Power of a sewage pump instalation
Power of a sewage pump instalation
(OP)
Hello (anf sorry for my english)
Well, I have a problem measuring the Transformers of an instalation of sewage pumping.
It consist in 8 pumps of 560 kW of power, two of them must have a PWM to control the speed. They work in 690 volts (50 Hz) and have a cos(phi)=0.85. The company supply in 15.000 volts.
We were thinking in using 4 transformers of 2.500 kVA and to separate the pumps in 2 groups of 4 pumps each group and using 2 transformers in pararell for each group.
The pumps have a start up current of 5 times the basic one and they stop and start may be 3 times per hour each one. They don´t have to start up at the same time.
There are some doubts about if the transformers are enough to hold up the heat cause of the many start ups.
Can anybody help me to obtain a solution??
Thanks
Martín Davila
sammy@talgo.uvigo.es
Well, I have a problem measuring the Transformers of an instalation of sewage pumping.
It consist in 8 pumps of 560 kW of power, two of them must have a PWM to control the speed. They work in 690 volts (50 Hz) and have a cos(phi)=0.85. The company supply in 15.000 volts.
We were thinking in using 4 transformers of 2.500 kVA and to separate the pumps in 2 groups of 4 pumps each group and using 2 transformers in pararell for each group.
The pumps have a start up current of 5 times the basic one and they stop and start may be 3 times per hour each one. They don´t have to start up at the same time.
There are some doubts about if the transformers are enough to hold up the heat cause of the many start ups.
Can anybody help me to obtain a solution??
Thanks
Martín Davila
sammy@talgo.uvigo.es






RE: Power of a sewage pump instalation
Also consider forced fan cooling on transforemrs, controlled by temprature sensors in the transformers.
RE: Power of a sewage pump instalation
10MVA of transformers is definetly enough for 5.25MVA of motors. If your aim is redundancy you may want to consider 2.5MVA with forced cooling for times when only one of the two parallel units is in service.
If the motors are VFD controlled than you may want to check your harmonics and get a K Rated transformer which has extra margin for transformer heating due to harmonics.
RE: Power of a sewage pump instalation
For sewage pumping, reliability is a key concern - you should suggest that additional pumps be equipped with adjustable speed drives to improve reliability. Just two may not be enough because of the limited flow range that the pumps can operate over. You will probably need the two pumps with AFDs running all the time in order to control the wet well level.
Anyway, you don't want to be starting and stopping 560 kW motors 3 times an hour if you can possibly avoid it.
Transformers will be fine.