George556
Electrical
- Mar 22, 2020
- 7
Our utility is looking into using small generators (500kW or 1000kW) to pick up portions of distribution circuits (12kV). The main utility 12kV source will be disconnected.
The generator will be connected to a step up 480V/12kV transformer.
The vendor provided a spec sheet for the generator shows that it has a Permanent Magnet Generators with an AVR. The spec sheets shows a Sustained Short Circuit Current Decrement curve which indicates that a 3ph fault is sustained for 10 seconds at about 300% of the full load rating of the generator. They also give multiplying factors for a LL fault which says it is 1.5x3ph fault (and lasts 5 seconds) and a LG fault which says its 2.5x3ph fault (and lasts 2.5 seconds).
Our short circuit program is not a dynamic model. Do I manipulate the steady state reactance to get a 3ph fault current that equals the decrement curve value at the 480V terminal? Does that mean I need three different reactances for the different fault types (3PH, LL, LG) due to the multiplying factors?
My goal is to see if the overcurrent relay connected to the 12kV breaker at the 12kV side of the step up transformer will adequately see an end of line 12kV fault. It seems based on the multiplying factors of the spec sheet, that a 3ph fault will give the least amount of amps (highest clearing time), which is my main concern.
How do you model these type of generators in a short circuit program to most closely see what the fault current will result in?
The generator will be connected to a step up 480V/12kV transformer.
The vendor provided a spec sheet for the generator shows that it has a Permanent Magnet Generators with an AVR. The spec sheets shows a Sustained Short Circuit Current Decrement curve which indicates that a 3ph fault is sustained for 10 seconds at about 300% of the full load rating of the generator. They also give multiplying factors for a LL fault which says it is 1.5x3ph fault (and lasts 5 seconds) and a LG fault which says its 2.5x3ph fault (and lasts 2.5 seconds).
Our short circuit program is not a dynamic model. Do I manipulate the steady state reactance to get a 3ph fault current that equals the decrement curve value at the 480V terminal? Does that mean I need three different reactances for the different fault types (3PH, LL, LG) due to the multiplying factors?
My goal is to see if the overcurrent relay connected to the 12kV breaker at the 12kV side of the step up transformer will adequately see an end of line 12kV fault. It seems based on the multiplying factors of the spec sheet, that a 3ph fault will give the least amount of amps (highest clearing time), which is my main concern.
How do you model these type of generators in a short circuit program to most closely see what the fault current will result in?