D1 Use Electrical Circuit Concepts

Question 1

How do you get average value of current?

Answer 1

Eav = 0.637 x peak value (Im)

Question 2

How do you get effective value? (E or I)

Answer 2

E is equal to 0.707 x peak value (Em)

I is equal to 0.707 x peak value (Im)

Question 3

How do you find peak value from RMS?

Answer 3

To find peak value from RMS:

ERMS x 1.414(90• sine) = peak (Em)

ERMS / 0.707(45• sine) = peak (Em)

ERMS = Em x 0.707

Question 4

What is RMS and what is it’s formula

Answer 4

RMS=Root mean square, the power in a resistor is directly proportional to the square of the current or voltage:

P = I*2R
P = E*2/R

• = squaring

Question 5

List all six effective resistances

hint S-H-R-E-D-O

Answer 5

Skin effect
Hysterisis loss
Radiation loss
Eddy currents
Dielectric loss
Ohmic resistance in pure form

Question 6

What is the skin Effect?

Answer 6

Skin effect:

Most current flows on the outer surface of the conductor. The expanding and contracting lines of force in a conductor are most dense at the center and as such push the current to the outside of the conductor. This is the same as reducing the cross sectional area of the conductor and this effectively increases it’s Ohmic resistance value

The Higher the hertz (Hz) the more extreme the effect

Question 7

What is Hysterisis loss?

Answer 7

Hysterisis loss, as AC frequency is constantly. Changing the magnetic domain, the direction is constantly being reversed, this creates an energy loss in the form of heat

Question 8

What is Eddy current loss?

Answer 8

Eddy currents,

The core of the magnetic field acts like a conductor and has currents induced within it, these are called eddy currents

( 1Tesla)

Question 9

What is Dialectric loss?

Answer 9

Insulating material exposes to and electric field is referred to as a Dialectric. When voltage is applied against a dielectric and this results in a heat loss, this heat is generated from the circuit.

Question 10

What is radiation loss?

Answer 10

Radiation losses, at higher frequency some of the magnetic lines of force escape from the conductor and do not return, these lines of force are energy, this energy loss results in a higher effective resistance.

Question 11

What is Ohmic resistance in pure it’s pure form?

What is it’s formula?

Answer 11

Pure Ohmic resistance, as the conductor heats up due to it’s positive temperature co-efficient it’s effective resistance goes up

(R= P/I*2)

*means squared

Question 12

What is the formula for factors affecting inductance?

Answer 12

L= N*2uA/ &

L= inductance
N= Number of turns in the coil
u= permeability of the core material in webers per ampere turn in metres.
&= length of the core in metres.

Question 13

How do you get instantaneous voltage? (e)

Answer 13

e =Em x Sine angle theta degree

Question 14

What is Faradays law of electromagnetic induction?

Answer 14

Faradays law of electromagnetic induction:

B= flux density in Teslas
L= active Length in meter form
V= velocity meter per second
E= Voltage generated in volts

E= BLV
L= E/BV
B= E/LV
V= E/BL

Question 15

What is the time constant formula?

Answer 15

Time constants
During each time constant, the current increases by 63.2% of the difference between it’s starting value and steady state. After five time constants (¥), the current reaches 99.3% of steady state value. Achieved after five time constants

¥= length of one time constant in seconds
L= inductance of the circuit in Henries
R= Resistance of the circuit in Ohms

¥= L/R

¥= not symbol for the Greek letter Tau

Question 16

What are the formulas for the rise of current in a theoretical inductor?

Answer 16

Es= -L ^I/ ^t = Eav

^I/^t= - Es/L

Es= Er + E L
Es= IR+ L ^I/^t

- = induced voltage as a counter electromagnetic force (emf)
t= time in seconds
Eav = average generated voltage 
Es= source voltage
L= inductance in Henries
^I/^t= average rate of change in a current over time in amp per seconds.

Question 17

What is the formula for energy stored in an inductor?

Answer 17

W= 0.5 LI*2

W= energy stored in the inductor ok joules
L= induction in the inductor in Henries
I= max current flowing through the inductor. ( this is a steady state)

Question 18

What is the formula for the fall of current (I) in a practical motor?

Answer 18

E= IR

Ohms law

Question 19

During each Time constant how much does the current increase between the different starting values and it’s steady state?

Answer 19

63.2%

Question 20

After five time constants, the current reaches ______ of steady state value for practical proposes, it is agreed that current reaches steady state after __ time constants.

Answer 20

Current reaches 99.3%

Current reaches a steady state after 5 time constants.