BPL TYPE CURRENT TRANSFORMER
Indotech BPL (types) Current Transformer (CT) – A current transformer is a type of transformer that is used to measure alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary. They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device.
- Bar types are available with higher insulation levels and are usually bolted to the current caring device.
- Bar type current transformers are insulated for the operating voltage of the system.
- Bar-type CTs operate on the same principle of window CTs but have a permanent bar installed as a primary conductor
TYPE OF METERS : BPL TYPE CT
BAR PRIMARY TYPE :
Coil is wound on a toroidal core of high per-me ability silicon steel. The Bar which is passed through the core, acts as single turn on the primary side and the turns on the core act as secondary. BPL CT’s are available both for metering as well as for protective purposes.
(a) METERING CT’s :
These CT’s are meant for feeding measuring instruments. Accuracy class of the CT will be selected on the basis of the accuracy class of the instrument to be operated. When the instrument is installed far away from the CT, the secondary is chosen as 1A instead of 5A.
(b) PROTECTION CT’s :
These CT’s are meant for operating the protective devices viz., Circuit Breakers and Relays etc. The magnitude and the nature of fault to be controlled and the electrical characteristic of the device decide the class and type of Current Transformer.
PRINCIPAL OF OPERATION
The standards define a voltage transformer as one in which “the secondary voltage is substantially proportional to the primary voltage and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections.”
This, in essence, means that the voltage transformer has to be as close as possible to the “ideal” transformer. In an “ideal” transformer, the secondary voltage vector is exactly opposite and equal to the primary voltage vector, when multiplied by the turns ratio.
| Limits of Errors & Phase Displacement As per ISS 2704/81 | ||||||||
| Class | Percentage Current Error at Percentage of Rated Current | Phase Displacement in Minutes at Percent of Rated Current | ||||||
| 0.1 0.2 0.5 1.0 | 5% 0.4 0.75 1.5 3.0 | 20% 0.2 0.35 0.75 1.5 | 100% 0.1 0.2 0.5 1.0 | 120% 0.1 0.2 0.2 1.0 | 5% 15 30 90 180 | 20% 8 15 45 90 | 100% 5 10 30 60 | 120% 5 10 30 60 |
