resonant grounded
resonant grounded
(OP)
We are design a hydro powerplant with generator (13,8kV-85MVA) grounding by neutral grounding transformer
with high resistance at the secondary.
Generator will be acopled in a bubble turbine under river.
We decided to limit ground fault with 15A to avoid any kind of overvoltage stress in generator winding.
Is was not possible because of high capacitive generator system(bus duct, generator, surge protector...).
We intend to use GROUND-FAULT NEUTRALIZER(GFN).
We never used it before, so we need some information about voltage, tapes for regulation, calculation.
We appreciate very much some experiene about it.
with high resistance at the secondary.
Generator will be acopled in a bubble turbine under river.
We decided to limit ground fault with 15A to avoid any kind of overvoltage stress in generator winding.
Is was not possible because of high capacitive generator system(bus duct, generator, surge protector...).
We intend to use GROUND-FAULT NEUTRALIZER(GFN).
We never used it before, so we need some information about voltage, tapes for regulation, calculation.
We appreciate very much some experiene about it.






RE: resonant grounded
"Protective relaying for power generation systems By Donald Reimert pp 130"
http:
"Application of Sensitive Earth Fault Relays to Petersen Coil Earthed and Insulated Power Systems" Alstom:
http:
RE: resonant grounded
RE: resonant grounded
Im fully agree with xxjohnh . Very big generators have a high resistor systems with 5A GF limit.
Petersen coil is good thing, but for distribution network.
best Regards.
Slava
RE: resonant grounded
Is was not possible with high resistors system grounding.
I dont know why, but in Brazil capacitive currents of equipments (busduct,generator...) are very high,
close to 30-40A.
GROUND-FAULT NEUTRALIZER(GFN) is the unique solution.
All american grounding standard Guide include this method of grounding.
RE: resonant grounded
I would review the calculations that came up with 30 A of capacitive charging current. This is an exceptionally high value. Unless you have a mile of bus between the generator and the transformer, there may be an error in the calculations.
RE: resonant grounded
2- I never analised calculation of hydrogenerator high resistance grounding with 5A current.
3-Last calculation of unit-connected hydrogenerator high resistance grounding were 32.4A. It was revised. They change to 29.2 A (!!??) What to do?
4-Does anyone could mention what are problems with GFN?
RE: resonant grounded
I will post the reference if I can find it though.
RE: resonant grounded
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If we learn from our mistakes I'm getting a great education!
RE: resonant grounded
Very true! And that is because when using a resistor that is wire-wound of small-sized wire these are prone to damage. We use a distribution type single-phase transformer with a grid-type resistor on the secondary which is very reliable compared to wire-wound resistor!
RE: resonant grounded
- 1 step up transformer of 300MVA-525 kV(solid grounded star) – 170MVA-13,8kV (delta)- 170MVA-13,8kV(delta)
- 4 generators of 84MVA -13,8kV – cosFi 0,9
- 2 13,8kV generation busbar(ungrounded) are connected to low voltage side of step up transformer.
Each 2 generators are connected to 1 busbar by generator circuit breaker.
Originally neutral of each generator was grounded by single phase distribution transformer with a resistive burden on the secondary.
It was verified very high capacive currents to ground.
We decided to install CB in neutral of each generator, in order to keep only one grounded.
As generator wil be installed underwater was decide to reduce ground current to 15A.
It was only possible using resonant grounding.
We are verifying possibility to remove surge arrester at the generator surge cubicle ,
in order to reduce capacitive to ground current and perhaps avoiding resonant grounding.
burnt2x,
Beside consideration of ScottyUK (utility class), all time you request IEEE generator circuit breaker standard,
automatically you are using high impedance grounding scheme, because this standard does not admit ground to fault
more than 50A for generator CB.
RE: resonant grounded
...................
We are verifying possibility to remove CAPACITOR SHUNT at the generator surge cubicle ............
RE: resonant grounded
RE: resonant grounded
If you require adopt IEEE Std C37.013-1997- generator circuit breaker standard - in your CB generator technical specification , automatically you are using high impedance grounding scheme, because this standard does not admit grount to fault more than 50A for generator CB.
I really dont known explain why this.