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Power Flow and Electric Machinery Basics
Published in Pedro Ponce, Arturo Molina, Omar Mata, Luis Ibarra, Brian MacCleery, Power System Fundamentals, 2017
Pedro Ponce, Arturo Molina, Omar Mata, Luis Ibarra, Brian MacCleery
A current transformer differs from the other transformers described in this chapter as its windings are loosely coupled. Unlike all the other transformers, the mutual flux ΦM $ \Phi M $ is smaller than the leakage flux ΦL $ \Phi L $ . Because of the loose coupling, the voltage and current ratios do not hold. Nevertheless, the secondary current in a current transformer is directly proportional to the much larger primary current, and the device can provide an accurate sample of a line’s current for measurement purposes. Current transformer ratings are given as ratios of primary to secondary current. A typical current transformer ratio might be 600 : 5, 800 : 5 or 1000 : 5. A 5[A] $ 5\ [A] $ rating is standard on the secondary of a current transformer.
Real-World Control Device Interfacing
Published in A. Arockia Bazil Raj, FPGA-Based Embedded System Developer's Guide, 2018
Next, we discuss current measurement. A current transformer is a device that is used for the transformation of current from a higher value into a proportionate current to a lower value. It transforms a high-voltage current into a low-voltage current such that the heavy current flows through transmission lines and is safely monitored by an ammeter or other digital measurement system. A current transformer is used with an AC instrument, meter or control apparatus when the current to be measured is of such magnitude that the meter or instrument coil cannot conveniently be made of sufficient current carrying capacity. A current transformer is shown in Figure 9.21. The primary and secondary currents of current transformers are proportional to each other. A current transformer is used for measuring high-voltage current because of the difficulty of inadequate insulation in the meter itself. The current transformer is used in meters for measuring current up to 100 A. The core of the current transformer is built up with lamination of silicon steel. For a high degree of accuracy, Permalloy or Mumetal is used for making cores [121,122]. The primary windings of current transformers carry the current to be measured, and it is connected to the main circuit. The secondary windings of the transformer carry current proportional to the current to be measured, and it is connected to the current windings of the meters or the instruments. The primary and secondary windings are insulated from the cores and each other. The primary winding is a single-turn winding and carries the full load current. The secondary winding of the transformer has a large number of turns.
Transformers
Published in David W. Tyler, Electrical Power Technology, 2016
The primary of the current transformer is connected in series with the load on the circuit, replacing an ammeter, and has an extremely small voltage drop. The core flux is therefore small. (See e.m.f. equation.) The value of the primary current is determined entirely by the load in the main circuit and not by the load on its own secondary as in the case of the double-wound power transformer. The current transformer secondary load is an ammeter with a low impedance so that the terminal voltage is low, the effective load being typically between 2.5 VA and 30 VA.
Detection of Power Theft in Low Voltage Distribution Systems: A Review from the Indian Perspective
Published in IETE Journal of Research, 2022
Arvind Kumar Gupta, Aurobinda Routray, VN Achutha Naikan
Gupta et al. have proposed a novel and low-cost method to identify the electricity pilferage in [11] through the unauthorized load connection and bypassing of the energy meter with no changes in the existing infrastructure. In this system, the two ends of the consumer's service line are under surveillance. The zone of possible power theft is identified by two low pass (LP) traps. For effective detection of unauthorized load connection, a high-frequency signal will be injected from a high-frequency signal generator through a coupling circuit to the line section between LP filter blocks. A microcontroller unit (MCU) measures current in the line section ascribed to a high-frequency component. The current is sensed by a current transformer (CT). The high-frequency component of the current will be separated from the line frequency component by power spectral density (PSD). The magnitude of the said current as ascertained by analog to digital converter (ADC) of the MCU and a threshold would decide upon the presence of any power theft situation. The proposed method in [11] is shown in Figure 7.
Impulse-voltage Measurement of Distribution-class Surge Arresters by D-dot Probes
Published in Electric Power Components and Systems, 2011
Current transformer “coil” measures total (algebraic) current on a conductor threading through it. Like the B-dot probe, it actually senses magnetic field, not current, even though the output results in a voltage that may drive a current through a load. It consists of a toroidal core of high-permeability material around which the coil is wound. If a time-dependent current flows through the toroid hole, the magnetic field of the former threads through the coil and induces a voltage at the output [18, 21].