What is knee point voltage in CT?

As per IEC, the Knee Point Voltage of a Current Transformer is defined as the voltage at which 10 % increase in voltage of CT secondary results in 50 % increase in secondary current.

What is CT class 5p20?

It means the maximum permissible error will be 5% 20 = Accuracy limit factor indicates that the CT will sense the current with the specified accuracy even with 20 times of its secondary current flows in the secondary.

What is knee voltage of Current Transformer?

However, the concept of knee point voltage is very pertinent to protection current transformers, since they are necessarily exposed to fault currents of 20 to 30 times rated current.

How do you test CT knee voltage?

Excitation tests are performed by applying an AC voltage to the secondary winding of the CT and increasing the voltage in steps until the CT is in saturation. The “Knee” point is determined by observing a small voltage increase causing a large increase in current.

What is knee point?

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 do you mean by 5P10 and 5P20?

accuracy numbers are 5 and 10. The number 20 (called accuracy limit factor) indicates that. the CT will sense the current with the specified accuracy. even with 20 times of its secondary current flows in the. secondary.

How do you read a CT nameplate?

CT Ratio: 100/5-5 A The ratio 100/5 means If the CT primary carries 100 Amps then the output of the CT secondary will be 5 Amps. The dual 5-5 A means the first core used for protection and second core used for metering purpose.

How do you calculate CT ratio?

Calculate the CT ratio. The CT ratio is the inverse of the voltage ratio. In this example, the voltage ratio is 1:5, so the CT ratio is 5:1. This means the current level is stepped down 5 times where, if the primary current is 200 amps, the CT output is 40 amps.

What is CT ratio?

The CT ratio is the ratio of primary current input to secondary current output at full load. For example, a CT with a ratio of 300:5 is rated for 300 primary amps at full load and will produce 5 amps of secondary current when 300 amps flow through the primary.

How to increase knee point voltage of a CT?

Apply 5-10 % voltage of the knee point voltage to the secondary of the CT by auto-transformer. Note down the secondary current. Increase the voltage gradually to 20,30,40,50,60,70,80,90 % of the rated knee point of the CT and note down the secondary current. Now increase the voltage to 100% of KPV and note down the current.

What is knee point voltage of a current transformer?

According to IEC, Knee Point Voltage of a Current Transformer is defined as the voltage at which a 10 % increase in voltage of CT secondary results in a 50 % increase in secondary current. Above knee point, the CT gets saturated. The knee point is a important parameter for CT selection for a particular electrical installation.

What is the knee point voltage for PS-class core?

For this CT the knee point voltage for PS-Class core is V k >= 120V for 3S1-3S3 winding and V k >=60V for 3S1-3S2 winding. Also the excitation current should less than or equal to 100mA at V K /4 for anyone of Core-3 windings. Current Transformers magnetization curve helps to understand the knee point voltage.

What is the knee point of a magnet?

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 voltage, the magnetizing current increases considerably even for small increments in voltage across the secondary terminals.