Showing papers by "Vattenfall published in 1995"

Distribution network and method and device for regulating electric current from the network

Abstract: The present invention relates to a distribution network comprising electric wires (5) for distribution of electric current, a plurality of tap-off facilities (6) with at least one socket means (9) for tapping off electric current to optional power-consuming units (1), and a central computer unit (10) communicating with the individual tap-off facilities. At least some tap-off facilities (6) in the network comprise a switch (13) and a regulating device (11) with a microprocessor (21), a user connecting a power-consuming unit (1) to one of said tap-off facilities being identifiable to the central computer unit (10) or to the regulating device (11) via a microprocessor in the power-consuming unit, and the regulating device, in case of accepted identification, keeping the switch (13) closed and permitting tap-off of electric current from the socket means (9), whereas, in case of non-accepted identification, the regulating device keeps the switch open and prevents tap-off of electric current from the socket means (9). The invention also relates to a device and a method for respectively permitting and preventing current supply from the network.

Unicellular natural circulation in a shallow horizontal porous layer heated from below by a constant flux

Abstract: Natural convection in a saturated horizontal porous layer heated from below and cooled at the top with a constant flux is studied both analytically and numerically. Linear stability analysis indicates that unicellular recirculation remains a stable mode of flow as the aspect ratio ( A ) of the layer is increased, in contrast to the situation for an isothermally heated and cooled layer. An analytical solution is presented for fully developed counterflow in the infinite-aspect-ratio limit; this flow is found to be linearly stable to transverse disturbances for Rayleigh number ( Ra ) as high as 506, at which point a Hopf bifurcation sets in; however, further analysis indicates that an exchange of stability due to longitudinal disturbances will occur much sooner at Ra ≈ 311.53. The velocity and temperature profiles of the counterflow solution, whilst not strictly speaking valid in the extreme end regions of the layer, otherwise agree very well with full numerical computations conducted for the ranges 25 [les ] Ra [les ] 1050, 2 [les ] A [les ] 10. However, for sufficiently high Rayleigh number ( Ra between 630 and 650 for A = 8 and Ra between 730 and 750 for A = 4, for example), the computations indicate transition from steady unicellular to oscillatory flow, in line with the Hopf bifurcation predicted by the linear stability analysis for infinite aspect ratio.

An investigation of the spatial resolution requirements for two-point correlation measurements using LDV

Abstract: The spatial resolution requirements for accurate two-point correlation measurements at small separations are investigated. Practical guidelines in terms of characteristic measuring volume sizes and estimated Kolmogorov length scales are given. Sample measurements of two-point one-component longitudinal correlations on the centerline of a turbulent jet are presented.

Three phases conductor arrangement

Abstract: Method for generating low magnetic fields from a three-phase-conductor arrangement, as well as such an arrangement. Four phase conductors are used, one phase (R) being split into two phase conductors (R/2, R/2) which are arranged one on each side of the phase conductors (S, T) of the unsplit phases in a planar phase arrangement. The two outer phase conductors (R/2, R/2) are interconnected, thereby forming a loop. Capacitive elements (53) can be arranged in the loop, preferably in loop-forming cross connections (51).

Three phase conductor arrangement

Abstract: Method for generating low magnetic fields from a three-phase conductor arrangement. Four phase conductors are used, one phase being split into two phase conductors which are arranged one on each side of the phase conductors of the unsplit phases in a planar phase arrangement. The two outer phase conductors are interconnected, thereby forming a loop. Capacitive elements can be arranged in the loop, preferably in loop-forming cross connections.

Resilience of macroinvertebrate communities in acidified and limed streams

Abstract: Benthic macroinvertebrate communities in 13 acidified South Swedish streams were sampled in 1981. The same localities were revisited in 1994 when most of the streams had been limed. Untreated streams were used as references. Species richness and proportion of predators increased between the two years. The differences are probably due to the warm and dry summer in 1994. However, the proportions of acid-sensitive species in various groups of streams were about the same the two years, indicating that liming had an insignificant effect on the return of these species. The resilience of the bottom fauna may be attributable to biotic conditions or the failure of the practiced liming methods to maintain healthy chemical conditions.

Device for the automatic testing of joints in electrical high voltage lines

Abstract: A device for automatic testing of electrical high voltage lines is described, comprising a support (1), a driving wheel (2) for lying against the line (3) with a remotely controlled device (4) and a means for remotely controlled automatic measurement of physical data at the joint (11) in question) Means for the transfer of measurement data to a receiver is provided along with a shielding means (15) to shield the transfer means The device is characterized primarily in that it is provided with a guide rails means (7,8,9) for steering of the device, carried by a lifting means such as a helicopter or crane for lying the driving wheel against a line Physical measurement may comprise contacting as well as non-contacting measurement in the vicinity of and at a joint in question To compensate for voltages which may be induced in the measuring means, a compensation circuit is provided The compensation circuit may be provided with a flat coil which may be rotated by a stepper motor or the like Voltage in the measuring circuit may be measured continuously during stepwise rotation of the flat coil to determine a measured voltage minima and maxima The minimum voltage measured correctly compensates for currents induced in the measuring circuit