Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations JAE on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
generator sizing 2
- Thread starter wangi
- Start date
davidbeach
Electrical
Contact any of the Genset manufacturers. They all provide free sizing software.
-
1
- Moderator
- #3
I have found the manufacturers sizing programs to be quite conservative. You will be safe using a program from Caterpillar or other manufacturers.
A prime rated set will allow a 10% overload for 1 hour in 10 or 12.
So, a 100 KVA set will be capable of supplying 110 KVA. It will be rated at 80 kW but will be capable of supplying 88 kW.
The same set rated as a standby set will be rated at 110 KVA continuous and 88 kW.
The point is, be aware of the difference in ratings when comparing sets.
An over-sized set will not only cost more to buy and install but it will burn more fuel.
Bill
--------------------
"Why not the best?"
Jimmy Carter
A prime rated set will allow a 10% overload for 1 hour in 10 or 12.
So, a 100 KVA set will be capable of supplying 110 KVA. It will be rated at 80 kW but will be capable of supplying 88 kW.
The same set rated as a standby set will be rated at 110 KVA continuous and 88 kW.
The point is, be aware of the difference in ratings when comparing sets.
An over-sized set will not only cost more to buy and install but it will burn more fuel.
Bill
--------------------
"Why not the best?"
Jimmy Carter
-
1
- #4
Be aware of the boss. He will tell you one thing and the demand more. "I just need to add X as well no it is working. Sorry, played that game before.
Please watch out for the size and sequence of starting your loads. A 100 kW machine will battle to start an 80 kW single load without some special starter. DOL will not work. If you have lots of loads, try start the large one first and the smaller ones last.
Please watch out for the size and sequence of starting your loads. A 100 kW machine will battle to start an 80 kW single load without some special starter. DOL will not work. If you have lots of loads, try start the large one first and the smaller ones last.
- Thread starter
- #5
- Moderator
- #6
Borderline. This will not be suitable if there are any other loads on the generator. The Voltage and frequency drops when starting will be too much for most loads.
If this is a dedicated generator-pump application, it may be possible to start the motor. You may have to make provision such as a UPS to supply the control panel so that your controls will be able to ride throegh the starting voltage dip.
I would NEVER advise a customer to purchase that gen-set to start that motor. However, I understand the pressures you may be under to make existing equipment function.
When that pump is started on that set, the load will cause both the voltage and the frequency to drop. Lights will dim annoyingly and relays and contactors may drop out. However, the speed and frequency drop will activate the UFRO (Under Frequency Roll Off) feature of the AVR (Automatic Voltage Regulator) and maintain close to the optimum Volts per Hertz ratio for the motor. Now the gen-set is acting in a similar manner to a VFD, and will accelerate the motor up to speed. As the motor comes up to speed, the load will reduce and the AVR will ramp up the voltage. This is actually easier on the motor than a DOL start on a firm grid, and much easier than a DOL start on a soft supply.
This is a standby rated set. If this were a prime power rated set, there would be a 10% margin of overload available. Great if you buy a prime set rated at 87 kW but in this case, this set would be rated at 80 kW for prime service.
Bill
--------------------
"Why not the best?"
Jimmy Carter
If this is a dedicated generator-pump application, it may be possible to start the motor. You may have to make provision such as a UPS to supply the control panel so that your controls will be able to ride throegh the starting voltage dip.
I would NEVER advise a customer to purchase that gen-set to start that motor. However, I understand the pressures you may be under to make existing equipment function.
When that pump is started on that set, the load will cause both the voltage and the frequency to drop. Lights will dim annoyingly and relays and contactors may drop out. However, the speed and frequency drop will activate the UFRO (Under Frequency Roll Off) feature of the AVR (Automatic Voltage Regulator) and maintain close to the optimum Volts per Hertz ratio for the motor. Now the gen-set is acting in a similar manner to a VFD, and will accelerate the motor up to speed. As the motor comes up to speed, the load will reduce and the AVR will ramp up the voltage. This is actually easier on the motor than a DOL start on a firm grid, and much easier than a DOL start on a soft supply.
This is a standby rated set. If this were a prime power rated set, there would be a 10% margin of overload available. Great if you buy a prime set rated at 87 kW but in this case, this set would be rated at 80 kW for prime service.
Bill
--------------------
"Why not the best?"
Jimmy Carter
- Status
Similar threads
- Locked
- Question