It can raise or lower the voltage in a circuit but with a corresponding decrease or increase in current. Electrical engineering multiple choice questions and answers. The power transformer is used to convert voltage using the number of windings in the two coils as ratio, while the current transformer is just an inductor placed around a wire to sense the magnetic field caused by the changing current. Potential transformers pts and current transformers cts. Transformation ratio for voltage transformer primary. Transformer, current an instrument transformer for the measurement and monitoring of large currents by means of standard measuring instruments and automatic control and monitoring devices. Voltage transformers are in most situations connected between phase. 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. A current transformer is a device which produces an alternating current in its secondary which is proportional to the alternating current in its primary. Which of the following does not change in a transformer. Voltage transformer article about voltage transformer by. The voltage in the load loop is measured across rl and is induced in the load inductor by the source inductor. Voltage transformer potential transformer these are used for measurement of high voltages using low range voltmeters. For a primary current greater than 10 times the rated current, in other words here.
A transformer couples two circuits magnetically rather than through any direct connection. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. 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. In other words we can say that the voltage, actually applied to the primary. Current transformer definition of current transformer by. But, keep in mind that as the reflected burden resistance becomes higher, your transformer will have more voltage drop and it will behave more like a voltage transformer. Current transformers cts are instrument transformers that are used to supply a reduced value of current to meters, protective relays, and other instruments.
It also serves to insulate apparatus from the potential of the circuit that is being measured or monitored. The basics of current transformers nk technologies. Electrical engineering multiple choice questions and. Current and voltage transformer symbols and simplified concepts 5 i 1 i 2 v 1 v 2 symbol of a current transformer symbol of a voltage transformer conceptual picture of a current transformer. A current flowing in the primary coil generates a timevarying magnetic field in the core. In other words, cts work at their best when they are connected to very low impedance burdens. Generally, aircore transformers are used when the voltage source has a. Transformer, voltage an instrument transformer for stepdown of voltage in measurement and monitoring circuits. Most often, the older relay gets replaced with a newer relay with the rest of the installation such as current transformer ct and lead. Current transformers reduce high voltage currents to a much lower value and provide a. The basics of current transformers current sensors for. So that amount of current will flow across the inductor which can induce the same amount of the applied voltage. A current transformer is a type of stepup transformers while voltage transformer is a type of step down transformers. In principle, the only difference between a current transformer and a voltage transformer normal type is that the former is fed with a constant currentwhile the latter is fed with a constant voltage, where constant has the strict circuit theory meaning.
Damping of the ferroresonance in voltage transformers type range tjx. Medium voltage switchboard system from 1 to 36 kv sepam protection relays masterpact protection switchgear from 100 to 6300 a trihal mvlv dry cast resin transformer from 160 to 5000 kva evolis mv vacuum switchgear and components from 1 to 24 kv. When the circuit burden gets too large, the ct secondary voltage becomes. The transformer winding voltage ratio is directly proportional to the winding turns ratio. Protection of single pole insulated voltage transformers against feroresonance phenom ena is stated in appendix 3. 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. The current in the secondary coil always changes by the inverse of the ratio by which the voltage changes. Difference between current transformer and voltage. Correct operation of currentcurrent, voltagevoltage, or currentvoltage devices usually depends on the relative instantaneous directions.
The constant current transformer 38 the constant voltage transformer 40 saturable reactor control of a. 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. Transformer, current article about transformer, current. Transformer definition, a person or thing that transforms. Voltage transformer how is voltage transformer abbreviated. Primary winding of voltage transformer is connected across line whose voltage is to be measured. I 1 n 2 i 2 n 1 i 1 i 2 n 1 n 2 i 1 x n 1 i 2 x n 2 ampere lilitan selalu seimbang i1 i2. The operation of current transformer is similar to the conventional power transformer.
Narrowprofile current transformer with a builtin converter, with an output of 0. Allentown, pa abstract more and more substations are retrofitted with numerical relays, meters and monitoring devices. Does a current transformer produce a proportional voltage. It can be designed to step up or step down voltages and works on the magnetic induction principle. Jkm5c single ratio ansi metering class at 60hz continuous thermal rating factor. The word primary refers to the primary winding of a transformer. Cts are basically stepup voltage transformers, on the other hand, these are stepdown transformers in view of current. 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. The word monitored refers to the circuit under test or being measured.
Cts provide isolation from the high voltage primary, permit grounding of the secondary for safety, and step down the magnitude of the measured current to a value that can be. The low secondary voltage allows protective relay equipment and measuring instruments to be operated at a lower voltages. Ac voltage can be transformed to another voltage of the same frequency using a transformer. Instrument transformers convert signal levels from dangerous high voltage or inconvenient high current, or current at high voltage to levels appropriate for metering. Commonly used core materials are air, soft iron, and steel. Compare the results found in step 1 with those of step 3, and the. Cts current transformers pts potential transformers. Difference between current transformer,voltage transformer. High short time current dan rating arus kecil lilitan amper kecil.
If the voltage is raised to 10 times its original value by the transformer, the current in the secondary coil will be reduced to onetenth the value of the current in the primary coil. Current transformer basics and the current transformer. A secondary shortcircuit will cause the unit to overheat and fail in a very short period of time. It is used to raise or lower voltage and current between one circuit and the other, and plays a major role in almost all ac circuits. Typically the ct ratios must be the same, but different ratios can be used with a.
Can resistance change or am i missing something else. Indoor instrument transformers schneider electric belgie. 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. Medium voltage products current and voltage instrument. It transforms the high voltage current into the low voltage current due to which. Doubling voltage and halving the current seems to completely contradict this basic law. Projects on transformer, distribution transformer, electrical transformer, current transformers, distribution transformers repairs, transformer oil, voltage. Typically current transformers consist of a silicon steel ring core wound with many. Calculation of cts if the current transformer has primary to secondary current ratio of 100. The primary coil is connected to an ac voltage source.
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. Current transformer definition is a transformer whose primary carries the whole of an alternating current to be measured or controlled and whose secondary is connected to a measuring or control device. Model around small power transformers, with up to 63 mva and up to. The technical guide these technical guides help you comply with installation standards and rules i. The instrument transformers like voltage transformer and current transformer are used for connecting the electrical instruments to the measuring instruments. The voltage circuit is connected across the secondary winding. What is a voltage transformer and a current transformer. The output of the summing transformer is connected to the input of a wt series watt transducer. Scribd is the worlds largest social reading and publishing site. 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. 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 meter. A voltage transformer is intended to present a negligible load to the supply being measured.
This fact ascertains that the current will not increase to an abrupt value. A current transformer is used to calculate current and power, to operate the protective relay and to monitor the power grid operation, etc. There is no sharp border between a voltage and current transformer. Transformer core the composition of a transformer core depends on voltage, current, and frequency. Chapter 25 electric power measurement and control systems. The transformer works on the principle of electromagnetic induction. Transformers are a necessary part of all power supplies. All schneider electric instrument transformers are in conformity with iec. A distinction is made between ac transformers usually. A transformer is a static or stationary piece of apparatus by means of which electric power in one circuit is transformed into electric power of the same frequency in another circuit. Voltage transformer which is also called as a potential transformer. K tf values required in practice depend on relay type and design.
In other words, the number of turns and the current in the primary and. In other words, the polarizing voltage is 3 times the zerophase sequence. In the limiting case of zero burden impedance and a small zx2 i1. Voltage transformers are together with current transformers known as instrument transformers. Recommendations are provided by manufacturers see application guides. In mv electrical distribution, the high current and voltage values mean that they. A transformer is an electrical apparatus designed to convert alternating current from one voltage to another.