# Developed by engineers for engineers.

### What is knee point or cut-in voltage of PN junction

The minimum amount of voltage required for conducting the diode is called knee voltage and it is also known as cut-in voltage. before knee voltage diode behave like a high resistor(means it’s not conduct).

knee voltage is different for different elements for e.g for Si knee voltage is 0.7v, knee voltage is Ge 0.3v. To know more about knee or cut-in…

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### Why filament/ Incandascent lamp is non linear device?

The bulb resistance has a positive temperature coefficient. The resistance of the bulb increase with an increase in the temperature. The filament resistance changes with increase in the current due to temperature increase. The filament resistance does not remain constant with an increase of current. Therefore, the incandescent/filament lamp does not obey the Ohm's law and filament lamp is a non ohmic.…

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### Why are some conductors non ohmic?

The category of non-ohmic conductors includes semiconductors, where conduction is not due to a sea of free electrons but to either a predominance of electrons or of holes, depending on how the material is doped. Put oppositely doped layers adjacent to one another and you get a diode which will only conduct significantly in one direction. Even the galena crystals which used to be used in crystal radios were semiconductors, although over much of the period in…

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### What are some examples of non-ohmic conductors?

The example of Ohmic conductor is the resistor The current flowing through the resistor is directly proportional to the applied voltage and voltage across the resistor and current flowing through it have a linear relationship. The resistamce of the conductor depends on the temperature and the resistance increases with an increase in temperature according to temperature coefficient of the resistance. If the current flowing through the resistance increases above…

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### Difference between Ohmic and non-Ohmic Conductor

This characteristic is related to how the conductor’s resistance reacts to voltage. What I mean is, the conductor’s resistance will change linearly if the conductor is ohmic, and in a non-ohmic conductor the resistance will not follow a straight line. It can be checked measuring voltage and current trough the conductor and making a VxI graph.

According to Ohm's Law…
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### Why can a 50Hz CT work on 60Hz systems, and why can't a 60Hz C.T. work on a 50 Hz system?

CT or PT functions on the principle of electromagnetic induction. The electrical energy is first converted into magnetic energy and again the magnetic energy is converted in the electrical energy. The electrical current first converted in magnetic energy. The magnetic energy is nothing but converting electrical current into flux. The flux then flow through the core. The core of the CT or PT has its maximum flux carring capacity.…

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### What is Battery Acid?

In general battery acid refers to the electrolyte in a lead acid battery. That is a diluted form of sulfuric acid (H2SO4) in water generally in the concentration of 36–40%. As such it does not have the burning properties of concentrated sulfuric acid.

Battery acid is rather unique in battery electrochemical systems because it not only carries ionic…

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### What is insulation class of transformer oil?

The insulation class of the transformer refers to the max (hot spot) temperature that can be safely withstood by the specific insulation material. It is the weakest of the materials used in transformer (as far as temperature withstand capability is concerned) as the other materials like steel core & copper winding can withstand much higher temperature during operation. There are different classes of insulation materials (Y, A, B, F, H & C) with max temperatures 90, 105, 130,…

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### The terminal voltage is less than the EMF of a cell or a train of cells. The cell voltage is the voltage available at the terminals of the battery. This is equal to EMF - Voltage drop(s)due to intern…

• The terminal voltage is less than the EMF of a cell or a train of cells. The cell voltage is the voltage available at the terminals of the battery. This is equal to …
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### Why battery terminal voltage is less during discharging of battery?

• The terminal voltage is less than the EMF of a cell or a train of cells. The cell voltage is the voltage available at the terminals of the battery. This is equal to …
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### What is the relatioship between power factor and air gap of an induction motor?

Airgap of the induction motor is inversely proportional to the power factor and efficiency. The Airgap between stator and rotor decides amount of energy transferred from stator to rotor. Airgap incteases the loss of fluxes transferred from stator to rotor. Thus efficiency decreases if Airgap increases ,

now comming to the part of power factor :-…

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### What is the relatioship between power factor and air gap of an induction motor?

Airgap of the induction motor is inversely proportional to the power factor and efficiency. The Airgap between stator and rotor decides amount of energy transferred from stator to rotor. Airgap incteases the loss of fluxes transferred from stator to rotor. Thus efficiency decreases if Airgap increases ,

now comming to the part of power factor :-…

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### What happens if air gap of induction motor increase?

If the air gap of an induction motor is increased, the following will happen:

• The permeability of the magnetic circuit rotor-to-stator will decrease.
• The magnetizing inductance of he motor thus decreases.
• The…
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### What is the effect of the air-gap length on the efficiency of an induction motor?

The reluctance of the magnetic circuit increases with an increase in the air gap length. To produce the same flux in the motor, the stator winding draws more current if the air gap length is increased. with an increase in air gap length, the fixed losses in the motor increase and the motor efficiency deteriorate.

Flux= MMF/Reluctance of the magnetic circuit…

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### What is dispersion coefficient of induction motor?

The dispersion coefficient is defined as the ratio of magnetizing current to ideal short circuit current. 34. What is the condition for obtaining the maximum torque in case of 3 phase induction motor? The maximum torque occurs in induction motor when rotor reactance is equal to rotor resistance.

### What is dispersion coefficient of induction motor?

The dispersion coefficient is defined as the ratio of magnetizing current to ideal short circuit current. 34. What is the condition for obtaining the maximum torque in case of 3 phase induction motor? The maximum torque occurs in induction motor when rotor reactance is equal to rotor resistance.

### What are Triplen Harmonics?

Lower order harmonics are of more concern than higher order harmonics. Harmonics by default refers to current harmonics. The impedance of the device or circuit is mostly inductive and so is equal to R+jwL, where w=2*pi*f. Hence it can be observed from the equation that the impedance offered is directly proportional to frequency. The frequency of the 3rd order is 3w, 5th order is 5w ... Hence as the order of the harmonics increases, the impedance offered to them increases and so they are less in… Continue

### CT Knee Point Voltage Calculation Method

Test Procedure for knee point Voltage calculation of CT :

1.Disconnect the CT from all external connection

2.Note down the knee point voltage of CT ( as per datasheet of the CT).

3. Apply 5-10 % voltage of the knee point voltage to the secondary of the

CT by auto-transformer. Note down the secondary current.

4.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.

5. Now increase… Continue

### Effect of Over fluxing in Transformer

Some of the effects of over fluxing are as follows:

i. Significant increase in core losses.

ii. Formation of hot spots.

iii. Increased leakage flux and magnetizing current.

iv. Delayed operation in case of inverse-time over current relay.

v. Over-reach and under-reach problems in impedance relays.

vi. Introduction of harmonics.

### Over fluxing in Transformer

ransformers are among the most important and expensive equipments that always been used in industry and power system. Transformers are generally designed to work just below peak value of magnetic flux, so proper analysis of transformer behaviour under over fluxing condition is necessary.

Transformers are designed in such a way that under steady state operating conditions they can operate near peak magnetizing flux but below the saturation level. When the transformer core is… Continue