4 ms·

> Offhand I am not quite sure what the damage from off-nominal frequency operation I can think of at least a couple potential issues: * If the grid frequency

> Offhand I am not quite sure what the damage from off-nominal frequency operation I can think of at least a couple potential issues: * If the grid frequency is lower than the frequency the machine is trying to turn, it's possible for the generator to jump forward and mechanically slam forward to the next pole. * Some turbines have problems running too far off rated speed. (IIRC, torsional resonance issues.)

rhodozelia 6y ago
Resonance slightly above rated speed I have heard of. Pole slipping, a loss of synchronism, i would associate more with transient events such as large losses of load or generation that cause big changes in power flows as opposed to a sustained operation at 58 Hz. Loss of synchronism or pole Slipping should be protected against by out of step protection elements?
- thu2111 6y ago
  I think their assumption is that if the grid collapses completely it will take place in a short period of wild frequency fluctuations as generators trip out, demand swings wildly and so on, so you could get very large frequency distortions very quickly, perhaps too quickly for some safety equipment to kick in? Or some equipment can disconnect itself "safely" in the sense of not putting humans in danger but may still sustain damage to itself. I guess it's also quite hard to regularly test this sort of safety mechanism end to end, so there's surely a fear that it wouldn't work.
  - mschaef 6y ago
    > if the grid collapses completely it will take place in a short period of wild frequency fluctuations as generators trip out, demand swings wildly and so on, so you could get very large frequency distortions very quickly, perhaps too quickly for some safety equipment to kick in? Or some equipment can disconnect itself "safely" in the sense of not putting humans in danger but may still sustain damage to itself. My general read on this is that generation can trip off more easily than most kinds of load, so when reserves are low, they need to be more explicitly proactive about taking load offline. That In case a generator trips offline that consumes all the remaining responsiveness and takes the grid to a collapse. I assume what a total collapse looks like is every generator tripping offline in a matter of a few seconds or minutes. Hopefully, though, there'd be enough ability to disconnect transmission lines to isolate the failure to a specific part of the grid. Back in the 2003 NY blackout, the failure was isolated to the northeast because NJ disconnected its grid. The last couple steps of this timeline are illustrative: https://en.wikipedia.org/wiki/Northeast_blackout_of_2003#Sequence_of_events https://en.wikipedia.org/wiki/Northeast_blackout_of_2003#Seq... * .., * 4:11:57 p.m. The Keith-Waterman, Bunce Creek-Scott 230 kV lines and the St. Clair–Lambton #1 230 kV line and #2 345 kV line between Michigan and Ontario fail. * 4:12:03 p.m. Windsor, Ontario, and surrounding areas drop off the grid. * 4:12:58 p.m. Northern New Jersey separates its power-grids from New York and the Philadelphia area, causing a cascade of failing secondary generator plants along the New Jersey coast and throughout the inland regions west. * 4:13 p.m. End of cascading failure. 256 power plants are off-line, 85% of which went offline after the grid separations occurred, most due to the action of automatic protective controls. I know people that were working at PJM when that happened, and they tell stories of essentially continual announcements on the PA system announcing various emergency states they needed to respond to. Which they did. > I guess it's also quite hard to regularly test this sort of safety mechanism end to end, so there's surely a fear that it wouldn't work. Generators trip all the time. In fact, one of my first jobs was working at a TX based utility company analyzing the frequency disturbances that occur when generators trip offline. You can learn a lot about the way the grid responds by looking at the plot of frequency over time right around a trip.

rhodozelia 6y ago

Resonance slightly above rated speed I have heard of. Pole slipping, a loss of synchronism, i would associate more with transient events such as large losses of load or generation that cause big changes in power flows as opposed to a sustained operation at 58 Hz. Loss of synchronism or pole Slipping should be protected against by out of step protection elements?

thu2111 6y ago
I think their assumption is that if the grid collapses completely it will take place in a short period of wild frequency fluctuations as generators trip out, demand swings wildly and so on, so you could get very large frequency distortions very quickly, perhaps too quickly for some safety equipment to kick in? Or some equipment can disconnect itself "safely" in the sense of not putting humans in danger but may still sustain damage to itself. I guess it's also quite hard to regularly test this sort of safety mechanism end to end, so there's surely a fear that it wouldn't work.
- mschaef 6y ago
  > if the grid collapses completely it will take place in a short period of wild frequency fluctuations as generators trip out, demand swings wildly and so on, so you could get very large frequency distortions very quickly, perhaps too quickly for some safety equipment to kick in? Or some equipment can disconnect itself "safely" in the sense of not putting humans in danger but may still sustain damage to itself. My general read on this is that generation can trip off more easily than most kinds of load, so when reserves are low, they need to be more explicitly proactive about taking load offline. That In case a generator trips offline that consumes all the remaining responsiveness and takes the grid to a collapse. I assume what a total collapse looks like is every generator tripping offline in a matter of a few seconds or minutes. Hopefully, though, there'd be enough ability to disconnect transmission lines to isolate the failure to a specific part of the grid. Back in the 2003 NY blackout, the failure was isolated to the northeast because NJ disconnected its grid. The last couple steps of this timeline are illustrative: https://en.wikipedia.org/wiki/Northeast_blackout_of_2003#Sequence_of_events https://en.wikipedia.org/wiki/Northeast_blackout_of_2003#Seq... * .., * 4:11:57 p.m. The Keith-Waterman, Bunce Creek-Scott 230 kV lines and the St. Clair–Lambton #1 230 kV line and #2 345 kV line between Michigan and Ontario fail. * 4:12:03 p.m. Windsor, Ontario, and surrounding areas drop off the grid. * 4:12:58 p.m. Northern New Jersey separates its power-grids from New York and the Philadelphia area, causing a cascade of failing secondary generator plants along the New Jersey coast and throughout the inland regions west. * 4:13 p.m. End of cascading failure. 256 power plants are off-line, 85% of which went offline after the grid separations occurred, most due to the action of automatic protective controls. I know people that were working at PJM when that happened, and they tell stories of essentially continual announcements on the PA system announcing various emergency states they needed to respond to. Which they did. > I guess it's also quite hard to regularly test this sort of safety mechanism end to end, so there's surely a fear that it wouldn't work. Generators trip all the time. In fact, one of my first jobs was working at a TX based utility company analyzing the frequency disturbances that occur when generators trip offline. You can learn a lot about the way the grid responds by looking at the plot of frequency over time right around a trip.