__CORRECTION FACTOR TO BE USED FOR DETERMINING
THE ACTUAL POWER/ENERGY AFTER
CONSIDERATION OF
RATIO AND PHASE ANGLE ERRORS OF
C.TS. AND P.TS.
USED IN
METERING.__

**It
would be seen from the vector diagram that the meter reading shall be
corresponding to Vs.Is.Cos a which does not correspond to the power/energy which shall be VICos f.
A correction needs to be applied to the meter reading depending upon the errors
of C.Ts. and P.Ts.**

**Phase
angle seen by the meter is a which obviously is**

**a = f - q ± d**

**In
the vector diagram d is shown as positive that is P.T. secondary voltage leads the primary voltage
reversed. The phase angle of meter pressure coil is ignored and is assumed to be
zero.**

**V -
System Voltage **

**I
- System Current **

**f
- Load P.F**

**Is
- C.T Secondary Current **

**Vs
- P.T Secondary Voltage**

**q
- Phase
angle error C.T**

**d - Phase
angle error P.T
a
- Phase angle seen by meter **

**
**

**Thus, the correction corresponding to phase
angle errors of C.Ts**

**and P.Ts. shall be**

**K
= Cos f **

**Cos
(f - q ±
)
(1)**

**Note - d may be positive or negative.**

**About ratio errors of C.Ts and P.Ts. let the
C.T. ratio error be e%**

**and P.T. ratio error be p%.**

**
**

**Actual
Ratio of C.T. = RCTA = Primary Current**

**Actual
Secondary Current**

**
**

**
**

**Actual
Ratio of P.T. = RPTA = Primary Voltage**

**Actual
Secondary Voltage**

**
**

**
**

**Considering the rated primary
current (Ip) as primary current**

**(100%) for C.T. and rated
primary voltage Vp (100%) as primary**

**voltage for P.T, (Errors e and
p are assumed to be at rated primary**

**current and rated primary
voltage with rated burden connected**

**across the secondary.**

**
**

**Actual
Ratio of
C.T.
=
Ip **

**Is
- e x Is
100
(2)
Actual Ratio of
P.T
=
Vp **

**
Vs - p x Vs**

**
100
(3)**

**where Is and Vs
are rated secondary current for C.T. and rated**

**secondary voltage
for P.T. respectively.**

**
**

**Dividing numerator
and denominator of equation 2 and 3 by Is**

**and Vs
respectively**

**
Actual Ratio of
C.T. =
Ip /
Is **

**
1- e x Is / Is **

**
100
(4)**

** **

**
Actual Ratio of P.T.
= Vp /
Vs **

**
1- p x Vs / Vs**

**
100
(5)**

**or
rewriting equation 4 and 5 it will be seen that**

** **

**
Actual Ratio of
C.T. =
Nominal Ratio**

**
1- e **

**
100
(6)**

** **

** **

**
Actual Ratio of
P.T.
= Nominal Ratio**

**
1- p **

**
100
(7)**

**
or simply for C.Ts A.R.
=
N.R. **

**
1-
e
100
(8)**