Transformer impedance
Transformer impedance
(OP)
Hi all, this is my first post ever.
I have recently graduated, so in a way, I'm still studying.
I'm trying to find some kind of transformer impedance "range" for different types of transformers, to use in short-circuit calculations.
It's my understanding that, you never get to know the "real" %Z of a transformer in the "project" stage, not until you get to see its nameplate, and by the time you actually get to see the nameplate, you're supposed to be in the "construction" stage, so that's one of the reasons I'm looking for some kind of "design ranges". But looking on the net for information, I've come up with some questions:
1. When you order a transformer; can you specify the impedance?
2. How do YOU get your information when you do short-circuit calculation and it's a new project?
3. In IEEE std c57.12.00 and c57.12.01, it says that you can find the typical impedance values from the "Product Standards", what are these?
I would also appreciate if you could tell me which IEEE standards have this information. I've found that the color books may have this info, but also the C57 series and the NEMA standards, or if I have to get it from manufacturers (if this is the case, how?, web info or direct asking?)
Sorry if there are any grammatical errors, the thing is I'm from Mexico, and sorry if I ask too many questions, but like I said, even if I have graduated I consider myself to still be studying.
Thanks in advance, I would really appreciate any information, or at least a north to do more research, seriously thanks.
I have recently graduated, so in a way, I'm still studying.
I'm trying to find some kind of transformer impedance "range" for different types of transformers, to use in short-circuit calculations.
It's my understanding that, you never get to know the "real" %Z of a transformer in the "project" stage, not until you get to see its nameplate, and by the time you actually get to see the nameplate, you're supposed to be in the "construction" stage, so that's one of the reasons I'm looking for some kind of "design ranges". But looking on the net for information, I've come up with some questions:
1. When you order a transformer; can you specify the impedance?
2. How do YOU get your information when you do short-circuit calculation and it's a new project?
3. In IEEE std c57.12.00 and c57.12.01, it says that you can find the typical impedance values from the "Product Standards", what are these?
I would also appreciate if you could tell me which IEEE standards have this information. I've found that the color books may have this info, but also the C57 series and the NEMA standards, or if I have to get it from manufacturers (if this is the case, how?, web info or direct asking?)
Sorry if there are any grammatical errors, the thing is I'm from Mexico, and sorry if I ask too many questions, but like I said, even if I have graduated I consider myself to still be studying.
Thanks in advance, I would really appreciate any information, or at least a north to do more research, seriously thanks.






RE: Transformer impedance
RE: Transformer impedance
RE: Transformer impedance
RE: Transformer impedance
RE: Transformer impedance
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If we learn from our mistakes I'm getting a great education!
RE: Transformer impedance
An authentic source for transformer impedance values in different countries is IEC Technical Report IEC/TR 60909 -2Ed2.0-2008-11,Short Circuit Current in three phase AC systems -Part2 Data of Electrical equipment for SC calculations.Of course your local transformer manufacturer can guide you regarding local norms for transformer impedances.
RE: Transformer impedance
RE: Transformer impedance
If they have 200 transformer in stock with impedance 5.5% and 10 of impedance 3.5% they will use (and tell you to use) 3.5%. The theory the lower impedance tranformer has a chance of showing up on your job.
RE: Transformer impedance
So in the end, the best source will always be the manufacturer.
Do they charge for this information?
RE: Transformer impedance
When you specify the preferred impedance for a given transformer, it must balance the following criteria.
a.) The impedance must be high enough to limit short-circuit currents to an acceptable values.
b.) The impedance must be low enough to keep steady-state regulation to an acceptable values.
Regards,
Bilegan
Murphy's Law - If anything can go wrong..it will.
RE: Transformer impedance
RE: Transformer impedance
2) Start with industry "standard" impedances. In the U.S., they are found in the C57.12.xx series of standards (the product standards). Each of these standards covers a specific range of transformer types (i.e. C57.12.26: IEEE Standard for Pad-Mounted,Compartmental-Type, Self-Cooled, Three-Phase Distribution Transformers for Use With Separable Insulated High- Voltage Connectors (34 500 Grd Y/19 920 V and Below; 2500 kVA and Smaller) and C57.12.20: Standard For Overhead Type Distribution Transformers, 500 kVA and Smaller: High Voltage, 34500 Volts and Below; Low Voltage, 7970/13800Y Volts and Below. There are probably similar sets of standards in the IEC world.
3) Some of the product standards explicity mention impedances, but some of the small transformer types do not. See C57.12.10 for typical transmission impedances (paragraph 4.6 & Table 10).
RE: Transformer impedance
I'll look for the info in those standards