1. Introduction. 1.1 Background. 1.2 Electrical Transmission Networks. 1.3 Conventional Control Mechanisms. 1.4 Flexible ac Transmission Systems (FACTS). 1.5 Emerging Transmission Networks. 2. Reactor--Power Control in Electrical Power Transmission Systems. 2.1 Reacrive Power. 2.2 Uncompensated Transmission Lines. 2.3 Passive Compensation. 2.4 Summary. 3. Principles of Conventional Reactive--Power Compensators. 3.1 Introduction. 3.2 Synchronous Condensers. 3.3 The Saturated Reactor (SR). 3.4 The Thyristor--Controlled Reactor (TCR). 3.5 The Thyristor--Controlled Transformer (TCT). 3.6 The Fixed Capacitor--Thyristor--Controlled Reactor (FC--TCR). 3.7 The Mechanically Switched Capacitor--Thristor--Controlled Reactor (MSC--TCR). 3.8 The Thyristor--Switched capacitor and Reactor. 3.9 The Thyristor--Switched capacitor--Thyristor--Controlled Reactor (TSC--TCR). 3.10 A Comparison of Different SVCs. 3.11 Summary. 4. SVC Control Components and Models. 4.1 Introduction 4.2 Measurement Systems. 4.3 The Voltage Regulator. 4.4 Gate--Pulse Generation. 4.5 The Synchronizing System. 4.6 Additional Control and Protection Functions. 4.7 Modeling of SVC for Power--System Studies. 4.8 Summary. 5. Conceepts of SVC Voltage Control. 5.1 Introduction 5.2 Voltage Control. 5.3 Effect of Network Resonances on the Controller Response. 5.4 The 2nd Harmonic Interaction Between the SVC and ac Network. 5.5 Application of the SVC to Series--Compensated ac Systems. 5.6 3rd Harmonic Distortion. 5.7 Voltage--Controlled Design Studies. 5.8 Summary. 6. Applications. 6.1 Introduction. 6.2 Increase in Steady--State Power--Transfer Capacity. 6.3 Enhancement of Transient Stability. 6.4 Augmentation of Power--System Damping. 6.5 SVC Mitigation of Subsychronous Resonance (SSR). 6.6 Prevention of Voltage Instability. 6.7 Improvement of HVDC Link Performance. 6.8 Summary. 7. The Thyristor--Controlled SeriesCapacitor (TCSC). 7.1 Series Compensation. 7.2 The TCSC Controller. 7.3 Operation of the TCSC. 7.4 The TSSC. 7.5 Analysis of the TCSC. 7.6 Capability Characteristics. 7.7 Harmonic Performance. 7.8 Losses. 7.9 Response of the TCSC. 7.10 Modeling of the TCSC. 7.11 Summary. 8. TCSC Applications. 8.1 Introduction. 8.2 Open--Loop Control. 8.3 Closed--Loop Control. 8.4 Improvement of the System--Stability Limit. 8.5 Enhancement of System Damping. 8.6 Subsynchronous Resonanace (SSR) Mitigation. 8.7 Voltage--Collapse Prevention. 8.8 TCSC Installations. 8.9 Summary. 9. Coordination of FACTS Controllers. 9.1 Introduction 9.2 Controller Interactions. 9.3 SVC--SVC Interaction. 9.4 SVC--HVDC Interaction. 9.5 SVC--TCSC Interaction. 9.6 TCSC--TCSC Interaction. 9.7 Performance Criteria for Damping--Controller Design. 9.8 Coordination of Multiple Controllers Using Linear--Control Techniques. 9.9 Coordination of Multiple Controllers using Nonlinear--Control Techniques. 9.10 Summary. 10. Emerging FACTS Controllers. 10.1 Introduction. 10.2 The STATCOM. 10.3 THE SSSC. 10.4 The UPFC. 10.5 Comparative Evaluation of Different FACTS Controllers. 10.6 Future Direction of FACTS Technology. 10.7 Summary. Appendix A. Design of an SVC Voltage Regulator. A.1 Study System. A.2 Method of System Gain. A.3 Elgen Value Analysis. A.4 Simulator Studies. A.5 A Comparison of Physical Simulator results With Analytical and Digital Simulator Results Using Linearized Models. Appendix B. Transient--Stability Enhancement in a Midpoint SVC--Compensated SMIB System. Appendix C. Approximate Multimodal decomposition Method for the Design of FACTS Controllers. C.1 Introduction. C.2 Modal Analysis of the ith Swing Mode, C.3 Implications of Different Transfer Functions. C.4 Design of the Damping Controller. Appendix D. FACTS Terms and Definitions. Index.

