Why Does a CT Saturate? In an ideal world, the secondary current leaving the CT (IS) is an exact replica of the primary current (IP) divided by the ratio of the number of turns in each winding (CT ratio). However, when a CT saturates, IS does not accurately replicate IP.
What causes saturation of current transformer?
Symmetrical saturation is caused by a primary current that is too large for the CT core to handle for a given load or burden.Asymmetrical saturation occurs as the result of dc offset in the primary current. This offset causes the current wave to no longer be symmetrical around zero, as illustrated in Fig.
What happens if CT gets saturated?
If a CT has reached saturation and a switch is opened to remove the primary current, we would expect the magnetic field (H) to disappear and the flux density (B) to reduce to zero. However, flux density does not go to zero when the primary current stops flowing.
How can you prevent CT saturation?
One of the hardware solutions to prevent the occurrence of core saturation in CT is the fixed switched resistor demagnetization method. Due to disadvantages such as dependence on CT parameters and inefficiencies in severe core saturation, the use of this method has not been expanded.
Why CT get saturated in differential protective scheme during external fault?
Current-transformer (CT) saturation has a major impact on the operation of differential protection schemes. Transformer differential protection must maintain security during CT saturation for external faults while preserving high sensitivity and speed of operation for lower magnitude internal faults.
How do you measure CT saturation?
A saturation test is performed by applying an AC voltage to the CT secondary and increasing the voltage in steps until the CT is in saturation. The test voltage is slowly decreased to zero to de‐magnetize the CT.
What is saturation current in semiconductor?
The saturation current (or scale current), more accurately the reverse saturation current, is that part of the reverse current in a semiconductor diode caused by diffusion of minority carriers from the neutral regions to the depletion region. This current is almost independent of the reverse voltage. (
What is CT burden?
The burden of the CT is the resistive load used to create the voltage on the output. It varies with turns ratio, desired output and current rating of the primary.
How do you demagnetize a CT core?
The easiest way to demagnetize a CT is to apply test current at a level that approaches it’s excitation ‘knee’, then slowly decrease the input current to zero. ◦ This can be done with secondary excitation or primary current injection.
What is CT excitation?
Excitation curve represents a curve of CT secondary rms voltage plotted against rms current with the primary open circuited. The reasonably accurate secondary excitation curve for a given CT can be obtained by open circuiting the primary and applying AC voltage of appropriate frequency to the secondary.
What happens in a differential relay when the saturation is too high?
Under the saturation condition, the protection relay connected to the CTs circuit may mal-operate, indiscriminately and trip the current without coordination with other relays in the networks; or it may completely fail to operate for a fault.
Why does CT fail?
1) shows that the leading reasons for early failure are dominated by five main classifications: corrosion, mechanical damage, manufacturing flaws (or defects), operator error, and hydrogen sulfide (H2S) cracking. These groups account for approximately 94% of all failures.
What causes spill current in differential protection?
Ignoring iron losses the transformer input current is thus the magnetizing current, which is limited by the magnetizing impedance. This current flows only in the winding connected to the source of supply, and thus causes a spill current into the biased-differential-operate winding.
Why Metrosil is used in ref protection?
Metrosil is used to limit the peak voltage developed by the current transformer (CT) under internal fault conditions to a value below the insulation level of the CT, relay and interconnecting leads.
Why CT polarity is important?
It is important to avoid continuous contact, which will short circuit the battery. If polarity is correct, the momentary contact causes a small deflection in the analog meter in the positive direction. If the deflection is negative the polarity of the current transformer is reversed.
What is CT error ratio?
Explanation: Ratio error of a C.T. is defined as the ratio of the magnitude of the difference between the nominal and actual ratio with respect to the actual ratio.n is the turns ratio.
What is a CT Analyzer?
CT analyzer is a necessary instrument of on-site verification accuracy of current transformer.The CT analyzer designed and developed in this paper use the new method of indirect test – low pressure method, which gets current transformer contrast and angle difference by measuring the internal parameters of the CT.
Is saturation current diode?
The saturation current is a combination of the generation current caused by thermal generation of electron hole pairs within the depletion region of the diode and the diffusion current due to minority carriers in the n and pregions diffusing across the depletion region.
What is meant by saturation current?
Definition of saturation current
: the limiting current through an ionized gas or an electron tube such that further increase of voltage produces no further increase in current.
Why is reverse saturation current constant?
Since this current is due to minority carriers and these number of minority carriers are fixed at a given temperature therefore, the current is almost constant known as reverse saturation current ICO.This is due to surface leakage current. The surface of diode follows ohmic law (V=IR).
What is the output of CT?
The output voltage of the CT should be 333 mVac when the full-scale current rating of the CT is flowing in the conductor.
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