A thin superconducting solenoid has been designed for an upgrade to the Fermilab D detector, one of two major hadron collider detectors at Fermilab. The original design of the D detector did not incorporate a central magnetic eld which necessitates a retro t within the parameters of the existing tracking volume of the detector. The two l a yer solenoid coil is indirectly cooled and provides a 2 T magnetic eld for a central tracking system. To minimize end e ects in this no iron con guration, the conductor width is varied thereby increasing current density at the ends and improving eld uniformity. This paper summarizes the results of the conceptual design study for the D superconducting solenoid.
Comments about the use of a ZigZag transformer to reduce the neutral current created by unbalanced nonlinear loads. INTRODUCTION The subject of AC line currents with high harmonic content and the potential for overloaded neutral wires caused by the non-linear loading of electronic power supplies has become one of the most popular and at the same time a very complex topic among electrical engineers. Different solutions are offered for this problem. Some examples are specially desi~ned K-rated AC distribution transformers 1, delta connected primary windings , and L-C tuned filters3.4. All of the above methods have some limitations. For instance, a K-rated transformer does not eliminate harmonics, but transmits them into the feeder. Neutral currents that flow from various loads to the K-rated transformer are still very high. These K-rated transformers are more expensive and are larger in physical size than conventional transformers. The delta connected primary of a power distribution transformer can only eliminate triplen harmonics for balanced loads. Neutral currents caused by the loads are not eliminated. The primary side circuit breaker may also not protect a transformer against overcurrents because the circuit breaker will not see the triplen harmonic current that is circulating in the primary of the transformer5. L-C filters can create undesirable resonances, which will lead to an increase in harmonic currents. Another solution6 is to use a number of small ZigZag transformers to reduce the neutral current. This is attractive for the following reasons: relatively low cost, simplicity, ease of installation on existing distribution systems, ability to keep neutral currents local thus eliminating the need for larger neutral wires, and the ability to improve the fundamental load current balance as well. FIELD TEST 1 A site plagued by harmonics, which required investigation, was the 208 V, 3 phase, 60 Hz AC distribution for the second floor of the DO movable counting house. The counting house has many 5 Vdc and 15 Vdc switch mode power supplies connected to the 120 Vac line. The symptoms were as follows: the 150 KVA (480-208Y/120 V) distribution transformer located on top of the counting house ran very hot. The conduit that contained the transformer secondary wires was also hot. In order to find the cause, we measured phase and neutral currents at the two Panelboards fed by the transformer. The currents were-2measured with a BMI PowerScope (the BMI PowerScope plots the current waveforms, analyzes the waveform for harmonic content and charts the spectrum analysis of the first 33 harmonics). The neutral current value was 215 A RMS with 554.3% of total harmonic distortion (THO). The phase current was about 140 A RMS with a THO of about 70%. All three phase currents were balanced within 20%. The prevailing harmonic was the third harmonic. As a matter of fact, the neutral carried an almost pure third harmonic current (see Fig. 1 and 2). In order to investigate the source of the distortion further we measured the rack curr...
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