Eaton SEFELEC 5 Series User Manual

User manual SEFELEC 5x Series 192 v1.0619.5.1.2. DIELECTRIC STRENGTH TESTS WITH DC VOLTAGEBENEFITS:* The power of the HV source can be lower than the one necessary in AC voltage (lessweight and more safety for the operator). The current flows through the specimen only dur-ing the charging phase.DISADVANTAGES:* The charging current can trigger the breakdown detection* The specimen being charged, it must be discharged through the built-in discharge resistance(1.5 Mohm).WARNING: Wait enough for the discharge of the specimen capacitance before disconnectionfrom the unit (about 8 seconds per uF).* The specimen is tested in only 1 polarity* The test voltage must be higher than the one provided with AC test voltage. A common rule isto use a 1.4 correction factor between the DC and the AC voltages (= square root of 2 = ratiobetween the rms value of a sinusoidal wave and its crest value):Udc = UAC * 1.419.5.2. Breakdown detection mode selectionThe most common and simple leakage current control mode is the threshold current controlmode or IMAX mode. This mode allows setting a maximum limit of current flowing in the speci-men under test above which the unit detects a breakdown and stops the test by cutting off theHV generation and memorizing the voltage value on the LCD screen. As described, the HVsource has to supply the leakage current as well as the reactive current coming from its capaci-tance. Therefore this requires to adjust the breakdown threshold regarding the reactive currentof each specimen, and to follow the procedure:* Make a test on a good specimen* Collect the total current flowing* Adjust the current threshold to a value greater than the total current.The XS range units offer the above described detection mode, combined with the ∆-I detectionmode (called sometimes ARC detection mode). The ∆-I mode allows to release from the reactivecurrent flowing in the capacitive specimens.To detect a breakdown, the ∆-I mode (ARC detection) monitors only the fast-current variations(t > 10 uS and amplitude > 1 mA). This does not require any adjustment regarding the specimencapacitance. However this mode cannot detect a dielectric strength default in case of a speci-men in short-circuit since the high voltage application. That is why the MG range units allow tocombine the IMAX and the ∆-I modes in order to make reliable and without adjustment of dielec-tric strength tests. The IMAX value is set to a value close to the unit short-circuit current underthe test voltage.The MG range units allow to inhibit the detection systems (OFF mode) in order to locate visuallywhere is the dielectric strength fault. WARNING: this mode does not cut off the high voltage and