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What is purpose of demagnetizing test during current transformer test?
Wiki User
∙ 12y ago
The residual magnetisation present in the current transformer coils may cause the errors during measurement of high currents. So that it is necessary to check that.
Wiki User
∙ 12y ago
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Why are stripes of iron plates joined instead of using a single block of iron core in a transformer?
To reduce heat generated and eddy current losses in transformer's core during operation.
What is current voltage transformer?
A transformer is a device that steps up, or steps down voltage. During this process current is also stepped up or down:however, voltage and current are inversely proportional ( meaning an increase in voltage results in a decrease in current and vice versa ) As an example: A step up transformer of 10:1 ratio with 12 volts and 10 amper of current applied to the primary will have ten times the voltage ( 120 volts ) and ten times less current ( 1 amrere ) at the secondary...and a step down transformer with the same turns ratio with 120 volts and 1 ampere applied to the primary will have 12 volts and ten ampere available at the secondary. The electricity supplied into homes and business uses wires carrying very high voltage and low current over long distances, then uses step down transformers to step down the voltage and step up the current. However, in power engineering and protective relaying applications, there are what are called "instrument transformers" which have the specific purpose of providing information to devices (such as relays or meters) about the voltages or currents in the power system. Therefore, there are some differences in construction and connectivity between a Current Transformer (CT) and a Voltage (or Potential) Transformer (PT). A CT will typically have a toroidal core and evenly distributed secondary windings so as to minimize leakage reactance. The primary is typically the main power line conductor, which passes directly through the toroidal core. This type of transformer is specifically for the purpose of measuring current values, and the secondary windings cannot be left open-circuited, or a large voltage will be produce, resulting in dielectric failure (and often an explosion). If a device is not connected to the CT, its secondary must be short-circuited. A PT is connected between the main conductor and ground and can be either wound in the normal way, or the voltage can be taken from a subsection of a string of capacitors (this is called a Capacitive Voltage Tansformer or CVT, and is usually cheaper than the wound type, but is typically not as accurate). This type of transformer measures voltage values, and the secondary winding cannot be short-circuited, as this will produce excessively high currents, resulting in the failure of the PT or the wires it is connected to. A PT can be left open-circuited.
Why during loading the voltage get decreased at output?
Output voltage (...of a transformer, for example...) will decrease as it is loaded because of the transformer's internal resistance. As output current increases/load resistance decreases, a larger voltage will be dropped across the internal transformer resistance. This same phenomenon is present in AC and DC systems (such as batteries).
Why rated current should flow in the secondary for short circuit test in transformer?
Open Circuit test is done to find out core losses of the transformers.which include Eddy Current Losses and Hysteresis Losses only, if during open circuit test secondary will have some load then I2R losses due to load current in secondary as well primary will be included in test results which is not desired while performing Open circuit test.
What is short circuit voltage?
Short circuit voltage is the voltage that has to be applied to the primaries of a transformer, so that the nominal current flows through the secondaries, when they are shorted. This value is important, if transformer secondaries shall be used in parallel. Ideally all transformers with parallel secondaries should have the same short circuit voltage. When their short circuit voltages are different, the transformer with the lower short circuit voltage will be loaded more than their relationship of power ratings would predict. The short circuit voltage is also important in the design of a transformer, because it predicts, how much the secondary voltage will drop at nominal output current. This knowledge helps the designer to find out, how many further windings the secondary needs for a certain voltage in relation to an ideal transformer. Short circuit voltage is also known as impedance voltage.
What are the precautions using current transformer and potential transformer?
Secondry of CT should never kept open during functioning
Why are stripes of iron plates joined instead of using a single block of iron core in a transformer?
To reduce heat generated and eddy current losses in transformer's core during operation.
What types of current transformer?
Current transformer are used for measuring current in a bus bar without disconnecting it by means of ammeter.There are three types 1.bar type current transformer 2.toroidal current transformer 3.wound type current transformer
What is the impedance of a transformer?
Impedance (Z) voltage is the amount of voltage applied to the primary side to produce full load current in the secondary side. It is usually listed on the transformer nameplate, expressed as a percent, and measured by conducting a short circuit test.
What is current voltage transformer?
