Static electricity and circuit breakers

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Discussion Overview

The discussion revolves around the safety procedures related to static electricity and residual charge when working on high tension circuit breakers. Participants explore the necessity of grounding techniques and the potential for static or residual charges to build up, even when breakers are isolated. The conversation includes technical insights into the behavior of electrical components and safety practices in high voltage environments.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the necessity of grounding a wire before touching bus bars on a circuit breaker, even when it is isolated, raising concerns about static charge buildup.
  • Another participant suggests that static charge can be induced, emphasizing that workers may not be aware of the previous conditions affecting the component.
  • A third participant discusses the capacitance in large power transformers, noting that residual charge can remain after rapid supply removal, which can be dangerous during testing.
  • One participant prefers to refer to the charge as residual rather than static, highlighting safety practices that require grounding all conductors before touching them.
  • Another participant mentions that charges can reaccumulate even after being discharged, suggesting the use of insulated tools to avoid direct contact.
  • A later reply points out that while "do not touch" is a common guideline, it is impractical when working on breakers, and emphasizes the importance of discharging and grounding before testing.

Areas of Agreement / Disagreement

Participants express differing views on the terminology and nature of the charges involved, with some preferring "residual charge" over "static charge." There is no consensus on the necessity of grounding procedures, as opinions vary on the risks associated with working on isolated breakers.

Contextual Notes

Participants mention various factors that may contribute to charge buildup, including environmental conditions and the design of electrical components. The discussion reflects a range of safety practices and experiences in high voltage environments, with no definitive resolution on the best approach.

Who May Find This Useful

Electrical technicians, engineers working with high voltage systems, and safety professionals in the electrical field may find this discussion relevant.

magmash
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Hi

I have seen electric technicians while racking out high tension circuit breakers, use a wire that has one end grounded and they use the other end to touch the bus bars on the breaker in case of a static charger, they carry out this procedure before they do any work on the CB in case they get shocked by a static charge, is it necessary to carry out such a procedure even tho the breaker is completely isolated ?

How can static charge be built in a case like that, where there is no friction ?
 
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...is it necessary to carry out such a procedure even tho the breaker is completely isolated ?
That's like asking if it is necessary to always assume that a gun is loaded.

How can static charge be built in a case like that, where there is no friction ?
Charge can also be induced.

The main point is that the workers have no idea what has been happening to the component.
 
Large power transformers can have a lot of capacitance between the windings and the core and the metal case.

This capacitance gets charged and discharged from the voltages on the windings in normal operation.
If the supply is removed rapidly some residual charge could be left on the capacitance from the winding to its metal surroundings.

This capacitance can be deadly when transformers are being tested. Large DC voltages are used to test transformer breakdown capability and if this is not carefully discharged, it can persist for days.

Someone was killed about 20 years ago by a transformer which was still holding a charge two days after high voltage testing.
 
A few points : In general I would not refer to this as static, but residual charge - because the insulation on Medium (600-72KV) and High Voltage ( >72KV) - although I do not know of any rack out HV breakers... ok back on track, because of the very high insulation, it is typical / common to have a residual charge left on the breakers conductors.
As a matter of practice - safety policy etc... EVERY conductor you touch MUST be grounded..discharged first. You do not touch ANYTHING unless you KNOW ( not just think) it is safe.
-- A note back on the HV systems, it is also common for just the wind to leave a static charge on UNGROUNDED conductors - large transformers have pumped oil cooling systems, also a problem.
 
I think I would add "don't touch it anyway".

I have seen these charges build up again even after being discharged.

You can always use insulated pliers etc to keep your fingers away from potential danger.
 
"Do not touch" does not really work if you have to work ON the breaker - the disconnect points (stabs/receivers) are cleaned and this is where many of the test connections are made. Once dawn out of the cubicle, and discharged - there is little risk, make on these is 36KV Class, up to about 3000A - I have not seen draw out breakers higher voltage than that. - Although we used to wrap a wire or have light alligator jumpers on all points not under test - these can get induced V from hi-pot testing.
 

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