Technical question with answer

Why capacitor pass A.C and Block D.C ?

The way capacitors and resistors behave is totally

different. While resistors allow a current to flow through

them which is proportional to the voltage drop across the

resistor, capacitors oppose a change in voltage across them

by either drawing in or supplying current as they charge or

discharge resp. The flow of current through a capacitor is

thus directly proportional to the rate of change of voltage

across it.

This is given by the relation, i = C* (de/dt) where de/dt is

the instantaneous change in voltage.

As the voltage does not change in the case of DC, de/dt = 0

and the current that is allowed to pass through by the

capacitor is 0. For AC voltage the voltage changes in a

regular manner. Hence here de/dt is not 0 and a current is

allowed to flow through by the capacitor.

what happen to a dc series motor if it given as ac supply 

accidentaly

if ac supply accidently given to dc series motor, for first

half cycle it run but another negative half cycle it should

be run opposite direction but due to rotor inertia it will

not happend but there is opposite force excerted on rotor &

motor stop this process require fraction of second so it

look like its not running.so motor will not running.

what will happen if transformer given dc input

If DC is applied to transformer its winding will act as 

source of unidirectional flux which causes core saturation 

(if DC supply of sufficient magnitude is applied 

continuosly).Thee will not be indused EMF in either 

winding.Due to this reason transformers are not used in DC 

supply .

it is clear that volts equal to the current as per ohms law. is it appliable to the AC power or only for DC. if it is appliacable to AC in transformers when voltage increases the voltage decreases ????? why??????????????

Ohm's Law holds good in both AC as well as DC,however, with 

a slight modification in case of AC. In DC, the ratio of 

voltage(V) across  load(conductor)terminals to the current

(I) flowing through it,at any instant of time, always gives 

the "RESISTANCE" of the load(conductor); while in AC, it 

always gives "IMPEDANCE" of the load(conductor). However, 

in both the cases the external physical conditions(such as 

temperature , pressure,etc;)  should remain same; otherwise 

Ohm's Law will not hold good. 

A transformer is a static machine which just transforms

(changes) the voltage levels on either side of its 

connection. It does not generate any energy of its own. It 

rather consumes some portion of energy inthe form of losses

(Copper loss & Iron loss). If we neglect these losses, then 

power(energy) supplied to the transformer will always be 

equal to the power(energy) drawn from it.In other words, a 

transformer is a constant power machine, it has to keep 

power on both sides same. Since power(P) is given by 

P=V*I. So for changing voltage levels, it has to change the 

current levels also.Here the valid expression would be 

V*I=Constant and it has nothing to do with Ohm's Law. Ohm's 

law has its own definition and holds good in its own 

conditions, While as voltage transformation holds good in 

its own conditions. These are two different things. 

However, in any case Whatever voltage,AC or DC(from any 

side of the transformer or any other source) is applied to 

any load, Ohm's Law will hold good with  the modifications 

as described above in para 1.

what is the simple meaning of harmonics?

Harmonics are the integer multiple frequncy signals present 

along with the fundamental frequency in a circuit. e.g.

2nd harmonic freq = 2*fundamental freq.

3rd harmonic freq = 3*fundamental freq.

What are the complete specifications of a motor?.

Motor phase, type of motor,voltage rating, type of

connection (star/delta), Maximum current, operating

frequence, tolerance level, class of insulation, serial no,

design code, thermal resistivity, operating temperature,

class of frame, rated KW,

 power is the product of voltage and current.so we can measure the value of power just by using ammeter and voltmeter.......then why do we use a wattmeter?

apperent power = voltage X current,

we can calculate apperent power by ammeter and voltmeter 

reading but

real power = voltage X current X power factor

to measure real power we need wattmeter

 what are the standard transmision voltages in india?

 Standard transmission voltages in india is 11kv, 33 

kv,66kv,132kv,220kv,400kv and 760kv

 What is the principle of Induction Stove?

Induction stove works on the principle of electromagnetic induction and EDDY currents. Its basically a transformer with your utensil acting as a shorted secondary. The primary coil is embedded just below the heating surface. When a ferromagnetic utensil is kept on the surface, it acts as a shorted secondary which induces heavy eddy currents in the secondary (utensil) which heats up the food. In this case, for the food, the container acts as the heat source (this is the reason why food seldom gets stuck on the container and also the container gets heated up very slowly resulting in very less heat loss and the efficiency is very high (close to 90% or more).

If the material of the utensil has a greater area under the hysteresis, then heating will also be contributed through magnetizing and De-magnetizing effect (apart from eddy currents). The frequency is used such that it has optimum skin depth for typical utensil thickness.

At a circuit level, it is basically a LC tank circuit which is energized via a H-Bridge circuit (typically implemented using IGBTs due to higher operating power).

The best part about induction stove is that it consumes very less power due to the switching nature of circuitry. When you don't place a container on the stove or place a non-ferromagnetic container, the secondary acts as an open circuit and the current sensing circuit in the primary will turn off the device. 

The only drawback i see is the material dependence and flat bottom utensil requirement.

What is Ten Delta Test ?

In our substations,tan delta tests were carried out on 

transformer Bushing.This test is done 

1)To ensure the dielectric strength of insulation or

2)to predict the life of bushing.

what they are doing is they are measuring the capacitance 

values.If the capacitance values are good means insulation 

is good.

what is the difference in inductance and resistance.both oppose the flow of current but how.resistance having + ve power in both cycle while inductance having both power.

Resistance will produce electrical quantity in to heat,but 

inductance will store electrical energy as a magnetic 

energy.

While currrent flowing in resistance that will be in phase 

with voltage so it will produce positive power in both cycle

(+P=+V * +I  ,+P=-V * -I),but in inductance current will 

lag the voltage by 90deg,so power will produced positive 

and negative sign alternatively.

What is the principle of Induction Stove?

Induction stove works on the principle of electromagnetic induction and EDDY currents. Its basically a transformer with your utensil acting as a shorted secondary. The primary coil is embedded just below the heating surface. When a ferromagnetic utensil is kept on the surface, it acts as a shorted secondary which induces heavy eddy currents in the secondary (utensil) which heats up the food. In this case, for the food, the container acts as the heat source (this is the reason why food seldom gets stuck on the container and also the container gets heated up very slowly resulting in very less heat loss and the efficiency is very high (close to 90% or more).

If the material of the utensil has a greater area under the hysteresis, then heating will also be contributed through magnetizing and De-magnetizing effect (apart from eddy currents). The frequency is used such that it has optimum skin depth for typical utensil thickness.

At a circuit level, it is basically a LC tank circuit which is energized via a H-Bridge circuit (typically implemented using IGBTs due to higher operating power).

The best part about induction stove is that it consumes very less power due to the switching nature of circuitry. When you don't place a container on the stove or place a non-ferromagnetic container, the secondary acts as an open circuit and the current sensing circuit in the primary will turn off the device. 

The only drawback i see is the material dependence and flat bottom utensil requirement.