Skip to main content

[ CT ] Current Transformer


A present transformer is a gadget for the change of current from a higher incentive to lower esteem, or for the change of current at a high voltage into a proportionate current at a low voltage as for the earth potential. Current transformers (CTs) are utilized related to air conditioning instruments, meters or control-mechanical assembly where the current to be estimated is of such extent that the meter or instrument curl can't helpfully be made of adequate current-conveying limit. Current transformers are additionally utilized where hv current is to be metered because of the trouble of giving satisfactory protection in the meter itself. In meter practice, CTs are utilized when the current to be estimated is more than 100 A.



The centers of CTs are normally developed with overlays of silicon steel. High-Permeability nickel steel, for example, Mumetal or Permalloy is utilized for cores where a high level of exactness is wanted. The essential winding conveys the current to be estimated and is associated with the primary circuit. The optional winding conveys a present relative to the current to be estimated and the second terminals are associated with the present windings of the meter or the instrument. Both the windings are protected from the center and from one another. The primary circuit of a CT (Fig. 2.46) is commonly a solitary turn winding B (called a bar primary)and conveys full-load current. The optional winding S has countless.

Current transformer ratios are generally specified in terms of full-load primary and secondary currents. Usually, the secondary windings are designed for rated values of 5 A, although 1 A and 2 A ranges are also used. For example, 1000/5 A current transformer may be úšed with a 5-A ammeter to measure currents up to 1000 A. Fig. 2.46 shows the connections of a current transformer.

Current Transformer Symbol

[caption id="" align="aligncenter" width="295"]CURRENT TRANSFORMER (CT) CURRENT TRANSFORMER (CT)[/caption]


The burden of a CT is the value of the load connected across the secondary terminals. It is expressed as the output in voltampere (VA), The rated burden is the value of the burden marked on the nameplate of the CT.


Under ordinary working conditions, the optional twisting of a CT is its weight and the auxiliary is constantly shut. At the point when the current flows through the essential winding a current additionally moves through the optional winding and the ampere-turns (mmf) of each winding are considerably equivalent and inverse dynamic, the auxiliary ampere tums will be really 1% to 2% not exactly essential ampere-turns, the distinction is used in charging the center. In this way, if the auxiliary twisting of a CT is opened, while the current is moving through the essential twisting, there will be no demagnetizing motion due to the secondary current. Because of the nonattendance of the counter amperetums of the optional, the unopposed essential mmf will set up an unusually high motion in the center. This motion will create over the top center misfortunes with resulting warming and a high voltage will be instigated over the optional terminals. This high voltage might be adequate to make a risk life and breakdown of the protection. Likewise, loss of exactness in the future may happen, in light of the fact that the extreme mmf leaves remaining attraction in the center. In this way, the auxiliary of a CT ought to never be open when the essential is conveying current.

Read More 

Ground Wire In Transmission Line

Popular posts from this blog

Limitations of Terzaghi Theory

Limitations of Terzaghi Theory The value of the coefficient of consolidation has been assumed to be constant.  The distance d of the drainage path cannot be measured accurately in the field. The thickness of the deposit is generally variable, and an average value has to be estimated.  There is sometimes difficulty 1n locating the drainage face, sometimes thin previous seams that can act as good drainage face are missed in the boring operations. The equation is based on the assumption that the consolidation is one-dimensional. In the field, the consolidation is generally 3-dimensional. The lateral drainage may have a significant effect on the time rate of consolidation. The initial consolidation and secondary consolidation have been neglected. Sometimes these form an important part of the total consolidation. In actual practice, the pressure distribution may be far from linear or uniform. Read More Muller-Breslau principle

Price Guard Wire Method

Price Guard Wire Method Some form of  Price Guard Wire Method  is generally used to eliminate the errors caused by leakage currents over insulation. Fig. 3.14 illustrates the operation of This Method. In fig 3.14(a), a high resistance mounted on a piece of insulating material is measured by the ammeter voltmeter method. The micro-ammeter measures the sum of the current through the resistor (IR) and the current through the leakage path around the resistor. The measured value of resistance computed from the readings indicated on the voltmeter and the microammeter, will not be a true value but will be in error.   Figure 3.14 Application of  guard  circuit for measurement of high resistance In fig, 3.14 (b), the  guard  terminal has been added to the resistance terminal block. The  guard  terminal surrounds the resistance terminal entirely and is connected to the battery side of the micro-ammeter. The leakage current IL now bypasses t

Negative Booster

Negative booster A negative booster is employed to conform to the regulation that the potential difference between any two points of the rail return shall not exceed 7 V. Two boosters, positive and negative, are used which are mechanically coupled together and driven by a DC motor. The positive booster is connected to the trolley wire (near the generating station) and the negative booster (separately excited) is connected to the track rail.  The 'positive booster' adds voltage to the line while the 'negative booster lowers the potential of the point it is connected to. As we go along the trolley wire away from the generating station/sub-station, the potential drop increases, and the voltage of the trolley wire falls. Since the current returns via the track rail points away from the generating station acquire high potentials. This potential is brought down by the negative boost provided by the negative booster. When the load is sufficiently far away from the generating stati