SHORT CIRCUIT STUDY 2

Question 1

when will be the stability of system will be lower?

Answer 1

when we have higher impedance

Question 2

what are the inputs of grid we must get from client or utility?

Answer 2

1) 8 info(max and min 3ph Isc and corresponding X/R(4),max and min 1ph Isc and corresponding X/R(4))
with considered C factor
or
2)12 INFO(max sc current’s +ve,-ve,zero seq impedance and correspondin X/R(6) and min sc current’s +ve,-ve,zero seq impedance and correspondin X/R(6))

Question 3

when will be +ve and -ve sequence will not be equal

Answer 3

if rotating machines are present near

Question 4

sc mva formula

Answer 4

1.732open circuit voltage(V)sc current

Question 5

3ph fault current will be higher or lower than SLG fault current generally

Answer 5

higher except in few cases

Question 6

where SLG fault current will be more than 3 ph fault current?

Answer 6

1) solidly grounded gen(Z0 and Z2 less than Z1 for larger capacity)
2) solidly grounded wye side of a delta wye trafo of the 3phase core(three leg design)with no load
3) the ground wye side of auto transformer with tertiary delta
4) in delta/wye trafo, if there is no fault contribution from lv side

Question 7

does SLG fault is affected by winding configuration?

Answer 7

yes

Question 8

role of Isc/iL?

Answer 8

1) dictates what is the voltage drop in normal condition
2) dictates what is the voltage drop in motor starting
3) )dictates what is the THD in harmonics
4) dictates what is the system strength
5) dictates what is the fluctuation for oscillation(transient stability)
6) dictates what is the voltage for faults at other places

Question 9

when sc current is more,how will be the voltage change?

Answer 9

less

Question 10

in between peak value and RMS value, X/R and Z decides which one?

Answer 10

1) X/R decides peak value(higher X/R ,higher peak current)

2) Z decides RMS value

Question 11

what decides what is the current for L-L fault?

Answer 11

+ve and -ve seq impedance

Question 12

does NGR limits 3 phase fault current

Answer 12

no.it will limit SLG fault only

Question 13

can we ask higher Xd” from gen manufacturer ?why?

Answer 13

yes because we can reduce fault current by means of higher impedance

Question 14

in which system X/R value is higher ?

Answer 14

in HV .MV and LV has lower X/R

Question 15

my X/R at different level?

Answer 15

1) X/R up to 60 when your system is close to trafo
2) X/R is 20 for long TL with high conductor size
3) X/R is 5 or 10 for long TL with small conductor size
4) X/R is small for distribution system

Question 16

is 3ph fault dependent on winding configuration?

Answer 16

no