Are tap changers required?
Are tap changers required?
(OP)
Are automatic tap changers still recommended for a 10 or 12% impedance, 132 or 66 to 22kv distribution transformer where source voltage does not deviate beyond 1.00pu?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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Are tap changers required?
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RE: Are tap changers required?
If so then you need a tap changer.
Regards
Marmite
RE: Are tap changers required?
My understanding this comes from the naturally high impedance of the transformer itself?
RE: Are tap changers required?
We have a number of 115/13.8 kV transformers that do not have LTC's. We usually maintain the transmission voltage within a tight tolerance, but we think of tight as 1 to 2%. Even if your voltage is 1.00 during normal conditions, you should also consider the impact of abnormal conditions. In our area without LTCs, the most limiting factor is low voltage rather than the thermal rating of components.
RE: Are tap changers required?
RE: Are tap changers required?
For example, on board tap changers maintain voltage close to 1.00pu on all 33kv and most 66 kv sub transmission busses. Anything attached to these busses always sees + or - 1.5% at most. In some 33kv lines pole mounted regulators maintain the voltage close to boundaries because commercial and industrial customers tap directly from the sub transmission system. The pad mounts have no automatic tap changers so its essential the LV output be within +or- 6%. As a result, when distribution substations tap immediately after these regulated lines voltage is considered to be within bounds.
IMO the primary voltage is not a concern in itself, however the naturally high impedance of the transformers (10 to 12% to limit fault current) is raising concerns. My understanding is that voltage regulation is excellent in low impedance transformers, but less so in higher impedance versions.
RE: Are tap changers required?
RE: Are tap changers required?
Given the relatively wide load range you're suggesting, I'd much prefer to have the regulators in place.
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Are tap changers required?
2) Have you added in the +- 1.5% source variation you mentioned to the worst case of (1)?
3) Is there ANY possibility of a variance from this source of more than 1.5% under THEIR emergency conditions? What is their ALLOWABLE range rather than the range you usually see? Did you allow for this in your answer to (1)?
4) Is there a GUARANTEE that the supplier's regulators will always be present and functional, or is that simply an artifact of their present configuration?
5) Is there any possibility that you could be supplied from a more distant source under planned maintenance or emergency contingency plans? Have you allowed for the worst case from that?
6) Is there any chance that you may want to move these units somewhere else in your system where a tap-changer would be needed?
7) Does your organization have to match specs on their xmfrs for 'spares' purposes? Do these other xmfrs have tap-changers?
If you are satisfied with the answer to all of these and still do not see a need for tap-changers, than maybe you can do without.
RE: Are tap changers required?
RE: Are tap changers required?
Hmmm, I never thought like that. Why would higher Z equal more voltage regulation? I was always under the impression that a lower Z would mean less fluctuation... kind of like a pole pig that can take a 300% overload with minimal voltage drop.
Crunching the numbers as long as the source output is within +or- 1%, it will still yield an expectable bandwidth from light to full load.
Normally I wouldn't count on feeders to have voltage regulation within range but because the feeders here are fairly short voltage drop will be limited.
Not to the primary side no, just the secondary.
Possible, yet unlikely due to reliability standards. The source has its own tap changing transformer (the life saver here) which keep a pu close to 1.00, however under serve line outages a voltage drop is not impossible.
I will have to think about this, another good point, but if it gets to the point where the supply transformer taps fall out of range it would indicate a very severe contingency. Now that you say it, it might be just an artifact to some degree.
Loss of all sources would cause an outage, but as far as I know under all known contingency (except voltage collapse) pu is maintained from where the transformers will tap from.
This is a valid point. While there is usually no immediate hurry to move units, in the future there might be.
Not usually, its generally done case by case, but going back to #6, if a unit is ever moved under emergency situations the one its replacing could end up being a tap changer type.
Most satisfied but you do make points that are well worth re-evaluating in depth.