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Locator of ground fault on ungrounded

Locator of ground fault on ungrounded

Locator of ground fault on ungrounded

(OP)
this is a 13.8kV closed  ring auxiliary system of about 1.3km , to supply a hydropower plant of 25 generator(25x80MVA). See thread238-315981: synchronization with one generation.
This system is grounding with high resistance , with phase-to-earth current no more the 10A.
All fault to ground will alarm. There are 1 hour to look for the fault and recomposition of system.

 Do you know any electronic device that can be installed during assembly, installation or maintenance of the system of 13.8 kV, which allows to locate ground fault in the system without having to open the ring of 13.8 kV?
  

RE: Locator of ground fault on ungrounded

There are plenty of fault passage indicators available that work with core balance CT's but with such a low fault current you might struggle to find one that will operate satisfactorily.
Regards
Marmite

RE: Locator of ground fault on ungrounded

Any sensitive directional earth fault function.
with core balance CT of course and with broken delta PT connection.
Possible use RMU with special indicators are operated with voltage from capacitance led's
 

RE: Locator of ground fault on ungrounded

(OP)
slavag,
what is  RMU?

RE: Locator of ground fault on ungrounded

Ring Main Unit.
secondary switchgear.

RE: Locator of ground fault on ungrounded

For the situation that you described - with 10A ground fault current on 13.8 kV system - I would tend to assume that no substantial ground fault current source is available and some sort of sequential tripping scheme is used.  Of course, I would also be lobbying for a grounding transformer on the MV bus that gives me enough fault current to provide full discrimination.

RE: Locator of ground fault on ungrounded

(OP)
mgtrp,
A 13.8kV  auxiliary services system consists of 5 substations (SE1, SE2, SE3, SE4, SE5) interconnected in a closed loop configuration. Each substation has loads and only SE1 has generation.

Each subestation are connected by on-load disconnect switch except generation subestation SE1 where is protection and circuit breakers.
Any fault phase-phase between SEs, will operate protection  and trip at SE1 circuitbreakers.
Any fault phase-to-ground between SEs,  will operate protection(59N)  and alarm at SE1.
My problem is to locate ground fault in the 13,8kV ring system.

 

RE: Locator of ground fault on ungrounded

Problem is clear, solution is possible, next step is only cost and installation.
Are you have VT, core balanced CT at the substations?
BTW, what about indication of phase to phase fault, usually it's same problem.

Try check the following devices: Hortsmann Alpha, Hortsmann Gamma,
Alpha automatic.

 

RE: Locator of ground fault on ungrounded

(OP)
all equipment has been tested and are being installed in the field.
 There is only 59N sensor for the detection of fault to ground generator installed in the substation SE1.
 To locate a fault to earth on a stretch of line, each section should be opened and closed the line again if the alarm does not stop.
 The process is repeated for each section until the alarm ceases, which indicates the stretch of line where the fault is located.

RE: Locator of ground fault on ungrounded

not so good solution, but its work in such systems.

RE: Locator of ground fault on ungrounded

I think the 1.3 km line length could be a problem. There is some nice digital relay equipment out there that can provide oscillograph traces which can be used to estimate fault positions. But this approach works better on long transmission lines. I don't think you have a system that would be considered electrically long (too short, too low Z).

Is this an overhead system?

RE: Locator of ground fault on ungrounded

(OP)
No.
It is insulated cable Eprotenax Compact 105-8.7/15kV - 35mm2

 

RE: Locator of ground fault on ungrounded

Quote:

It is insulated cable Eprotenax Compact 105-8.7/15kV - 35mm2
The core balance CT approach might work. But the installation of enough CTs along the line is going to be non trivial from a cost point of view. Hopefully, you have existing vaults/handholes at suitable locations sufficient to place them.

How is the cable shield grounded? That can have an impact on how such CTs will work.

RE: Locator of ground fault on ungrounded

(OP)
PHovnanian,
all equipment has been tested and are being installed in the field.

 

RE: Locator of ground fault on ungrounded

(OP)
slavag,
there is a problem in my description:
To locate a fault to earth on a stretch of line, each section should be opened and closed the line again if the alarm does not stop.
 The process is repeated for each section until the alarm ceases, which indicates the stretch of line where the fault is located.

problem is:
in a ungrounded system with a solid phase-to-ground fault,
there is a voltage shift at the point of fault relative to normal balanced system.
This voltage shift is can be maximum voltage 13.8/V3 kV at point of fault and reducing up to normal balanced system at generation point.
In this circumstances I guess could be dangerous to close with fault.
Conclusion: I still do not know how to locate the falt.

   
  

RE: Locator of ground fault on ungrounded

(OP)
slavag,
there is a problem in my description:
To locate a fault to earth on a stretch of line, each section should be opened and closed the line again if the alarm does not stop.
 The process is repeated for each section until the alarm ceases, which indicates the stretch of line where the fault is located.

problem is:
in a ungrounded system with a solid phase-to-ground fault,
there is a voltage shift at the point of fault relative to normal balanced system.
This voltage shift is can be maximum voltage 13.8/V3 kV at point of fault and reducing up to normal balanced system at generation point.
In this circumstances I guess could be dangerous to close with fault.
Conclusion: I still do not know how to locate the fault.

   
  

RE: Locator of ground fault on ungrounded

Without sensitive directional protection in each substation is difficult to isolate the faulty line. The cable lengths as also the ring layout of the network are problems for any fault locator's functions based on impedance measurement.  

G.F.
www.engineering-services.gr

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