Substation Fault Mechanical Effects - Ground Chain "Whip"?
Substation Fault Mechanical Effects - Ground Chain "Whip"?
(OP)
Hi there,
I am a mechanical engineer currently working at a transmission substation and have been reviewing safety protocols. One safety rule has to do with ground chains connecting construction equipment to the station ground grid. We have been recommending that crews place sandbags or a tire or something else to hold down the ground chain in the event of a substation fault or other accidental energization. Evidently the ground chain can "whip" when a surge of current flows through it.
However, I cannot identify any physical mechanism that would cause this to happen. I am familiar with z-pinch on multi-conductor lines as well as transformer short-circuit effects, and of course mutual inductance between multiple conductors can cause mechanical effects, but what would cause a mechanical force on one single conductor?
Eg. a 1/2" diameter, 25ohm ground chain suddenly experiences 11,000 amps for 4 cycles.
Any guidance in explaining "why" for this safety rule (if any reasoning exists) would be appreciated. Thanks!
I am a mechanical engineer currently working at a transmission substation and have been reviewing safety protocols. One safety rule has to do with ground chains connecting construction equipment to the station ground grid. We have been recommending that crews place sandbags or a tire or something else to hold down the ground chain in the event of a substation fault or other accidental energization. Evidently the ground chain can "whip" when a surge of current flows through it.
However, I cannot identify any physical mechanism that would cause this to happen. I am familiar with z-pinch on multi-conductor lines as well as transformer short-circuit effects, and of course mutual inductance between multiple conductors can cause mechanical effects, but what would cause a mechanical force on one single conductor?
Eg. a 1/2" diameter, 25ohm ground chain suddenly experiences 11,000 amps for 4 cycles.
Any guidance in explaining "why" for this safety rule (if any reasoning exists) would be appreciated. Thanks!






RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?
RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?
RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?
RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?
RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?
I think I see it. You've got all those magnetic force rings (right-hand-rule) jumping out perfectly perpendicular to the conductor. If the conductor is bent those force rings are forced to overlap on the inside of the bend with some repulsive force generated.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?
Weighting extra cable to control movement does not seem like a very reliable method. In my experience an appropriate length is chosen for the task. See http://www.usbr.gov/power/data/fist/fist5_1/vol5_1... 6.2.2.
RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?
I agree with stevenal. Use an appropriate length so that there are no loops or coils in the ground "chain".
Anecdote. Many years ago, when I was starting out, experienced field workers would "Safe Out" bus bars and cables by wrapping them with a piece of logging chain. Safety grounds are now almost universally made of copper but the name "Chains" persists.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Substation Fault Mechanical Effects - Ground Chain "Whip"?