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The method I have seen employed is to estimate the maximum current that will flow in the secondary side of the CT due to fault currents on the primary side, and calculate the total load (resistance) on the secondary side, including the CT resistance, cable resistance (2 way for ground faults, 1 way for three phase and L-L), resistance of any meters/relays connected to the CT. Once this is known, the voltage rise in the CT can be determined to see if the CT is likely to saturate.
Alternately, you can determine the VA burden by the above, VA = V*I = (I*R)*I, using Ohm's law.
The above answers the question of how to calculate the VA burdon on a current transformer. The VA burden of a CT is determined by the resistivity of the CT, multiplied by the current squared through the secondary. In general, this will be provided by the manufacturer in the form of a CT burden characteristic, developed through testing of the CT in question, not through calculations.
What else can I help you with?
What are the disadvantages of a double wound transformer?
There is no disadvantage with a current transformer -it does exactly what it's supposed to do, that is:reduce the current flowing in the primary circuit to a value that can be handled by its burden (ammeter or protective relay).electrically-isolate its secondary circuit from the primary circuit.
What precaution should be taken when working with current transformer that is in service?
Its secondary must never be open circuited. If its burden is to be removed, then the secondary must be short circuited first, and removed only after the burden is replaced.
What is VA burden in electrical engineering?
The term 'burden' is used to describe the secondary load applied to an instrument transformer; the reason for this is so that it is not confused with the 'load' supplied by the high-voltage circuit to which the transformer's primary is connected. A burden is either a measuring instruments (ammeter,voltmeter, wattmeter, etc.) or protective relay, depending on the function of the instrument transformer. 'V.A' is the symbol for 'volt ampere', which defines the 'power' rating of the instrument transformer.
How does an auxiliary transformer work?
Auxiliary transformer- current transformer The current transformer is working based on two theories. 1.Ampheres law. 2.Faradays law. Amp.law- whenever a current flows through the conductor it will produce magnetic flux around the conductor. based on above principle- current flows through the primary will induce a magnetic flux in the CT core. Faraday law- whenever a conductor cuts the magnetic flux or magnetic flux cuts the conductor will induce a emf across the conductor based on above principle- the magnetic flux in the core will cuts the windings. so emf is induced across the secondary terminals . whenever the secondary terminals connected with burden will make a closed path and current flows through the secondary to burden.
Is it ok to have the dot on a current transformer upside down?
You are probably referring to a 'polarity mark'. This is very important if the CT's burden requires current to flow through it in a particular direction in order to work properly. For example, it won't make any difference if the burden's an ammeter. But if the burden is, say, a wattmeter, then it's very important to observe the CT's polarity mark when it is wired, otherwise the wattmeter might read 'downscale' (backwards). It's also very important when the CT supplies protection relays.
How can you connect burden in current transformer?
Yes
What are the disadvantages of a double wound transformer?
There is no disadvantage with a current transformer -it does exactly what it's supposed to do, that is:reduce the current flowing in the primary circuit to a value that can be handled by its burden (ammeter or protective relay).electrically-isolate its secondary circuit from the primary circuit.
Fundamental principle of current transducer?
The basic principle of current transformer is same as that of the power transformer. Like the power transformer current transformer also contains a primary and a secondary winding. Whenever an alternating current flows through the primary winding alternating magnetic flux is produced, which then induces alternating current in the secondary winding. In case of current transformers the load impedance or "burden" is very small. Therefore the current transformer operates under short circuit conditions. Also the current in the secondary winding does not depend load impedance but depends on the current flowing in the primary winding.
What precaution should be taken when working with current transformer that is in service?
Its secondary must never be open circuited. If its burden is to be removed, then the secondary must be short circuited first, and removed only after the burden is replaced.
What is CT burden in electrical engineering?
CT (current transformer) Burden is the maximum load that the CT secondary can drive (e.g. meters or protection relays) Why do you care about burden when ordering current transformers? The burden is the termination impedance of the measuring instrument. The measuring instrument can be an analog or digital energy meter, a data logger or a recorder. All instruments that use a current transformer to measure line current must terminate the CT with a resistance (impedance in same case which means there is some inductance involved). A CT supplier should be given the burden when ordering. Technically, the total burden for a CT is the internal winding resistance, the connecting lead resistance and the measuring instrument input resistance. Some Ct's are installed a long distance from the measuring instrument and the connecting leads can have a resistance as much as 0.002 ohms per foot (both ways because the current makes a complete round trip). This resistance will cause an error if not taken into account.
What is VA burden in electrical engineering?
The term 'burden' is used to describe the secondary load applied to an instrument transformer; the reason for this is so that it is not confused with the 'load' supplied by the high-voltage circuit to which the transformer's primary is connected. A burden is either a measuring instruments (ammeter,voltmeter, wattmeter, etc.) or protective relay, depending on the function of the instrument transformer. 'V.A' is the symbol for 'volt ampere', which defines the 'power' rating of the instrument transformer.
Why the burden of a relay has to be determined?
The burden of a relay is given in Ohms or VA and power factor. It is needed to find the accuracy of the current transformer circuit and thus to determine when the protective relay will trip. It is mostly interesting given high fault currents and inaccuracy of measurements.
How does an auxiliary transformer work?
Auxiliary transformer- current transformer The current transformer is working based on two theories. 1.Ampheres law. 2.Faradays law. Amp.law- whenever a current flows through the conductor it will produce magnetic flux around the conductor. based on above principle- current flows through the primary will induce a magnetic flux in the CT core. Faraday law- whenever a conductor cuts the magnetic flux or magnetic flux cuts the conductor will induce a emf across the conductor based on above principle- the magnetic flux in the core will cuts the windings. so emf is induced across the secondary terminals . whenever the secondary terminals connected with burden will make a closed path and current flows through the secondary to burden.
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.
How do you calculate DBR?
The way to calculate DBR (Debt Burden Ratio) is to take all of a persons debt burden and add it together. Next, divide that debt burden by the after-tax income. This is the DBR.
Is it ok to have the dot on a current transformer upside down?
You are probably referring to a 'polarity mark'. This is very important if the CT's burden requires current to flow through it in a particular direction in order to work properly. For example, it won't make any difference if the burden's an ammeter. But if the burden is, say, a wattmeter, then it's very important to observe the CT's polarity mark when it is wired, otherwise the wattmeter might read 'downscale' (backwards). It's also very important when the CT supplies protection relays.
What is mean by burden of the current transformers?
The burden on a CT is the sum total impedance connected to the secondary - including the CT secondary winding coil resistance, lead resistance, and any loads attached (relays, meters, etc.).If this is for power calculations and CT saturation in three phase systems, remember you must multiply the lead resistance by two to get the total path resistance.Another AnswerWe use the word, 'burden', to describe the load supplied by the instrument transformer's secondary. This is normally a measuring instrument or protection relay. We use the word 'burden' to distinguish it from the 'load' supplied by the circuit to which the primary winding is connected.
