Current transformer selection and calibration accuracy

Accuracy refers to within the scope of the provisions of the secondary load, a current of the maximum error when rating. China's current transformer accuracy and error limits as shown in table 1, for different measuring instrument, should choose different accuracy of current transformer. The choosing principle of accuracy: billing measurement with the current transformer is the accuracy of 0.2 ~ 0.5; Used to monitor the size of the load current in outlet and inlet line of each loop current meter should choose 1.0 3.0 level current transformer. In order to guarantee the accuracy of error is less than specified value, generally also check current transformer secondary load (ei), transformer secondary load S2n S2 is not greater than the rated load, the selected accuracy can be guaranteed. The accuracy of calibration formula: S2 S2n or less. Secondary loop load l: www.dongfeng-motor.com depends on the value of the secondary loop impedance Z2 is: S2 electric motor 12v 500w = I2n2 ︱ Z2 ︱ material I2n2 (∑ ︱ Zi ︱ + + RXC RWl) or S2V1 material ∑ Si + I2n2 (RWl + RXC), Si, Zi as the secondary circuits of the instrument, the rated load and impedance of the relay coil RXC for all joints in the secondary loop, contact contact resistance, generally take 0.1 Ω, RWl for the secondary loop wire resistance, calculation formula is: the RWl = LC/(r (S). Type, r for the conductivity of the wire, copper wire 53 m/r = (Ω was), aluminium wire r = 32 m (Ω was), S for cross-sectional area (was), LC for the calculation of the wire length (m). A multitude of transformer to instrument one-way length of L1, is: L1 transformer is star. LC = L1 two-phase V wiring. 2 a phase l1 type connection. The accuracy of current transformer used for the relay protection has 5 p and l0P. Protection level of accuracy is based on accurate rating limit down an electric epsilon % of the maximum error of the composite to nominal (such as 5 p corresponding epsilon % = 5%). So-called rated accurate limit a rated current is a current Induction motor is a current multiples (n = I1 small three phase motor / I1n), also known as rated limit coefficient accurately. Is asked to protect by current transformer in the range of possible, its biggest composite error is less than epsilon % value.