k.prakashchandra


{ City } karkala
< Country > india
* Profession * rtd e.e.
User No # 54717
Total Questions Posted # 0
Total Answers Posted # 521

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Users Marked my Answers as Wrong # 525
Answers / { k.prakashchandra }

Question { 2711 }

A group of machines (wind turbines) connected with 33KV
feeder and each machines are having individual VCB. The 33KV
feeder connected with 110KV/33KV substation. The 33KV feeder
tripped by over current at Substation and fault recorded at
Substation as OC-R&Y phase. Same time the group of machines
VCB tripped by over voltage, the fault recorded voltage was
above 66KV by numerical Under/Over voltage relay. While grid
drop time, this much of voltage hike is possible?


Answer

The load throw-off may result in run-away speed being equal
to twice the normal speed ,hence the voltage may also become
twice. Over voltage relay should be set at not more than
120%.You can employ the AVR so that the voltage does not
increase with the speed.

Is This Answer Correct ?    1 Yes 0 No

Question { HBL Power Systems, 5442 }

What is the permissible value of earth resistance and as per
which standard / act / rule ?


Answer

In case of stations the minimum values in ohms are 33
KV-5,66 KV-2,110 to 400 KV-1 and for gen stn -0.5

Is This Answer Correct ?    0 Yes 0 No


Question { 3019 }

in magnetic field we send current to generate flux,why not
voltage?


Answer

mmf(AT) depends on number of turns and current

Is This Answer Correct ?    0 Yes 0 No

Question { GE, 16463 }

why battery dc voltage become Half when we check with
respect to ground for example 120volts + and - terminals
and when we check + terminal with Earth thats 60volts why
60volts we can not ground the battery.


Answer

The midpoint of rectifier transformer secondary is
earthed.The potential of ground is taken as +/- 0.The
voltage measured between any terminal wrt ground will be +/-
half the full voltage.This method is helpful to trace a
single polarity and for earth fault locator.

Is This Answer Correct ?    6 Yes 3 No

Question { GE, 16463 }

why battery dc voltage become Half when we check with
respect to ground for example 120volts + and - terminals
and when we check + terminal with Earth thats 60volts why
60volts we can not ground the battery.


Answer

The above answer is correct.If you use an earth fault
indicator ,you are able to measure voltages. And if you run
both leads along the ground or a metal surface ,you can
measure voltages with a digital voltmeter ,as the
capacitances between the leads and the surface/ground, bring
the surface/ground to +or- zero potential.

Is This Answer Correct ?    0 Yes 0 No

Question { 6344 }

HOW TO CALCULATE BATTERY BACKUP TIME & AH CAPACITY AGAINST UPS
KVA RATING?


Answer

Battery back up time depends on actual/real load in KW ,not
the KVA rating of the UPS.

Is This Answer Correct ?    3 Yes 0 No

Question { GE, 6493 }

DEAR ALL
I have motors ( 10 units )each one is 90kw 380V 50 HZ 1000rpm
but new local pwer is 220v 60 hz
requierd rpm should be 1000
pleas what the beast solution is used frequncy converter or
rewinding all motos or chang all motors
thanks


Answer

VFD/ gear box is mandatory as 1000 rpm can not be the
synchronous speed with supply at 60Hz.

Is This Answer Correct ?    1 Yes 0 No

Question { Etimaad, 4042 }

why battery dc voltage become Half when we check with
respect to ground for example 120volts + and - terminals
and when we check + terminal with Earth thats 60volts why
60volts same result on 24Volts and with ground 12Volts only
expert answer that thanks
we can not ground the battery.


Answer

In case of bridge rectifier , the mid tap of the rectifier tr is earthed or two high resistances in series are connected across the charger out put terminals and the common point of the resistors is earthed . Hence the ground potential becomes (+ or -) zero

Is This Answer Correct ?    0 Yes 0 No

Question { 4206 }

In a incandescent bulb, if the glass is punctured, and then
power is supplied, the tungsten filament blows up with a
flash.Why?


Answer

Presence of oxygen

Is This Answer Correct ?    2 Yes 1 No

Question { 3146 }

how to calc. current for 5MVAR,50hz,33kv


Answer

Only MVAR is present ,calculate current treating it as MVA

Is This Answer Correct ?    5 Yes 3 No

Question { NTPC, 6692 }

For 300MW and over a distance 250 km, what voltage be
selected? and no. of circuit?


Answer

At least, 220KV DC ,with kundha/zebra/deer/drake/moose ACSR
conductor

Is This Answer Correct ?    0 Yes 2 No

Question { NTPC, 6692 }

For 300MW and over a distance 250 km, what voltage be
selected? and no. of circuit?


Answer

It is better to have a gen station nearby or go in for HV DC transmission

Is This Answer Correct ?    0 Yes 0 No

Question { 4204 }

what are the reasons for overheating in electrical machines?


Answer

Cooling vs heat generated

Is This Answer Correct ?    0 Yes 6 No

Question { 35884 }

What happen when the AVR of the generator fails? Will it cause
power instability and total failure of the alternator?


Answer

Generally if there is failure of AVR , excitation will switch over manual mode .

Is This Answer Correct ?    1 Yes 0 No

Question { 35884 }

What happen when the AVR of the generator fails? Will it cause
power instability and total failure of the alternator?


Answer

Further ,the ' loss of excitation relay ' should act to trip . If it does not and the prime mover is still working , then the gen will run as induction generator . It may disturb stability as the pf is very low .

Is This Answer Correct ?    0 Yes 0 No

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