Page 9 - Catalogo FTM 2017

14. Characterization of protection classes:
DeSIgnATIon
exPLAnATIon
P / PR
Defining a current transformer to meet the composite error requirements of a short-circuit current under symmetrical steady state conditions
CoRRELATED TERMs
Composite error, under steady-state conditions, the r.m.s. value of the different between: the instantaneous values of the primary current, and the instantaneous values of the actual secondary current multiplied by rated transformation ratio. Normalizzed values 5 or 10 %.
Accuracy limit factor (ALF), is the ratio of the rated accuracy limit primary current to the rated primary current. Rated values of ALF are 5 – 10 – 15 – 20 –30.
Accuracy class designation, The accuracy class is designated using the highest permissible percentage of the composite error, followed by the letter “P” (standing for “protection”) and the ALF value. Normalized values 5P / 5PR e 10P / 10PR (es. 5P20).
error limits for protective current transformers class P and PR, look table 3.
Px / PxR
Defining a current transformer by specifying its magnetizing characteristic CoRReLATeD TeRMS
Rated knee point e.m.f., (ek), is the minimum sinusoidal e.m.f. at rated power frequency when applied to the secondary terminals of the transformer, all other terminals being open-circuited, which when increased by 10% causes the r.m.s. exciting current to increase by no more than 50%.
Rct: actual secondary winding d.c. resistance in ohms corrected to 75 oC or such other temperature as may be specified.
Rb: rated value of the secondary connected resistive burden in ohms.
Ie: r.m.s. value of the current taken by the secondary winding of a current transformer, when a sinusoidal voltage of rated frequency is applied to the secondary terminals, the primary and any other windings being open-circuited.
TPx / TPY / TPZ
Defining a current transformer to meet the transient error requirements under the conditions of an asymmetrical short-circuit current.
CoRReLATeD TeRMS
Remanence factor (Kr), ratio of the remanent flux to the saturation flux, expressed as a per-
centage.
Rated symmetrical short-circuit current factor (Kssc): ratio of the rated primary short circuit current to the rated primary current.
Transient dimensioning factor (Ktd): dimensioning factor to consider the increase of the se- condary linked flux due to a d.c. component of the primary short circuit current.
Secondary loop time constant (Ts): value of the time constant of the secondary loop of the current transformer obtained from the sum of the magnetizing and the leakage inductances (Ls) and the secondary loop resistance (Rs).
Specified primary time constant (T P): that specified value of the time constant of the d.c. component of the primary short-circuit current on which the transient performance of the cur- rent transformer is based.
Rb: rated value of the secondary connected resistive burden in ohms.
error limits for TPx, TPY and TPZ current transformers: look table 4.
15. Reference standard, if not specified in different way:
IEC 61869-1 Instrument transformers , part 1 general requirement.
IEC 61869-2 Instrument transformers , part 2 Additional Requirements, for Current Transformers.
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