PREVENTIVE MAINTENANCE & ROUTINE INSPECTION OF CONTACTORS

Transcription

1 Page # 1/5 PREVENTIVE MAINTENANCE & ROUTINE INSPECTION OF CONTACTORS A. GENERAL INSPECTION: A.1. Check for loose, missing, broken or corroded hardware, pivot pins, cotter pins, springs and other mechanical parts. B. ARC BOXES: B.1. Check arc boxes for broken or eroded parts and Grid plates and also for excessive collection of contact material or other foreign conducting material on the surface of insulating parts. B.2. Replace broken or badly eroded parts. B.3. Clean or replace parts having excessive build of conducting material. C. CONTACTS: C.1. C.2. C.3. C.4. C.5. D. SHUNTS: D.1. D.2. Remove oxide or large beads of contact materials from the faces of contacts, using a fine file or sandpaper.(emery cloth should not be used for cleaning contacts.) Do not file or sand silver or alloy contact faces unless considerable foreign matter has collected on the surface of the contacts. When replacing contacts or other current-carrying parts, clean surfaces, which are to be bolted together. Realign contacts and set over travel if necessary. Do not substitute contact material without factory approval. Replace shunts having broken of frayed strands. Clean connection points if current-carrying parts are discolored. E. BLOWOUT COILS: E.1. Inspect blowout coils for discolored connections, shorted turns, and loose hardware. F. TERMINALS, CNTACT SUPPORTS, BUS BARS, AND CONNECTORS. F.1. Discolored connections usually indicate that overheating has occurred, probably because of loose connections. F.2. Clean connection points which are discolored and tighten all hardware.

2 Page # 2/5 G. INSULATORS. G.1. Remove dust and dirt from insulating parts. G.2. If carbonized tracks or cracked or broken insulators are found, replace the defective parts. G.3. As a last resort, carbonized tracks may be scraped clean and painted with insulating varnish. G.4. Before a repaired part is put into service give it an over voltage test. H. MAGNET ASSEMBLY. H.1. Check magnet for dirty or corroded pole faces, pivot points, and other moving parts. H.2. Check for loose, broken, or missing shading coils, residual shims, and hardware. H.3. Inspect operating coil for evidence of electrical or mechanical damage. H.4 Operate armature by hand and check for mechanical interference and friction. I. ELECTRICAL OPERATION. I.1. Operate the contactor electrically without load and observe magnet operation to be sure it opens and closes cleanly and that armature is fully sealed in the closed position. If an a-c magnet is used, check for abnormal Magnet noise. I.2. Test a sample of oil used with oil-immersed contactors and fill oil tank to the proper level with good oil. I.3. Megger insulation between phases, to ground, and to the control circuit. I.4. Operate the contactor under load and check for abnormal report and arcing both on opening and closing. A Loud report and arcing on closing is usually due to contact bounce. The magnitude of the report and arcing found on opening and closing will depend upon the type of contactor, operating load, and phase angle at which the contacts separate or touch. Since no absolute standard can be set for covering this detail, it will be necessary to judge performance on the basis of past experience with equipment when it was new or with other applications having similar equipment and operating conditions. J. ELECTRICAL OPERATION. The following table will be of great help in trouble shooting of contactors: Sl Trouble/Defect Cause What to do/remedy A. MAGNET. 01 Coil Burned out. Mechanical damage. Replace. Protective resistance or high resistance winding is not Inserted in series with d-c coil when armature seals in. Coil voltage is too high. Adjust, repair, or replace interlock and series resistance so that continuous rating of coil is not exceeded when armature is sealed. Correct coil voltage. Use higher-voltage coil.