A transformer is a device that steps up, or steps down voltage. During this process current is also stepped up or down:however, voltage and current are inversely proportional ( meaning an increase in voltage results in a decrease in current and vice versa ) As an example: A step up transformer of 10:1 ratio with 12 volts and 10 amper of current applied to the primary will have ten times the voltage ( 120 volts ) and ten times less current ( 1 amrere ) at the secondary...and a step down transformer with the same turns ratio with 120 volts and 1 ampere applied to the primary will have 12 volts and ten ampere available at the secondary. The electricity supplied into homes and business uses wires carrying very high voltage and low current over long distances, then uses step down transformers to step down the voltage and step up the current. However, in power engineering and protective relaying applications, there are what are called "instrument transformers" which have the specific purpose of providing information to devices (such as relays or meters) about the voltages or currents in the power system. Therefore, there are some differences in construction and connectivity between a Current Transformer (CT) and a Voltage (or Potential) Transformer (PT). A CT will typically have a toroidal core and evenly distributed secondary windings so as to minimize leakage reactance. The primary is typically the main power line conductor, which passes directly through the toroidal core. This type of transformer is specifically for the purpose of measuring current values, and the secondary windings cannot be left open-circuited, or a large voltage will be produce, resulting in dielectric failure (and often an explosion). If a device is not connected to the CT, its secondary must be short-circuited. A PT is connected between the main conductor and ground and can be either wound in the normal way, or the voltage can be taken from a subsection of a string of capacitors (this is called a Capacitive Voltage Tansformer or CVT, and is usually cheaper than the wound type, but is typically not as accurate). This type of transformer measures voltage values, and the secondary winding cannot be short-circuited, as this will produce excessively high currents, resulting in the failure of the PT or the wires it is connected to. A PT can be left open-circuited.
Why during loading the voltage get decreased at output?
Output voltage (...of a transformer, for example...) will decrease as it is loaded because of the transformer's internal resistance. As output current increases/load resistance decreases, a larger voltage will be dropped across the internal transformer resistance. This same phenomenon is present in AC and DC systems (such as batteries).
What is impedance of transformer?
The transformer impedance is the amount of voltage applied for transformer during the load test.Answer.I really don't agree with the answer given by the previous user.Impedance is the total vector opposition offered by the transformer to the flow of current i.e the vector sum of its pure resistance (R) and it's inductive reactance (XL). http://en.wikipedia.org/wiki/Electrical_impedanceAnother AnswerThe 'impedance' of a transformer is usually expressed as a 'percentage impedance', which is defined (perhaps rather confusingly!) as the ratio of the primary voltage that will result in the full rated current flowing through the secondary, to the rated primary voltage.
What is a inruse current in transformer?
since the dc resistance is very low if you close the switch during a peak voltage time you have a very high current for at least a portion of the first cycle Most large transformers use a starting reactor
What is the purpose of grounding the common leg of a 240 vac transformer in a residential air handler have seen some built with it and some without it?
It is the same reason as with the larger transformers, to provide a return circuit in case of a short circuit to ground. The large rush of current will take out the fuse or trip the circuit breaker. The second advantage is in trouble shooting, one lead of the tester is connected to the ground while you test for the voltage with the other. If the transformer was not grounded when trouble shooting , one lead of the tester would have to be on one leg of the transformer all during the test.
Did Nikola Tesla invented ac current?
During his lifetime, Tesla invented fluorescent lighting, the Tesla induction motor, the Tesla coil, and developed the alternating current (AC) electrical supply system that included a motor and transformer, and 3-phase electricity.
Where you use transformer?
Transformers are use in those places where we want to step up or step down the voltage of current. Common examples of transformer are. 1.In camera flash light. Batteries which we use in camera are insufficient to provide enough voltage to cathode tube that it can cause such a bright light therefore two transformers are use which one by one higher the voltage of current and the voltage reaches up to 300 to 350 volts. 2. Another example is in transportation of current, from the source where current is made to the consumer like us, in order to reduce the losses during the long wire movement of current the supplier higher the voltage by transformer and through wire current reaches to urban cities where we use it but before it reaches us, the current is again passes form transform which lower down the voltage of current. by Syed Ahmed Nasir Tirmizi (Pakistan, karachi)
What is a c200 current transformer?
This is a class of current transformers, and is a fairly low class. This has to do with what kind of burden can be placed on the secondary. A general rule is a C200 current transformer can supply ~200 volts at full ratio to its' secondary. If the burden (the CT resistance + cable resistance + relay or instrument resistance) times the maximum expected current is higher than 200 volts, the CT is likely to saturate. During multiple fault events, a CT may keep some magnetizing current causing CT saturation to be higher on a reclose event. Typically CT's are sized and their ratios are chosen to minimize saturation when feasible.
