Contents
What are the characteristics of current transformer?
Main electric characteristics of CT are:
- Rated voltage (maximum voltage the CT can withstand)
- Rated primary current.
- Ratio.
- Accuracy class.
- Burden power.
- Rating factor (RF)
- Magnetizing curve.
What are the characteristics of CT and PT?
Comparison Chart
| Basis for Comparison | Current Transformer | Potential Transformer |
|---|---|---|
| Primary Circuit | Has a small number of turns | Has a large number of turns |
| Secondary Circuit | Has a large number of turns and cannot be open circuit. | Has a small number of turns and can be open circuit. |
| Range | 5A or 1A | 110v |
| Transformation Ratio | High | Low |
What is current transformer and its use?
A current transformer is a device used to produce an alternating current in its secondary, which is proportional to the AC current in its primary. This is primarily used when a current or voltage is too high to measure directly. The CT ratio is equal to the number of secondary turns.
Why CT is used in substation?
Current transformers are used for protection, measurement and control in high-voltage electrical substations and the electrical grid. Live tank CTs are useful because the primary conductor is short, which gives better stability and a higher short-circuit current rating.
Why CT and PT are used?
CT and PT both are measuring devices used to measure currents and voltages. They are used where large quantities of currents and voltages are used. The role of CT and PT is to reduce high current and high voltage to a parameter.
How is a current transformer used in a protection circuit?
The instrument transformers isolate measurement or protection circuits from the high voltage of the primary system. A current transformer provides a secondary current that is accurately proportional to the current flowing in its primary. The current transformer presents a negligible load to the primary circuit.
What do you need to know about current transformers?
Current transformers are thus expected to have an Accuracy Limit Factor (ALF) that is usually fairly high. Note that the associated “relay” must be able to withstand high overcurrents. An “instrument”current transformer (CT) requires good accuracy around the nominal current value.
What should the ALF be for a current transformers?
A “protection” current transformer (CT) must saturate sufficiently high to allow a relatively accurate measurement of the fault current by the protection whose operating threshold can be very high. Current transformers are thus expected to have an Accuracy Limit Factor (ALF) that is usually fairly high.
What should the load impedance of a current transformer not exceed?
The burden (load) impedance should not exceed the specified maximum value to avoid the secondary voltage exceeding the limits for the current transformer. The primary current rating of a current transformer should not be exceeded or the core may enter its non linear region and ultimately saturate.