"Fault" verses "Short-Circuit" 3

[umrpwr]

This is a somewhat of a philosophical or at least subjective question, but I would appreciate some other thoughts and opinions on the topic. I recently had discussion and debate with some fellow power engineers on the topic of whether a “fault” is the same as a “short-circuit” and the answers were divided evenly with some passionate arguments for each case.

One argument was that a short-circuit is a type of fault, although a fault may not necessarily be a short-circuit as in the case of an open conductor where there may not be short-circuit current which flows. Anderson’s classical text would tend to support this theory as is it titled “Analysis of Faulted Power Systems” since he breaks analysis into series and shunt faults, but does not refer to them as short-circuits.

However some others argued that a fault is a short-circuit and that an open conductor is neither a fault or a short-circuit so they are one in the same.

It is a question that comes down to terminology, but I am curious to hear what others opinions are on this subject. Thanks for your input.

 

[ScottyUK]

A fault is just that - something which is working outside of its normal operating envelope. A short circuit is a specific type of fault, and just one of a number of conceivable faults. You already considered open circuit: what about reverse phase rotation, voltage imbalance, high resistance to earth and so on? These are all abnormal conditions which can lead to equipment damage or to danger, which in my opinion is a better basis on which to define a 'fault'.


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If we learn from our mistakes I'm getting a great education!

 

[DRWeig]

I vote with Scotty. Well said!

Good on ya,

Goober Dave

 

[Skogsgurra]

I agree that this is a "philosophical" question. If you just ask "What is stiff?" you could as well ask "How stiff is a stiff stick?"

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[jraef]

I might also be said that not all short circuits are faults. A motor or transformer winding for example, in that first instance on energizing, it not much different than a phase-to-phase short circuit. That is why protective devices must be capable of discriminating against it looking like a fault.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[jghrist]

Faults are usually assumed to be of the short circuit variety. For instance, IEEE Std 80, IEEE Guide for Safety in AC Substation Grounding refers to fault current flowing through a ground grid. It isn't referring to the current resulting from an open conductor.

 

[stevenal]

IEEE 100 answer:

fault (1) (wire or cable) A partial or total local failure in the
insulation or continuity of a conductor. See also: center of
distribution. (T&D/PE) [10]
(2) (components) A physical condition that causes a device,
a component, or an element to fail to perform in a required
manner, for example, a short-circuit, a broken wire, an intermittent
connection. See also: pattern-sensitive fault;programsensitive
fault. (C/T&D/PE) [20], 1048-1990, [85]
(3) (surge arresters) A disturbance that impairs normal operation,
for example, insulation failure or conductor breakage.
(PE) [8], [84]
(4) (thyristor power converter) A condition existing when
the conduction cycles of some semiconductors are abnormal.
Note: This usually results in fault currents of substantial magnitude.
(IA/IPC) 444-1973w
(5) See also: short circuit. (SWG/PE) C37.100-1981s
(6) (test, measurement, and diagnostic equipment) A degradation
in performance due to detuning, maladjustment, misalignment,
failure of parts, and so forth. (MIL) [2]
(7) (A) (software) An incorrect step, process, or data definition
in a computer program. Note: This definition is used
primarily by the fault tolerance discipline. In common usage,
the terms “error” and “bug” are used to express this meaning.
See also: intermittent fault;program-sensitive fault; data-sensitive
fault;fault masking;equivalent faults. (B) (protective
grounding of power lines) (current). A current that flows
from one conductor to ground or to another conductor owing
to an abnormal connection (including an arc) between the
two. (C) (software reliability) An accidental condition that
causes a functional unit to fail to perform its required function.
(D) (software reliability) A manifestation of an error
in software. A fault, if encountered, may cause a failure. Synonym:
bug. (C) 610.12-1990
(8) (reliability data for pumps and drivers, valve actuators,
and valves) Any undesired state of a component or system.
A fault does not necessarily require failure (for example,
a pump may not start when required because its feeder breaker
was inadvertently left open—a “command block”).
(PE/NP) 500-1984w
(9) A defect in a hardware device or component;for example,
a short circuit or broken wire. Synonym: physical defect.
(C/BA) 896.9-1994w, 610.10-1994w, 610.12-1990
(10) (components) A physical condition that causes a device,
a component, or an element to fail to perform in a required
manner, for example, a short-circuit, a broken wire, and an
intermittent connection. (T&D/PE) 524a-1993r
(11) Erroneous hardware or software state resulting from
component failure, operator error, physical interference from
the environment, design error, program error, or data structure
error. (C/BA) 896.3-1993w
(12) A physical condition that causes a device or a diagnostic
unit to fail to perform nominally. (ATLAS) 1232-1995
(13) A defect or flaw in a hardware or software component.
(SCC20) 1232.1-1997