Thyristor-Based Facts Controllers for Electrical Transmission Systems

The continuously increasing demand for electric power and the economic access to remote renewable energy sources such as off-shore wind power or solar thermal generation in deserts have revived the interest in high-voltage direct current (HVDC) multiterminal systems (networks). A lot of work was done in this area, especially in the 1980s, but only two three-terminal systems were realized. Since then, HVDC technology has advanced considerably and, despite numerous technical challenges, the realization of large-scale HVDC networks is now seriously discussed and considered. For the acceptance and reliability of these networks, the availability of HVDC circuit breakers (CBs) will be critical, making them one of the key enabling technologies. Numerous ideas for HVDC breaker schemes have been published and patented, but no acceptable solution has been found to interrupt HVDC short-circuit currents. This paper aims to summarize the literature, especially that of the last two decades, on technology areas that are relevant to HVDC breakers. By comparing the mainly 20+ years old, state-of-the art HVDC CBs to the new HVDC technology, existing discrepancies become evident. Areas where additional research and development are needed are identified and proposed.

HVDC Circuit Breakers: A Review Identifying Future Research Needs

This paper endeavors to present a comprehensive summary of the causes and effects of voltage unbalance and to discuss related standards, definitions, and mitigation techniques. Several causes of voltage unbalance on the power system and in industrial facilities are presented as well as the resulting adverse effects on the system and on equipment such as induction motors and power electronic converters and drives. Standards addressing voltage unbalance are discussed and clarified, and several mitigation techniques are suggested to correct voltage unbalance problems. This paper makes apparent the importance of identifying potential unbalance problems for the benefit of both the utility and customer.

Assessment of Voltage Unbalance

After baseline studies, 21 patients with osteoporosis were treated with human parathyroid hormone fragment (PTH 1-34) given as once-daily subcutaneous injections for 6-24 months. The dose used did not cause hypercalcaemia even in the first few hours after injection. Calcium and phosphate balances improved in some patients, but there was no significant improvement in the group values. There were, however, substantial increases in iliac trabecular bone volume: the mean increase, confirmed by repeat blind measurements, was 70% above mean baseline volume. The new bone was histologically normal. Those patients who had the largest increases in 47Ca-kinetic and histomorphometric indices of new bone formation showed the greatest increases in trabecular bone volume, suggesting that treatment with human parathyroid hormone fragment caused a dissociation between formation and resorption rates that was confined to trabecular bone. Since vertebrae are four-fifths composed of trabecular bone, this hormone fragment may prove useful in treating patients with the crush fracture syndrome.

https://www.bmj.com/content/bmj/280/6228/1340.full.pdf

Anabolic effect of human parathyroid hormone fragment on trabecular bone in involutional osteoporosis: a multicentre trial.

This paper discusses and compares different control techniques for damping undesirable interarea oscillation in power systems by means of power system stabilizers (PSS), static VAr compensators (SVCs), and shunt static synchronous compensators (STATCOMs). The oscillation problem is analyzed from the point of view of Hopf bifurcations, an "extended" eigenanalysis to study different controllers, their locations, and the use of various control signals for the effective damping of these oscillations. The comparisons are based on the results obtained for the IEEE 50-machine, 145-bus test system, which is a benchmark for stability analysis.

