Structure and purpose current transformer

The Transformers in the infrastructure systems of energy provision can have different meanings. Classic designs are used to transform individual power parameters to values suitable for carrying out measurements. There are other varieties to the list of tasks which included correction of the voltage to the level that is optimal from the point of view of further transmission and distribution of energy resource. The appointment of the current transformer determines not only its structural device, but the list of additional functions, not to mention the principle of operation.

Device transformers

Almost all versions of transformers of this type are equipped with magnetic circuits of which are supplied by the secondary winding. The last is loaded when operating in accordance with regulatory values in terms of resistance. Compliance with certain stress indicators is important for the subsequent measurement accuracy. Open coil cannot generate a compensation magnetic fluxes in the core, which contributes to the overheating of the magnetic core, and in some cases - and its combustion.

At the same time, the magnetic flux generated by the primary winding of the series has a more high performance that can also contribute to overheating of the magnetic wire and core. I must say that the current infrastructure provides a common system which is already in the current transformers and voltage. The purpose of electrotechnical unit in this case does not matter – features of functioning rather are due to the materials used. In the case of current transformers, for example, a core of magnetic core made from amorphous nanocrystalline alloys. This choice stems from the fact that the design gets the opportunity to work with a wider range of technical and operational values depending on the accuracy class.

The appointment of the current transformer

The Main task a traditional current transformer is to convert. Hardware electrical filling corrects the characteristics of the accepted current using the primary winding, included in series. In turn, the secondary winding performs the function of directly measuring the converted current. For the purpose of this part is provided for relays, measuring devices and devices of protection and automatic control. In particular, the appointment of the current transformer may consist in the measurement and accounting using devices of low voltage. Observed condition in which a high-voltage current is registered with the access of personnel to the direct observation of the process. Fixation of the working variables required for the more rational use of energy in transmission to subsequent lines. Perhaps this is one of the few common subfunctions that have transformative power and models of transformers. Read more it is necessary to consider the differences between these units.

Differences from voltage transformer

Most Often, experts point to the way to perform insulation between the windings. In current transformers the primary winding is isolated from the secondary in accordance with the indicators accept full voltage. In this case the secondary winding will be grounded, therefore the potential is the same figure. In addition, transformers operate in conditions close to the situations of short circuit, because they have a very modest level of resistance in the secondary line. This nuance is manifested specific purpose of measuring transformers of current and voltage, as well as the difference in the requirements for operating conditions.

So, if the work is under the threat of a short-circuit for power transformer voltage invalid due to the risk of an accident, for the average Converter current this mode of operation is considered normal and safe. Although, of course, there are such transformers and their threats, to prevent which provide for special protection.

Working Principle

Electromagnetic induction is the basic principle on which is based the working process of such transformers. As already mentioned, the main functional elements are magnetic conductor, and two levels of windings. To the first electric charge is supplied fromalternating current and the second level implements directly the work function in the measurement type. With the passage of the current through the windings of the induction occurs.

Further, according to the law of electromagnetic induction, which determines the purpose and the operating principle of current transformers, fixed working size on the line. The user with special equipment can identify the characteristics of magnetic flux – therefore, fixed frequency and voltage of the current source. Technical parameter survey of the performance chain will be the speed of work measurement – this value is not the target, but it is important to assess to understand the efficiency of the transformer.

Varieties of current transformers

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

Also popular toroidal model, the design of which provides for the possibility of their installation on the cable or bus. For this reason, all vanishes the need for the primary winding, which is equipped with standard current transformers and voltage. The purpose and structure of such models are determined by their special working principle – in this case the primary current will flow through the Central conductor in the casing, allowing the secondary winding to directly capture the performance. But due to various reasons, including low accuracy and unreliability of the design, such models are rarely used to assess characteristics of current. Most often they are used in purposes ancillary protective link in case of short circuit.

We Also used high voltage transformers – gas and oil. They usually involve specialized projects in industry.

Conversion

To evaluate the efficiency of the transformer was introduced, the magnitude of conversion factor. Its nominal value is typically specified in official documentation to the transformer. This ratio denotes the ratio of the primary nominal current to the similar index of the second winding. For example, it can be value 100/5 A. It can change dramatically depending on the number of sections with the turns.

Also note that the nominal rate does not always match the actual. The deviation is determined by the conditions for the operation of current transformers. The purpose and principle of operation largely determine the rates of error, but this nuance is not the reason for the refusal to take into account the nominal transformation ratio. Knowledge of the magnitude of the error, the user is able to level by means of special electrical equipment.

Installation of the current transformer

The Simplest tire models of transformers require little or no special equipment and even tools. Such a device can install a single master, using special clamping fixtures. Standard designs require the creation of a Foundation on which are mounted carrying racks. Further, the welding is attached to the frame, which will serve as the electrical box for the conclusion of the necessary equipment. The final stage is the installation of the equipment. What is a set of technical equipment determines the assignment of the current transformer and especially its future operation. At least integrates the infrastructure required for measurement of the characteristics of the service chain.

Ways to connect transformers

To facilitate wiring connection with the equipment component manufacturers put on their labeling – for example, overcurrent relays and transformers may be referred to TAA, TA1, КА1, etc. Thanks to this labeling, the staff will be able to quickly and accurately produce a pairing between the elements, which is equipped with a current transformer. The device, function and principle of operation in this case are closely interrelated and have an impact on the connection method, but considerable influence on the nature of the technical implementation of the system transformation and has served the network as such.For example, three-phase line with insulated neutral allow the installation of the transformers only in two phases. This feature is due to the fact that networks with a range of 6 -35 kV do not have the neutral wire.

Testing of transformers

The Complex span measures consists of several operations. First and foremost is a visual inspection of the object, which evaluate the integrity of the design, the correctness of the same markings, the conformity of passport data etc. followed by the demagnetization of the equipment – for example, by a smooth increase of current in the winding of the first level. Thereafter the current value gradually decreases to zero.

Next, prepare basic calibration operation, which will be subject to current transformers. The purpose and principle of operation it is important to consider if such training because the level load and other operational factors cause different values of the errors to record the characteristics of the working environment. The verification includes an assessment of the compliance of the polarity of the terminals of the windings of normative parameters, but also commit errors and their subsequent reconciliation with the values specified in the passport of the unit.

Safety transformer

The Main dangers in the operation of current transformers associated with the quality of the run windings. It is important to consider that under layers of turns works metal base, which in the bare form may represent a significant threat to staff. Therefore, a schedule of service, which regularly checks the current transformers. The purpose and principle of operation in this case can be oriented to the transformation of voltage and current measurement. In both cases, the staff should carefully monitor the condition of the windings. As measures of protection in the working design are introduced shunt short, and also supported the grounding of conclusions of a winding.

Conclusion

With increasing operating loads on the line wiring significantly reduced working life serving stations. Despite the fact that the appointment of the current transformer is not connected with the transformation of high voltage, such equipment is also subject to severe wear. In order to increase the operating life of these plants manufacturers use more sophisticated materials and electromagnetic snap, and runs the same winding. With this improved equipment for measuring relays, with the result that minimizes the error rate measurements.