What is ALF in current transformer?

What is ALF in current transformer?

The measure of this characteristic is known as the “Accuracy Limit Factor” (A.L.F.). A protection type CT with an A.L.F. of 10 will produce a proportional current in the secondary winding [subject to the allowable current error] with primary currents up to a maximum of 10 times the rated current.

What is FS in current transformer?

The rated accuracy limit factor (FS) is the factor which, when applied to the rated primary current (IN), gives the r.m.s. value of the maximum current at which the current transformer complies with the accuracy requirements Fg.

How do you calculate alf of CT?

The ALF is 20. CT accuracy class is 5. It means if 20 times of the rated primary current(4000 amperes) flows in the primary at the time of fault, the CT reads the current with 5 \% accuracy. This factor (In x 20)20 is called the accuracy limit factor(ALF).

What is VK in current transformer?

If we consider the magnetising curve V(Io) of the CT, the knee point voltage Vk is defined as the point on this curve from which a 10\% increase in voltage causes a 50\% increase in the magnetising current Io. Class X corresponds to a better metering accuracy than classes 5P and even more so 10P (see figure 3).

What are the CT classes?

CT Class. The standard accuracy classes according IEC are class 0.2, 0.5, 1, 3 and 5. The CT with accuracy class of0.1, 0.2, 0.5, 1.0 accuracy class are used for measurement of electric current. 0.1 and 0.2 accuracy class CT are used in a revenue metering application.

What is CL in current transformer?

Accuracy Class – Accuracy Class describes the performance characteristics of a Current Transformer and the maximum burden that can be allowed on its secondary circuit.

How do you calculate current transformer?

Definition: 1) The ratio of primary amps divided by secondary amps. 2) The current ratio provided by the windings of the CT. For example, a CT that is rated to carry 200 Amps in the primary and 5 Amps in the secondary, would have a CT ratio of 200 to 5 or 40:1.

What is knee voltage of current transformer?

The knee point is defined as the voltage at which a 10\% increase in applied voltage increases the magnetizing current by 50\%. For voltages greater than the knee point, the magnetizing current increases considerably even for small increments in voltage across the secondary terminals.

What is PS class CT?

PS Class CT is also known as PX Class or simply Class X Current Transformer. It is special type of current transformer meant for protection purpose. Deviation in characteristics of CTs may lead to spill current in the secondary and even lead to actuation of protection element even under through fault condition.

What is PS in CT?

PS Class CT is also known as PX Class or simply Class X Current Transformer. It is special type of current transformer meant for protection purpose. Various protection class CTs as described in IS 2705 part-3 is only useful for overcurrent protection.

What is instrument Safety Factor (ISF) of metering current transformer?

Instrument Safety Factor (ISF) is defined as the ratio of CT saturation current to its rated current. Suppose the CT ratio is 2000/1 and the CT gets saturated if there is flow of 10 kA current through its primary, then Instrument Safety Factor is given as ISF is defined only for metering current transformer (CT).

What is accuracy limit factor of current transformer?

The instrument limit primary current of metering CT is the value primary current beyond which CT core becomes saturated. For protection current transformer, the ratio of accuracy limit primary current to the rated primary current is called accuracy limit factor of current transformer.

What is the use of ALF in power supply?

ALF is used in the Protection Class CT’s. Purpose of protection class CT is to sense the current under fault conditions and the output is fed to the protective relay or circuit breaker which in turn cut off the power supply.

Why is ALF used in metering CT’s?

Metering CT is desiged with ISF which is normally less than 5 or less than 10, that means CT will be saturated when the current produced is more than 5 or 10 times of the maximum inteneded output. In that way devices connected to the secondary of CT is protected. ALF is used in the Protection Class CT’s.