AEMC 6417 User Manual

Also see for 6417: Service/Calibration Manual Quick start user guide User manual User manual

Clamp-on Ground Resistance Tester Model 6417 153. PRINCIPLE OF OPERATIONTypically, a grounded distribution system can be simulated by the basic circuitshown in Figure 3-1 or an equivalent to the diagram shown in Figure 3-2. Ifvoltage (V) is applied to any measured grounding electrode Rx through aspecial transformer; current (I) flows through the circuit, thereby establishing thefollowing equation:VI = Rx + 1Σni=11RiRx » 1Σni=11Riwhere, usuallyTherefore, V/I = Rx is established. If I is detected and measured with V keptconstant, the measured grounding electrode resistance Rx can be obtained.A signal is fed to a special transformer via a power amplifier from a 2403Hzconstant voltage oscillator. The resulting current is then sensed by a detectionCT (current transformer). An active filter is used to dampen earth current atcommercial frequency (50/60Hz) and high-frequency noise.Example: If clamped around any grounding electrode in a multi-groundedsystem, the measured value of the electrode under test will be the resistanceof that particular rod in series with the equivalent parallel resistance value thatthe rest of the multi-grounded system represents. If an electrical system had101 grounding electrodes and each had a resistance value of 25W, and it wereclamped around any electrode in the system, the measured value would be 25Win series with the equivalent parallel resistance of the other 100 electrodes or0.25W. The displayed value would be 25.2W (instrument resolution to 0.1W).V/I = 25W + 0.25WRx = 25.2WIn most field applications, the number of electrodes that make up a multi-grounded system would be higher; therefore the equivalent parallel resistance isnegligible with respect to the rod under test.IVRx R 1 R 2 R n-1 R nFigure 3-1www. GlobalTestSupply .comFind Quality Products Online at: sales@GlobalTestSupply.com