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  1. Carlos Melim

    Electrical Engineering MSc regulated activities

    Hello everybody. I’m from Portugal and we have many Electrical Engineering MSc degrees with different branches, like energy, telecommunications, automation and electronics. In your own countries, can an Electrical Engineering MSc in branches, other than energy, be responsible for the project...
  2. Carlos Melim

    Safety butterfly valve reset operation

    Good evening everybody. I’m an electrical engineer and I have a safety question regarding a safety butterfly valve that closes automatically after an excess flow detection. I’m familiar with these systems and, if the valve does close, I think it’s mandatory that the reset is always a manual...
  3. Carlos Melim

    Relux Desktop Tunnel lighting software

    Hello everybody. I am looking for a lighting calculation software for a road tunnel project. I have come across Relux Desktop which is free. There is a Tunnel lighting add-on available to buy. But it seems it’s included in the free downloadable Relux Desktop package. Has anybody tried the...
  4. Carlos Melim

    400 V LV System - Short circuit calculations - Impedances Method

    Good afternoon everybody. I am involved in a project and I want to calculate the fault currents on several locations to validate the short-circuit power needed for each panel and the upstream trip switches nominal currents and its types A, B, C or D. I use the impedances method and determine...
  5. Carlos Melim

    SIR - Synchronous inertial response of generators with different inertia constants H

    Hello waross, The inertia constants were calculated. When I refer thermal power plants I mean fuel or natural gas prime-movers. Based on bacon4life infos, I think I´ve made a step forward on the subject. One should consider the Kinetic Energy which is H x S. A 2s inertia constant, 10MVA...
  6. Carlos Melim

    SIR - Synchronous inertial response of generators with different inertia constants H

    Bacon4life let me clarify my concern. I’m not focusing only on inertial response. I work for the power generation department. We have old 14 MVA fuel generators, with mechanic speed governors, with 2 s H inertia constants. Then we have modern 21 MVA natural gas generators, with digital speed...
  7. Carlos Melim

    Induction motors inertia contribution

    Good morning everybody. Some grid stability studies neglect the demand side inertial contribution. Only compute the synchronous generators inertial contribution. Other studies refer that, on the demand side, there are synchronous motors that must be considered. The majority of electrical...
  8. Carlos Melim

    SIR - Synchronous inertial response of generators with different inertia constants H

    I work for the utility so the difference costs of fuel and natural gas is not really an issue. Of course we want to stop the fuel thermal power plants in due time for ecological reasons. We don’t have what we call an isochronous machine. All work on 3% droop. That’s the primary control. Then...
  9. Carlos Melim

    SIR - Synchronous inertial response of generators with different inertia constants H

    Good afternoon Waross. Thanks for your quick reply. I live in Madeira island and our isolated grid is only 120 MW worth, isolated. We have natural gas and fuel thermal power plants. Also, hydro, windpower and photovoltaic power plants. The natural gas power plant is equipped with three 21 MVA...
  10. Carlos Melim

    SIR - Synchronous inertial response of generators with different inertia constants H

    Good afternoon Suppose I have two synchronous generators. One rated 10 MVA with H=4s and the other 20 MVA with H=2s. I understand that the SIRs of the generators don’t depend on their operating point. But if both are working at, let’s say, 5 MVA, and there’s an outage of another generator in...
  11. Carlos Melim

    system RoCoF calculation

    Good night experts. I work for the utility in Madeira island. Our grid is small and not connected to Portugal mainland. I want to validate our RoCoF figure. I have calculated all the synchronous generators (Si) inertia constants (Hi). I´ve used Hi= (J*Wi^2)/(0.5*Si). I´ve read somewhere...
  12. Carlos Melim

    Diesel generator connected to grid absorbing reactive power

    Good evening everybody. Can a diesel generator, connected to the grid, absorb reactive power while producing active power? A small grid, with underground power cables and frequency converters everywhere, can have a surplus of capacitive reactive power. That raises the grid voltage, mainly...
  13. Carlos Melim

    Hello everybody. I’m planning an

    Hello electricuwe You are correct. IT system is only for the pumps. I understand the emergency equipments must comply with IT requirements. For example, if they are single phase, they must be suitable to a 400VAC voltage between phase and earth. The pumps will be delta connected but the...
  14. Carlos Melim

    Hello everybody. I’m planning an

    This is what I meant: https://files.engineering.com/getfile.aspx?folder=111e953e-d217-43be-991e-61de2b75aaae&file=14D65E04-7406-4865-BF49-0F4BEB2904F8.jpeg
  15. Carlos Melim

    Hello everybody. I’m planning an

    Hello everybody. I’m planning an IT earthing system to feed some emergency pumps within an existing building. The existing electrical installation is on a TT scheme. There will be, of course, a specific LV/LV transformer with a Permanent insulation monitor. I will install an equipotential...
  16. Carlos Melim

    Pelton turbine minimum flow / power

    Good morning everybody. I need your expert advices. We are retrofitting an hydro power plants with three Pelton turbines that drive 8 MW alternators. Historically, the turbines cannot be operated below 2 MW. But I cannot find any manufacturer documents that support this figure. I know that...
  17. Carlos Melim

    Earth Resistance Testing by Loop Method vs. Earth Ground Clamp

    Hello Palletjack I am dealing with TT system. TT, TN-S and IT, all have PE. TT has different earth electrodes for the neutral (RB) and for protective earth (RA). Connecting RA and RB with a temporary jumper and applying an earth ground clamp the result is RA+RB. If the value obtained is...
  18. Carlos Melim

    Earth Resistance Testing by Loop Method vs. Earth Ground Clamp

    Hello ScottyUK. I know that clamp type instruments work better if there are several electrodes in parallel with the one I want to measure. I’m really just paralleling the PE and neutral electrodes through a temporary jumper. But I would expect the measured resistance to be higher that the real...
  19. Carlos Melim

    Earth Resistance Testing by Loop Method vs. Earth Ground Clamp

    Hello Kiribanda I want to measure the earth electrode resistance RE. The installation is TT so it has two different grounds: neutral and PE. With the earth ground clamp, I connect both with a temporary jumper and measure the sum of the two grounds. I get 5 ohm and I’m happy with it. I make...
  20. Carlos Melim

    Earth Resistance Testing by Loop Method vs. Earth Ground Clamp

    Good morning everybody, I want to measure the earth-resistance on a primary substation with separate N and PE grounds. I have measured it with 3-wire connection earth resistance loop test on the LV panel. I am using a FLUKE 1653B tester. The result was over 40 Ohm. I have also connected the...

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