I agree with the TOV consideration mentioned above.
Just to directly answer the original question. The purpose of the grounding transformer is to limit TOV during fault and less to do with fault detection. Here is a sequence of events.
- Feeder SLG fault
- Upstream substation breaker trips...
you definitely need a separate relay for the differential function, probably CT as well since it might not be possible to split the recloser ct output to the differential relay. the restricted earth fault element also need to CT the transformer neutral.
using the recloser as the interrupting...
look at the arrestor data sheet again, the clamping voltage (or residual voltage or discharge voltage) should be given for multiple surge waves. The most common one is 8/20 micro seconds 10 kA. this clamping voltage is the kV that develops across the arrester when the arrester is subjected to a...
no it has nothing to due with the delta windings. This happens when zero sequence impedance is lower than positive sequence impedance or single phase ground fault current is higher than 3 phase fault current. It could happen on distribution system too as mentioned above, you can open circuit the...
Yes i agree, it is realistic for phase to ground current to be higher 3 phase fault current for those reasons. I just never considered/understood the voltage impact of it.
ok PSCAD support was no help, but at least I understand mathematically why the healthy phase voltage can drop during SLG fault.
For phase A to ground fault, connect the sequence network in series blah blah, we can calculate V1 V2 V0. Typically Z0 is higher than Z1 (also satisfying X0/X1<3)...
Hi
I have an effective grounded 500kV system. If I apply a single phase to ground fault, I expect the fault phase to ground voltage to be 0 at the point of the fault, while the other two healthy phase to ground voltage to increase (amount affected by system grounding).
However the simulation...
thanks for everyone's reply.
modelled a sample system in CYME using two transformers, one is DY11, the other one is Yg Yg. (44/12kV 5MVA). closing the tie switch cause 1000A circulating current in the loop. Not the biggest fault, but certainly would trip all the feeder protection.
A theoretical question. If I have 2 feeders supplied from 2 different substations with different vector group. These 2 feeders are 30 degrees apart, what happens if I close a tie switch between the 2 feeders?
The instantaneous voltage is different so there should be fault at the tie switch...
if you're certain the relay is nuisance tripping on transformer inrush, then SEL already have a solution.
It's called 2nd harmonic blocking logic, basically during inrush, current contains high magnitude of 2nd harmonic signal. The relay detects this condition and uses it to supervise various...
@che12345
"2. The power source phase AB (is a single vector) supplying T1 load I1 and T2 load I2 respectively"
this is not true, when you flip the H1H2 for the second transformer, the voltage vector BA is supplying this transformer, Vab amd Vba is 180 out of phase. Also Phase A = Phase B is...
yeah I figured it out with vector diagrams. turned out it doesn't matter which bushing goes on which phase,
if one transformer is connected AB, primary feeder phase A current is I, B would be -I.
now add a second transformer, regardless of connection order AB or BA, the primary feeder phase...
thanks che
what about return current of I1? let's remove the second transformer for now. the system is just 1 transformer connected between A and B. phase A will have I1 like you said, but the current on phase B will be negative I1 or I1 angle 180.
now add the second transformer. I don't...
well, if i have only 1 transformer on the system connected between A and B, the current will flow from A to B. If i connect a transformer between B and A, theoretically the current for this connection is from B to A? Now if we have both connection on the same feeder, what happens to the current...
thanks for the reply, but the two transformer secondary are not tied together in any way. treat them as independent locations.
if these two transformers are supplying the same amount of load each, i was wondering how does the current flow on the primary phase conductors assuming the system...
well transformers have two primary bushing (H1 and H2), secondary is just single phase to ground, assume X1 is the high side and X2 is connected to ground, load will be connected from X1 to ground(X2)
when i say connected to phase A and B, i meant the H1 connected is to A phase and H2...
Hi
I have two identical distribution single phase transformers. If the first one HV bushings are connected to phase A and B, and the second one is connected to phase B and A. Then does that mean the loading current flow on the feeder phase A and B are 0 (cancel out)?
thanks
1)
http://engineering.electrical-equipment.org/electrical-distribution/delta-wye-transformer-phase-phase-fault.html
another simpler explanation is LL fault current = (Va-Vb)/(Z1+Z2) = (Vab)/(Z1+Z2) = (1.732*Van)/(2*Z1) = (1.732/2)*(Van/Z1) = 0.866*(Van/Z1)= 0866*(3ph fault) this is where the...
