Tap changer location in transformers
Tap changer location in transformers
(OP)
Normally ,in many parts of the world,on-load tap changers are provided on HV side of Transformers for getting voltage variation on HV side or on LV side (variable flux regulation)But in USA most of the cases,tapchangers are provided on LV side for LV variation. This invariably make on- load tapchanger of high current rating with consequent complications in tap changer and tap winding .Historically what is the reason for this?I could not find any advantage for locating tap changer on LV side of the winding. Can any one shed light?






RE: Tap changer location in transformers
1- Tap changer (LTC) connected on Delta side will require and Insualtion level (BIL) rated Line-to-Line. For LTC connected to the Wye side, the BIL will be Line-to-Neutral. The cost of LTC appear to favor the LV location for typical transformer size.
2- LTC is the single higher cause of failure in power transformer are caused by moving part mechanism. Operation and maintaintenance cost of LTC on HV is considered more complex and expensive.
3- Reliability index favor LTC on LV side since SLG fault on secondary side including the LTC will not affect the utility side because the Delta winding will not provide zero sequence path to the fault on the HV side.
4- Utility and industrial users have extensive experience on the LTC performance on the LV side. There are not evidence that LTC on HV side will provide better reliability, operation and mainatenability performance.
There are cases of use of LTC on the primary side went the tap changer current on the LV side could be excesive or specific requirement imposed by the system applications.
RE: Tap changer location in transformers
One more thing goes in favour of providing LTC on HT side is that it make the voltage change smooth in because in HT side number of turns are more so corresponding change is LT voltage is smooth but in LT, number of turns are less so for one tap position change, corresponding voltage variation in HT will be more.
RE: Tap changer location in transformers
The solid state electronic advances are proliferating into transformer on-load tap changers. The electronic switching on the load side will not have any sparking involved.
Also, the make-before-break versus break-before-make on-load-tap changers shall be scrutinized. Apparently, the make-before-break was more convenient on the low voltage side to avoid high potential differences during switching and resulting consequences.
RE: Tap changer location in transformers
RE: Tap changer location in transformers
RE: Tap changer location in transformers
Putting Ltc on interior wdg will not reduce voltage stresses.In big trfs for better magnetic symmetry tappings are always provided as a separate winding.In case of HV tappings it will be at neutral end,as outer most wdg and tap achanger will not see much stresses.LV tap changer ask for inner tap winding with consequent difficulties in taking out lead etc,etc.So from mfg angle, design angle,reliability angle Hv tap changers are always better.No doubt manufacturers are capable of providing any requirement.
But from system operation angle any advantage?
HV LTc: HV voltage variation can be done at constant flux in trf. But if LTC is used to get higher lv Terminal voltage it results in variation in flux in core and so change in losses and if excessive, overfluxing in trf.
LV LTC: Opposite condition to above.
I have seen 100 MVA 220/66 Kv trfs star/star with hv or lv tapchanger depending on utility.Some countries go for OCTC on HV side with OLTC on LV side making trf more complicated.
RE: Tap changer location in transformers