Where does it come from?

[ptonsparky]

I've always used MFD=(2650*I)/E to see if a capacitor was good prior to meters that would read MFD directly.
I've forgotten or maybe never knew where the 2650 comes from?
Anyone?

 

[Dennis Alwon]

I don't know where the 1,000,000 comes from

The multiplier is derived from

1,000,000/(2 x pi x hz)

 

[drcampbell]

I = C dv/dt

The current in a capacitor (at every instant in time) is proportional to its capacitance and the instantaneous voltage rate of charge.

All the rest is just unit conversion.

 

[drcampbell]

I don't know where the 1,000,000 comes from

From the unit conversion between Farads and microFarads.

 

[Jpflex]

Has anyone here installed capacitors in parallel between phases to correct power factor?

 

[ptonsparky]

Has anyone here installed capacitors in parallel between phases to correct power factor?

I would buy the units designed for PFC. None were paralleled in the small units I used, but would guess that's a possibility in larger.

 

[jim dungar]

Has anyone here installed capacitors in parallel between phases to correct power factor?

I would never build my own. Factory Power Factor Control capacitor banks include things like fuses and cell rupture protection.

 

[petersonra]

Has anyone here installed capacitors in parallel between phases to correct power factor?

Pretty common to have PFC capacitors on motors that are not on drives if the motors are above a certain size. Generally switched in with the motor starter.

 

[ptonsparky]

Pretty common to have PFC capacitors on motors that are not on drives if the motors are above a certain size. Generally switched in with the motor starter.

I believe we started at 10Hp. At 100 hp and above it was SoftStart or VFD in the more recent years.

 

[Jpflex]

Pretty common to have PFC capacitors on motors that are not on drives if the motors are above a certain size. Generally switched in with the motor starter.

We have large 100 hp 3 phase motors at our company with large starters without drives but no capacitors.

In one of my motor books it talks about different scenarios of installing capacitors parallel between all three phases but whether you install it upstream or downstream of starter yielded different results

I forgot how to calculate the proper size capacitor to get power factor closest to 1

 

[Jpflex]

I would never build my own. Factory Power Factor Control capacitor banks include things like fuses and cell rupture protection.

Is cell rupture protection the same as the dielectric between capacitors failing and shorting, causing a direct short between phases?

 

[ptonsparky]

Is cell rupture protection the same as the dielectric between capacitors failing and shorting, causing a direct short between phases?

A disconnect occurs when the can expands due to overheating. It stops current flow before rapid disassembly occurs.

 

[jim dungar]

We have large 100 hp 3 phase motors at our company with large starters without drives but no capacitors.

In one of my motor books it talks about different scenarios of installing capacitors parallel between all three phases but whether you install it upstream or downstream of starter yielded different results

I forgot how to calculate the proper size capacitor to get power factor closest to 1

The best place to connect capacitors, for motor PF correction, is between the motor starter contacts and the motor overload relay. Every other option requires some type of adjustment or accommodation. this is why NEMA starters, size 4 and larger, have provisions for lugs to be mounted before their OLR.

 

[drcampbell]

Another popular option is providing a separate contactor for the capacitors so that they're disconnected from the motor when the motor's turned off.

 

[drcampbell]

I = C dv/dt

The current in a capacitor (at every instant in time) is proportional to its capacitance and the instantaneous voltage rate of charge.

All the rest is just unit conversion.

Should have read, "... voltage rate of change ... "
Sorry about that.

 

[ptonsparky]

Another popular option is providing a separate contactor for the capacitors so that they're disconnected from the motor when the motor's turned off.

Most have discharge resistors now, but we always left them connected so they would discharge through the windings

 

[petersonra]

Another popular option is providing a separate contactor for the capacitors so that they're disconnected from the motor when the motor's turned off.

Never seen this done.

 

[ptonsparky]

We have large 100 hp 3 phase motors at our company with large starters without drives but no capacitors.

In one of my motor books it talks about different scenarios of installing capacitors parallel between all three phases but whether you install it upstream or downstream of starter yielded different results

I forgot how to calculate the proper size capacitor to get power factor closest to 1

Let me look. Are you up for a Spreadsheet sent you way?

 

[Open Neutral]

Never seen this done.

I recall doing this on pipeline pumpstations decades ago. It allowed us to mount the caps outside of the starter cabinet.

 

[kwired]

We have large 100 hp 3 phase motors at our company with large starters without drives but no capacitors.

In one of my motor books it talks about different scenarios of installing capacitors parallel between all three phases but whether you install it upstream or downstream of starter yielded different results

I forgot how to calculate the proper size capacitor to get power factor closest to 1

It has same effect on incoming line regardless if before or after the starter.

Thing you need to do differently if after the starter (or at least the motor overload protector) is adjust the overload setting to the power factor corrected current, or your motor can potentially run overloaded without pulling enough current through the overload to detect it.

how to calculate what capacitor to use - maybe search for "power factor triangle" and you may find some info to jog your memory? Need to know some trigonometry to do the calculations as you need to have a triangle that represents non corrected PF and then compare it to one that has been corrected to desired PF and select the capacitor that makes up that difference.