Device and purpose of the current transformer

Transformers in the infrastructure of power supply systems can have different meanings. Classical designs are used to convert individual current parameters to values that are optimally suited for conducting measurements. There are other varieties, whose list of tasks includes correction of voltage characteristics to a level that is optimal from the point of view of further transmission and distribution of the energy resource. In this case, the purpose of the current transformer determines not only its construction device, but also a list of additional functions, not to mention the principle of operation.

Installation of transformers

Virtually all modifications of transformers of this type are equipped with magnetic circuits, which are supplied with a secondary winding. The latter is loaded during operation in accordance with the regulatory values in terms of resistance. Observance of certain load indices is important for the subsequent accuracy of the measurement. Open winding can not compensate for magnetic fluxes in the core, which contributes to the overheating of the magnetic circuit, and in some cases to its combustion.

At the same time, the magnetic flux generated by the winding of the primary row is characterized by higher performance characteristics, which can also contribute to overheating of the magnetic wire and its core. It must be said that the current-carrying infrastructure forms a common system on which current and voltage transformers are based. The purpose of the electrotechnical unit in this case is of no fundamental importance - the features of functioning are determined by the materials used. In the case of current converters, for example, the core of the magnetic circuit is made of amorphous nanocrystalline alloys. This choice is due to the fact that the design is able to work with a wider range of technical and operational values, depending on the accuracy class.

Current transformer assignment

The main task of the traditional current transformer is conversion. The hardware electrotechnical filling corrects the characteristics of the serviced current, using for this purpose the primary winding included in the circuit in series. In turn, the secondary winding serves as a direct measure of the converted current. For this purpose, relays with measuring devices, as well as protection and automatic regulation devices are provided in this part. In particular, the purpose of a current measuring transformer can be to measure and record with low-voltage devices. At the same time, the condition is satisfied that a high-voltage current is recorded with the personnel's access to direct observation of the process. The fixation of operating values is required for a more rational use of energy in transmission in subsequent lines. Perhaps, this is one of the few common subfunctions that transformers and power transformers have. More details should be considered differences between these units.

Differences from the voltage transformer

More often than not, experts point to a method of performing insulation between windings. In current transformers, the primary winding is isolated from the secondary in accordance with the values of the total received voltage. In this case, the secondary winding will be grounded, and therefore its potential corresponds to a similar parameter. In addition, the measuring transformers operate under conditions close to short-circuit situations, since they have a very modest level of resistance on the secondary line. In this nuance, the specific purpose of the current and voltage measuring transformers is revealed, as well as the difference in the requirements for the operating conditions.

So, if work under the threat of a short circuit for a power transformer is unacceptable because of the risk of an accident, then for a normal current converter this mode of operation is considered normal and safe. Although, of course, there are such transformers and their own threats, for the prevention of which special protection is provided.

Principle of operation

Electromagnetic induction is the basic principle on which the working process of such transformers is based. As already noted, the main functional elements are a magnetic conductor and two levels of windings. The first is supplied with an electric charge from the alternating current, and the second level implements the immediate operational function in the form of a measurement. As the current flows through the turns of the winding, induction occurs.

Further, according to the law of electromagnetic induction, which just determines the purpose and principle of operation of current transformers, the operating values on the line are fixed. The user with the help of special equipment can determine the characteristics of the magnetic flux - hence, the frequency and voltage of the current source are fixed. The technical parameter of the survey of the performance of the circuit will be the speed of the metering product - this value is not the target, but it is important to evaluate it to understand the efficiency of the transformer itself.

Types of current transformers

There are three main categories of current converters. The most common are so-called dry transformers, in which the first level of the winding is not completely isolated from the first. Accordingly, the secondary current parameters directly depend on the conversion factor.

