The working principle of a transformer is very simple. A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. Abb complete and comprehensive range of ct current trans formers is the. The current sense transformers turn ratios need to be the same. Apr 16, 2011 current transformers principle of operation of ct a current transformer is defined as as an instrument transformer in which the secondary current is substantially proportional to the primary current under normal conditions of operation and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections. Current and voltage transformers may be freestanding devices, or they may be built inside the bushing of some power apparatus such as a circuit breaker or a power transformer with a grounded tank. A transformer is a static device which transfers electrical energy from one circuit to another through the process of electromagnetic induction.
Pdf method of current transformer metrological properties. Pa 123pa 145 current transformer installation and operation manual your safety first. The current transformer is designed to connect in series with the line to transform the line current to the standard 5 amperes suitable for the. A study of the current transformer with particular. The following calculations can be used to select transformer reset resistors r1 and r2. This would cause a voltage drop in the primary impedance that would bring about an excessive error in ratio of phase angle. In other words, for a transformer there is no direct electrical connection between the two coil windings, thereby giving it the name also of an isolation transformer. In this video you will learn about what is current transformer, important concepts of current transformer, how current transformer work, use of. Mar 10, 2016 to start with, both are instrument transformers basically used for measurement and protection purpose in power systems.
Tape wound measuring and protection current transformers. It produces a current in its secondary which is proportional to the current in its primary. Portable ct pt analyzertransformer testgfuve electronics. When current flow exceeds that rating, the metering core will become saturated, thereby limiting the amount of current level within the device. It can be designed to step up or step down voltages and works on the magnetic induction principle. Current transformers are available at mouser electronics. Generally, the primary winding of a transformer is connected to the input voltage supply and converts or transforms the electrical power into a magnetic field.
Polarity refers to the instantaneous direction of the primary current with respect to the secondary current and is determined by the way the transformer leads are brought out of the case. Effects of a current transformer s magnetizing current on the driving voltage in selfoscillating converters. The main elements of the transformer are the primary and secondary windings and the steel core. While the latter configuration would not be used today, one may be required to make this calculation on an existing system. Current sense transformer application design guidelines by ariel general applications engineer, datatronic distribution inc. A current transformer, abbreviated ct, is a type of transformer used to measure the current of a given circuit.
The basics of current transformers nk technologies. Instrument transformers convert signal levels from dangerous high voltage or inconvenient high current, or current at high voltage to levels appropriate for metering. Pdf effects of a current transformers magnetizing current. On subtractive polarity transformers the h1 primary lead and the x1 secondary lead will be on the same. It is most commonly used to increase step up or decrease step down voltage levels between circuits. From the above equation, by knowing secondary ammeter current and current ratios, we can easily determine the current flowing through the primary which is connected to the main line.
A current transformer is an instrument transformer, used along with measuring or protective devices, in which the secondary current is proportional to the primary current under normal conditions of operation and differs from it by an angle that is approximately zero. It buffers the meter from experiencing excessive torques that might be. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to. The transformers consist of a core, a primary and a secondary winding. When the circuit burden gets too large, the ct secondary voltage becomes distorted. The core of the current transformer is built up with lamination of silicon steel. Observe the technical data given in the rating plate and in the specification. Instrument transformer basic technical information and. N 5 freeelectricity current transformer you can make 201120 refer to the photo below. The classification of protection current transformers follows the following. Coupled with an ammeter, cts are used to protect the main lines of the power grid, by measuring highvoltage electrical current and preventing damage to sensitive equipment. The core of the transformer is made up of silicon steel in order to provide a continuous magnetic path. Currentsense transformer application design guidelines.
A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load. When an alternating current flows through the primary winding, a magnetic flux is created which then. Cts current transformers pts potential transformers. This is the reason why our instruction begins with the following guidelines. Pdf current transformer ct is one of the important element of power system protection. To enquire about class px current transformers consult the factory with the above. They are accurate, easy to implement, and reliable under harsh. Nov 15, 2019 a current transformer is an instrument transformer, used along with measuring or protective devices, in which the secondary current is proportional to the primary current under normal conditions of operation and differs from it by an angle which is approximately zero. Transformer basic objective introduce basic transformer theory as it relates to diagnostics provide a better understanding of the diagnostic test environment identify important information that should be collected in the diagnostic test process. If i turn this heater on and pass one leg of its cord. Electrical tutorial about current transformer basics and current transformer theory on how the current transformer works with just one secondary winding. The fundamentals of current sense transformer design patrick a.
The current transformer function is different than that of a voltage transformer. Operating a current transformer as a voltage transformer provides a costeffective alternative to injection transformers sold as test accessories see pdf. Current transformer design guide an effective design of a ring type c. Construction of a transformer the transformer mainly consists of the magnetic circuit, electric circuit, dielectric circuit, tanks, and accessories. This protects connected metering devices from overloading in the presence of fault level current flows. Cattermole typically, the transformer is designed so that the impedance of the primary winding is much greather than the shunt resistance reflected into the primary side and thus the primary impedance is mostly resistive.
Current transformer white paper the basics of current transformers ratio the ct ratio is the ratio of primary current input to secondary current output at full load. A current transformer ct is a type of transformer that is used to reduce or multiply an alternating current ac. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the. A transformer has no moving parts and is a completely. High voltage products pa 123pa 145 current transformer. What is the working principle of a current transformer. Apr 25, 2017 the current transformer the current transformer c. The standard for precise current measurement in instrumentation and other high reliability equipment applications has been the current sense transformer. Chapter 16 current transformer design university of north. Current transformers ct are devices that are used to transform the current from a high current into a lower current so that the power can then be measured and controlled. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in an ac. Jun 02, 2015 as an example, a typical 100 to 5a current transformer has a nominal ratio of single primary turn to 20 secondary turns or 1. Pdf during transformation of power frequency currents inductive current transformers cts are characterized by precise, acceptable in. The resultant accuracy depends on these parameters.
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