Comparison of PSS, SVC, and STATCOM controllers for damping power system oscillations

Forty-six patients with juvenile chronic arthritis maintained on glucocorticoid therapy have been reviewed retrospectively for evidence of vertebral collapse. The 23 patients who had sustained vertebral fractures had received a daily dose 2.3 times higher than those without. No patients sustained a vertebral collapse until they had received a prednisolone cumulative dose of at least 5 g. It would appear that the ideal dose, if collapse of vertebrae is to be avoided, should be not more than 5 mgs daily, probably best given as 10 mg on alternate days; unfortunately, some children with serious systemic disease cannot be controlled on these low doses. In such cases it seems justified to investigate the possible use of the oxazoline derivative of prednisolone (deflazacort) in view of its reported bonesparing properties in adults.

Vertebral collapse in juvenile chronic arthritis: its relationship with glucocorticoid therapy.

Papers published over a 17 year period, on the concept of extending 2-terminal HVdc transmission to multiterminal systems, are reviewed. In classifying the contributions, the design and performance expectations are discussed and the prospects for applications are evaluated. Reference is also made to the implications of dc interrupting switches. A comprehensive bibliography is included.

Multiterminal HVDC Power Systems

Any configuration of multiterminal HVdc system is accommodated in a generalized Newton dc load-flow program. It readily interfaces with any ac load flow program. Pract ical operating requirements have been given particular attention to permit aspects such as converter transformer tap-limits, pole and bipolar dc outages, emergency pole-paralleling and detailed control and scheduling strategies. Examples are provided of typical solutions incorporating realistic dc and ac systems, and accomplished in conjunction with an established modern ac load flow program.

Versatile load flow method for multiterminal HVDC systems

Various indices are proposed and studied to detect and predict oscillatory instabilities associated with Hopf bifurcations (HBs) in power systems. A methodology is also presented to produce a linear profile for these indices. They are based on eigenvalue and singular values of the state and extended system matrices. Their application to several test power systems is presented to demonstrate their usefulness, particularly for online applications.

Linear performance indices to predict oscillatory stability problems in power systems

1. A new method for measurement of skeletal blood flow is described which depends on the complete extraction of 18 F in a single passage through bone. 2. Plasma concentration and urinary excretion are measured over a 2 h period. The technique of impulse analysis is used to determine the initial transfer rate of 18 F to bone and extravascular extracellular fluid (ECF). The ECF component is evaluated by using a second tracer ( 51 Cr-EDTA or 82 Br) and the bone transfer rate obtained by difference. The 51 Cr-EDTA data also provide an estimate of glomerular filtration rate and enable a correction to be applied for urinary bladder retention when necessary. 3. Duplicate measurements of skeletal blood flow in eight normal male volunteers gave mean flows between 4·4 and 5·9% of blood volume/min, or about 4 ml min −1 100 g −1 of bone. The variation between normal subjects was least when the results were expressed as % of blood volume/min rather than ml/min, ml min −1 kg −1 or ml min −1 1·73 m −2 body surface area. The precision of the technique was estimated to be 16·4%. 4. Addition of 1·5% random noise to the input data resulted in an uncertainty of 8·5% in the measurement of skeletal blood flow, suggesting that improved precision depends on closer control of physiological variables. 5. In six patients with severe untreated Paget9s disease of bone, skeletal blood flow was 8·4–15·3% of blood volume/min. The increase was significant in all cases. 6. The absorbed radiation dose is low, so that the measurement can be repeated.

John Reeve

Papers

Vertebral collapse in juvenile chronic arthritis: its relationship with glucocorticoid therapy.

Multiterminal HVDC Power Systems

Versatile load flow method for multiterminal HVDC systems

Linear performance indices to predict oscillatory stability problems in power systems

The clinical measurement of skeletal blood flow.