Eaton 50VCPW-ND250 Installation, Operation And Maintenance Manual

Also see for 120VCP-W25: Instructions for installation/operation/maintenance/servicing Instructions for installation, operation and maintenance

Contents

I.B. 32-255-1G Page 35Effective 12/026-4 VACUUM INTERRUPTER INTEGRITY TESTVacuum interrupters used in Type VCP-W VacuumCircuit Breaker Elements are highly reliable interruptingelements. Satisfactory performance of these devices isdependent upon the integrity of the vacuum in the inter-rupter and the internal dielectric strength. Both of theseparameters can be readily checked by a one minute achigh potential test. Refer to Table 6.2 for the appropri-ate test voltage. During this test, the following warningmust be observed:APPLYING ABNORMALLY HIGH VOLTAGEACROSS A PAIR OF CONTACTS IN VACUUM MAYPRODUCE X-RADIATION. THE RADIATION MAYINCREASE WITH THE INCREASE IN VOLTAGEAND/OR DECREASE IN CONTACT SPACING. X-RADIATION PRODUCED DURING THIS TEST WITHRECOMMENDED VOLTAGE AND NORMAL CON-TACT SPACING IS EXTREMELY LOW AND WELLBELOW MAXIMUM PERMITTED BY STANDARDS.HOWEVER, AS A PRECAUTIONARY MEASUREAGAINST POSSIBILITY OF APPLICATION OF HIGH-ER THAN RECOMMENDED VOLTAGE AND/ORBELOW NORMAL CONTACT SPACING, IT IS REC-OMMENDED THAT ALL OPERATING PERSONNELSTAND AT LEAST FOUR METERS AWAY IN FRONTOF THE BREAKER ELEMENT.With the breaker element open, connect all top primarystuds (bars) together and to the high potential machinelead. Connect all bottom studs together and groundthem along with the breaker frame. Start the machine atzero potential, increase to appropriate test voltage andmaintain for one minute.A successful withstand indicates that all interruptershave a satisfactory vacuum level. If there is a break-down, the defective interrupter or interrupters should beidentified by an individual test and replaced before plac-ing the breaker in service.AFTER THE HIGH POTENTIAL IS REMOVED,AN ELECTRICAL CHARGE MAY BE RETAINED BYTHE VACUUM INTERRUPTERS. FAILURE TO DIS-CHARGE THIS RESIDUAL ELECTROSTATICCHARGE COULD RESULT IN AN ELECTRICALSHOCK. ALL SIX PRIMARY TERMINALS AND THECENTER RING OF EACH VACUUM INTERRUPTEROF THE CIRCUIT BREAKER SHOULD BE GROUND-ED TO REDUCE THIS ELECTRICAL CHARGEBEFORE COMING IN CONTACT WITH THE PRIMA-RY CIRCUIT.To avoid any ambiguity in the ac high potential test dueto leakage or displacement (capacitive) current, the testunit should have sufficient volt-ampere capacity. It isrecommended that the equipment be capable of deliv-ering 25 milliamperes for one minute.Although an ac high potential test is recommended, adc test may be performed if only a dc test unit is avail-able. In this case the equipment must be capable ofdelivering 5 milliamperes for one minute. When a DCtest voltage is used, a high field emission current from amicroscopic sharp spot on one contact can be misinter-preted as a sign of a vacuum interrupter filled with air.To avoid a misinterpreted test result, the open inter-rupter should always be subjected to both voltagepolarities. That is, apply the DC Voltage:- first, so that one contact of the interrupter is thecathode, and- second, so that the other contact of the interrupteris the cathode.A bad interrupter filled with air will have a similarly highleakage current in both polarities. A good interrupterwith a good vacuum level may still have a high leakagecurrent, but this will generally be in only one polarity.Such an interrupter usually has a tiny sharp spot on onecontact that produces a high field emission currentwhen the sharp spot is a cathode, but not on an anode.In addition, such an interrupter would also normallywithstand the required AC voltage which is the definitivetest of its vacuum integrity.The current delivery capability of 25 ma ac and 5 ma dcapply when all three VIs are tested in parallel. If individ-ual VIs are tested, current capability may be one third ofthese values.Vacuum Interrupter Integrity Test Voltageac 60 Hz dcUp to and including17.5 kV24 kV and 27 kVBreaker RatedMaximum VoltageTable 6.2 Test Voltage27 kV 40 kV45 kV 45 kV! WARNING! WARNING