I work onboard a yacht where we have 3 pieces of 765kVA diesel gensets composed of the engine MTU 12V2000 M51A and the alternator Stamford HCM634J2. The gensets are producing 3 phase 400VAC/50Hz.
First of all, I am not sure if there is even a problem with the gensets so here goes my first question:
1. What is the allowed frequency tolerance on these type of gensets or on diesel gensets in general?
Our frequency varies less than 1%, but even that is enough to cause problem with our Main UPS and Fire detection system which are sensitive to input power quality. Because of frequency variation, UPS does an automatic bypass (just transfers input immediately to the output) and Fire detection system has a Power input quality fault. Btw, UPS' tolerance to the input power can be adjusted and it is already at the max, although I don't know what the max is because it was done 2 years ago by the service technician on some potentiometer deeeeep inside the UPS.
So...this is the situation:
When gesets are working off the grid, their frequency is super stable.
When any of them is connected to the grid, there is a frequency fluctuation.
When 2 of them are connected, fluctuation is smaller and when all 3 are connected, fluctuation is smallest, but still bigger than when they are running off the grid.
Below table shows readings when only one of the gensets was connected to the grid. So, for example, when just Centre genset was connected, genset frequency (which is in that case grid frequency as well) varies between 49.67 and 50.33 Hz, current varies fluctuates around 50A and power around 25kWA.
2. Do you have any idea what might be causing this kind of behavior?
First of all, I am not sure if there is even a problem with the gensets so here goes my first question:
1. What is the allowed frequency tolerance on these type of gensets or on diesel gensets in general?
Our frequency varies less than 1%, but even that is enough to cause problem with our Main UPS and Fire detection system which are sensitive to input power quality. Because of frequency variation, UPS does an automatic bypass (just transfers input immediately to the output) and Fire detection system has a Power input quality fault. Btw, UPS' tolerance to the input power can be adjusted and it is already at the max, although I don't know what the max is because it was done 2 years ago by the service technician on some potentiometer deeeeep inside the UPS.
So...this is the situation:
When gesets are working off the grid, their frequency is super stable.
When any of them is connected to the grid, there is a frequency fluctuation.
When 2 of them are connected, fluctuation is smaller and when all 3 are connected, fluctuation is smallest, but still bigger than when they are running off the grid.
Below table shows readings when only one of the gensets was connected to the grid. So, for example, when just Centre genset was connected, genset frequency (which is in that case grid frequency as well) varies between 49.67 and 50.33 Hz, current varies fluctuates around 50A and power around 25kWA.
f, kW & A readings (Analog meters) | Port generator | Center generator | Starboard generator | Time frame measurement |
Frequency on power analyzer | 49.75 to 50.15 Hz | 49.67 to 50.33 Hz | 49.63 to 50.28 Hz | 30 sec |
Ammeter readings on the main switchboard | 50 A fluctuation | 50 A fluctuation | 50 A fluctuation | 18 sec |
kW readings on the main switchboard | 25 kW fluctuation | 25-30 kW fluctuation | 25 kW fluctuation | 25 sec |
Voltage fluctuation on all three generators is from 400 to 402 VAC |
2. Do you have any idea what might be causing this kind of behavior?