Therefore, the selection of Protective Current Transformers in relation to accuracy class and ALF require a close examination of relay characteristic and. CT winding resistance. CT excitation / saturation (unsaturated and saturated). ALF and FS (direct and indirect). Burden impedance. CT residual magnetism. Page 3. Rct: CT secondary winding resistance. RL: wiring resistance. Rp: protection relay resistance. ALF: accuracy limit factor. CT: current transformer. Rct. [Ω]. Uk. [V]. Io. [mA]. [VA] FS. [VA] FS. [VA] FS. [VA] ALF. [VA] FS. [VA] ALF. A 2. 6. 2. 4. 8. A 2. 4. All parameters of single- and multi-ratio CTs (ratio, phase, excitation, resistance, ALF/FS) are determined within minutes. The CT assessment automatically.

The accuracy designation "P" (which stands for protection) uses the highest percentage composite error followed by the Accuracy Limit Factor (ALF). Standard. document discusses the calculation of accuracy limit factors for current transformers (CTs) during external and internal faults. For an external fault, the. **In order to select the right rating of the current transformer, we will have to iterate for the solution by making a guess of the nominal ALF. Other.** Current transformer selection guide page 10 date. 11/ - B•1•4 - revised. 08/ The relay will operate perfectly provided that: (effective ALF ofthe CT) >. 5P = 5 percent accuracy at up to 10 times the rated current or the standard Accuracy Limit Factor (ALF). “P” designates protection class. IEEE Metering. Ratio and phase accuracy · Winding resistance · Excitation characteristics (knee points) · Composite error (ALF, ALFi, FS, FSi, Vb) · Burden impedance · Transient CT. What is ALF & ISF in case of case of instrument transformer. ALF current transformer that belongs to the group of 5P or 10P type protection CT. current transformer at rated current of the secondary and at a given power factor To transform the fault current without saturation, the ALF factor has to be. CT winding resistance. CT excitation / saturation (unsaturated and saturated). ALF and FS (direct and indirect). Burden impedance. CT residual magnetism. Page 3. The ratio of the accuracy limit current to the rated primary current. kALF = IAL/IN. (eq. 2). The standard accuracy limit factors are 5, Usage of actual burden lower than the rated value will increase FS by another factor as in the case of ALF in protection class. Reasonable Knee Point Voltage, E.

The accuracy designation "P" (which stands for protection) uses the highest percentage composite error followed by the Accuracy Limit Factor (ALF). Standard. **ALF helps to maintain the accuracy of CT under fault condition such that it does not saturate. it is simply the maximum allowed limit of error. CT(Current Transformer) Burden Calculation and CT Accuracy Limit Factor (ALF) · Comments3.** voltage transformer due to the load current voltage drop. Single phase To transform the fault current without saturation, the ALF factor has to be. Definition- The accuracy limit factor (ALF) of a current transformer (CT) is a parameter that indicates the highest multiple of the rated current at which. There for, the selection of Protective Current Transformer in relation to accuracy class and ALF require a close examination of relay characteristics and. Accuracy limit factor (ALF): The value of primary current upto which the CT complies with composite error requirements. This is typically 10, 15 or The accuracy limit factor (ALF) of the CT is defined as the ratio of rated accuracy limit primary current to rated primary current. The. A 10 VA 5P10 CT with 25% load gives actual ALF values from. when the winding resistance varies from Ω to Ω. The actual accuracy limit factor kA.

know as the "Accuracy Limit Factor"(ALF). Therefore, the selection of Protective Current Transformers in relation to accuracy class and ALF require a close. The ALF of a CT is inversely proportional to the actual burden connected. For example, if one has a protection CT of Class 5P10 & a rated burden. Thermal short circuit current. (lth). 60xIn for Bus Bar type CT. Dynamic short circuit current. (ldyn). xIth. Accuracy Limit Factor (ALF). 5, BENEFITS. Therefore, the selection of Protective Current Transformers in relation to accuracy class and ALF require a close examination of relay characteristic and. This creates a measuring error in the current transformer due to the magnetizing current, and in the voltage transformer ALF factor “” multiplied with the.

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