Trying to improve power factor
Trying to improve power factor
(OP)
Hello,
We are attempting to improve or service power factor by installing soft starters on various pieces of equipment with large squirrel cage motors. Starting at the 30hp motors down to the 7.5hp. This is my first time considering something like this and would appreciate any information you are willing to provide to get me started in the correct direction. What types of thing need to be considered and what do we need to pay close attention to? In your opinion how effective are these soft starters. We are currently at 87 percent and need to get into the mid 90 percent to start seeing reward from our service provider. Can we effectively get there by installing these unit through out?
Thank you for taking the time to respond in advanced.
2571
We are attempting to improve or service power factor by installing soft starters on various pieces of equipment with large squirrel cage motors. Starting at the 30hp motors down to the 7.5hp. This is my first time considering something like this and would appreciate any information you are willing to provide to get me started in the correct direction. What types of thing need to be considered and what do we need to pay close attention to? In your opinion how effective are these soft starters. We are currently at 87 percent and need to get into the mid 90 percent to start seeing reward from our service provider. Can we effectively get there by installing these unit through out?
Thank you for taking the time to respond in advanced.
2571





RE: Trying to improve power factor
If you only need 3%, try calculating (From the power bill) how many KVARHrs per month you are consuming. Then calculate how many KVARHrs are needed to correct to 90%. Divide this figure by the number of hours in a month and you get the number of KVAR of capacitors needed to correct to 90%.
You then have to evaluate your system to see if permanently connected capacitors will have an adverse affect when your facility is idle.
This approach is not always suitable, but if your utility is charging power factor penalties on the average monthly consumption of KVARHrs and you only need 3% it is often an economical solution.
respectfully
RE: Trying to improve power factor
could you exsplain this statement better,
"You then have to evaluate your system to see if permanently connected capacitors will have an adverse affect when your facility is idle". Please
2571
RE: Trying to improve power factor
I doubt if you will see any improvement in power factor by use of SS starters. And by having the starters continuously energized, your real power consumption will increase due to losses in the starter. Generally, bypass contactors are used to run the motor after starting.
Waross is correct that the best approach to power factor correction is generally adding capacitors somewhere in the system. If you have a lot of VFDs on your system, you will need to be careful about sticking caps on the system with proper harmonic filtering.
RE: Trying to improve power factor
Soft starters will not improve your plant power factor.
Soft starters with energy saving algorithms may reduce the magnetizing current of motors that are operating at very light load only, but will not alter the VARs of loaded motors.
If a significant proportion of your load was small very lightly loaded motors, then you may see some effect, but in general, there will be no PF improvement.
Power factor correction capacitors will correct a displacement power factor under all loading conditions and if pf is the only reason for fitting soft starters, your money would be better spent on capacitors.
Soft starters do however offer many other advantages, just not power factor correction.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Trying to improve power factor
To jump in on waross' statement, when your lagging PF is caused primarily by motors, PF correction is best done with what is called "at load" capacitors, meaning the capacitors are only switched on when the motors are running. This is easily accomplished by placing the capacitors near the motors,thus downstream from the starters so they are only on-line when the starter is closed and the motor is running. Leaving capacitors on-line all of the time (called "bulk correction") means that when the motors are not running, the capacitors are still in the circuit and can result in your facility having an overall leading PF, which has almost as many detrimental consequences as too lagging. Automatic PF control systems can prevent this, but they are expensive compared to just placing capacitors downstream from your motor starters.
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Trying to improve power factor
That 4505 advantage is why I like to start with bulk correction.
This is the art of power factor correction as opposed to just spending a lot more of the customers money to put in an automatic correction panel. Typically an automatic correction panel will correct to 100% at the worst possible case. There are some places in the world where you are charged for any deviation leading or lagging. You need an automatic panel there.
When you are charged on the KVARHrs over your monthly average and are allowed to drop to 90% AVERAGE, a little art and ingenuity will save a lot of money.
I have learned most of the "ART" in the field, as I suspect jraef has. I've never seen a book or paper with the tricks and art of PF correction. Have you, jraef?
Another exersize, for someone, Estimate the KVARs required to correct the power factor to 100% under the worst case conditions. Now calculate the KVARs required to bulk correct the PF from 87% to 90%. You will be looking at another very large and expensive ratio.
I love the art of power factor correction. It is a rewarding challenge.
respectfully
RE: Trying to improve power factor
http://www.myronzucker.com/docs.html
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Trying to improve power factor
RE: Trying to improve power factor
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376