I was disagreeing with the last paragraph of your post #46.
Over correction
- Thread starter ptonsparky
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mivey
Senior Member
So you want a high slip like a design D? Those might be used in oil fields but I would think a standard pump would have a design B.
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Gentlepeople...
I believe an explanation of my PFC rant might be useful! In most Electrical-Energy analyses I've conducted, the primary goal was to reduce PF (kVAr)! After all, for the typical commercial business or industrial plant, the assigned penalty for low PF can have steep economic consequences!
However, a PFC installation usually results in some kW reduction! PtonSparky's case piqued my interest because while a substantial line-current change occurred, the expected kW change didn't! So that led to this "investigation!"
Phil
I believe an explanation of my PFC rant might be useful! In most Electrical-Energy analyses I've conducted, the primary goal was to reduce PF (kVAr)! After all, for the typical commercial business or industrial plant, the assigned penalty for low PF can have steep economic consequences!
However, a PFC installation usually results in some kW reduction! PtonSparky's case piqued my interest because while a substantial line-current change occurred, the expected kW change didn't! So that led to this "investigation!"
Phil
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Mivey...
Exactly, NEMA Design, 30Hp, 460V!
Phil
Exactly, NEMA Design, 30Hp, 460V!
Phil
mivey
Senior Member
May not be noticeable at the measuring point.
Small feeder losses, capacitors producing heat, inductive heating on mis-wired circuit, etc. Not sure you can tie it to the motor but please proceed.
kwired
Electron manager
- Location
- NE Nebraska
Honestly, I don't think there's much VD in there is the system was designed properly.
Do some wiring on farms and you learn when to be precise with voltage drop and when to settle for a little more then you maybe would inside an industrial plant. With irrigation work we often run anywhere between 1300 to 3000 feet. Then you get the occasional 400 to 800 foot run and that is nothing when it comes to VD effects.
Power factor correction does help lower VA on such runs which will help with VD.
There may be a voltage improvement, depending on the fault level of the power system, on the motor terminals with a capacitor connected across it and an increased KW output of the motor but at the same time it causes an increase in the active current component of the motor current thereby increasing the voltage drop along the lines. Whether there is a net decrease in voltage drop and so there is still an increased KW output from the motor may have to be ascertained by calculation or,more properly, in the field.
You meant to tell me there are still crazy designers out there?
Why run a low voltage supply for about a mile?
mivey
Senior Member
What gets me is the irrigation companies make these long runs and act surprised when the controller drops out during a motor start. I suggest a UPS or power supply that has a little more flicker withstand and they want to complain about service voltage. It ain't the service voltage, its the secondary voltage regulation problem cause by the long circuit.
Consider a paper mill, for example, which has a large area. There is scope for VD reduction by employing capacitors.You meant to tell me there are still crazy designers out there?
Why run a low voltage supply for about a mile?
Then I'll have to choose between 1) running MV lines, install load centers to serve the group of low-voltage loads at select locations or 2) run conductors sized to consider the possible voltage drops in your paper mill.
Decide depending on which costs more in the long run.
Capacitors are a bit problematic in paper mills.
Like?
Harmonics. I don't know how much you know about paper mills.
There are lots of variable speed drives in a paper mill. A typical paper machine may have a drive suite with 15 variable speed drives usually from about 100 kW and upwards.
The harmonic distortion can be considerable. At one mill I measured 15% voltage distortion. That does not sit comfortably with capacitors and they often fail spectacularly. I've seen lots that did.
kwired
Electron manager
- Location
- NE Nebraska
You meant to tell me there are still crazy designers out there?
Why run a low voltage supply for about a mile?
We have enough troubles with farmers thinking they are fixing things operating at 480 volts, we don't need them working on medium voltage.
Most of the higher horsepower motors have supply conductors up to about 1500 feet. The 1/2 mile runs are usually from a pivot on one quarter section to another quarter section and only supplies about 30 amps max at 480 volts. You can run a pretty large aluminum conductor for less then what transformers and medium voltage cable cost.
Only time I recall seeing POCO run their primary out to a well location was for a 200 hp pump. Otherwise there are thousands of them between 30 and 125 hp that have service at the road and the well is about 1/4 mile out into the field.
Your solution?
For what? Poor power factor, voltage drop or harmonics?
First, there is no "one size fits all" solution
But I can tell you a few of the measures we have taken.
On a few paper machine installations, we have fed the VSDs with DC. The DC is produced by an uncontrolled, 24-pulse rectifier. The rectifier is fed from local step down transformers. That takes care of harmonics, voltage drop, and power factor concerns at a stroke.
An example from one we provided earlier.
The 24-pule rectifier was fed from two local 2MVA, 11kV/600V transformers.
The rectifier was in the centre of a contiguous suite feeding 16 VSDs.
All performance criteria were met or exceeded.
So would your ideas have been to go about it?
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Gentlemen...
I want to thank all that were patient. Below is the Table of the 30Hp motor I found. It will be used in subsequent analysis of PtonSparky's case
For the Submersible cable parameter I'll use NEC Table 9, for #6, AWG!
Attn Nitpickers: I'm ignoring the imbalance-factor associated with unrolled, flat-cable!
Phil
I want to thank all that were patient. Below is the Table of the 30Hp motor I found. It will be used in subsequent analysis of PtonSparky's case
| INDUCTION MOTOR RATED PARAMETERS | ||||||||
| Hp | Volts | Amperes | PF | Eff'y,% | # Poles | Hz | Slip,% | Nr |
| 30 | 460 | 36.5 | 0.82 | 94.1 | 4 | 60 | 1.5 | 1,173 |
| ELECTRICAL INPUT | POWER DISTRIBUTION in PERCENT | |||||||
| kVA | kW | kVAr | Pin | Pout | Pcu, Str | Pcu, Rr | Pfe | Pfw |
| 29.1 | 23.9 | 16.6 | 100 | 94.1 | 1.90 | 1.70 | 1.30 | 1.25 |
For the Submersible cable parameter I'll use NEC Table 9, for #6, AWG!
Attn Nitpickers: I'm ignoring the imbalance-factor associated with unrolled, flat-cable!
Phil
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