Effect of change in burden and power factor on CTs
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This document discusses the effects of burden and power factor on the ratio and phase angle errors in current transformers. It explains that burden is the load imposed on the secondary winding, and errors depend on the impedance connected, known as burden. An increase in burden impedance causes ratio error to increase and phase angle to shift to more positive values. The errors also decrease with increasing primary current. The power factor and frequency of the secondary burden circuit can also impact ratio and phase angle.
Effect of change in burden and power factor on CTs
- 1. INSTRUMENT TRANSFORMERS PRESENTED BY: MANISH SADHU(090450109039) 6TH SEM ELECTRICAL ENGINEERING
- 2. What is mean by Burden on CT? Burden is the load imposed on the secondary of the CT at rated current and is measured in VA (product of volts and amps). The errors in ratio and phase angle depend on the impedance connected to the secondary of the transformer. This impedance is commonly referred to as “burden”.
- 3. Burden of Instrument Transformer Burden across the secondary of an instrument transformer is also defined as the ratio of secondary voltage to secondary current.
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- 6. Effect of change in burden and power factor on ratio and phase angle of CTs 18/03/2013
- 7. 1.Effect of P.F. of secondary winding burden on errors-ratio error. It is observed that for all inductive burdens the secondary induced voltage Es, so that δ is positive . Under this condition, the actual transformation ratio is always greater than turns ratio. For burdens which are sufficiently capacitive Is leads Es and so δ is negative and δ approaching - 90°
- 8. For inductive burdens, phase angle θ is positive for small values of δ but becomes negative as secondary burden becomes more inductive and δ approaches 90°
- 9. 2.Effect of change of primary winding current. At low values of primary winding current Ip or secondary winding current Is magnetizing component Im and loss component Ie are greater proportion of primary winding current Ip and therefore error are greater. As current Ip increases, there is a decrease in ratio error and phase angle. Variation of ratio error and phase angle are shown in Figure 2 and 3
- 12. 3.Effect of change in secondary winding circuit. An increase in secondary winding circuit burden impedance means increase in volt ampere rating. This necessitates an increase in the secondary winding induced voltage which can be generated by an increased flux and flux density. Therefore both magnetizing component Im and loss component Ie are increased.
- 13. Thus it is excepted that error will increased with increased in secondary winding burden. In general, a greater burden impendance not only increases the transformation ratio, but also shifts the phase angle between primary winding current and secondary winding current reversed to more positive values as shown in Figure 2 and 3
- 14. 4.Effect of change of frequency. The effect of increase in frequency will result in proportionate decrease in the flux density. Thus, in general, the effect of change in frequency is similar to the product by decrease in impedance of secondary winding burden. A current transformer is seldom use at a freqency which is very different from the one or which it is designed and, therefore, consideration of this effect is not very important
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