What is the purpose of calculating knee point voltage for current transformers?

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 the voltage on the secondary of a current transformer?

The normal range of the current transformer for measuring the current is 5A or 1A whereas the standard voltage at the secondary winding of the potential transformer is up to 110V. The transformation ratio of the current transformer is always remained high, whereas for the potential transformer its remains low.

How do you calculate RCT in a current transformer?

RCT= 12.00 ohms Selected Burden =15 VA No. Of Relay =2 Relay Burden =0.20 VA RR (Relay resistance) = 0.20 ohm (VA/I2) Cable Size = 4mm (As per cable catalogue) Cable Resistance = 4.61 0hm/km (Resistance at 20®c) Cable Resistance at Ambient temperature= 5.61 ohm / km at 75®c temp.

How do you measure current in a transformer?

Standard measuring current transformers are used in conjunction with ammeters to measure high currents which are stepped down to a standard output ratio of either 5 A or 1 A. The VA rating of the CT is matched with VA rating of the measuring instrument or ammeter.

What is the point of a current transformer?

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 5P in current transformer?

Current Transformers for Protection The accuracy class 5P requires a higher demand in construction of the core as the accuracy class 10P. The accuracy limit factor is given by the figure behind the accuracy class designation 10P and 5P respectively. 10P10 (5P10): max.

What is knee point voltage?

Knee point voltage is nothing but a magnitude of the saturation limit of the current transformer. 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.

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 the knee point voltage of current transformer?

Knee Point Voltage of Current Transformer is of importance in Protection Class CT i.e. where CT is used for protection purpose. Protection Class CT is normally specified as PS (Protection Special). PS is defined by knee point voltage of current transformer Vk and excitation current Ie at Vk/2.

What is the knee point voltage of protection class CT?

Therefore Knee Point voltage of Protection Class CT must be more than the voltage drop across the burden to maintain CT core in its linear zone. The knee -point of the excitation characteristic is defined as the point at which a 10\% increase in secondary voltage produces a 50\% increase in exciting current.

How to verify the V K value of a current transformer?

To verify the V k value of a given Current Transformer, the process is as follows. Exciting currents is measured for several secondary e.m.fs. This is accomplished by applying voltage to the secondary winding, the primary and other windings being open circuited. The connections are shown in figure.

What is the meaning of 5knee point voltage?

Knee point voltage is basically the load of your relay connected to the CT, For each and every type of Relay the manufacture will have a formula to calculate its burden What is the meaning of 5p20 or 5p10 in a transformer? 5 = Accuracy Number in percentage. It means the maximum permissible error will be 5\%