presentation of instrument transformer

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.

4. ×

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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