How do you select a current transformer for metering?
For a metering CT, choose a burden VA equal to, or greater than, 125 % of the total combined VA of instruments connected to the secondary side. For a protective CT, please contact the manufacturer for assistance. Accuracy • For a revenue CT, the accuracy should be at least IEC 0.2 or 0.5 CL or IEEE 0.3 or 0.6 CL.
How is current transformer size determined?
Current transformers are specified by size (VA rating), ratio and accuracy. The VA rating determines the maximum secondary impedance (burden) that can be driven at the stated accuracy. The typical transformer-rated analog ammeter has a 5A AC movement (M).
How do you size a current transformer for protection?
Several methods exist to size current transformers….The IEC 60044 Method
- Kssc – rated symmetrical short-circuit current factor.
- K’ssc – effective symmetrical short-circuit current factor.
- Ktd – transient dimensioning factor.
What is current transformer metering?
Quick Answer. CT (Current Transformer) meters are installed on any connections with a load greater than 100 Amps. They measure a fraction of the amps (current) passing through the connection and a multiplier is applied to this reading to reflect the actual amps.
How do I choose a transformer size?
Transformer size is determined by the kVA of the load. Load voltage, or secondary voltage, is the voltage needed to operate the load. Line voltage, or primary voltage, is the voltage from the source. Single-Phase has two lines of AC power.
How do you determine the current rating of a transformer?
As discussed above, the key in selecting the proper CT should be based upon the minimum and maximum load size, selecting the CT that will give you the highest amount of sensor resolution. Using a 100 Amp CT on a 100 Amp Load will give you a better sensor resolution when compared to a CT that is rated to 5000 Amps.
What is a transformer ratio?
The transformer turns ratio is the number of turns of the primary winding divided by the number of turns of the secondary coil. The transformer turns ratio provides the expected operation of the transformer and the corresponding voltage required on the secondary winding.
How do you design a transformer rating?
Calculate & Find the Rating of Single Phase & Three Phase Transformers in kVA
- We know that, Transformer always rated in kVA.
- Rating of a Three Phase Transformer.
- Rating of a Three phase transformer in kVA.
- Here is the rating of Transformer is 100kVA.
- P = 11000V x 5.25A = 57,750 VA = 57.75kVA.
What is the main purpose of current transformers?
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.
What is the purpose of current transformer?
A Current Transformer (CT) is used to measure the current of another circuit. CTs are used worldwide to monitor high-voltage lines across national power grids. A CT is designed to produce an alternating current in its secondary winding that is proportional to the current that it is measuring in its primary.
How do you size a transformer for a load?
Do you know how to size current transformers?
The correct sizing of current transformers is required to ensure satisfactory operation of measuring instruments and protection relays. Several methods exist to size current transformers. This note will look at several methods, with particular attention being paid to protection class CTs sized in IEC 60044, which is adopted internationally.
How to choose the best Transformers for a substation?
The next thing to check is the maximum symmetrical fault current. Choose the primary rating so that with the maximum fault current, the CT secondary current is less than 100A. In short the primary rating shall be above the load current as well above 1/20th of the fault current in such applications.
What’s the maximum wire length for a transformer?
The “Current Transformer Wire Length Chart” below lists the maximum total lead wire length (Rlead1 + Rlead2) by VA rating for a CT with a 5A secondary. If the distance from the meter is 10 feet, then the total wire length for the chart is 20 feet.
How to size a current transformer-Weschler instruments?
The “Current Transformer Wire Length Chart” below lists the maximum total lead wire length (Rlead1 + Rlead2) by VA rating for a CT with a 5A secondary. If the distance from the meter is 10 feet, then the total wire length for the chart is 20 feet. Values listed are based on stranded wire, 0.02Ω meter resistance and 50°C temperature.