Can anybody guess a reason or solution for the Gas Turbine Generator tripping on differential current while charging its load transformer? The Gas Turbine got tripped for four times in the last four months due to differential current fail while charging its power load transformer.
any answers??

Your provided info is incomplete / inadequate. Is the transformer loaded? KVA size of Transformer ? KW size of Generator? Please explain "charging", what are you actually performing? Is it your generator differential relay or your transformer differential relay that tripped?

Does your 87T protection has 2nd and 5th harmonic blocking ?

What make and model relay do you have using the 87 element.

What make and model relays are you using ?

Can you post a protection one line diagram ?

Is this a new installation of is this a new problem ?

Hi there,
pls specifiy,
Is it a unit transformer ?.
Nevertheless, is the aforementioned transformer included in the differential Protection Scheme of the Genset or not?
What was the historical perfomance of the system like before the last four months that has been marked in your query? ie,,, Since when your system has been working satisfactory?

Provided the transformer is included in the differential zone, 2nd harmonic/inrush blocking should be implemented.

Dear Mr.Jagadeeswaran, I understood that your Generator is tripping while you charge the transformer. I would like to know that, have you altered % bias or % pick up settings of your Generator Differential relay or Have you changed the Generator Differential relay ? And is it your Generator differential relay is Harmonic restraint ?

Switch off the connected capacitor banks and battery banks, if any, while charging the transformer.

Follow Raymond Lee's lead.....presence of second harmonics during transformer inrush is the most likey culprit. There could be other culprits too. If the gen relay does not have harmonics blocking, alternative solutions could be to review the time delay for 87 or block the 87 for a few extra cycles ( to ride out the transformer inrush transients) only when first engergizing. There a few ways to accomplish this and you may want to work with the relay mfr on this.

Dear Sir Mr.Rafiq Bulsara.
Allowing time delay to 87 relay output is one method you suggested.
In another way you suggested, we have to block the sensing of 87 relay. How sensing can be blocked Please clarify ?
What could be the other ways to over come this problem. Please clarify ?

Chandra,
It depends on how programmable the relay is. Modern multifunction relays are pretty flexible and allow incorporating logic functions to configure outputs based on various inputs. I have implemented such a solution in one similar case. As I stated before, if you a have real issue at hand, ask the relay mfr and they will offer a soultion or seek professional assitance from an experienced consultant.

For example, some relays offer more than one group of settings and you can switch between the groups, based on an external input such as breaker closing. You can keep one group of setting for a certain period of time after the breaker closing and revert to another group after the expiry of the time delay.

Hope this helps.

Reading all the tread of discussions, I can agree strongly that the closest hint to the solution of the problem was stated on the first discussion of Rafic Bulsara. I cannot endorsed other solutions because It is not logical to cut and try when it has happened already as stated four (4) times. I like to address the burden of catching the problem to the originator of discussion. If you like to have a conclusive prognosis why not put a digital logger / transient analyzer on both sides of the transformer primary and secondary (if the power transformer has auxillary CTs on both sides). If they are fed by insulated power cables, then it will be more feasible do the hook-up.

I also like to comment that when it comes to differential relays of transformers, it should be a dedicated relaying function with dedicated CTs, not a multi-function relay shared by other functions since differential relay sensitivity adjustments may be compromised by the other relays requirement.

Dear Sir Mr.Rafiq Bulsara.

Thank you. I under stood the concept.

My understanding is the transformer is outside the generator differential circuit. If so, my guess would be there is a difference in your CT ratings/burden, causing one CT to saturate faster than the other. Hence causing the differential to pick up on tranformer inrush current. Or it could be that one or more of the CTs has shorted windings providing a lower ratio than rated for. Check the CTs.

Aunque la Información es un tanto difusa, parece que se refiere a la Protección Diferencial del Grupo Turbogenerador; esa protección solo "ve" una falla en el interior del Grupo que debe estar protegido contra armónicos de la red.
Generalmente es el grupo Turboalternador al cual pertenece el transformador de salida que es un Banco Trifásico.
La falla parece haber ocurrido en forma esporádica y puede ser el indicio de una posterior falla grave dentro del Grupo que por ahora solo se presenta de pronto en determinadas condiciones de carga.
Sugeriría programar un período de mantenimiento para el Grupo, incluyendo Generador, Banco Trifásico de salida, Transformador por Transformador.
Verificar la calibración y estado de la protección Diferencial y no está demás verificar los rodamientos de la Turbina.
Si nos aclaras mas las circunstacias de las fallas,en el Grupo te podemos ayudar mas.
Saludos
William Chaparro

Is this an overall differential combined woith GSU-GT .
Check for the CT polarity connections for the entire cktry,then conduct a stability test at low volatge and low current and check there is any spillage current or polarity mismatch or not.
After this check the relay progaramming/configurations and harmonic blockings ,systematically/meticulously go through the procedures and you get the solution.