| LOW VOLTAGE CURRENT TRANSFORMERS | | General:
| Measuring current transformers:
| Current transformer is a very useful device because it converts high AC current to small easily manageable value.Current transformers consist of primary winding, secondary winding, magnetic core and insulated body. If current transformers have no bus bar, they are manufactured without primary winding. Instead of this, it is possible to constitute primary winding by passing conductor or busbar inside toroidal core of transformer.
Dixsen current transformers are produced according to IEC IEC44-1. Furthermore, the secondary terminals are under a transparent seable cover. Low voltage current transformers are manufactured as of two types for measuring and protection.
| Measuring current transformers are constructed to feed on other low voltage apparatus such as measuring instrument, relay, watt-hour meter (kW meter), these type of current transformers are mainly used 0.5 and 1 class to transfer the current from highest rated current to rated secondary current.
| | Protection current transformers: | | Protection current transformers are constructed to feed the protection relay. These type of current transformers are mainly used class 3. (Customer supplied when required.) | | Current errors and phase shift in measuring current transformer:
|
|
Accuracy
Class
|
permissible ratio error ”Ąat
Various percentage of rated
secondary current
|
”Ąphase shift in various percentages of rated secondary current | |
Minute |
Centiradian | |
%5 |
%20 |
%100 |
%120 |
%5 |
%20 |
%100 |
%120 |
%5 |
%20 |
%100 |
%120 | |
0,1
0,2
0,5
1,0
| 0,4
0,75
1,5
3,0
| 0,2
0,35
0,75
1,5
| 0,1
0,2
0,5
1,0
| 0,1
0,2
0,5
1,0
| 15
30
90
180
| 8
15
45
90
| 5
10
30
60
| 5
10
30
60
| 0,45
0,9
2,7
5,4
| 0,24
0,45
1,35
2,7
| 0,15
0,3
0,9
1,8
| 0,15
0,3
0,9
1,8
| | | Current errors and phase shift in protection current transformer:(Fault conditions)
|
|
Accuracy
Class
|
permissible ratio error ”Ąat
Various percentage of rated
secondary current
|
”Ąphase shift in various percentages of rated secondary current |
Compound eror for
rated current %
| |
Minute |
Centiradian | 5P
10P
| ”Ą1
”Ą3
| ”Ą60
--
| ”Ą60
--
| 5
10
| | | Current errors and phase shift in measuring current transformer:
|
|
Accuracy
Class
|
”ĄPercentage ratio of current error for rated current percentage | |
%50 |
%120 | |
3
5
|
3
5
|
3
5
| | |
| |
| |
