Ct Ratio - Advanced Power technologies TTC-1000 Instruction & Operation Manual

The steady state winding temperature is calculated based on the following
1
equation :
  
( fl)
HS g
n
n
Where: n = 1, 2, 3


HS
n

(
fl)
g
n
Load
n
CTRatio
Rated
m 
1.0


First
TO
It is noted that the Hot Spot Rise over Top Oil at rated load is not always
available. In this case we recommend using a value between 18 to 22 ºC.
To accommodate the transient affect of changing load current, the winding
temperature can be estimated at any point in time by entering the winding time
constant. Therefore, the displayed winding temperature is calculated as follows:
  
) ( t (
HS HS
U
Where:
θ
(t)
HS

θ
HS
U

θ
HS
I


HS

θ
TO
Because data to calculate
the winding time constant is between 5 to 10 minutes.

4.4.1 CT RATIO

The CT RATIO is the CT ratio of the bushing CT which the split core CT is
applied to. The CT ratio must be relative to 1. Therefore, if the CT ratio is 300:5
the CT ratio to enter is 60. The ratio of the split core is already accommodated in
the unit. Should multiple turns of the CT wire through the split core window have
1
ANSI C57.91-1995
( * Load * CRatio / RatedLoad
n n
Ultimate c alculated windng tem

Hot Spot R ise #n ove

Measured load curre

Primary CT ratio
n n

Load Rated loa d of #n CT
n
for directed FOA or
Probe Measured
 
    
t /
)( 1 e )
HS
HS TO
I

Winding temperatur
Ultimate winding temperatur
Initial winding t emperature
Winding time constant
Measured top oil temperatu

may not be available, the recommended setting for
W
 2  
m
)
TO
n
perature
r Top Oil temperatur
nt #n
current
FOW, 0.8 for all other
Top Oil T emperature
[2]
e at tim e t
e using equation
using equation
in minutes
re
36
[1]
e at rated load
cooling
[1] above
[1]
V6.70 20131017