Abstract: In a vacuum switching device having first and second contacts, the first contact only is composed wholly or partly of a combination of at least a high-conductivity material and an arc-resistant material, e.g. chromuim, tungsten or tungsten carbide, and/or an anti-weld material, e.g. bismuth, antimony, tellurium or lead, while the second contact lacks the arc-resistant and anti-weld material. Metal vapor produced by the first contact during arcing is deposited on the opposing surface of the second contact to form a thin layer of high-conductivity and arc-resistant and/or anti-weld material which then dominates the properties of the arc and allows a low chopping current and/or an enhanced anti-weld performance of the contacts to be achieved without the expense of having both contacts of the same composition at manufacture.

Abstract: A polyphase thyristor-switched-capacitor static var compensator (SVC) arrangement employs a transformer circuit connected to the capacitors of the SVC and configured such that when the capacitors are switched out of circuit in sequence, a residual charge on the capacitors is reduced by the transfer of energy between the capacitor and an energy-dissipation circuit by way of the transformer circuit. The primaries of the transformer circuit are connected across respective capacitors, while the secondaries are connected in series in a delta configuration. Damping resistors may be connected in series with the primaries to help dissipate the capacitor energy. The transformer circuit may be saturable and may be constituted by individual transformers or one polyphase transformer.

Abstract: A switching control arrangement for a multilevel convertor minimizes the harmonic content of the converter voltage or current by an open-loop and/or a closed-loop control of the timing of the switching of the GTOs associated with the energy-storage components (e.g. capacitors) in the convertor. In a first open-loop arrangement the convertor current is quantized over its working range and different threshold values are provided in dependence on the quantization values of the current. In a second open-loop arrangement a continuous, non-quantized control is provided based on at least a quadratic approximation to the desired current-dependent behavior of the GTO switching angles. In a third, closed-loop arrangement, different GTO-switching threshold levels are provided as controlled by a Fourier integration process involving the nulling of those harmonics desired to be nulled.

Abstract: A control arrangement for a multilevel convertor employs an AC reference signal which is locked to the AC system frequency and is compared with a number of DC threshold levels. Intersections of the reference signal and threshold levels triggers the firing and turning-off of GTOs within the convertor to produce the desired multilevel voltage output. Normal changes in system voltage, for example, are compensated by variation of the phase relationship of the reference signal with respect to the system voltage, and/or of the voltage values of the threshold levels. Sudden and drastic changes, especially reductions, in system voltage level are sensed and used to alter the amplitude of the reference signal so as to reduce the difference between the convertor multilevel voltage and the system voltage, thereby reducing the stress on the GTOs during faults.

Abstract: The invention relates to the design of a fixed-blade assembly in an axial flow steam turbine and is based on the recognition that the design of the interfacing region (fillets) between the radial ends of the blades and the end-blocks to which they are attached or of which they form a part has a significant effect on stage efficiency. The invention recognizes an optimum fillet radius in the range 0.15-0.3 of the throat dimension between the trailing edge of one blade and the suction surface of an adjacent blade, and more particularly 0.20-0.50. The fillet configuration is advantageously applied to a turbine having blades which are of constant cross-section, are curved in the radial (height) direction and are convex from root to tip on its pressure face, the result being a considerable gain in stage efficiency.

Abstract: A rotating electrical machine has openings (105) in its stator teeth (101) occupying a substantial part of the surface area of each tooth so that the stator windings (103) have only a short thermal path to axial cooling ducts created by the openings. In another embodiment, each rotor tooth (109) is provided with a recess (110) at one corner of the tooth to form a recess axial cooling duct; the recess may be of such a depth as to expose part of an adjacent slot (118) to the recess duct. Cooling is by air, either in a single-ended or a double-ended axial ventilation system.

Abstract: A power-line trip circuit models the transient characteristic of a change in load (e.g. appearance of a fault current, or switch-on to a normal load) and compares the current actually flowing in the power lines with this modelled or simulated transient. Line currents that do have a transient component but do not exceed normal limits are not then sufficient to trip a circuit breaker associated with the power lines, whereas transient-bearing currents that do exceed such limits, i.e. fault currents, are recognized as such and the circuit breaker is tripped. This circuit allows fast, reliable tripping even in the presence of a substantial transient overshoot.

Abstract: A vacuum recloser in which an isolator switch is incorporated in series with the vacuum interrupter and is driven by the same actuator. The isolator must only be operated when the vacuum switch is open and no arc current remains. This is ensured in one of two ways (a) by providing a significant lost motion in the isolator drive, giving, say, 20 milliseconds between opening of the vacuum contacts and opening of the isolator contacts, and (b) by latching the isolator drive against opening, compressing a spring against the latch by the actuator attempting to open the isolator, and tripping the latch by a solenoid responsive to lock-out conditions.

Abstract: A method of locating the position of a fault on a power transmission line between first and second ends of the line is performed by calculating the complex fault impedance at each of a plurality of assumed fault positions along the length of the line, the fault impedance at each assumed position being calculated utilizing the measurement before and after fault occurrence of the voltage and current at the first end of the line, parameters of the line, and the impedance at the second end of the line; and selecting as the actual fault position the assumed fault position of the plurality of assumed fault positions for which the argument of the complex fault impedance most closely equals zero. The method may be used with single or multi-phase power transmission lines. There is also disclosed a method of determining the form of impedance network at a fault on a multi-phase power transmission line.

