at power plant when we close incomer feeder that feed customer plant (11kv/480v transformer) the main generator breaker tripped
I have read many topic about it but I need to discuss best solution to solve this out with someone who is familiar with
best regaeds

 

at power plant when we close incomer feeder that feed customer plant (11kv/480v transformer) the main generator breaker tripped
I have read many topic about it but I need to discuss best solution to solve this out with someone who is familiar with
best regaeds

A single line diagram would be good to begin here

Also what about protection alarms/trips sequence of events

I used to work as Control & protection commissioning engineer back in the days so i may support from here as others good engineers and technisians on this great forum

 

Do you mean that 87T protection on step up transformer tripping due to inrush currents

What have been changed since last good operation of the plant...

How is load behaviour

Is that incoming feeder is teh called 52L line breaker thats why a SLD woudl be a good idea

 

the breaker which has been tripped each time is the main generator breaker of the gas turbine due to differential protection relay acting each time we close 11kv CB which feed step down transformer.
this situation remain accruing since step down transformer replaced by new modern one.

 

Okay

We still need to review Generator and Line protection SOE trip log events list or similar from IED relays
SLD also would be welcome here

 

you are right SLD is needed for prefect analyses I agree with you but it will take quite time.
therefor let us discussed in general. the operation side override the signal of the generator differential protection relay prior closing the 11kv CB which feed mentioned transformer and then they remove the overriding of the signal.
my question : if it is inrush current caused by the transformer why is the differential really which act not overcurrent relay

 

Okay noted

You did not tell us which protection is activated during this event? 87G or 87T differential current protection scheme

They can be sort of blocking signal during inrush current transient mode thats why relay dont act as overcurrent during this period

 

Is there over alarms/trips shown during this GCB tripping ..

When problem started ?How old is the installation?

 

the problem accrue since transformer changed and that was 15 years ago and the relays is very old since 1972

 

Well I would check the ACB feeder Air circuit breaker or transformer protection if any alarms /trips is displayed

Also I would check the inrush current time blocking signal for overcurrent or 87 protection ...

 

i appreaciate your effort thanks a lot

 

What is inrush blocking?
In brief, inrush restraint is a temporary modification to protection elements to allow for transformer re-energisation without spurious tripping. It's achieved in two major ways: By applying a temporary multiplier to overcurrent settings thresholds. By looking for symptoms of inrush, more than overcurrent alone.

 

What is harmonic blocking?


With harmonic blocking, usually the second harmonic component is used (fourth harmonic is used by some relay manufacturers). When the ratio of the second harmonic component to the fundamental is greater than second harmonic set point, inrush condition is announced and the differential operation is blocked.

 

at power plant when we close incomer feeder that feed customer plant (11kv/480v transformer) the main generator breaker tripped
I have read many topic about it but I need to discuss best solution to solve this out with someone who is familiar with
best regaeds

The most important thing to put in consideration when you have such a problem is both the transformer and generator kVA or MVA,but if you step down 11kV to 480v you mustn't experience inrush currents that will trip protection because your current at the primary side is relatively lower and so inrush should be.
Give the name plate,specs of both equipment.

 

mbixmac
Welcome to Control.Com
Your suggestion asking transformer magnitude is helpful! Some additional information is also useful:
a) An SLD, or Single-Line-Diagram showing Source, Load circuitry, and Generator location.
b) Is the event something new in an operating plant? Or a problem occurring while commissioning a new facility?
c) Since problem involves 11kV, what protective relays are used and which operated?
d) What is Instrument-Current-Transformer (CT's) Ratio.
e) What is Potential-Voltage-Transformer (PT's) Ratio?
e) How are transformer primary windings connected, i.e., Y or Delta?
f) How are primary, secondary, and generator systems earthed (grounded)?
g) Under certain conditions even an Unloaded-Transformer can trip upon energization!
Regards, Phil Corso

 

Zoubi...
I apologize for not responding to you. Your sketch is sparse. Please respond to my comments in Message #15, excluding those items you revealed in previous posts! Thank you.
Regards, Phil Corso

 

Zoubi...
When problem occurs is Gen1 and Gen2 Tie-Brkr closed or open?

 

Zoubi...
h) What were parameters and Mfg of original Transformer?
i) What are parameters and Mfg of present Transfomer?
k) Have you done any voltage or current graphing?
l) Since problem is quite old, what have other engineers, specialists, or diagnostic persons, revealed?
Phil Corso

 

Zoubi...
m) Can you reclose G2 Brkr after Xfmr Brkr has closed?
n) In 11kV SwitchGear-Lineup is G2 Brkr next to Xfmr Brkr?
Phil Corso

 

Zoubi...
o) Have you tried replacing the Gen 2 Brkr?
Phil Corso