Ring type is the most usual type of core-balance current transformer (CBCT).
Guidance was given in the specifications to the application of high voltage lightning arrester to earth fault protection, but for this and for the majority of other protection applications it is better to refer directly to the maximum useful e.m.f. that can be obtained from the CT. Class PX is the definition in IEC 61869 for the quasi-transient current transformers formerly covered by Class X of BS 7626, commonly used with unit protection schemes. Protection ratings are expressed in terms of rated burden, class, and accuracy limit factor, for example 10VA Class 10P10.
For example, with an accuracy limit factor of 30 and a burden of 10VA, the CT may have to supply 9000VA to the secondary circuit. The ratio of the accuracy limit current to the rated current is known as the ‘accuracy limit factor‘. The accuracy class of measuring current transformers is shown in Table 1 and Table 2.
For lower value burden or a different burden power factor, the error would change in the positive direction to a maximum of +0.7% at zero burden; the leakage reactance of the secondary winding is assumed to be negligible. The secondary current is not affected by change of the burden impedance over a considerable range. The power system impedance governs the current passing through the primary winding of the current transformer.
Voltage and current transformers for low primary voltage or current ratings are not readily distinguishable. The errors in transformer output may delay the operation of the protection or cause unnecessary operations. 5SFT251 Current Transformer - 250:5A Current Ratio and other products, or for custom and large orders call us at (800) 446-4035 or contact us online.
And with the vast 50-1200 Amp current range, these current transformers are ideal for all types of current metering applications. 2. Bar-type Current Transformer - The bar type transformer has only secondary windings. The primary winding had a single turn and connected in series with the conductor that measured the current.
But in an actual current transformer, there is a phase difference between the primary and the secondary current because the primary current has also supplied the component of exciting current. Phase Angle Error - In an ideal current transformer the vector angle between the primary and reversed secondary current is zero. The current flows through the primary is the sum of the exciting current I0 and the product of the turn ratio and secondary current Kt Is.
The secondary current lags behinds the secondary induced voltage by an angle θº. The secondary current relocates to the primary side by reversing the secondary current and multiply by the turn ratio. The burden of a current transformer is the value of the load connected across the secondary transformer. The secondary windings of the transformer carry the current proportional to the current to be measured, and it is connected to the current windings of the meters or the instruments.