Abstract: An antiseismic static electrical converter installation comprises a valve assembly mounted on a platform, the platform being suspended at each of two opposite ends from a series of rods which are attached in a spaced-out relationship to a horizontal beam, the beam being mounted on the ground via rubber springs. During an earthquakes movement of the ground causes mainly lateral distortion of the rubber springs and elastic bending of the rods, and, since the natural resonant frequency of the suspension system is designed to be low and the rubber springs are deigned to have significant damping, a high degree of isolation is provided for the platform and the equipment mounted on it. During severe earthquakes, the rods are arranged to suffer a plastic bending which causes them to act like pendulums and changes the natural frequency of the suspension system to increase the damping and provide greater protection.

Abstract: The invention relates to the design of (particularly) a fixed blade in an axial flow steam turbine. A conventional blade is of prismatic form with an aerofoil cross-section and extends radially between annular end blocks. The inventive blade is curved in the radial (height) direction, being convex from root to tip on its pressure face. The setting angle relative to the corresponding prismatic blade is therefore fine at the root and tip and coarse at the blade mid-height. The throat opening is thus reduced at root and tip and increased at mid-height so displacing some mass flow away from both lossy end wall regions. A considerable gain in the stage efficiency results. A further improvement results from providing an optimum corner fillet between the blades and end walls at the root and tip.

Abstract: A mooring system comprises a length of hawser 3, a chafe chain 7, and a wire 5 to be wound onto a rotatable drum 1. Adjacent the drum 1 is positioned a stopper 2 adapted to receive and retain the chain 4, the chain 4 being disconnectable from the wire 5 in this circumstance.

Abstract: An inductive Superconductive Fault-Current Limiter (SCFCL) includes an iron core having a wound primary winding and a short-circuited superconductive secondary. The secondary remains superconductive up to a fault-current level in the primary, after which the superconductive secondary becomes resistive, the primary ampere-turns are not balanced, and the device becomes highly inductive, so limiting the fault-current. The fault-current threshold is increased without exceeding available critical superconductive current density levels and with a moderate superconductive coating thickness by using a stack of superconductive coated washers having a large radial extent compared to the coating thickness.

Abstract: Electronic control apparatus of a kind used in low voltage industrial equipment such as assemblies of motors or circuit breakers. Where an overall controller, e.g. a programmable logic controller (PLC) controls an array of (e.g.) motors (M1, M2, M3) by way of respective control units (13, 23, 33) identification or location of selected motors is usually effected by an address stored in the respective control unit. A faulty control unit entails replacement and loss of the location address which has to be reentered as a skilled operation. The invention provides a separate non-volatile memory (15, 25, 35) for the location address, this memory being physically associated with the particular motor (M1, etc.). A replacement control unit (13, 23, 33) is automatically loaded with the location address which was retained.

Abstract: The invention provides method and apparatus for identifying the faulted phases on the occurrence of a single phase fault simultaneously on both circuits of a double circuit electric power transmission line using measurements taken at one end only of the line. Using measurements of voltage and current at the one end of the line and a knowledge of various parameters of the line, a signal representative of the travelling wave arriving at the one end of the line in consequence of the faults is derived. This derived signal is used to deduce the values of the components of the derived signal attributable to the different faults for each of a number of assumptions as to which phases are faulted. The deduced values for the different assumptions are then used to determine which assumption is most likely to be correct.

Abstract: A fixed blade assembly for an axial flow turbine, in which each blade (23) is secured between a radially inner ring (21) and a radially outer ring (22). The trailing edge (25) of each blade is straight and leans at an angle .theta. away from a radial line (28) from the turbine axis through the inner end of that edge and in the circumferential direction that the suction side (24) of the blade faces. The blades (23) have this (negative) angle of lean in the range 5 degrees to 12 degrees.

Abstract: A distribution transformer has a wound magnetic core (50) of overall circular shape and rectangular cross-section with between two and four overall rectangular shape electric coils (20,30) extending through the core window. The coils (20,30) are pre-formed and assembled so that their parts (20A,30A) which meet form a circular section solid cylinder. A mandrel (40) is then located around this cylinder (20A,30A) and continuous non-amorphous steel strip is wound thereon to form an unannealed, uncut wound magnetic core of axial length in the range 250 mm to 1 m. In a modification, amorphous steel strip is first wound on to another mandrel, annealed, and then transferred from the other mandrel on to the mandrel around the coils.

Abstract: A multilevel convertor having a set of series-connected capacitors and a set of associated series-connected switching elements employs a main control loop which controls some aspect of an AC system, e.g. busbar voltage, by controlling the switching times of the switching elements. The convertor also comprises one or more subsidiary control loops for establishing a desired relationship between mean DC voltage levels on the capacitors. The subsidiary control loops combine first signals proportional to DC voltage levels on the capacitors and second signals proportional to tap currents associated with the capacitor nodes to provide signals which modulate the timing of the switching of switching elements connected to those capacitors which are out of balance, while leaving alone the timing of the switching of switching elements associated with those capacitors which have the required voltage across them.

Abstract: A distribution transformer has a wound magnetic core (50) of overall circular shape and rectangular cross-section with between two and four overall rectangular shape electric coils (20,30) extending through the core window. The coils (20,30) are pre-formed and assembled so that their parts (20A,30A) which meet form a circular section solid cylinder. A mandrel (40) is then located around this cylinder (20A,30A) and continuous non-amorphous steel strip is wound thereon to form an unannealed, uncut wound magnetic core of axial length in the range 250 mm to 1 m. In a modification, amorphous steel strip is first wound on to another mandrel, annealed, and then transferred from the other mandrel on to the mandrel around the coils.