Table of Contents
- 1 What is meant by ISF in CT?
- 2 What is STC rating of current transformer?
- 3 Which type of transformer The current transformer comes under?
- 4 What is the rating of current transformer?
- 5 How is CT ISF calculated?
- 6 What is instrument Safety Factor (ISF) of metering current transformer?
- 7 What is accuracy limit factor of current transformer?
- 8 What is ISF value in metering core of a CT?
What is meant by ISF in CT?
For any CT, Instrument Security Factor(ISF) is nothing but the ratio of Maximum limited Primary current to rated Primary Current. Basically, the ISF is used to protect the load connected in the secondary side of the metering CT i.e meters etc.
What is STC rating of current transformer?
A current transformer is overloaded while system short-circuit currents are flowing and is short-time rated. Standard times for which the CT must be able to carry rated short-time current (STC) are 0.25, 0.5, 1.0, 2.0 or 3.0 seconds.
What is meant by the accuracy limit factor?
The rated accuracy limit factor (Fn) is the ratio of the rated accuracy limit primary current to the rated primary current. The CT accuracy primary limit current defines the highest fault current magnitude at which the CT will meet the specified accuracy.
Which type of transformer The current transformer comes under?
There are three basic types of current transformers: wound, toroidal and bar. Wound Current Transformer – The transformers primary winding is physically connected in series with the conductor that carries the measured current flowing in the circuit.
What is the rating of current transformer?
Most current transformers have a the standard secondary rating of 5 amps with the primary and secondary currents being expressed as a ratio such as 100/5.
What is accuracy in current transformer?
Accuracy class of current transformer is the highest permissible percentage composite error at rated current. The standard accuracy classes of current transformer as per IS-2705 are 0.1, 0.2, 0.5, 1, 3 and 5 for metering CT.
How is CT ISF calculated?
The ratio of CT saturation current to primary rated current is 10000/1000=10. This ratio is called the security factor of current transformer. The instrument security factor(ISF) is defined for metering applications.
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 the instrument limit current of a metering current transformer?
Instrument limit current of a metering current transformer is the maximum value of primary current beyond which current transformer core becomes saturated. Instrument security factor of CT is the significant factor for choosing the metering instruments which to be connected to the secondary of the 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 ISF value in metering core of a CT?
If you see the name plate of metering core of a Current Transformer (CT), you will notice ISF value mentioned. A compensating device is generally used in metering CT as shown in figure above. The basic purpose of this compensating device is to achieve the Instrument Safety Factor. This device is nothing but high resistance.