Specification of MV utility distribution equipment

[apowerengr]

I was at the IEEE T&D conference this week in Chicago. One observation is that much of the new MV utility distribution equipment (reclosers and padmounted switchgear) using vac bottles and encapsulated gear is not maintainable, i.e. you can't check or change the bottles.

Any concerns about specifying gear which is constructed under an "operate until failure" premise, some of which you don't even have duty cycle monitoring from the control? I'm used to regular inspections, measurements and maintenance with access to wear items which can be replaced instead of having to throw away the entire unit and replace it.

Or am I just concerned about nothing..........?

 

[SteveFehr]

This sounds like something the manufacturer(s) need to address. If these components are reliable enough that maintenance is not required or even recommended, than burying components is acceptable. But if it's just poor design... shame on them!

If you think that sounds risky, consider UPS systems- for the critical applications they serve- are also maintained the same way, as there's pretty much no way to accomplish preventative maintenance on anything that's likely to fail. Best we can do is stick on an extra unit and hope they don't fail at the same time. PM pretty much consists of checking the filters, opening the doors and going "ayup, it's all still there, and nothing's left the smoke out quote yet."

 

[jghrist]

There's a difference between "maintenance-free" (maintenance not needed) and "maintenance-proof" (maintenance not possible).

 

[Zogzog]

Well put jghrist. The OEM's would rather sell you a new breaker than a vac bottle.

 

[dpc]

There's very little maintenance that can be done on a vacuum bottle, but designing a product where the vacuum bottle cannot be replaced would be a concern to me. But probably part of the current trend in product design.

Vacuum bottles are extremely reliable and probably the least likely thing to fail in the equipment.

 

[Marmite]

Just stumbled upon this when looking for something else:-
C37.12 American National Standard for AC
High-Voltage Circuit Breakers Rated
on a Symmetrical Current Basis—
Specifications Guide
These specifications apply to all indoor and outdoor types of ac high-voltage circuit breakers rated above 1000 volts.
9.4.1
Vacuum circuit breakers shall be provided with a means for determining contact wear.
9.4.2
Vacuum circuit breakers shall be designed with the capability for the customer to replace the vacuum interrupters.

Sounds eminantly sensible to me.
Regards
Marmite

 

[bmw9]

Hi, all
Actually, vacuum circuit breaker still needs maintenance. VCB has very strong ability to kill arc all depends on vacuum in the bottle. Since the stationary and moving contact are very close in the bottle, we can check the bottle vacuum by applying high voltage DC or AC to check its insultion resistance. usually I apply 40 KVDC to 15KV breker and 14-19 KVDC to 5KV breaker. This kind bottle test has to be done every three years.

bmw9

 

[Zogzog]

The test voltages for Vacuum integrity (Not the same as a insulation resistance test) should not exceed those recommended by that specific breakers manufacturer. If exceeded X-radation may occur, here is an example warning you will find in every VCB maint manual


"APPLYING ABNORMALLY HIGH VOLTAGE
ACROSS A PAIR OF CONTACTS IN VACUUM MAY
PRODUCE X-RADIATION. THE RADIATION MAY
INCREASE WITH THE INCREASE IN VOLTAGE
AND/OR DECREASE IN CONTACT SPACING. XRADIATION
PRODUCED DURING THIS TEST WITH
RECOMMENDED VOLTAGE AND NORMAL CONTACT
SPACING IS EXTREMELY LOW AND WELL
BELOW MAXIMUM PERMITTED BY STANDARDS.
HOWEVER, AS A PRECAUTIONARY MEASURE
AGAINST POSSIBILITY OF APPLICATION OF HIGHER
THAN RECOMMENDED VOLTAGE AND/OR
BELOW NORMAL CONTACT SPACING, IT IS RECOMMENDED
THAT ALL OPERATING PERSONNEL
STAND AT LEAST FOUR METERS AWAY IN FRONT OF THE BREAKER"

We must be careful posting generic test voltages.
There is also an insulation resistance test, contact erosion, contact resistance, and mechanical tests that should be conducted per maint manual or per recognized standards such as the International Elelctrical Testing Accn, (NETA)