02-09-2017, 12:21 PM
Core Balance Current Transformer or CBCT is a ring-type current transformer through the center of which passes a three-core cable or three single-core three-phase system cables. This type of current transformer is normally used for ground fault protection for low and medium voltage systems.
The CBCT secondary is connected to the ground fault relay. During the normal operating condition as the vector sum of the three-phase current, ie (Īa + Īb + Īc = 0) is zero, therefore there will be no residual current in the primary. Here the residual current means zero sequence current. Therefore, there will be no flow developed in the CBCT core and therefore there is no current in the secondary circuit of CBCT.
Current transformers reduce high voltage currents to a much lower value and provide a convenient way to safely monitor current current flowing in an AC transmission line using a standard ammeter. The operating principle of a basic current transformer is slightly different from that of an ordinary voltage transformer.
Unlike the voltage or power transformer seen above, the current transformer consists of one or very few turns as its primary winding. This primary winding may be a single plane turn, a coil of high strength wire wound around the core, or simply a bus or bus bar positioned through a central hole as shown.
Due to this type of arrangement, the current transformer is often referred to as a "serial transformer", since the primary winding, which never has more than a few turns, is in series with the current conductor supplying a load .
However, the secondary winding may have a large number of coil turns wound onto a laminated core of low loss magnetic material. This core has a large cross-sectional area so that the magnetic flux density created is low using wire of much smaller cross-sectional area, depending on how much the current must be decreased when it tries to output a constant current, regardless of the connection load.
The secondary winding will supply a current in a short circuit, in the form of an ammeter, or in a resistive load until the voltage induced in the secondary is large enough to saturate the core or cause a fault due to an excessive voltage failure.
Unlike a voltage transformer, the primary current of a current transformer does not depend on the secondary charge current, but is controlled by an external load. The secondary current is usually classified into a standard Ampere of 1 Ampere or 5 Amperes for higher primary currents.
The CBCT secondary is connected to the ground fault relay. During the normal operating condition as the vector sum of the three-phase current, ie (Īa + Īb + Īc = 0) is zero, therefore there will be no residual current in the primary. Here the residual current means zero sequence current. Therefore, there will be no flow developed in the CBCT core and therefore there is no current in the secondary circuit of CBCT.
Current transformers reduce high voltage currents to a much lower value and provide a convenient way to safely monitor current current flowing in an AC transmission line using a standard ammeter. The operating principle of a basic current transformer is slightly different from that of an ordinary voltage transformer.
Unlike the voltage or power transformer seen above, the current transformer consists of one or very few turns as its primary winding. This primary winding may be a single plane turn, a coil of high strength wire wound around the core, or simply a bus or bus bar positioned through a central hole as shown.
Due to this type of arrangement, the current transformer is often referred to as a "serial transformer", since the primary winding, which never has more than a few turns, is in series with the current conductor supplying a load .
However, the secondary winding may have a large number of coil turns wound onto a laminated core of low loss magnetic material. This core has a large cross-sectional area so that the magnetic flux density created is low using wire of much smaller cross-sectional area, depending on how much the current must be decreased when it tries to output a constant current, regardless of the connection load.
The secondary winding will supply a current in a short circuit, in the form of an ammeter, or in a resistive load until the voltage induced in the secondary is large enough to saturate the core or cause a fault due to an excessive voltage failure.
Unlike a voltage transformer, the primary current of a current transformer does not depend on the secondary charge current, but is controlled by an external load. The secondary current is usually classified into a standard Ampere of 1 Ampere or 5 Amperes for higher primary currents.