Video: RMM – Technical guide

Video transcript

How the RMM is connected to a motor or a generator, which sensors it uses and where they see, how the time-of-arrival set-up works, which operating signals are recorded, and how the results point to the defect. The RMM takes the signal from the partial discharge sensors on the machine of any brand, including those already installed, coupling capacitors on the line terminals or in the bus duct. The RTD temperature sensors in the slots through the RTDPD module and stator slot couplers where the machine has them.

Here is why both kinds of sensor are needed. The coupling capacitors on phases A, B, and C only reach the 10-15% of the winding nearest the terminals. The RTDs sit in the slots along the whole winding. Their signals go through the RTDPD module and from there to the RMM. turbo generators, small hydro sets and motors, a common setup uses two sets of coupling capacitors, one at the line terminals and one in the isolated phase bus duct,

at least two meters apart. The time each pulse takes to reach each set tells which side it comes from. Large hydro generators often need two to four sets, one per parallel group. time of arrival to work, the signal paths must be matched. The coaxial cable lengths are adjusted so that the signals arrive at the monitor at the correct times. That is the time of arrival calibration. It is done once, at commissioning, and it is what lets the

monitor separate the machine from what comes in from the bus. For parameters are recommended on every machine to correlate with the discharge, winding temperature, ambient temperature, relative humidity, and load current. The RMM has inputs for 6 RTD winding temperatures, 3 load currents, 3 voltages, and 6 user-defined 4 to 20 mA signals. For every channel the monitor measures and records the quantities that matter, magnitude, the number of pulses, the discharge intensity, and how they are distributed over the phase of the supply.

All industry-accepted graphic results and the IEC -defined quantities are calculated and stored. Locating starts with the trend. Every coupling capacitor and every RTD has a known place in the machine, so the channel with the highest maximum magnitude and the one that climbs over the months points to the area of the winding, even the slot, where the problem sits. phase pattern tells the type. Balanced polarities and a good correlation with the

operating parameters point to voids inside the insulation. Other patterns point to a loose winding or to the slot exit. Watching a start helps too. If the discharge does not react to the starting forces, the winding is tight. In a 300 MW generator, RTDs were fitted in the same slots as stator slot couplers. Both showed almost the same sensitivity and the same patterns. The RTD sits symmetrically between the bars and the slot coupler does not. So comparing the two helps to say whether a

defect is in the top bar or the bottom bar. Which sensor sees the most changes from one campaign to another? Sometimes the coupling capacitors, sometimes the RTDs. That is why they are used as complementary sensors, never one instead of the other. method in five steps. Install complementary sensors. Review the magnitude per numbered sensor to narrow the area. Read the phase patterns and polarity for the type. Use the RTD and slot coupler positions to tell top bar from bottom bar.

And confirm against operation and the trend, also after a repair. 13.8 kV motor showed growing activity, highest on RTDs 3, 4 and 6, with balanced polarities, voids in the insulation. Another diagnosis blamed loose windings and gradient paint was applied in an outage. Afterwards the discharge did not fall. It kept rising, which confirmed voids. The trend after the repair settled the question. monitor runs on its own, without a PC connected,

and keeps about two years of data in its eight megabyte memory. First in, first out. Ethernet, USB and RS-485 carry modbus, with DNP3 on request and dry relay contacts report alarm conditions and the health of the monitor itself. is mounted stand alone, on a panel, in an enclosure, or in the stainless steel enclosure for hazardous areas. And the mounting size grows with the number of optional modules. It accepts 90 to 264 volts AC or 100 to 300 volts DC.

Partial Discharge Detection from Amperis.