How do I check my knee point of CT?

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.

How is knee point voltage of a current transformer calculated?

Importance of Knee Point Voltage for PS class CT:

1. Differential protection Scheme:
2. CT Knee Point Voltage can be calculated using the formula;
3. Related Article:
4. Example:
5. If the system fault current is 30 KA, CTR-600/5, RCT+RL+RR=0.5 Ohm.
6. Vkp = K * If/CTR * (RCT + RL + RR)
7. Vkp = 2*30000/120*0.5 =250 Volt.
8. Test Set-up:

How do you test for CT burden?

Burden test is to ensure the connected burden to CT is with in the rated burden, identified on the nameplate. Burden VA = Voltage drop x rated CT sec. Current.

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 design a transformer rating?

Since you know kVA = V * l / 1,000, we can solve for V to get V = kVA * 1,000 / l. So you’ll multiply your kVA rating by 1,000 and then divide by the amperage. If your transformer has a kVA rating of 75 and your amperage is 312.5, you’ll plug those numbers into the equation — 75 * 1,000 / 312.5 = 240 volts.

What is reference values of rated secondary current of current transformer?

The rated secondary current is normally standardized at 1 or 5 amperes. For example, a 4000:5 CT secondary winding will supply an output current of 5 amperes when the primary winding current is 4000 amperes.

How is current transformer accuracy calculated?

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….Application of CT Core According to Their Class.

Application	Accuracy Class
Precession Metering	0.1 or 0.2	BL
Commertial Metering	0.5 or 1.0	AM, BM, CM
Ammeters	1 or 3	CD
Protection Relays	5P10 or 5P20	STU

What is knee point voltage of 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 knee point voltage of a current transformer?

According IEC, 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. Read More: Knee point voltage of CT

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.

What should be the excitation current of a core 3 transformer?

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. This curve is generally plotted in secondary volts vs exciting current measured in secondary.

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.