From majordom@mbari.org Thu Jun 1 18:48 PDT 1995 Received: from wave.mbari.org by barnacle.mbari.org with ESMTP (1.37.109.16/16.2) id AA050637731; Thu, 1 Jun 1995 18:48:52 -0700 Return-Path: Received: by wave.mbari.org ($Revision: 1.37.109.26 $/16.2) id AA240187724; Thu, 1 Jun 1995 21:48:44 -0400 Received: from reef.mbari.org by wave.mbari.org with ESMTP ($Revision: 1.37.109.26 $/16.2) id AA239807716; Thu, 1 Jun 1995 18:48:36 -0700 Received: by reef.mbari.org (1.37.109.16/16.2) id AA199927715; Thu, 1 Jun 1995 18:48:35 -0700 From: Ed Mellinger Subject: AC Thermal Test Results To: neji@wave.mbari.org (Jim Newman) Date: Thu, 1 Jun 95 18:48:34 PDT Cc: meed@wave.mbari.org (Ed Mellinger), rovtech@wave.mbari.org Mailer: Elm [revision: 70.85] Sender: owner-rovtech@mbari.org Precedence: bulk Status: RO Hi Jim - Just completed thermal testing of AC Power Can. This involved short circuiting one 240V output and applying full input current at much reduced voltage using a 60 Hz three phase variac. (Full power to one 240V output is the worst case thermal condition.) This test duplicates all losses experienced during full voltage operation except for transformer core excitation losses which are about 15% of the total. Testing was performed at 100% and 133% of nominal 75 A full load current (100% and 170% of nominal 800 W full load losses), with the can tilted 5 degrees either way in pitch and roll, and over the 40-56V range of the 48V supply. Test duration was limited to 1 hour at 100% current and 30 minutes at 133% current by inadequate cooling of the outside of the aluminum power can, and an arbitrary Fluorinert temperature limit of 60 C. Four runs were made at 100% and two at 133% current. The tests were generally successful, with comments as noted below: 1) Cooling of all components was adequate at all power levels tested. FC-72 (Fluorinert) temperature was estimated from absolute pressure and was within 5 C of can wall temperature at all power levels. Average copper temperature was estimated from resistance rise and was within 10 C of FC-72 temperature at all power levels. Rectifier heatsink temperature rise was measured directly with a thermocouple and was within 20-30 C of FC-72 temperature depending on absolute temperature and power levels. 2) FC-72 boiling characteristics were satisfactory, ranging from moderate to vigorous depending on power level. FC-72 boil-over varied from zero to minor depending on power level (boiling intensity) and temperature (thermal expansion). Boilover actually aided rectifier cooling at max power and temperature (prompting me to claim it as a feature...). 3) Pumps and controls performed adequately either singly or in combination under all conditions tested, including boilover plus 170% thermal load. The only exception was a vapor lock in one pump during one tilt transition, which required a power cycle to clear. 4) All components remained adequately submerged under FC-72 during all conditions of tilt. The FC-72 level sensors performed as expected and were usable for determining proper fill levels as well as loss of coolant, at all temperatures and supply voltages. However changes will need to be made to the "warning" threshold in the AC micro, and the "alarm" condition should occur only when *both* sensors reach the warning threshold. 5) At 100% load the tank boils from full to the low limit (components exposed) in about four minutes, faster than I expected. 6) FC-72 fill quantity in the prototype power can was 5.75 liters (or 9.7 kg), larger than the originally estimated 6 kg. (This is partly due to the transformers being smaller than expected, and could be partly compensated by adding plastic filler inside the transformer tank when the final transformers are installed.) FC-72 fill by vacuum backfill, and drain by siphon, were both successful and required 15-20 minutes each way. Drain is improved by 1-2 degrees of tilt (roll) during drain. Approximately 0.4 liters were lost to evaporation, retention in sump, transformer windings, etc. 7. Transformer tank contamination by grease or other solubles continues to be a concern. If we limit the AC Can's o-ring grease to DC-4 (silicone) this should only be a nuisance; I will make further hipot tests to ensure that the transformer isolation remains intact. This completes thermal testing, about 5 weeks behind schedule. There are a few mechanical fixes to make and the new centerwall to wire, after which I will go on to full voltage/full power testing. -Ed in transformer windings, etc.