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Most power Transformers I have seen are filled with oil, and have a base rating of ONAN - which stands for oil natural, air natural. This is a cooling type. There are two main ways to cool a transformer above this rating - by using forced air - essentially attaching fans to help pull heat away, or using oil pumps.

With air, the next typical rating is ONAF, or if there are two different ratings (meaning some fans turn on at one, and all fans turn on at two) they may be named ONAF1 ONAF2. thiws stands for oil natural, air forced.

If oil pumps are installed, the rating will be OFnn for oil forced. It is possible to have both oil forced and air forced, or just oil forced - OFAN or OFAF. Just an FYI, in my experience oil pumps are typically avoided. It was discovered that pumping the oil can cause a static voltage buildup in the oil, which can lead to catastrophic failures; this doesn't seem to be a problem if oil pumps are not used.

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What is the name given to the large transformers used in transmission systems to step up and step down?

step up transformer


30MVA power transformer can uprated to what extend?

You need to discuss with a transformer manufacturer, because modifications will need to be made. The transformer name plate will say the top rating of the transformer (I'm assuming in this case it is 30MVA). This top rating is generally limitted by heating. So to uprate, you need to modify the cooling system - add more or bigger fans, add pumps, etc. In my area, loading as high as 125% of max rating of transformers is allowed on a "short term" basis (in general), which gives system operators time to shift load without dropping customers. If 30MVA is the base rating, I see typical values of 166% and 186% for ONAF1 and ONAF2 (oil natural, air forced level #1 and #2). This is something that is specified when ordering the transformer, so it may be different in your case (look at the nameplate!). The 30MVA base transformers I've seen, therefore are rated at 30/49.8/56MVA (at 65 degree C).


What are the advantages of instrument transformer?

'Instrument transformer' is the collective name for current transformers (CTs) and voltage (or 'potential') transformers (VTs/PTs). These transformers have two functions:to reduce the current or voltage in a high-voltage primary circuit to values that may be measured using regular ammeters or voltmeters ('burdens'), or to provide the current or voltage inputs to protection relays.to electrically-isolate their secondary burdens from the high-voltage primary circuit for the purpose of safety.


Why distribution and power transformer are rated in mva?

Transmission transformers are rated in mva. Distribution transformers are rated in kva. Power transformers are measured in va. There are, of course, exceptions, but this is the normal nomenclature.Answer (for UK terminology)In the electricity supply industry, the name 'power transformer' is used to describe those transformers used in the transmission system (400/275/132-kV levels), while 'distribution transformers' are those used in the distribution system (33 & 11-kV and 400-230-V levels). Power transformers and primary-distribution transformers are rated in megavolt amperes (MV.A), while secondary-distribution transformers are rated in kilovolt amperes(kV.A).Note that 'mva', 'kva', and 'va' are incorrect symbols for 'megavolt ampere', 'kilovolt ampere', and 'volt ampere'. The correct symbols are shown in the above paragraph (except that the period, or full stop, should be placed above the line).However, I suspect your question is really asking why are transformers rated in (mega) volt amperes rather than in (mega) watts? The answer is simply that the load that a transformer can supply is determined by the product of the transformer's rated secondary voltage and rated secondary current -the product of which (for alternating current) is the volt ampere, not the watt.


What is the significance of vector-grouping in Power Transformers?

Vector group of Transformer: a.)The three stage transformer windings can be joined a few ways. In light of the windings' association, the vector gathering of the transformer is resolved. b.)The transformer vector gathering is shown on the Name Plate of transformer by the producer. c.)The vector gathering shows the stage contrast between the essential and auxiliary sides, acquainted due with that specific setup of transformer windings association. d.)The Determination of vector gathering of transformers is imperative before uniting two or more transformers in parallel. On the off chance that two transformers of diverse vector gatherings are associated in parallel then stage distinction exist between the optional of the transformers and huge coursing current streams between the two transformers which is extremely impeding.

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