSC) are the key control devices in HVDC, flexible ac transmission systems (FACTS) and distribution FACTS systems. To achieve the expected control objectives, suitable control strategies must be implemented based on the available devices, system, and control techniques. The self-commutated ac/dc converters control the electrical power by generating controllable ac fundamental and dc average outputs. These controllable outputs are controlled by the conducting state combinations of the converter switching devices, driven by their gate signals. The gate signals are specified by fundamental parameters of frequency, amplitude, and phase angle. The converter system model for describing the relation between the system-state variables and the gate signal parameters is essential for the converter system control. This paper (part I) derives the state variable equations for transmission systems using VSC while the second paper (part II) is for the transmission systems using CSC. The self-commutated converter systems provide active and reactive power control flexibility, but their nonlinearity makes their control difficult. The linearized state equations by using feedback linearization are presented to enable the controller design by using linear control theory. [ABSTRACT FROM PUBLISHER]

This paper presents a review with a concise description and analysis of the fundamentals, characteristics, analytical details, merits, and drawbacks associated with existing methods in frequency and time domain for harmonic analysis in practical power networks. The description and analysis are centered on methods developed in the harmonic domain, hybrid frequency-time domain, and time domain, respectively. Validation of the reviewed methods for harmonic analysis, against one of the widely accepted digital simulators, such as EMTP, EMTDC, or MATLAB/SIMULINK, is reported in the cited individual contributions. [ABSTRACT FROM PUBLISHER]

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]

A new concept referred to as reinjection AC/DC conversion is described, applicable to both self-commutating voltage source and current source conversions. It combines all the benefits of the multi-level, soft switching and ripple reinjection concepts. The aim is to achieve high-quality waveforms, simplify the structural configuration and the interface with the grid, improve the conversion efficiency, limit the dv/dt and provide flexible active and reactive power controllability. [ABSTRACT FROM AUTHOR]

In self-commutating multi-level voltage source conversion (VSC) transmission, the reactive power contributions of the two converter terminals are interdependent. To overcome this problem, a new control scheme is proposed, applicable to high voltage direct current (HVDC) interconnections of large power ratings with more than one 12-pulse group per converter. The basis of the proposed strategy is the use of a controllable phase shift between the firings of the individual converter groups. The theory is verified by extensive EMTDC simulation. [ABSTRACT FROM AUTHOR]

The self-commutating multilevel current reinjection (MLCR) reduces the converter current waveform to zero during the valves commutations and, thus, removes the converter dependence on line commutation. This property provides the conventional thyristor converter with the same flexibility as the self-commutating multi-level schemes in terms of reactive power control and harmonic elimination. This paper describes the structure and control of a current source HVDC transmission scheme using MLCR converters. Extensive EMTDC simulation is carried out to demonstrate the improved controllability of the proposed HVDC configuration. [ABSTRACT FROM AUTHOR]

A new self-commutated AC-DC converter is proposed based on the reinjection of multilevel DC pulses via the mid-point of the series double-bridge converter using a GTO-switched multitapped single-phase transformer. The ideal reinjection waveform for complete elimination of the harmonic content of the AC-side current is derived and a practical approximation proposed to increase the pulse number of double-bridge converters to any multiple of 12. A 60-pulse configuration is analysed in detail to show effectiveness on both the AC and DC sides of the converter. [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]

Previous work conducted in the unified harmonic domain has been primarily focused on HVDC systems. The paper outlines the extension of this technique to a hard switched FACTS device. A unified harmonic domain model is developed for a STATCOM and solved using a Newton solution based on DC side current mismatches alone. This generic formulation maintains modularity, allowing the interaction between multiple STATCOMs to be studied. The model has been verified against a time domain solution using PSCAD/EMTDC. The proposed technique provides practically identical results, without the time domain's inherent problems with respect to steady-state simulation. [ABSTRACT FROM AUTHOR]

A new multi-level VSC is proposed with highly reduced voltage and current harmonic distortion, without the need for filters or PWM. The multi-pulse waveform is achieved by means of two auxiliary reinjection bridges, which produce voltage pulses at six times the fundamental frequency. The proposed scheme simplifies the switching circuitry of present schemes for similar levels of waveform distortion and can operate in four quadrants without capacitor balancing problems. [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]

Electromagnetic transient simulation can be used to model complex non-linearities that are very difficult to represent adequately in the frequency domain. After reaching the steady state the voltage and current waveforms, represented by sets of discrete values at equally spaced intervals (corresponding with the integration steps), are subjected to fast Fourier transform processing to derive the harmonic spectra. However, the accuracy of the EMTP approach is limited by the restricted frequency dependence representation of the AC system components. It is shown that this problem is greatly reduced with the use of frequency-dependent network equivalents for the linear part of the system. [ABSTRACT FROM AUTHOR]

Presents the formulation for developing a 1- and 2-port frequency-dependent equivalent of AC system using z-domain rational function fitting of the frequency response. Key motivation for investigating z-domain fitting; Indication of the robustness and accuracy of 1- and 2-port frequency-dependent network equivalent (FDNE) for electromagnetic transient simulation; Discussion on issues of developing a 1- and 2-port frequency-dependent equivalent of the AC system.

