They are a simple devices designed to produce an alternating current in the secondary winding which is directly proportional to the current in the primary conductor. Some of our most popular transformers include the power transformer, low voltage transformer, electric transformer, flyback transformer, 24v transformer, high voltage transformer, current transformer, toroidal transformer and control transformer. Fundamentally can be distinguished between single conductor current trasformers and wound primary current transformers.
Generally current transformers are distinguished for measuring purpose and protection purposes. A.E. Emanuel, J.A. Orr, Current harmonics measurement by means of current Transformers, IEEE Transactions on Power Delivery, 22(3) (2007) 1318-1325. K. Erenturk, ANFIS based compensation algorithm for current transformer saturation effects, IEEE Transactions on Power Delivery, 24(1) (2009) 195-201.
N.L. Locci, C. Muscas, Hysteresis and eddy currents compensation in current transformers, Manufacturer Price LZZBJ9-20 Current Transformer With Good Quality on Power Delivery 16(2) (2001) 154-159. J. Pan, K. Vu, Y. Hu. An efficient compensation algorithm for current transformer saturation effects, IEEE Transactions on Power Delivery 19(4) (2004) 1623-1628. P.N. Miljanic, E. So, W.J.M. Moore, An electronically enhanced magnetic core for current transformers, IEEE Transactions on Instrumentation and Measurement, 40 (1991) 410-414.
In this paper, current transformer error compensation unit (CTECU) is developed which is specially intended for providing compensation to all types of measurement CTs. When the current is passed through the primary winding of a current transformer, the response can be examined by replacing the CT with an equivalent circuit as shown in Figure 2(b) The effects are most important, and were first observed in connection with balanced forms of protection, which were liable to operate unnecessarily when short-circuit currents were suddenly established.
As a protection CT may be required to deliver high values of secondary current, the secondary winding resistance must be made as low as practicable. CTs for measuring line currents fall into one of three types. The summation arrangement is a winding arrangement used in a measuring relay or on an auxiliary current transformer to give a single-phase output signal having a specific relationship to the three-phase current input.
Figure 6 - Bar Primary Type Current Transformer (CT having Single Primary turn with the Primary Conductor embedded) Such current transformers normally have a single concentrically placed primary conductor, sometimes permanently built into the CT and provided with the necessary primary insulation. Figure 5 - Wound Primary Current Transformer (Low ratio, wound primary current transformer, suitable for primary currents from 2.5A-100A with 5A outputs.
Current transformers are often used for the dual duty of measurement and protection. The accuracy class of protection current transformers is shown in Table 3. Protection class current transformers must retain a reasonable accuracy up to the largest relevant current.
The general vector diagram applicable for voltage transformer ( click to see it ) can be simplified by omitting details that are not of interest in current measurement. Many protection systems are required to operate during the transient disturbance in the output of the measuring transformers following a system fault. Such measuring transformers are required to produce a scaled down replica of the input quantity to the accuracy expected for the particular measurement.