3 Phase vs Single Phase Distribution Voltage Regulators

[ukgraduate]

Hello,

We have situation where we are feeding a large load aprox 20MW 5km over 33kV Overhead powerline. The load is such that the volt drop is aprox 12% at 33kV.

I understand that I have a few options for voltage regulation:

a) PF correction, however I have calculated that at 0.98 it will only correct about 4-5%, which would be OK but seems like a costly and large PF correction for such a small gain.
b) Increase conductor size, possible but due to limitations of contractor not preferred
c) Reduce load - Not posible
d) Autotransformer/Step Voltage regulators - Dont have much experience on these as a way of voltage regulation for distribution only for ensuring motor voltage constant

Can someone please tell me :

1) What in peoples experience is the most common and cost effective for voltage regulation on distribution networks
2) Where on the line would you put the voltage regulator. In the middle of the line or at the load?
3) Is it best to get a 3 phase voltage regulator or 3 single phase voltage regulators?
4) Why do people use 3 single phase voltage regulators, What is the benefit of this


Regards

Ukgrad

 

[7anoter4]

According to Phoenix Wire and Cable Corp. catalogue[ACSR conductor] taken into consideration:
conductor temperature of 75°C; ambient temperature of 25°C; wind velocity of 2 ft/sec; in sun.
for 427 A load we need 150 sqr.mm [a.c. resistance 0.0693 ohm/1000 ft-0.22736 ohm/km].The inductive reactance for 36kV is about 0.42 ohm/km. In this case the voltage drop for 0.86 p.f. has to be 4.6% [in my opinion].

 

[cranky108]

Single phase regulators at one time were catalog items. Three phase regulators are custom built, so I would expect to cost more.
Before you look into a three phase regulator, look at your line and see if it is fully transposed. If it is not, a three phase regulator might not fix the unbalance problem.

Even with additional regulation, you might also look into line capacitors.

My present company does not use line regulators, only LTC's, because they don't know how to work on regulators.

 

[bwen08]

1. This is really going to depend on each situation, regulators are typically used here to bring the voltage back up and delay the cost of reconducting the line.

3. Get a quote for a three phase unit vs three single phase units. Single phase units have been regularly much cheaper in the smaller sizes. Space requirements could also dictate whether the cost of a three phase unit is used vs the single phase units. Three phase units typically have a smaller footprint requirement than what is needed for three single phase units.

4. A few of the many reasons:
Three phase units are normally heavier than what many utility line trucks are capable of lifting, requiring a crane that many utilities likely would have to contract out.
Smaller single phase units can be staggered on the line over several poles if there is limitations with installing a regulator bank structure.
A three phase is ganged operated, if the system is unbalanced, you could end up causing over/under voltages on the other phases that are not the sensing phase. Utilizing single phase units can better handle the unbalanced system and regulate each phase voltage to the setpoint.

 

[jghrist]

If there is only one load at the end of the line, then the regulator would be best placed at the end of the line. Standard voltage regulators are limited to +/- 10%, so you might have to put the regulator closer to the source where the voltage drop is less than 10%. If there are other customers on the distribution line, you would have to place the regulator closer to the source to provide adequate regulation for the other customers.

I agree with Brian's comments on single vs. three phase units. I would add that if single phase units are used, and you need a spare, you could get by with a less expensive single phase spare.

Power factor correction could be used if the load power factor is low, particularly if the minimum reactive load is fairly high. Fixed capacitors would be relatively inexpensive to provide at least part of your voltage support.