Question { 31621 }

what is the difference between "ampere trip and ampere frame"

Answer

Ampere Frame [AF] it is the rating breaker current [maximum
current which the breaker will withstand for a long
time].Ampere trip [AT] it is the current set to trip the
circuit [usually from 60% up to 100% of the AF].

Question { 2369 }

Hello, I am just preparing my self for a university interview and struck on the 11kv ring main unit system network. I just know that ring main unit has total three breakers, fuses and use to supply a power to any load/ building without any interrupt. But i am not be able to visualize the connections, either Ring main unit getting power from two different power sources? or there is always one feeder in complete ring circuit??? I would be highly thanks full of you help me.

Answer

There are many possibilities.See:
http://ms.schneider-
electric.be/Main/RM6/catalogue/AMTED398032UK.pdf

Question { BARC, 4210 }

which cable is preferred PVC OR XLPE for voltage from 220V
to 11 KV with proper justification

Answer

See:
http://www.ijetae.com/files/Volume2Issue10/IJETAE_1012_57.pd
f

Question { Jindal, 5951 }

What is main difference between
earthing and neutral grounding?

Answer

See:
http://control.com/thread/1026202024
Posted by Bob Peterson on 20 October, 2004 - 11:41 pm

Question { SSC, 4833 }

a solenoid of inductance 250mH and resistance 10ohm is
connected to a battery. the time taken for the magnetic energy
to reach 1/4th of its maximum value will be?

Answer

Magnetic energy is W=B*H =miuo*H^2=K*i^2
Wmax=K*Imax^2 ¼*Wmax=K*Imax^2/4 i=Imax/2
The current equation it is: i=Imax*[1-e^(-t*L/R)] . If
i=1/2*Imax then : e^(-t*L/R)=1/2 and t=-LN(1/2)*R/L R=10
ohm L=0.250 H t=27.73 sec.

Question { Jindal, 3258 }

Our Company's Contract Demand is 110 kVA. We use 12
Capacitors each of 12.5 kVAr Capacity to maintain Power
Factor of 0.99. So, what steps should we take so that our
Contract demand does not exceed 110 kVA?

Answer

In order to know how much capacity to use one has to know
what is the now the actual power factor. Let’s say the
actual power factor is 0.8.Then the reactive power is
110*sqrt(1-0.8^2)=66 kVAr.
If the power factor is 0.99 then the reactive power from
the Utility will be 110*sqrt(1-0.99^2)=15.5 kVAr.
You have to compensate the difference 66-15.5=50.5 kVAr so
4*12.5=50 kVAr it is enough.

Question { 6011 }

Is there is any difference between AC and DC Cables

Answer

Practically there is not any difference.If the insulation is suitable for both
only the maximum permissible current will be different.In d.c.system the losses
in conductor are lesser-since no skin or proximity effect is involved and then the
conductor will reach the maximum permissible temperature for a more elevated current.

Question { 5532 }

difference between turns ratio and transformation ratio?

Answer

The transformation ratio of a power transformer it is the ratio between primary
EMF [Electric Magnetic Force-the voltage induced by magnetic flow in a coil] and secondary EMF.This ratio equals the ratio between primary and secondary number of turns.

Question { Aurobindo, 7465 }

what is the distance between two overhead lines

Answer

See:NESC National Safety Code clause 233.
See: http://www.rurdev.usda.gov/supportdocuments/uep_bulletin_1724e-200.pdf
Section 6

Question { ACPL, 1485 }

why ac wave is sinusoidal not square or triangular wave what will be reason

Answer

The a.c. electricity is produced in an a.c. generator which transform mechanical energy [from a turbine or diesel motor or else] into electrical energy.
In a synchronous generator the rotor produce a magnetic field -as permanent magnet or from d.c. current flowing through wired bobbins.
Let's take a single loop of the stator coil and expose it to a rotating magnetic field.
The EMF [electromotive force=induced voltage in the loop] =E=-dΦ/dt where:
Φ=magnetic flux through one stator [armature] loop
E=Electromotive Force [induced voltage]
Since the armature [stator] loop does not move then the magnetic flux shared with the loop is changing with the angle between loop surface and rotor pole surface. Φ=BxAxcos(α).where:
B =magnetic flux density produced from magnetic pole
A=magnetic pole area
rpm=no.of rotations per minute
Finally, E=BxAxsin(ωxt) where ω=2xπxpxRPM/60 p=no.of pole pairs t=time
That means the produced voltage depends on sinus of time.