Video: RMO-G

Video transcript

What the RMO-G measures, how it is connected to live and dead tank breakers, with both sides grounded or from a distance, and what its four test modes do. Where and arcing shrink the real contact area of a breaker, and its resistance rises. At 10 kA, a contact of only 0.1 million dissipates 10 kW in a single point. That is why contact resistance is measured with high direct current, at least 50 amps under IEC, and at least 100 under ANSI. Seven models deliver from 100 to 800 amps of ripple-free direct current.

The resolution goes down to 0.1 micro-ohm, or 0.01 with the high precision module, and the case is sealed to IP67. Everything is on the top panel, the mains inlet and switch, the two current sockets with the voltage sense sockets between them, the display and keys, and the USB interface. Two more sockets set the RMO-G apart, one for the remote control unit, and one for the current clamp. It ships with the PC software and the USB, mains, and earth cables.

The recommended set adds two current cables with battery clamps and two sense cables, five meters each, a transport case, and a cable bag. Longer cables, the test shunt, the current clamp, the remote control unit, a printer, and Bluetooth are options. connection follows the four-point Kelvin method. Current cables on the outside, sense cables inside them, as close to the contact as possible, so the cables and clamps stay out of the result.

On a live tank breaker, across the interrupter. On a dead tank breaker, across its two bushings. With both sides grounded, part of the test current escapes through the groundings. The RMO-G measures that part with the current clamp supplied from the instrument, around one grounding lead, and adds it to the output, so the set current really flows through the contact. The cables go on just as in a single test. The optional remote control unit starts and stops the test away from the instrument.

The current cables stay at the breaker, the sense cables run to the remote unit, and the operator stays outside the zone where induced current flows. a breaker with several interrupters in series, the current cables span the whole pole once. Then only the remote unit and its sense clamps move from one interrupter to the next, and each reading is started from there, at the same test current. For modes cover every case. Single takes one reading.

Content holds the current for a set time. BSG compensates the current lost through the groundings. And DTR test is for dead tank breakers with bushing current transformers. In a single test, the current rises along a regulated ramp, is held while the voltage drop is measured, and falls back to zero along another ramp. Sloping the current up and down practically eliminates magnetic transients from the reading.

In content mode, the current is held for a predefined time. Up to 100 amps, there is no limit. At 600 amps, it holds 20 seconds, followed by 2 minutes of rest. 800 amps for 5 seconds is available on request. On dead tank breakers, the bushing current transformers magnetize while the current rises, and that distorts the reading. DTRutist saturates them first. An internal algorithm detects the saturated condition,

and only then is the contact measured. Setting it up is as simple as a live tank test. high output voltage keeps the range wide at high current and allows thinner or longer cables. The RMO600G reads up to 5.3 milliohms at 600 amps with 5-meter, 50-square-millimeter cables. The RMO100G tests at 100 amps through 20 meters of 16-square-millimeter cable. Over USB or RS-232 as an option,

the PC software controls every function of the RMO-G. In content mode, it records readings at a sampling time set in seconds. Results download with search filters and become a spreadsheet and a configurable report. It measures any non-inductive low resistance that has to carry high current, breakers, disconnectors, GIS, busbar joints, cable splices, welds and fuses, and manufacturing, commissioning and maintenance.

Circuit breaker testing from Amperis.