Biddle Flood Mod 电路图.pdf

SALVAGING FLOOD DAMAGED ELECTRICAL EQUIPMENT Overview In all drying out of electrical windings, the regulation of temperature should be controlled carefully. Maximum drying temperatures on windings should not exceed 194oF (90oC) as measured by thermometer. This will prevent not only the rapid thermal deterioration of the insulation but damage from the high vapor pressures that would be obtained if steam were produced. Several methods are available for drying equipment. Probably the most satisfactory solution to the problem is when the windings can be placed in an oven with suitable temperature control and proper air circulation. Banks of infrared lamps may be used when this is not possible, or a suitable housing may be built around the machine, using steam coils or electric resistance type units for a source of heat. Openings should be provided for the free circulation of air. Blowers may be used to increase the air movement. Vacuum drying has also been effectively used to expedite the return of equipment to service. Certain precautions are necessary if this method is used, and it should be carried out only by experienced personnel. Another method often used is to circulate low-voltage current through the windings. This should not be done, however, until the insulation resistance has reached a value of at least 100,000 ohms. Look for Megger Insulation Testers that have kilohm ranges in order to perform this check prior to application of current. These models include the BMM Series and MIT320 this latter type is only recommended if the original varnish is in reasonably good condition. 11. Before any machine is started, check the entire installation, paying particular attention to lubrication and electrical connections. Determine that no tools or materials have been left in or on the machine. Three-phase motors being restored to service can have proper connection assured for correct rotation with the Biddle Motor and Phase Rotation Tester (560060). This model will check correct phase rotation for both motor and live line, while 3-phase lines can be separately checked with a Phase Sequence Indicator (565250). When put back into service, rotational speed of motors can be readily checked with the family of Biddle Contact and Photoelectric Hand Tachometers (359985, 359986, 359987). These handy instruments are particularly useful as flooding may have made digital on-line indicators inoperative. For routine electrical checks, remember that Megger offers a full line of hand-held and clamp-on multimeters. Switchboards and Electrical Controls 1. Thoroughly clean and dry out all control equipment, dismantling where necessary. Operating coils should be thoroughly dried and dipped in insulating varnish and baked or given one or more coats of air-drying insulating varnish. Check all contacts. Be sure moving parts operate freely. 2. Oil pans on starters and oil switches must be cleaned, dried out, and refilled with oil of proper dielectric strength. Insulating oil can be tested in full conformance to ASTM standards with the Megger OTS60PB and OTS60SX Oil Test Sets. Insulating barriers should be dried out or replaced if badly warped. 3. Meters and relays usually will have to be reconditioned at either the manufacturers service shop or factory. In many instances, it will be cheaper to replace them. 4. All bus insulators and control wiring on switchboards should be cleaned and dried thoroughly. Normally, an insulation resistance of at least one megohm per 1,000 volts operating potential, with a minimum of one megohm, should be obtained before energizing. This is a very basic and universal insulation requirement, and can be performed with any Megger Insulation Tester. Specific models should be further evaluated for additional features and functions against additional demands and operators preferences, as well as budget constraints. Standby batteries should be checked for their readiness to come on line using the BITE family of Battery Impedance Testers (BITE2, 2P, by short-circuiting one winding and energizing the other with low ac voltage; or by a combination of these two methods. Insulation resistance checks will determine the progress of drying. A curve should be plotted, showing resistance against time, as mentioned previously. It is best to start at the 5 V level of the kilohm range, then test periodically throughout the drying process. The effectiveness of the drying procedure will be noted by the steady rise in insulation values. If mechanical damage has been done, such as pinholes or burn tracks, the insulation will not spontaneously regenerate, and the drying process can be discontinued without costly expenditure of time, in favor of rewinding or similar repair actions. If the drying operation does proceed successfully, it can be monitored into the megohm range, and then higher voltage tests can be applied without damage until the final desired value is reached. Once the drying process has restored insulation resistance to acceptable values, full performance can be further verified by performing a turns ratio test with the Megger TTR20. Damage to insulation can produce turn-to-turn shorts that effectively alter the turns ratio between primary and secondary windings. The TTR is the most precise and sensitive means of determining the existence and extent of such problems. 4. The oil should be filtered to standard test value of not less than 22 kV, or a new supply of oil of high dielectric strength should be used. The above procedures also may be used with askarel-filled transformers, but with the following precautions. Oil should not be used as a substitute for any askarel-insulating fluid. Where dipping and baking, or re-insulating is necessary, the manufacturer should be consulted regarding proper materials and procedure. The askarel should be reconditioned, making standard IEEE tests until breakdown values reach not less than 25 kV, or replaced with new askarel. AVO International Page #5 Salvaging Flood Damaged Equipment Cables and Wiring All open wiring, including nonmetallic, sheathed cable, can be retained generally after thoroughly drying both cable and junction boxes and remaking connections. Armored cable usually will have to be replaced, as will lead cable if the ends have been under water. Salt water is particularly damaging. Rubber-covered cable in rigid conduit or in electrical metallic tubing may sometimes be reused, but it must be pulled out of the conduit or tubing in order to clean the conduit or tubing. Care must be exercised in this operation, as the cable insulation may be easily damaged. The conduit or tubing must be thoroughly cleaned of all silt and moisture prior to being used again. Potheads and all insulators should be cleaned and carefully inspected for cracks or other damage. Megger Insulation Testers are the ideal instruments for testing wire and cable for waterlogged condition, opens and shorts. If basic function proofing is all that is required, the MIT320 and 330 are all that is needed to perform all the fundamental checks associated with this application. For more detailed troubleshooting by skilled professionals, the BMM Series is preferable. And for higher rated equipment, MIT510. Also, dont overlook storage and downloading capabilities, available in BMM2500 and 2580, MIT330, and MIT510. For interfacing with insurance representatives, government regulatory agencies, and various third-party involvements, this function is invaluable in proving not only that tests have been done, but that theyve been done correctly. Electrical Tools Electrical tools can be reconditioned in the same general manner as described above. But to put them safely into the hands of employees, and to meet OSHA requirements, final proof can be done with a Biddle Tool & Appliance Tester (235303). Remember that in this application, the reconditioning of equipment for restoration to service, the AC high-pot function would be appropriate. Finally, dont overlook the DETEX line of Voltage Detectors and Phasing Testers for employee safety. Under the chaotic conditions of a post-flood situation, power lines may or may not be live. The most reliable way to determine if conditions are safe to proceed with maintenance and restoration is to test first with a DETEX indicator.