It is shown that there are strong relationships between the resistance to compression, the felt-ball diameter, and the curvature of the parent wool follicles. The relationship of these properties with follicle curvature is stronger than that with staple-crimp frequency. [ABSTRACT FROM AUTHOR]

40 patients with premenstrual symptoms were randomly allocated to receive placebo patches or active treatment with transdermal oestradiol patches (2 x 100 micrograms) to suppress ovulation. Norethisterone 5 mg was given in each group from day 19-26 of the cycle to ensure a regular withdrawal bleed. Treatment was for 6 months with crossover at 3 months. Patients completed the Moos menstrual distress questionnaire (MDQ) and the premenstrual distress questionnaire (PDQ) daily throughout the study. 5 patients withdrew, 4 because of skin reactions and 1 because of considerable improvement with initial (active) treatment. After 3 months, both groups showed improvement in MDQ and PDQ scores. In general, between 3 and 6 months, patients who switched from active treatment to placebo had deteriorating scores while patients who switched from placebo to active treatment maintained or improved upon their initial gains. Significant improvements occurred after changing to active treatment in five of six negative MDQ symptom clusters and in six of ten PDQ symptoms. [ABSTRACT FROM AUTHOR]

The effect of converter impedance is mostly ignored when performing harmonic analysis, as it is complicated to calculate, and a common assumption is that it has minimal effect. This paper compares the use of simplified techniques against a rigorous calculation of the converter impedance and demonstrates their effect on the frequency response of the system. [ABSTRACT FROM PUBLISHER]

Presents a case report of leiomyoma of the ovary. Signs and symptoms presented by the patient; Interventions done; Information on ovarian leiomyoma.

The proposed converter is based on the reinjection of a series of dc voltage pulses, at a frequency multiple of the fundamental, that shape the output voltage waveforms into a multilevel scheme. The reinjection ratio and frequency are chosen to convert the standard 12-pulse into 36-pulse configuration without the assistance of filters or PWM. Thus the switching losses are greatly reduced. The harmonic current injection can be kept within present standards by an appropriate choice of the interface transformer leakage reactance. [ABSTRACT FROM PUBLISHER]

One of the main problems in the area of power quality is voltage flicker, a variation in the RMS voltage that causes flickering of incandescent bulbs. Varying loads can lead to such fluctuations of the supply voltage and for historical reasons this type of disturbance is viewed as the principal cause of light flicker. With the constant increase of applications that employ power electronic devices, sub-and interharmonics are becoming more prevalent in the power system. These can also vary the instantaneous power supplied to incandescent lamps by means of beating and thus result in visible light flicker. In this paper the special conditions under which light flicker occurs are derived qualitatively. Computer simulations that are based on a realization of the UIE/JEC flickermeter are then used to produce quantitative data. [ABSTRACT FROM PUBLISHER]

Marginal pricing of harmonic injections can be shown to encourage each member of the network to independently act in such a way that the harmonic profile of the system is optimized. A problem encountered with marginal pricing is that loads can be charged complex amounts for their injections. This paper demonstrates that the real part of the amount charged for any injection reflects the "in-phase" component of that current, which will either increase or decrease the prevailing harmonic voltages. The imaginary part charged to a load reflects the quadrature component of their injections, which has no effect on the voltage magnitudes, at the margin. Each load need only be liable for the real amount they are charged, which has a direct correspondence with the total payments due. [ABSTRACT FROM PUBLISHER]

The relation of umbilical cord blood arterial pH, Apgar score, leucocyte count, and erythroblast count at delivery with the diagnosis of fetal distress in labour was studied prospectively in three groups of singleton pregnancies delivering at term vaginally (55 infants), by elective caesarean section (39 infants), or by emergency caesarean section for abnormal intrapartum fetal heart rate patterns (55 infants). In the emergency caesarean section group the umbilical cord blood arterial pH was significantly lower and the leucocyte and erythroblast counts were higher than in the elective caesarean section group. Comparison of the emergency caesarean section and spontaneous vaginal delivery groups showed significant differences for pH and erythroblast count, but not for leucocyte count. In the spontaneous vaginal delivery group erythroblastosis was associated with umbilical cord blood pH, whereas leucocytosis was associated with the length of labour. The five minute Apgar score was > or = 7 in all infants. This study suggests that leucocytosis is a non-specific response of the fetus to labour, whereas erythroblastosis reflects fetal tissue hypoxia. [ABSTRACT FROM AUTHOR]

Objective: To report a rare case of sequential bilateral adnexal torsion in a pregnant woman after a single cycle of gonadotropin ovulation induction with IUI. To review the literature with regards to the causation and aspects of the management of adnexal torsion, particularly after assisted conception., Design: Case report., Setting: Fertility department within a teaching hospital., Patient(s): A 35-year-old woman with a twin pregnancy after a cycle of gonadotropin ovulation induction and IUI., Intervention(s): Gonadotropin ovulation induction with IUI; two laparotomies, salpingo-oophorectomy, stabilization of adnexa with stay suture., Result(s): Continuation of pregnancy until 37 weeks gestation with the abdominal delivery of healthy twins., Conclusion(s): The case of a woman with a multiple pregnancy and ovarian hyperstimulation syndrome after ovulation induction and IUI who developed sequential bilateral adnexal torsion is used to illustrate the risk factors and management options for adnexal torsion. Physicians should be aware of the increased incidence of adnexal torsion in the rising number of women undergoing ovulation induction in order to effect early surgical intervention and adnexal salvage. Consideration should be given to the anchoring of bulky adnexae to prevent torsion recurrence.

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.

The recognition of the relationship between premenstrual syndrome and cyclical ovarian activity has enabled the rationalization of treatment. Placebo-controlled studies have established the efficacy of treatments that alter ovarian function, therefore it should no longer be necessary to rely on the placebo effect of unproven treatments such as progesterone.