Also popular toroidal models, the design of which provides for the possibility of their installation on the cable or bus. For this reason, the need for a primary winding, which is equipped with typical current and voltage transformers, is completely lost. The purpose and design of such models are determined by their special operating principle - in this case the primary current will flow through the central conductor in the housing, allowing the secondary winding to directly record performance. But for various reasons, including those associated with low-precision measurements and unreliable design, such models are rarely used to estimate current characteristics. Most often they are used for the purpose of an auxiliary protective link in the event of a short circuit.

Also used and high-voltage transformers - gas and oil. They are usually involved in specialized projects in the industry.

Coefficient of transformation

To evaluate the efficiency of the transformer itself, the conversion factor was introduced. Its nominal value is usually indicated in the official documentation for the transformer. This ratio denotes the ratio of the primary rated current to that of the second winding. For example, it can be a value of 100/5 A. It can vary dramatically depending on the number of sections with turns.

It should also be taken into account that the nominal coefficient does not always correspond to the actual coefficient. The deviation is determined by the conditions under which the current transformers are operated. The purpose and principle of operation largely determine the error indicators, but this nuance is not the reason for refusing to take into account the nominal coefficient of transformation. Knowing the magnitude of the same error, the user can neutralize it by means of special electrical equipment.

Installation of a current transformer

The simplest bus models of transformers practically do not require the use of special equipment and even tools. Such a device can install one master using a special clamping fixture. The standard designs require the creation of a foundation on which the bearing racks are mounted. Then the electric frame is attached to the frame, which will act as a kind of electrical box for the conclusion of the necessary equipment. At the final stage, the equipment is installed. What will be the set of technical equipment, determines the purpose of the current transformer and the features of its future operation. At a minimum, the infrastructure required to perform measurements of the characteristics of the served circuit is integrated.

Ways to connect transformers

To simplify the procedure for connecting the wiring to the equipment, the component manufacturers affix to them the marking - for example, current relays and transformers can be designated TAa, TA1, KA1, etc. Thanks to this marking, the service personnel can quickly and accurately interface between the elements that are equipped with a current transformer . The device, purpose and operation principle of the installation in this case are closely interrelated and influence the way of connection, but the service network as such has a considerable influence on the technical implementation of the conversion system. For example, three-phase lines with isolated neutral allow the installation of transformers in only two phases. This feature is due to the fact that networks with a range of 6 -35 kV do not have a zero wire.

Verification of transformers

The complex of verification measures consists of several operations. First of all, this is a visual inspection of the object, during which the integrity of the structure is evaluated, the correctness of the same markings, compliance with passport data, etc. Then the equipment is demagnetized - for example, by smoothly increasing the current on the first-level winding. After that, the current value gradually decreases to zero.

Further, the basic verification actions are prepared, which will be subjected to measuring current transformers. The purpose and principle of operation is important to take into account in this preparation, since the load level and other operational factors cause different errors in the registration of the characteristics of the working environment. The verification itself provides for an assessment of the correspondence of the polarity of the winding terminals to the standard parameters, as well as fixing the errors with their subsequent verification with the values indicated in the unit's passport.

Safety when operating a transformer

The main hazards in the operation of current transformers are related to the quality of the windings. It is important to take into account that under the layers of turns a metal base works, which in a bare form can pose a considerable threat to personnel. Therefore, a maintenance schedule is drawn up, according to which the current transformers are regularly checked. The purpose and principle of operation in this case can be oriented both to the transformation of the voltage and to the measurement of the current. In both cases, maintenance personnel should carefully monitor the condition of the windings. As protection measures, shunt shorts are introduced into the working structure, and grounding of the winding leads is also maintained.

Conclusion

As the operational loads on the power line increase, the service life of the service stations is markedly reduced. Despite the fact that the designation of the current transformer is not associated with the transformation of high voltage, such equipment is also subject to severe wear. In order to increase the operational life of such plants, manufacturers use more technological materials for both electromagnetic equipment and for the same winding. Along with this, the equipment at the measuring relays is improved, as a result of which the error of measurement is minimized.