capacitor bank effect on the transformer HV side
capacitor bank effect on the transformer HV side
(OP)
hello,
we have HV/ MV power transformers. we've installed capacitors on the MV side of the transformer. is there any chance that the capacitor affect the HV side by increasing the voltage or its only affecting the MV side of the transformer?
regards,
we have HV/ MV power transformers. we've installed capacitors on the MV side of the transformer. is there any chance that the capacitor affect the HV side by increasing the voltage or its only affecting the MV side of the transformer?
regards,






RE: capacitor bank effect on the transformer HV side
RE: capacitor bank effect on the transformer HV side
RE: capacitor bank effect on the transformer HV side
RE: capacitor bank effect on the transformer HV side
But if the transformer is networked and not radial, there are many other considerations that will impact how the vars flow. With an LTC you could have some steps where they go from low-side to high-side and others where they don't; the LTCs on other transformers will also matter.
RE: capacitor bank effect on the transformer HV side
Bill
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"Why not the best?"
Jimmy Carter
RE: capacitor bank effect on the transformer HV side
RE: capacitor bank effect on the transformer HV side
RE: capacitor bank effect on the transformer HV side
RE: capacitor bank effect on the transformer HV side
A real world example:
A city in Central America originally ran on diesel power.
About 30 or more years ago a large hydro-electric project was completed on the other side of the country.
The diesel plant was mothballed.
As the city grew, and the load increased, the capacity of the transmission and substation system was exceeded.
The capacity of the line was limited by the voltage drop and the ability of the OLTCs to compensate for the voltage drop.
A large part of the voltage drop was due to line reactance.
The diesel plant was taken out of mothballs and put back online. Due to the age of the equipment and the cost of fuel, the plants were only loaded enough to reduce slobbering.
The plants were used to supply MVARs to the system and reduce the reactive voltage drop on the transmission line.
This solution allowed the system to supply greater energy than the original design while maintaining the voltage at an acceptable level.{anecdote off}
Bill
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"Why not the best?"
Jimmy Carter
RE: capacitor bank effect on the transformer HV side
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is, for certain ù then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". û Nikola Tesla
RE: capacitor bank effect on the transformer HV side
Confirmed, you are wrong. Reactive power like real power flows from source to load whichever way is needed through any transformers in the path. See Davidbeach's example above.
RE: capacitor bank effect on the transformer HV side
On a weak 69 kV system, 6 MVAR could move the HV side more than 1%. On a strong 115 kV system, 6 MVAR could move the HV side less than 0.1%.
RE: capacitor bank effect on the transformer HV side
RE: capacitor bank effect on the transformer HV side
Within the more robust portions of my utility, our LT/MV capacitors [ 14, 28 & 44 kV ], being nominally rated at 20, 25 and 30 MX and located at our substations, do indeed have profound effects on the HV transmission system; our Independent Electrical System Operator does in fact in large part dispatch our LT capacitors to control the 115, 230 and 500 kV system voltages. Incidentally we do have 115 and 230 kV cap banks as well, typically with a nominal rating [ meaning at rated voltage ] of 100, 200, 300 and 400 MX, generally near or within major load centres, or at major transmission nexi.
There are some more remote and weaker portions of our system that have lengthy 115 kV lines and therefore significant impedance; at substations connected to these circuits even an 11 MX cap bank can cause major voltage perturbations, necessitating considerable prudence in dispatching same.
Certainly the HV caps do deliver great gouting amounts of reactive power, and have their place; but it is the LT caps that can often be tweaked to a relative nicety, maximizing the real power capability of the HV circuits and the substation transformers in question, something of great importance during both winter and summer peaks as well as during maintenance outages in the shoulder seasons.
It's just gone midnight here, and for us it is now Christmas Eve; I'm expecting the IESO to be calling fairly soon to request a bunch of said LT caps removed from service...
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: capacitor bank effect on the transformer HV side
The scenario is this: We have CAP banks installed at site #1 on the 13.8KV secondary's of 2 site transformers (138KV:13.8KV) and generally sit at PF of 99 to unity most days. We have a second site fed from the same transmission line at 138KV with poor PF dipping down to 87 some days which is about 10KM away from Site #1 as the crow flies.
Given that there is poor quality at the site #2, one of the Maintenance Engineers has suggested that we switch in the CAP banks at site #1 (overcompensating) in order to dump MVAR's through the secondary of the Transformers up to the Primary 138KV side in order to mitigate the PF at the second site.
To make matters more convoluted, the low PF at the second site is due to inductive load which is up to another 6KM away (on top of the 10KM) at 25KV (Underground Mining) for a total of about 16KM.
The total impedance of the 138KV line between the 2 sites is unknown at this point, but at a high level I'm concerned about the effect of voltage rise at 13.8KV system at site #1 . Will an independent PF correction CAP bank be a better solution at Site #2 vs. trying to utilize Site #1's CAP Banks? By switching in additional CAP banks at site #1, my thought is that we would be overcompensating for MVAR demand at site #1 and potentially cause an overvoltage condition at Site #1 due to the distance between the 2 sites. Given that Site #2's MVAR demand will counter the Additional MVAR's dumped onto the transmission line it could be argued that the net effect will achieve the desired outcome, but I'm not fully convinced that this would be the case.
Does anyone have expertise on this that could weigh in from a high-level standpoint?
I thank you in advance for any input on this!
Best Regards!
RE: capacitor bank effect on the transformer HV side
Adding caps at one site will not affect the metering of KVARs or PF at a second site.
If the system operator will allow you to combine the kWHr and KVARHr consumption of both sites and bill the PF penalty on the combined total this will allow you to correct the PF on the 138 kV line by adding caps at one site.
One site would have a leading PF and the second site would have a lagging PF, but the effect on the incoming 138 kV line could be a unity PF.
However it is doubtful that the sys-op's tariffs will allow combining of the two power bills.
The voltage rise will be greatest in most cases at the point where the caps are connected.
Bill
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"Why not the best?"
Jimmy Carter
RE: capacitor bank effect on the transformer HV side
As far as the system operator goes, that would be a whole other set of negotiations for the company to carry out regarding combining the 2 power bills which is out of my realm of influence and highly unlikely at this point.
You have confirmed what I was thinking earlier regarding the voltage rise and that makes me wary of pursuing this scenario.
Thanks for your input!