short circuit (1) (gas-tube surge protective devices) An abnormal
connection of relatively low impedance, whether
made accidentally or intentionally, between two points of different
potential in a circuit.
(SPD/PE) C62.31-1987r, C62.32-1981s
(2) An abnormal connection (including an arc) of relatively
low impedance, whether made accidentally or intentionally,
between two pointsof different potential. Note: The term fault
or short-circuit fault is used to describe a short circuit.
(SWG/IA/PE/PSP) 1015-1997, C37.100-1992
(3) The condition in which the output terminalsof the power
supply are directly connected together, resulting in near-zero
output voltage. (PEL) 1515-2000

 

[slavag]

Hi.
Stevenal, thanks a lot for the so full explanation.

I would like vote star to Scotty too, I like this answer.
Best Regards.
Slava

 

[oldfieldguy]

Don't forget the "undercurrent fault" in motor controls. It's definitely NOT a short circuit. Nor is the "current unbalance" fault.

Faults are unintended conditions reflecting incorrect operation and requiring action for safety and protection. A short circuit is a particular type of fault.

old field guy

 

[jraef]

According to my wife, everything is my fault...

 

[NAZ55]

Oh boy! thanks for the laughs jraef. I agree with you on that

wonder if that means you have a short circuit in your head somewhere?

 

[jimgineer]

I can not think of any short circuit that would be purposeful. In that respect, I would think any short circuit would be a fault. Whether or not it causes a system to fail or not does not determine whether there is a fault occuring.

Also see (5) in that IEEE definition that someone copied in...

 

[burnt2x]

Arc furnaces are "short-circuits" - it's useful!

 

[ScottyUK]

jimgineer,

Fault throwers produce intentional short circuits in order to operate a remote breaker where intertripping via pilot wires is unavailable. In this case is the S/C a 'fault'? The remote end treats it as a fault and operates the protection, but it was introduced deliberately. Oh the things that keep engineers awake at night...


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If we learn from our mistakes I'm getting a great education!

 

[ozmosis]

The following are explanations according to Siemens (my previous employer):
Fault Current (~ residual current)
Fault current is the current that flows as a result of an insulation fault. It is measured, for example, as the difference between the currents flowing into and out of an installation via a measuring device (EN 61008/IEC61008/DIN VDE 0664)
Short Circuit
Connection with a negligibly small impedance between conductors that are live during operation. The current in such cases is a multiple of the operating current, which can give rise to thermal(~ rated short-time current) or mechanical (~rated peak withstand current)overloading of the electrical equipment and parts of the installation

 

[ScottyUK]

Oz,

That first definition sounds like it relates to Earth Fault Current - the EN 61008 standard concerns RCDs used for protection of LV circuits against low level earth faults.


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If we learn from our mistakes I'm getting a great education!

 

[suhagpatel]

I vote with Scotty as well. Generally speaking, a short circuit is a specific type of fault, in most textbooks this is referred to as a shunt fault. If you've worked for a utility you know that an open conductor (this can occur without a short circuit) is a definitely a fault, and clearly not a short circuit. Most texts refer to these as series faults. Have fun debating