Question { 5210 }

why 3 phase motors are preferable over single phase motors ?

Answer

because if u take a same capacity rating of both 1 phase
and 3 phase ,the size of 3 -phase motor is small compared
to 1-phase.

Question { Engineering, 62001 }

1.In two wattmeter method if one wattmeter shows Negative
reading then wat is reason?
2.Wat is the reason for low voltage in houses?
3.Wat is meant by current and voltage? wat is difference
between the two?

Answer

two watt meter method is used in measurement of power under un balanced condition.there are two reasons for - ve value
1). if load consist of more inductivd or capacive load with negligible resistive then it will show _ve value .pf angle is more than 65 deg
. in case of induction motor no load test one of the watt meter will indicate _ve because no load pf is 0.2 lag pf angle is nearer to 75 deg
2).reverse. connections of current coil

Question { 4452 }

why we are using large cross section cable at load side and small at other (11kv to trsfr)side of transformer?
when the load increses current at both side increases,right?

Answer

conductor size will be depends upon of the current carrying capacity. wen i m talking about transformers,transformer voltage, current changing device but constant power(KVA) device.so if it is a step down transformer ,current will flow through the secondary is greater than primary to ensure thAt maintain const power on both sides thats why LV conductors are more size compared to HV.if it is a step up transformer vice_versa

Question { 5872 }

Which system is best for industries 3ph 3w or 3ph 4w?

Answer

3ph 4 wire is best suitable for un balaced loads & wher we can have single phase loads also.but it will require more volume of conductor than compared to 3 ph 3 w..

Question { Avalon, 5990 }

why the neutral point of star connnection oscillates?

Answer

i want to tell you about neutral flowting .if 3-phases are
balanced then neutral displacement is zero degrees.if fault
occured in any fault neutral will displaced from zero
degrees to those faluty phase thats why neutral will
displace from one phase to anothe phase.

Question { 7584 }

Why the electron
flow in reverse
of current.

Answer

currents are two types 1).conventional current
2).directional current
if u take a semi conductors then current is due
to both of electrons and holes .electrons will flow towards
+ve terminal battery supply,in case of holes flows to -ve
terminal conventional current .in case of diodes arrow head
shows that conventional current i.e opposite to electron
current so in semiconconductors u are correct
but in case of metals current is due to
electrons only holes will not exit .direction of current is
same as voltage polarity