Voltage Unbalance Reason

[mrmuneeb]

The OP has left the discussion; so in other words it's all speculation after post #5.

i was off grid and went on the said project, so couldn't catch up with the discussion, any ways, i have made an outline to the problem, hope it could give you a better picture to understand my problem, i am really confused here, never heard of such problem before.

 

[Sahib]

no sir, with primary grounded our problem is still present......

I am sorry to hear it, mrmuneeb. For immediate relief to you, you should remove the neutral to ground connection on the MV side and re-energize. This time, the power supply will resume. Good luck.

 

[Ingenieur]

when a gen 'trips' or is taken off line is its associated cb open or closed?
how is their field powered? external or gen supplied source?

 

[Sahib]

when a gen 'trips' or is taken off line is its associated cb open or closed?
how is their field powered? external or gen supplied source?

The OP problem is over voltage damage to controllers. This happens when both LV and MV sides are ungrounded. I think if he grounds either side or disconnects the supply to the controllers also as soon as both the 'engines' i.e generators are tripped, his problem is solved.

 

[mrmuneeb]

I am sorry to hear it, mrmuneeb. For immediate relief to you, you should remove the neutral to ground connection on the MV side and re-energize. This time, the power supply will resume. Good luck.

removed already, i did it for days back, but since as soon as i switched that transformer ON, all system blacked out, had to remove then.

 

[Ingenieur]

The OP problem is over voltage damage to controllers. This happens when both LV and MV sides are ungrounded. I think if he grounds either side or disconnects the supply to the controllers also as soon as both the 'engines' i.e generators are tripped, his problem is solved.

the way I read it
if mv and gen are grounded and a gen is off system goes down
if only gen is grounded he is good

if both gens in a pair are running he is ok
if one is running he is ok
if both are off bus v goes high ~800-1200

 

[mrmuneeb]

when a gen 'trips' or is taken off line is its associated cb open or closed?
how is their field powered? external or gen supplied source?

yes sir,

CB opened, but since the bus voltage sensing supply is taken from the output side of the breaker.(Bus sensing is taken from primary, power/sensing voltages from secondary comes to primary and then to generator in idle mode, generator senses those voltages and closes its breaker when power matches)

bus sensing wires(3 wires) are connected to module through 2 Amps fuses.

these are PMG controlled generators..

 

[Sahib]

removed already, i did it for days back, but since as soon as i switched that transformer ON, all system blacked out, had to remove then.

Hmm. Are you saying when the transformer, with neutral to ground connection removed, causes all system blacked out when switched on?

 

[Ingenieur]

yes sir,

CB opened, but since the bus voltage sensing supply is taken from the output side of the breaker.(Bus sensing is taken from primary, power/sensing voltages from secondary comes to primary and then to generator in idle mode, generator senses those voltages and closes its breaker when power matches)

bus sensing wires(3 wires) are connected to module through 2 Amps fuses.

these are PMG controlled generatorse..

so with both sets off (and isolated by their cb's) the bus v goes high ~800-1200?
the prim/480 side still provides control power, although too high and causes damage

so basically the delta side low load/open ckt voltage goes high

do all 7 sets react the same?

 

[mrmuneeb]

the way I read it
if mv and gen are grounded and a gen is off system goes down
if only gen is grounded he is good

if both gens in a pair are running he is ok
if one is running he is ok
if both are off bus v goes high ~800-1200

if mv and gen are grounded and a gen is off system goes down(some are off and some on, depending on load)
if only gen is grounded he is good (no sir, high bus voltage still remains on bus sensing lines of off engines)

if both gens in a pair are running he is ok (yes Sir)
if one is running he is ok (yes Sir, as soon as this one trips, its bus voltage also goes high, sensing input of controller gets damaged)
if both are off bus v goes high ~800-1200 (yes Sir)

it seems to me that engines that are running absorbs that high voltage, because as soon as we open the main MV circuit breaker that is feeding power to client everything gets normal, no high voltage, no unbalanced voltage.

i suspect any line to ground fault present far away on transmission lines.

since govt is evacuating the homes and cutting power to homes, the lines are not that managed after disconnection in that area.

 

[Ingenieur]

Hmm. Are you saying when the transformer, with neutral to ground connection removed, causes all system blacked out when switched on?

I think he is saying if gen set wye is grounded and mv xfmr wye are grounded he goes black

 

[mrmuneeb]

so with both sets off (and isolated by their cb's) the bus v goes high ~800-1200?
the prim/480 side still provides control power, although too high and causes damage

so basically the delta side low load/open ckt voltage goes high

do all 7 sets react the same?

yes sir, exactly..
running engines having their breaker closed and synced together have no impact.

Off engines have high voltages on their Bus sensing input.

this usually happens during rain or if any insulator on transmission poles gets damaged.

client is pushing us that our main breaker i.e. MV breaker must trip, if we are claiming that there is fault in customer lines there must be tripping of our main MV circuit breaker.

Regarding "the prim/480 side still provides control power" we are only sensing these for synchronization.

 

[mrmuneeb]

I think he is saying if gen set wye is grounded and mv xfmr wye are grounded he goes black

gen set star/neutral grounded = no problem, i.e. no tripping, but bus voltage high problem remains;
mv xfmr star/neutral grounded= blackout, can't even put power back on in that condition, had to remove it


high bus voltage vanishes only when we cut power to client.....

 

[mrmuneeb]

Hmm. Are you saying when the transformer, with neutral to ground connection removed, causes all system blacked out when switched on?

no sir, when neutral to ground connected and took that transformer into service via ring switch, all system blacked out.

when removed that neutral, system turned on successfully,

engine circuit breaker opened with blast during attempt to energize dead bus. so had to remove that neutral-ground link

 

[Ingenieur]

when the client is isolated sensing v is normal?

when gen set ungrounded and mv grounded can't operate?

how is the delta v sensed? pt's, zig-zag, step down xfmr, solid state xdcr, etc

sounds like a ground fault on the clients end

 

[mrmuneeb]

when the client is isolated sensing v is normal?

when gen set ungrounded and mv grounded can't operate?

how is the delta v sensed? pt's, zig-zag, step down xfmr, solid state xdcr, etc

sounds like a ground fault on the clients end

when the client is isolated sensing v is normal? Yes Sir,

when gen set ungrounded and mv grounded can't operate? Yes, Can't operate(both cases, even if genset grounded and MV grounded can't operate)

how is the delta v sensed? pt's, zig-zag, step down xfmr, solid state xdcr, etc its direct sensing from the step up transformers to which generator have to feed power, voltages are initially returning from MV side to LV side, from there we have connected sensing cables (see attachment for sensing voltage illustration)
all our medium voltage projects are running fine like this,

our assumption is also that, its fault on client's side, but i am unable to prove it with logic.

 

[Sahib]

mrmuneeb, does the power supply to the controllers has neutral conductor and can you ground it ?

 

[mrmuneeb]

mrmuneeb, does the power supply to the controllers has neutral conductor and can you ground it ?

yes sir, it has neutral

already grounded that neutral, for all generators.

 

[Sahib]

yes sir, it has neutral

already grounded that neutral, for all generators.

During over voltage, is the neutral conductor to the controllers disconnected from the ground?

 

[mrmuneeb]

During over voltage, is the neutral conductor to the controllers disconnected from the ground?

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