Knee Voltage

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 cause of knee voltage?

Knee voltage: The forward voltage at which the flow of the current during the PN Junction of the diode begins increasing very quickly is commonly known as knee voltage. This voltage is also known as cut-in voltage.

What is knee and breakdown voltage?

1.The knee voltage or cut-in voltage is the forward voltage at which the current through the junction begins to rapidly increase. Break down voltage is the reverse voltage at which the P-N junction of a diode fails due to a sudden increase in reverse current.

What is knee voltage of Si and Ge?

Knee voltage of threshold voltage values for Si and Ge diodes are 0.7 V and 0.3 V respectively.

How do you measure knee voltage?

Importance of Knee Point Voltage for PS class CT:

1. Differential protection Scheme:
2. CT Knee Point Voltage can be calculated using the formula; Vkp = K * If/CTR * (RCT + RL + RR) Where,
3. Example:
4. Vkp = K * If/CTR * (RCT + RL + RR)
5. Vkp = 2*30000/120*0.5 =250 Volt.
6. Test Set-up:
7. Related Posts on Current Transformers:

What is the difference between knee voltage and barrier potential?

If the applied voltage is greater than the barrier potential, the current flows. When an external voltage aids the barrier potential, the diode is reverse biased. The voltage at which the forward diode current increases rapidly is known as Knee voltage or cut in voltage .

What happens after knee voltage?

Once the light-emitting diode is connected to an external voltage in the forward bias, the potential barrier height across the PN junction will be decreased. This exact voltage is known as the knee voltage of the LED. When this voltage is achieved, then the flow of current may raise however the voltage does not vary.

What happens at knee voltage?

When the applied voltage is more than the barrier potential, the resistance is small (ideally 0) and the current increases rapidly. This point is called the Knee-point or turn-on voltage or threshold voltage (Fig. 2-b). This voltage is about 0.3 volts for Ge diodes and 0.7 volts for Si diodes.

What is knee voltage in simple words?

The voltage is cross toward the barrier potential, the diode current raises quickly and diode performs greatly. This barrier voltage at which the flow of current will increase is known as knee voltage.

What is knee voltage of CT?

The point where CT saturates also known as the knee point, which according to IEC, knee point is the voltage at which a 10% increase in voltage of CT secondary results in a 50% increase in secondary current.

Why is Si preferred over Ge?

The energy gap for germanium is less (0. 72eV) than the energy gap of silicon (1. 1eV). Therefore, silicon is preferred over germanium for making semiconductor devices.

Why is PN junction used?

P-N junction diode can be used as a photodiode as the diode is sensitive to the light when the configuration of the diode is reverse-biased. It can be used as a solar cell. When the diode is forward-biased, it can be used in LED lighting applications.

What is the voltage of Si?

Here are a few: Silicon diode - Silicon is the most common material used to make diodes. Silicon has a typical forward voltage of 0.6 − 0.7 V 0.6-0.7\,\text V 0.

What is the knee voltage of red LED?

What you should find is that red, green, or yellow LEDs have relatively low forward voltage ranging from 1.6-2.2V.

Is knee voltage constant?

Once the knee voltage is reached, the current may increase but the voltage does not change.

What is barrier voltage explain?

"The barrier voltage is the amount of electromotive force required to start current through the P-N junction. Barrier voltages for silicon typically range from 0.5 - 0.7 volts. Barrier voltages for germanium typically range from 0.2 - 0.3 volts. " 100%

Why does knee voltage decrease when temperature increases?

In a cold semiconductor below the knee voltage electrons from the n side haven't enough energy to enter the p side and, likewise, holes from the p side haven't enough energy to enter the n side. When you heat it, a large fraction of charge carriers (on one of these sides, or both) acquire necessary energy.

Why does current increase rapidly after knee voltage?

But when the reverse voltage is increased beyond the breakdown voltage limit, the electric field across the junction becomes sufficient to pull out the valence electrons from the atoms at the p side and sweep them to the n side. Due to this, the reverse current suddenly increases.

What is is standard for CT & VT?

The main Standard references for the inductive type of CTs and VTs (with iron laminates) in medium voltage networks are: EN 60044-1 current transformers; EN 60044-2 voltage transformers.

What is CT and VT ratio?

Generally, when measuring high voltage and high current transformer signals, you use a VT (voltage transformer) and CT (current transformer). The ratios between the primary and secondary rated voltages and rated currents are the VT and CT ratios.