3 Ambient temperature is too high. Provide better ventilation. Relocate starter. Intermittent coil is energized too long. Re-adjust operating cycle. Check factory for special coil. Jogging duty is too severe. Readjust operating cycle. Check factory for special coil. Abnormal atmosphere. Relocate starter. Check factory for special coil. 02 Does not pick up. Defective coil. Replace. Low voltage. Correct coil voltage or system Voltage. Mechanical interference or friction Adjustments and/or repairs. Magnetic lockout. Use nonmagnetic-armature-stop details. Add nonmagnetic Shim between armature and armature stop. 03. Does not seal; hesitates at Contact touch; drops open Mechanical interference or friction. adjustments and/or repairs. to contact touch. (This condition may exist only Contact force too high. Replace springs. Remove friction from moving contact assembly. Adjust spring length if adjustment is provided. when operating coil is hot or line voltage is low.) Coil voltage too low. Correct coil Voltage or System Voltage. Use lower-voltage coil. Series protective resistance or high-resistance coil Adjust, repair, or replace interlock and/or series resistance. winding is inserted too early, or series resistance is too high (For DC Magnets). Coils of two-coil d-c magnet have bucking polarity. Reverse polarity of one coil and check operation with load disconnected. 04. Does not dropout, or Dirt or grease on pole faces. Clean. dropout is sluggish. Mechanical interference or friction. adjustments and/or repairs. Residual shim is pounded down or is missing. Replace residual shim or magnet assembly. Residual air gap is pounded down. Kick out spring is defective or missing. Replace (Kick out spring is not used on all contractors). Control relay does not open d-c side of rectifier. Control relay has long arcing time. Add contact in control circuit. Repair or replace relay. Repair or replace relay. Shorted coil turns. (DC Magnet) Replace coil. 05. Magnet chatter or Shading coil broken or out of place. Adjust or Replace.

4 pumping. PREVENTIVE MAINTENANCE & ROUTINE INSPECTION OF CONTACTORS: Series protective resistance or high-resistance coil Winding is inserted too early, or series resistance is too high or is open. (Applies to DC magnets having over voltage during Pickup.) Chattering contacts on control relay, control switch, Pressure switch, temperature switch, etc. Adjust, Repair or replace interlock and/or series resistance. Check over travel and contact force on control device. Replace control device. Move control device to a location having less vibration, or insulate control device from shock And vibration. Tighten connections. Loose connections. 06. Noisy a-c magnet. Armature does not seal in tight. Clean pole faces. Remove mechanical interference and/or friction. Pole faces rough. Replace magnet assembly. File pole faces as a last resort If new parts are not available. Magnet misaligned. Realign. Shading coil broken or out of place. Replace. Coil voltage is low. Correct coil voltage or system voltage. B. Contacts. 01. Overheating. Load current too high. Loose connections. Reduce load. Use larger contactor. Clean discolored or dirty Connections and retighten. Over travel and/or contact force too low. Adjust over travel, replace contacts, and replace contact Springs as required to correct defect. Collection of copper oxide or foreign matter on contact Faces. Clean with fine file or sandpaper. Use dust -tight enclosure for dusty atmosphere. Load is on in excess 8hr. Change operating procedure. Check factory for more Suitable contacts Ambient temperature is too high. Reduce load. Provide better ventilation. Relocate starter. Use larger contactor. Line and/or load cables are too small. Apply cable in line with existing load. 02. Welding of contacts. Over travel and/or contact force is too low. Adjust over travel, replace contacts, and replace contact spring Magnet stalls or hesitates at contact touch point. See Magnet, this table. Magnet drops open at contact touch due to voltage See Magnet, this table. dip. Magnet chatter. See Magnet this table. Contact bounce on closing. Correct coil over voltage condition. Correct mechanical defects.

5 Contacts rebound to contact touch when opening. Correct mechanical defects in stop assembly. Correct Mechanical defects in latch if one is used. Poor contact alignment. Adjust contacts to touch simultaneously within 1/32 in. Jogging duty is too severe. Reduce jogging cycle. Check factory for more weld-resistant contact material. Use larger contactor. Excessive inrush current. Readjust accelerating time or operating sequence. Use larger contactor. Check factory for more weld-resistant contact material. Vibration in starter mounting. Move starter to location having less shock and vibration. Insulate starter from shock and vibration. Provide more rigid Support for starter. Jogging cycle is too severe. Reduce jogging cycle. Check factory for more durable contact material. Use larger contactor. Oil-immersed contactor is used where an air break Contactor could be used. Air break contactors may have 10 to 20 times longer contact life than oil-immersed contactors of equal ratings C. ARC INTERRUPTION Poor arc interruption. Arc box not in place. Install arc box in line with instruction-leaflet data. Arc box damaged. Replace broken or eroded insulating parts, arc horns, and grid plates. Clean or replace insulating parts having a heavy Coating of foreign conducting material. Dirt or paint on arc horns or steel grid plates. Remove insulating materials, which may have accumulated on arc horns and steel grid plates. Magnetic hardware substituted for nonmagnetic Replace with correct hardware. hardware in arc box and blowout assemblies. Blowout coil reversed or short-circuited. Replace coil. Correct defect. Magnet opening is sluggish. See Magnet, this Table.