Electrical outages. cyber attacks ?

The purpose of LoM protection (and in this it differs from UF, OF, etc protections) is not to protect the generator.  It is designed to detect if the generator is feeding an isolated part of the network which has become detached from the grid - islanded.  An islanded generator will still run but will subject any connected loads, your neighbours for instance, to a voltage and frequency which is uncontrolled and therefore potentially damaging.  So LoM protection is not to protect the generator, it is mandated to protect other consumers still connected to an islanded generator.


The most common and effective method of detecting LoM for larger generators is by detecting rate of change of frequency (RoCoF).  This works because it's extremely unlikely, in the event of a network trip that leaves a generator still connected to some consumers, that the power output of the generator exactly matches the power demand of the loads.  So there will be a rapid change of frequency, either up or down depending on how big the islanded section of the network is.  It is possible to measure the fact that the frequency is changing rapidly long before it has changed enough to trigger OF or UF relays.  Until earlier this year the mandated setting of LoM RoCoF relays was at a rate of change of frequency of 0.125Hz/s, and that still applies to existing generators.


One of the things demonstrated by the event earlier this month is that, as the inertia of the network falls, the entire grid can now experience rates of change of frequency approaching or exceeding 0.125Hz/s.  So the ability of RoCoF protection to correctly and rapidly detect an islanded situation is becoming compromised.


Don't get me wrong - I'm not suggesting a return to the good old days of heavy coal burners so that LoM protection works properly.  We shouldn't be choosing the generation we build just to suit the needs of the grid.  We should choose the generation we build for more fundamental reasons, like saving the planet, and then adapt the grid to cope with that.  And one overdue change that is needed to adapt to the changing generation mix is a change in the mandated settings of LoM RoCoF relays. 

The purpose of LoM protection (and in this it differs from UF, OF, etc protections) is not to protect the generator.  It is designed to detect if the generator is feeding an isolated part of the network which has become detached from the grid - islanded.  An islanded generator will still run but will subject any connected loads, your neighbours for instance, to a voltage and frequency which is uncontrolled and therefore potentially damaging.  So LoM protection is not to protect the generator, it is mandated to protect other consumers still connected to an islanded generator.


The most common and effective method of detecting LoM for larger generators is by detecting rate of change of frequency (RoCoF).  This works because it's extremely unlikely, in the event of a network trip that leaves a generator still connected to some consumers, that the power output of the generator exactly matches the power demand of the loads.  So there will be a rapid change of frequency, either up or down depending on how big the islanded section of the network is.  It is possible to measure the fact that the frequency is changing rapidly long before it has changed enough to trigger OF or UF relays.  Until earlier this year the mandated setting of LoM RoCoF relays was at a rate of change of frequency of 0.125Hz/s, and that still applies to existing generators.


One of the things demonstrated by the event earlier this month is that, as the inertia of the network falls, the entire grid can now experience rates of change of frequency approaching or exceeding 0.125Hz/s.  So the ability of RoCoF protection to correctly and rapidly detect an islanded situation is becoming compromised.


Don't get me wrong - I'm not suggesting a return to the good old days of heavy coal burners so that LoM protection works properly.  We shouldn't be choosing the generation we build just to suit the needs of the grid.  We should choose the generation we build for more fundamental reasons, like saving the planet, and then adapt the grid to cope with that.  And one overdue change that is needed to adapt to the changing generation mix is a change in the mandated settings of LoM RoCoF relays.