Load Shedding System

[fran007]

I have severals Power Generators of different Sizes connected to more than 20 Loads.

I'm reading the Load (MW) and Breaker Position for each Generator and each Load connected to the System.

When one of the generators open with load (Failure) I need to make a Load Shedding, removing a closer ammount of load from the system (Opening the Breakers)

The loads are variables, so I need to find the way to sheeding the load or the sum of the loads that are closer to the failed generator.

For Example:

A Generator with 5.94 MW Fail and I have the following load connected:

Load 1: 2.31 MW
Load 2: 3.52 MW
Load 3: 3.14 MW
Load 4: 4.25 MW
Load 5: 2.93 MW
Load 6: 3.89 MW
Load 7: 4.56 MW
Load 8: 2.67 MW
Load 9: 1.82 MW
Load 10: 0.98 MW
etc...

I need to Open the breakers for the Load or the Loads SUM closer to the load of the generator failed (In this case 5.9 MW).

I'm using Twincat (IEC 61131-3 PLC), I can use any of the programming lenguage.

Any Idea or Recomendation will be appreciated.

 

[ebalarde]

You might be locked in your design requirements, but for what it's worth.... here are a few thoughts.
I've designed a PLC-based Load-Shedding system before, but with a different twist to it.

1) All the load breakers are assigned an order of priority (lowest priority opens first regardless of its current load) based on the importance of the load they are feeding. This way, when it comes time to shed, the system drops out the lowest priority breaker, then the next, until the remaining load falls below the generating capacity.
2) The amount of load to shed is not based on how much generating power has been lost, but rather on how much the current load exceeds the remaining active generating capacity. This logic helps to prevent unnecessarily shedding load if the remaining generators are able to absorb some or all of the load from the failed generator.
3) Because of how quickly the system can collapse when losing a significant amount of generating power, I used an undervoltage/underfrequency relay to trigger a breaker to open every second? (it might have been as fast as 50ms, I don't remember) until the UV/UF condition relay cleared. This provides the ultimate backup in case the calculated load vs generating capacity load shedding logic is a little off (That was to account for how long (only a few seconds, but an eternity in the power generating world) it took for a load or generating capacity value change to be reflected in the PLC).

Hope this helps some.

 

[shooter]

A weighing system works the same way, they calculate the closest to the setpoint.
You can do it recursive or just straight out.
i will explain the calcs, you will have to use DWORD (being 32 bits)
as every combination is a possibility, lots of compares are needed.

forloop 1 to 2^32
forloop2 0 to 32
sum=0
if bit(loop2) is true
add load(loop2) to sum
if sum > setpoint then loop2=32
next loop2
store loop1
next loop1

This will take very much of calculation time but is the first possibility. (You must include this in your schoolproject)

another way is to make a totalling sum of all loads, and put them in a percentage table.
sort the table
loop
start with biggest add the next to it and check if above setpoint if so store result else add next one
next

 

[shooter]

and yes i do know codesys /twincat so if having problems just put it here or at codesys forum.