May 8, 20233 yr 1 hour ago, Bobster. said: Thanks. That goes some way to dealing with a question in my non-engineer head: synchronisation of all the working sources that are available to the grid. Eskom gave a press presentation in 2021 (IIRC) in which they talked about another factor that causes delays. The warmer a generator is, the quicker it can get up to it's rated output. And vice versa. So you fire up the black start stations - this takes hours, but relatively few hours. But all the while the other stations are cooling, so the next set of stations takes longer to start up and so on. 2-4 weeks? In that same presentation, Eskom said 6 to 14 days in a worst case scenario, with some parts of the grid coming back on quicker than others. The temperature of the steam that feeds the turbine must be at +_ 375 degrees c, so called dry steam. anything below that is dangerous as it may contain water droplets. Turbine will be turning at 3000 RPM any droplets of water may cause the turbine to vibrate, and the vibration protection system in the turbine will trip it. So, it takes a few hours to bring the pipe work that feeds steam to the turbine to temperature.
May 8, 20233 yr 4 minutes ago, Jacques Ester said: Frequency dropped to 49.3Hz this morning. Not good. I had 49.5 at about 5am - what's the lowest it can go safely?
May 8, 20233 yr 21 minutes ago, Jacques Ester said: Frequency dropped to 49.3Hz this morning. Also got 49.3 This morning. Before we had a 50.5. We were suppose to have 4 hour loadshedding and the power remained on(Tshwane). Technicians are getting slack towards switching off and this will cause the system to collapse. Edited May 8, 20233 yr by iiznh
May 8, 20233 yr On 2023/05/07 at 9:30 AM, hoohloc said: I doubt this will ever happen. After all, this is why we have loadshedding. Other countries like Nigeria and Tanzania have been having loadshedding long before SA and till today, they are still managing. We will be ok, 😀 That does assume load shedding is always done correctly though. Are there not other safety mechanisms that would result in smaller scale and shorter term blackouts? Regarding the frequency subject, here is a quote from 2021: Quote Energy expert Chris Yelland has reported that the frequency of the pool dropped to 49.31 Hz. This is noticeably below the normal range Eskom documentation: Quote Any power with a frequency of as little as 1% above or below the standard 50hz risks damaging equipment and infrastructure if it persists. Small frequency deviations (i.e. -0.5 Hz on a 50 hz network) will result in automatic loadshedding or other control actions to restore system frequency Edited May 8, 20233 yr by whateversa
May 8, 20233 yr 3 hours ago, Antonio de Sa said: So in my opinion with 7 to 10 days the entire grid will be back online. In a perfect world. This country is far from perfect.
May 8, 20233 yr Re Frequency,also had the 49.3 twice in the morning hours From past discussion on MyBB it seems to usually align to generation capacity loss
May 8, 20233 yr 10 hours ago, iiznh said: Also got 49.3 This morning. Before we had a 50.5. We were suppose to have 4 hour loadshedding and the power remained on(Tshwane). Technicians are getting slack towards switching off and this will cause the system to collapse. Our sparky are wide awake. We used to get the switching at 6-10min past the hour and not the last week they switch off right the hour.
May 8, 20233 yr Botswana had a grid anomoly that brought the country out. South Africa is pushing the limits of load shedding/curtailment. Probably with a cloudy cold front this winter bad things will happen (if not due to sabotage)... back to the intention of the thread: People should organize their communities. KZN riots provided a good example. Buy some Baofeng radios!
May 8, 20233 yr 12 hours ago, Antonio de Sa said: Generator circuit breakers will disconnect from the grid. before the generators go in to reverse mode and start to work as a motor thus importing power from the grid. Thanks for your explanation Antonio. 👍 But why do the generators go into reverse / motor mode before disconnection from grid, and then cause catastrophic shutdown after disconnection? Surly the control system should disconnect before the generators go into reverse / motor mode. Maybe it is a function that just occurs when a generator is stressed beyond its capabilities, but still no reason to push the generator until it reaches this point. Rather disconnect and keep it running. More input please.
May 8, 20233 yr 13 hours ago, iiznh said: Technicians are getting slack towards switching off and this will cause the system to collapse. Not only that. In the industry we have concentrators and smelters you cannot just shut down. They do not load shed. Eskom would give them a call and request they shut down their operation. It normally takes an hour or two to shut down these operations. I read an article where one of these smelters were requested to shut down and they just ignored the call and kept going. Eskom is now under the impression the smelter will go down shortly, but it never does. That puts the grid at risk. Should 3 or 4 of their generating units suddenly go down, Eskom are in deep trouble trying to keep the grid up.
May 9, 20233 yr Our mine is also loadshedding free but do get request to shed load. This means we need to shut down some of our modules. Eskom is also not allowed to just switch off because off our contract. If they do it will take us more than 2 weeks to start up again and Eskom will have to pay penalties.
May 9, 20233 yr 30 minutes ago, Jacques Ester said: Our mine is also loadshedding free but do get request to shed load. This means we need to shut down some of our modules. Eskom is also not allowed to just switch off because off our contract. If they do it will take us more than 2 weeks to start up again and Eskom will have to pay penalties. It is called load curtailment but don't think that Eskom will honour supply agreements. They made laws to make it legal not to provide power.
May 9, 20233 yr 1 hour ago, frivan said: It is called load curtailment but don't think that Eskom will honour supply agreements. They made laws to make it legal not to provide power. There are all sorts of things that are really shedding but are called something else. "Load reduction" is applied in townships, usually during peak consumption hours. Eskom say they do this because the infrastructure is overloaded.
May 10, 20233 yr We were also supposed to be shed for 2 hours last night between 8pm-1opm - never happened...
May 10, 20233 yr 14 minutes ago, Douw G. Gerber said: We were also supposed to be shed for 2 hours last night between 8pm-1opm - never happened... Luck you, in my area in the last 4 days we been having load shedding 10 hours daily.
May 10, 20233 yr 36 minutes ago, Douw G. Gerber said: We were also supposed to be shed for 2 hours last night between 8pm-1opm - never happened... We also skip sessions at times, the most recent one this morning between 4 and 6. It makes you wonder how critical/needed this loadshedding thing really is.
May 10, 20233 yr Eskom lying about load-shedding – energy expert https://dailyinvestor.com/energy/16637/eskom-lying-about-load-shedding-energy-expert/
May 10, 20233 yr On 2023/05/08 at 10:48 PM, TimCam said: Thanks for your explanation Antonio. 👍 But why do the generators go into reverse / motor mode before disconnection from grid, and then cause catastrophic shutdown after disconnection? Surly the control system should disconnect before the generators go into reverse / motor mode. Maybe it is a function that just occurs when a generator is stressed beyond its capabilities, but still no reason to push the generator until it reaches this point. Rather disconnect and keep it running. More input please. There is protection against generator reverse power. That is why we use protection relays that will isolate the generator once reverse power is detected
May 10, 20233 yr 25 minutes ago, hoohloc said: There is protection against generator reverse power. That is why we use protection relays that will isolate the generator once reverse power is detected Yes, indeed there are protection relays connected to the Gen breaker, there are there to do exactly that, the question is? are they operational? I worked for many years installing, commissioning and optimizing boiler/turbine control systems, I know of all the protection system there are installed in both boilers and turbines, any protection system can be bypassed. And that is exactly of what I'm afraid it can happen, Many, many years ago I saw a 60 Mw turbine going thru the roof at Taibos PS, the vibration protection system was faulty and by the time the operator realized was to late.
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