Satyadev Vyas's Blog (8)

Transformer Over Fluxing Protection

The cooled rolled grain oriented(CRGO) core is used in the transformer. The flux produced in the primary travels through the magnetic core and gets linked to the secondary. The maximum flux density of the CRGO core is 1.9 Tesla and if the core is magnetized above the rated capacity, the core gets saturated. The saturation of the core cause heating in the core and the other parts of the transformer. The flux density in the core should not increase above the…

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Added by Satyadev Vyas on June 24, 2019 at 9:44pm — No Comments

Significance of back EMF in DC Motor

When the DC voltage is applied to the armature of the DC motor,the motor draws enormously high current at the starting time and it decrease as the motor accelerates.Why the DC motor draws high armature current at the starting and how the current get decreased as the motor accelerates is because of the counter potential force developed across the armature winding. The counter voltage induced across the armature winding is called the back EMF. 

The counter EMF…

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Added by Satyadev Vyas on June 24, 2019 at 5:30am — No Comments

True Power Factor

True Power Factor :

In a harmonic rich network, the over all power factor of the electrical network not only depends on the displacement power factor but it also depends on the harmonic distortion in the electrical network. The…

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Added by Satyadev Vyas on June 9, 2019 at 10:22pm — No Comments

Why induction motor takes high starting current?

The induction motors are widely used worldwide for various applications.The motor takes high starting current at start.When the three phase supply is fed, a rotating magnetic field set up in the air gap.The flux get linked to the rotor winding and voltage is induced in the rotor conductor.The magnitude of the induced voltage depends on the difference between the synchronous speed and the actual speed of the motor.At start, this difference is maximum and equals to 1. We can say the slip of the… Continue

Added by Satyadev Vyas on May 28, 2019 at 11:44pm — No Comments

Polarization Index Test -PI Test

The polarisation index test of electrical insulation is the key criteria for testing the healthiness of electrical system.

The failure of the insulation cause the device to fail. The insulation resistance value goes down as the temperature increases. The insulation resistance gets halved with  every increase in temperaure by 10 degree centigrade.The moisture also cause the insulation failures. The checking of insulation resistance is one of the method for ensuring healthiness. However,…

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Added by Satyadev Vyas on May 1, 2019 at 10:23am — No Comments

CT Grounding practices- CTs must be grounded at a single point- Why?

The CTs must be grounded at the single point. The grounding of the CTs at the multiple points lead to the voltage of different magnitude at two points. The realy used for the differential protection may operate when the fault is outside of the protection zone.

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Added by Satyadev Vyas on April 22, 2019 at 6:24am — No Comments

Why V/f ratio is kept constant in VFD?

The flux produced in the core can be calculated with the formula as given below.

The EMF in the stator/phase(Eb)= -n* Rate of change of flux


Flux = Eb/ 4.44 f*n ----------(1)
Where Eb is the back EMF/phase produced in the stator, f-frequency,…
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Added by Satyadev Vyas on April 19, 2019 at 4:30am — No Comments

Knee Point Voltage of current Transformer and How to calculate it?

The knee point voltage(KPV) of the current transformer tells the information about the magnetization characteristics of the current transformer. According to IEC,the knee point voltage is defined as a point where 10% increase in the secondary voltage cause an increase in the secondary current by 50%. The current transformer gets saturated at this point.…

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Added by Satyadev Vyas on April 19, 2019 at 4:30am — No Comments

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