Voltage Unbalance Reason

[Sahib]

both cases, whether connected or not, over voltages are present at bus , i just connected it to ground as routine practice

Over voltage is phase to neutral, no phase to phase over voltage. Correct?

 

[Ingenieur]

Over voltage is phase to neutral, no phase to phase over voltage. Correct?

my guess yes
his measurement of ph-ph 150,150,300 and ph-n of 600 bear this out
plus the ph displacement of 0 +/- 15 deg indicate 0 seq values
ph-ph is normal
ph-n is elev
gnd fault with some fault Z on an ungrounded wye system

that is why :
when he gnds the mv it trips

when at least 1 gen is online he is grounded and isolated by the xfmr
so lv is good, ie, stable reference

when he loses both he has no gnd ref and the backfeed mv to lv via xfmr is elev


if when you isolate the customer and all things are good is not enough proof for him I have no idea what will be
the feeder (s) need megger'ed
but it may be internal to his equip
may not be easy to isolate
good luck

 

[mrmuneeb]

Over voltage is phase to neutral, no phase to phase over voltage. Correct?

whenever we take meter prob near to the bus bars to measure from approx 3 mm meter prob catches spark, crriii crri criiiiiii......

phase to phase are ok apparently...

 

[Sahib]

Ingeniur: the OP says the neutral conductor to controller is grounded. Then how over voltage damage to the controllers?

 

[Sahib]

In continuation of the above question, here is another question. mrmuneeb, is the transformer, you use for sensing the voltage, connected on the MV side phase to neutral or phase to phase?

 

[Ingenieur]

Ingeniur: the OP says the neutral conductor to controller is grounded. Then how over voltage damage to the controllers?

the prim n-gnd is elevated ph/sqrt3

so imo across the controller ph-n sensing input he is seeing >277
he said he measured 600!

I would guesd the input is a solid state input, not a xfmr

 

[Ingenieur]

In continuation of the above question, here is another question. mrmuneeb, is the transformer, you use for sensing the voltage, connected on the MV side phase to neutral or phase to phase?

from his sketch and response he is sensing directly (no xfmr) from the lv side
wonder how the xfmr ph shift is handled?

 

[mrmuneeb]

In continuation of the above question, here is another question. mrmuneeb, is the transformer, you use for sensing the voltage, connected on the MV side phase to neutral or phase to phase?

for sensing, we are not using anything extra, same power transformer is being used also for voltage sensing to which we are feeding power from generator.

as of phase to phase voltages, i have one phase at higher voltage,

check video below;

https://youtu.be/hsPc9VpYDXU

 

[mrmuneeb]

further inside panel, see below video where fuses have been removed for panel safety,

Two of the phases are ok, thord one is sparking when measured with rest of the two...

https://youtu.be/NIxo3jV8sQ0

 

[mrmuneeb]

for sensing, we are not using anything extra, same power transformer is being used also for voltage sensing to which we are feeding power from generator.

as of phase to phase voltages, i have one phase at higher voltage,

check video below;

https://youtu.be/hsPc9VpYDXU

this spark is coming with every phase, i mean to say that, even when single prob of meter is taken closer to the bus bars or connector strips, it catches an arc, meter basically is max of 600v, that's why i am assuming of higher that 600 as can be seen by the spark.

messed up.....

 

[Sahib]

mrmuneeb, why can't you automatically isolate the controllers also when both the engines i.e the generators are tripped, thereby avoiding over voltage damage to the controllers?

 

[mrmuneeb]

mrmuneeb, why can't you automatically isolate the controllers also when both the engines i.e the generators are tripped, thereby avoiding over voltage damage to the controllers?

yes sir, they can be isolated automatically, but to sync again we need to connect to bus, and connecting again will cause damage as bus voltages remains high, we have to switch off the main Ring unit that is feeding to the client in order to sync additional engine.

engine needs bus sensing before closing on to bus.

on each pair(as shown in previous diagram) there must be one engine closed onto bus in order to sync the 2nd generator on the same transformer.


issue is on client side and is phase to ground, also seems to me that its location is far from our power plant, residential loads, distributed over a huge area.

