Current Transformer vs. Voltage Transformer

There are a number of  the electrical transformers which  is manufactured and produced for various functions and requirements. Regardless of their particular style and design variations, various kinds utilize exactly the same concept of Michael Faraday. Which states the interaction of electric and magnetic field  produces an electromotive force, changing electric field produces magnetic field whereas changing magnetic field produces an electric field. Two main types of transformers i.e current transformer and voltage transformers have many differences but the major one is that voltage transformer is used to regulate the voltage at the secondary side of the transformer  whereas in current transformer current is regulated  on the secondary side, keeping in mind the product of voltage and current which is power remains the same, if current is regulated either it is raised or lowered voltage will reciprocally change its value to keep the value of power, because power is the product of current and voltage. In voltage transformer,  Secondary current is directly linked with the Primary current. Secondary current is dependent upon the voltage in addition to the load resistance. whereas in a Current transformer: Secondary could be short-circuited. The open secondary may lead to failure of the transformer. The current transformer in addition to the potential transformer is referred as instrument transformer.

What is Voltage Transformer?

Voltage transformer which is also called as a potential transformer. It employed in electrical energy power system for stepping down the voltage of the system to some protected value which is often provided to low rating meters and relays. Commercially accessible relays and meters utilized for coverage and metering are prepared for low voltage, so the potential transformer is normally used for stepping down the voltage in distribution systems. But it can be used to step up the voltage as well. In transmission lines where the sole aim is to minimize the line losses, potential transformer serves the purpose, it steps up the voltage so that line losses can be avoided as much as can. Therefore, usually in transmission lines, voltages are very high. In the case of the typical step-down transformer. A voltage transformer concept or potential transformer concept is the same as a theory of basic  step down transformer. Between the phase and the ground primary of the voltage transformer is connected. voltage transformer has lower primary turns than its secondary windings, for the purpose of stepping down. The  voltage of the system is applied over the terminals of the primary winding of that transformer, after which  secondary voltage appears in proper proportion over the secondary terminals of the potential transformer. Normally the secondary voltage is 110 volts. The ideal voltage transformer is one in which the ratio of primary and secondary voltages is same as the turn ratio, as turn ratio is the ratio of the primary and secondary wire turns and it decides the function of the transformer as step up or step down. but in actual transformers phase angle between the secondary and primary voltage vary and voltage ratio gives  an error. Phasor diagrams help in understanding those errors.

What is Current Transformer?

Current transformer which is often referred as CT regulates alternating current i.e on its secondary terminal alternating current is proportional to the value of current on its primary. A current transformer is normally used to provide isolated lower current on its secondary terminals. Current transformers are utilized broadly for the purpose of computing current and checking the whole process of the power grid. Together with voltage prospects, revenue-grade Current transformers  force the electric powered utility’s watt-hour gauge on practically every building with three-phase services and single-phase services more than Two hundred amperes. Transformers with High-voltage current  are attached to porcelain ceramic or polymer bonded insulators to segregate them from the ground. Several CT designs slip across the bushing of the high-voltage transformer or even circuit breaker, which immediately facilities the conductor within the CT window. Current transformers could be attached to the lower voltage or even high voltage prospects of a power transformer. Current transformers can be used to keep an eye on dangerously higher currents or currents at risky high voltages, so excellent proper care should be ingested the structure and use of CTs during these scenarios. The secondary of an existing transformer really should not be turned off from the load while current is within the primary, as the secondary will endeavor to carry on driving current into a highly effective limitless impedance as much as its insulation breakdown voltage and, therefore, give up operator safety. Current transformers decrease high voltage currents to some reduced value and supply a handy method of properly checking the particular electric powered current moving within an AC transmission line utilizing a standard ammeter. The key  operation of the current transformer is absolutely no different from those of a regular transformer.

Key Differences between Current Transformer and Voltage Transformer

  1. In current transformer current and density vary over a wide range but in potential or voltage transformer it varies over a small range.
  2. The primary of the current transformer has small voltage across it while that of the potential transformer has a full supply voltage
  3. A current transformer is applied in the circuit in series while the potential transformer is applied in parallel
  4. Primary current of the transformer is independent of the load while that of potential difference depends on the load
  5. Secondary of the current transformer is almost short whereas secondary of the potential transformer is almost open
  6. One can measure high voltages by small voltmeters using potential transformer whereas high currents are measured with small ammeters using current transformers
  7. Primary current is independent of the load  whereas  primary current of voltage transformer depends on external conditions that are load
  8. The primary of the current transformer is linked within the power line. The secondary winding supplies for the devices and relays a current that is a constant small fraction of the current within the line, Likewise, a potential transformer is associated with its primary in the power line. The secondary supplies the equipment and relays a voltage that is a known fraction of the line voltage.

Video Explanation

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