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Anonymous Poster #1

Transformer manufacturer standard for %Z

12/02/2021 9:30 AM

what is the Transformer manufacturer standard for %Z.

FOR SMALL TRANSFORMERS 50KVA UPTO 5MVA, SINGLE OR THREE PHASE

NEMA, IEEE, IEC, OR OTHER

I NEED THE STANDARD NUMBER TO ORDER

THANK YOU

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#1

Re: Transformer manufacturer standard for %Z

12/02/2021 10:24 AM

IEEE standard values for % impedance (%Z) for liquid-filled power transformers can be found in IEEE Std C57.12.10-2017, Table 3. The standard values are defined on the basis of the HV winding BIL voltage. However, it is possible for transformer manufacturers to modify their design to achieve a different, custom value of %Z if there is a desire or need for it, such as to match another, existing transformer with a non-standard %Z.

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#2

Re: Transformer manufacturer standard for %Z

12/03/2021 1:39 AM

IEC 60076-5 also stipulates %Z values (in Table-1). These are minimum values for different kVA ratings.

Customer is supposed to decide the required %Z value that suits the downstream distribution system, circuit breaker rating, busbar rating etc.

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#3

Re: Transformer manufacturer standard for %Z

12/07/2021 7:23 AM

So enter into discussion with the manufacturer over the telephone for further advice, though do turn off CAPS lock before doing so, please; it is considered akin to SHOUTING, and quite rude.

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Anonymous Poster #2
#4

Re: Transformer manufacturer standard for %Z

01/24/2022 11:02 AM

4% to 7%is the short circuit impedance of the transformer as per IEC 60076-5

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#5

Re: Transformer manufacturer standard for %Z

01/25/2022 11:42 PM

Usually, for voltage drop calculation we shall take 7.5% more the rated short-circuit impedance.See

IEC 600076-5 4.2.7.4 a) Transformers of categories I and II 5) the short-circuit reactance values, in ohms, evaluated for each phase at the end of the tests, do not differ from the original values by more than: – 7,5 % for transformers with non-circular concentric coils having a short-circuit impedance of 3 % or more. The value of 7,5 % may be reduced by agreement between the manufacturer and the purchaser, but not below 4 %. – 7,5 % for transformers with non-circular concentric coils having a short-circuit impedance of 3 % or more. The value of 7,5 % may be reduced by agreement between the manufacturer and the purchaser, but not below 4 %.

– category I: up to 2 500 kVA;

– category II: 2 501 kVA to 100 000 kVA;

– category III: above 100 000 kVA.

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