 

[Sahib]

yes sir, they can be isolated automatically, but to sync again we need to connect to bus, and connecting again will cause damage as bus voltages remains high, we have to switch off the main Ring unit that is feeding to the client in order to sync additional engine.

engine needs bus sensing before closing on to bus.

on each pair(as shown in previous diagram) there must be one engine closed onto bus in order to sync the 2nd generator on the same transformer.


issue is on client side and is phase to ground, also seems to me that its location is far from our power plant, residential loads, distributed over a huge area.

When the two engines i.e the two generators are off, there is back feeding of power from MV side. Due to grounding of one phase (B phase in your case), the voltages are not balanced and as a result, there is over voltage in the LV bus damaging the controllers. So the first thing you have to do is to trace the ground fault in B phase and rectify. For that, why can't you engage a specialized agency to trace and rectify the ground fault in B phase?

 

[mrmuneeb]

When the two engines i.e the two generators are off, there is back feeding of power from MV side. Due to grounding of one phase (B phase in your case), the voltages are not balanced and as a result, there is over voltage in the LV bus damaging the controllers. So the first thing you have to do is to trace the ground fault in B phase and rectify. For that, why can't you engage a specialized agency to trace and rectify the ground fault in B phase?

as the fault is on client end so we have informed client, but to prove that its on client end i am looking for a valid reason/proof.

i only have following reason "opening the main ring switch to client makes system normal"

for that client is arguing "why your main ring switch not tripping if there is any earth fault?"

however our main ring switch is set at 10% for 51(ANSI) & 50% for 50N(ANSI) these are the lowest possible settings for that ring main switch.

 

[Sahib]

as the fault is on client end so we have informed client, but to prove that its on client end i am looking for a valid reason/proof.

i only have following reason "opening the main ring switch to client makes system normal"

for that client is arguing "why your main ring switch not tripping if there is any earth fault?"

however our main ring switch is set at 10% for 51(ANSI) & 50% for 50N(ANSI) these are the lowest possible settings for that ring main switch.

Your MV supply is ungrounded. It may terminate on a MV-LV transformer with secondary grounded for supplying power to the client. If it is so, the client is not responsible for the subject ground fault unless the ground fault is on the primary side of MV-LV transformer and the client owns it.

 

[mrmuneeb]

Your MV supply is ungrounded. It may terminate on a MV-LV transformer with secondary grounded for supplying power to the client. If it is so, the client is not responsible for the subject ground fault unless the ground fault is on the primary side of MV-LV transformer and the client owns it.

yes, the client owns the MV-LV transformers at the distribution & the transmission lines as well.

our scope is only up to the main ring unit that is located inside our facility.

 

[Sahib]

yes, the client owns the MV-LV transformers at the distribution & the transmission lines as well.

our scope is only up to the main ring unit that is located inside our facility.

Fine. Then check if there is any ground fault in MV B phase up to ring main by disconnecting it and meggaring taking all precautions. That way you can prove the ground fault is on client side. Also note 51and 50N would not operate for such faults.

 

[mrmuneeb]

Fine. Then check if there is any ground fault in MV B phase up to ring main by disconnecting it and meggaring taking all precautions. That way you can prove the ground fault is on client side. Also note 51and 50N would not operate for such faults.

I see, so what type of protection is required for such faults.

we will do hi-pot testing, for sure. thanks a lot pal..:thumbsup:

 

[Ingenieur]

as the fault is on client end so we have informed client, but to prove that its on client end i am looking for a valid reason/proof.

i only have following reason "opening the main ring switch to client makes system normal"

for that client is arguing "why your main ring switch not tripping if there is any earth fault?"

however our main ring switch is set at 10% for 51(ANSI) & 50% for 50N(ANSI) these are the lowest possible settings for that ring main switch.

it is not tripping because the mv wye is ungrounded
no fault return path

show them
open feeder, ungrounded
measure lv bus voltages, normal
close feeder, measure voltages, high
measure current(s), should be nml load

open feeder and ground mv wye
measure lv bus voltages, normal
close feeder, should trip out
measure current, should spike very high

 

[Sahib]

I see, so what type of protection is required for such faults

Provide ground fault alarm/ indication for each phase on MV side as it is an ungrounded power system.