Earth fault protection of transmission line connected to step up transformer (delta 6.3kv and star 11kv). A ring core is provided on cable to delta side for earth fault protection through AE-102 RELAY. two ct on phase of this cable are used for over current protection through RMS 7990 RELAY. a separate ring core ct is installed on grounded neutral of star side which is used for sensing of earth fault for RMS 7990 Relay. Please advise that will this arrangement work as it is different from regular earth fault arrangement ???

 

Muhammad... does the generator on the delta-side of the xfmr have its neutral earthed?

To be sure I have properly interpreted your request can you send a hand-drawn sketch or simple SLD (Single-line-Diagram) to me at:

cepsicon[at]AOL[dot]com

Regards, Phil Corso

 

Thank you for your prompt response . . I've mailed you the said sketch ...
The star point of generator is solidly grounded . .

 

if I recall, the generator is grounded through some resistor.. plz correct me if i m wrong..

 

> if I recall, the generator is grounded through some resistor.. plz correct me
> if i m wrong..

yes the generator is grounded through resistor . .

 

> To be sure I have properly interpreted your request can you send a hand-drawn
> sketch or simple SLD (Single-line-Diagram) to me at:

please check ..
http://www.eng-tips.com/viewthread.cfm?qid=194427

 

Muhammad... your 14-Feb-12 (08:13) post directing me to review a Eng-Tips Forum, Aug '07 topic, suggests you did receive or understand my 06-Feb-12 e-mails to you.

Do you want me to repeat my answers via the Control.Com Forum?

Phil Corso

 

> Muhammad... your 14-Feb-12 (08:13) post directing me to review a Eng-Tips Forum,
> Aug '07 topic, suggests you did receive or understand my 06-Feb-12 e-mails to you.

> Do you want me to repeat my answers via the Control.Com Forum?

Thank you Phil Corso
Yes i got your said mails and problem is resolved now. It was for the very first time i saw the E/F arrangement of current transformer like this but now its clear to me. But it would be beneficial for other people if you repeat your answer here at this forum too.

 

MUHAMMAD... per your 15-Feb-12 (23:50):

05-Feb-12 (12:13) Phil C:
Mohammad, further to my earlier email: Can you provide additional detail on the AE-102 and RMS-7990 Relays. Specifically, are they "Programmable Digital" units, and not stand-alone units? Phil C

05-Feb-12 (13:03) by Phil C:
Mohammad, I asked the previous question(s) because:
1) Normally, the 50/51 relays are phase-connected. Your drawing shows 2xCTs!

2) The 51N is residually-connected. It requires that 3xCTs be installed.

3) Devices connected to a window-type CT are ANSI/IEEE tagged "G"! Example; 50G if instantaneous, 51G if intentionally delayed.

4) The "64" device is usually associated with insulation-failure... For example, Insulation-Resistance, not one that is current-derived! (See "Note 64" following 06-Feb-12 (08:17) post!)

5) The xfmr neutral-CT has little to do with the generator neutral-CT! Phil

06-Feb-12 (03:45) by Muhammad:
Dear Sir, Following are my observations:

1) 50/51 relays have sensing from two current transformers, one on blue phase and other on red phase. The effect of fault on yellow phase will also be felt on the two other phases which ultimately will let the relay to sense some over current in the circuit to be protected.

2) Yes usually 51N requires 3 X CT s to be installed, more specifically the current in neutral of star combination of these 3 XC T is fed for sensing to 51N relay. But in our case the inputs of 51 N are fed from ring core on grounded neutral of power transformer’s star point.

3) The 64 relay (AE-102) is associated with insulation failure detection. Now I need advise that whether this 51N input from core balance CT is correct?

AE-102 is electrostatic relay, definite time residual current relay. It is not programmable. For detection of small residual currents the AE-102 relay is supplied from a ring core CT.
RMS 7990 is programmable relay with three independent over current measurements (each with 2 stage) and one earth fault measurement (2 stage configuration).

These are set to operate in definite time; ANSI 50, 51, 51N, 50N. ECPL is one of our main competitors. Best regards

06-Feb-12 (07:39) by Muhammad:
Dear Phil, AE-102 is electrostatic relay, definite time residual current relay. It is not programmable. For detection of small residual currents the AE-102 relay is supplied from a ring core CT.

Phil’s reply:
Why tag it "64"? What is its primary function? (See "Note 64" following 06-Feb-12 (08:17) post!)

RMS 7990 is programmable relay with three independent over-current measurements (each with 2 stages) and one earth fault measurement (2 stage configuration.) These are set to operate in definite time; ANSI 50, 51, 50N, and 51N. Best regards.
Phil's reply:
So, the 50N/51N function is to sum the 3-phase currents, hence it needs 3 CTs? Does it trip the generator, CB, or both? Without the 3rd phase measurement, it will trip for any ph-ph fault in the 11kV system! Including outgoing feeders! Is that what you want?
Also, for a ph-ph fault in the 11kV-side, the 6.3kV-side phase-currents are 1.0, 0.5, and 0.5, per-unit! And, for an EF on the 11kV-side, the 6.3kV phase-currents are 0.58, 0.58, and 0.00, per-unit!

06-Feb-12 (08:17) by Phil C:
See answers above. I'm still unclear? Like I'm viewing your system thru a key-hole. I can't see the other parts? I understand if you use RMS as backup! But, why do you use primary-current, @ 6.3kV, measurements to see secondary (11kV) EFs?
------------------------------------------
(Note 64) Ground Protective Relay:
A protective-relay that functions on failure of the insulation of a machine, transformer, or of other apparatus to ground, or on flashover of a d-c machine to ground.

Note: This function is assigned only to a relay that detects the flow of current from the frame of a machine or enclosing case or structure of piece of apparatus to ground, or detects a ground on a normally un-grounded winding or circuit. It is not applied to a device connected in the secondary circuit of a current transformer, in the secondary neutral of current transformers, or connected in the power circuit of a normally grounded system!

Regards, Phil Corso