Medium voltage vs low voltage

[Sahib]

MV is superior in many ways,

But it is liable to corona damages.

 

[mbrooke]

But it is liable to corona damages.

Only when done by untrained people. Seriously, the only one one who should be making up MV splices and joints are licensed people trained in handling MV.

 

[Sahib]

Only when done by untrained people. Seriously, the only one one who should be making up MV splices and joints are licensed people trained in handling MV.

Those MV panels with polymer insulators developed corona discharges and were damaged, when heater stopped working.

 

[mbrooke]

Those MV panels with polymer insulators developed corona discharges and were damaged, when heater stopped working.

Keep the heater running :thumbsup:

 

[Jraef]

Only when done by untrained people. Seriously, the only one one who should be making up MV splices and joints are licensed people trained in handling MV.

I once put in a 600HP 4160V soft starter for a local water utility and after doing the startup and training, the maintenance supervisor wrapped up by asking their electricians if they all understood. They said yes, but their lead electrician added; "It doesn't matter though, none of us are qualified to work on MV anyway." Longer story short, the district had to pay to send them all to additional training, after which they then all hit the utility up for raises. A year later they needed another 600HP soft starter, it was designed for 480V...

 

[meternerd]

I once put in a 600HP 4160V soft starter for a local water utility and after doing the startup and training, the maintenance supervisor wrapped up by asking their electricians if they all understood. They said yes, but their lead electrician added; "It doesn't matter though, none of us are qualified to work on MV anyway." Longer story short, the district had to pay to send them all to additional training, after which they then all hit the utility up for raises. A year later they needed another 600HP soft starter, it was designed for 480V...

Yup...different world with different problems and dangers. But there's plenty of it out there, so with training and proper installation, it's pretty darn reliable and cost effective. Been around it most of my career and not much trouble. The main advantage I see is that employers are not nearly as likely to want the electricians to work it hot, unlike LV. Gee, just wear your PPE....We can't afford any down time and that's what you're getting paid for. Yeah, right!

 

[mbrooke]

I once put in a 600HP 4160V soft starter for a local water utility and after doing the startup and training, the maintenance supervisor wrapped up by asking their electricians if they all understood. They said yes, but their lead electrician added; "It doesn't matter though, none of us are qualified to work on MV anyway." Longer story short, the district had to pay to send them all to additional training, after which they then all hit the utility up for raises. A year later they needed another 600HP soft starter, it was designed for 480V...

Yup- thats how it is come real world. LV wins 9 out of 10 for this reason.

 

[Jraef]

Just got an RFQ come in for 3 x 900HP VFDs, 480V for submersible pumps, 1006A FLC, 200' deep; they want the output cables to be 3x700kCMIL/phase. Running, hanging and terminating those cables is NOT going to be fun...

I helped design this system 2 years ago and it was 4160V, but the pump supplier was selected ahead of time and is now insisting on LV motors. I think that's because they don't have MV rated terminations into the pump housing and they don't have to to deal with the other consequences of using LV.

 

[Tony S]

I once put in a 600HP 4160V soft starter for a local water utility and after doing the startup and training, the maintenance supervisor wrapped up by asking their electricians if they all understood. They said yes, but their lead electrician added; "It doesn't matter though, none of us are qualified to work on MV anyway." Longer story short, the district had to pay to send them all to additional training, after which they then all hit the utility up for raises. A year later they needed another 600HP soft starter, it was designed for 480V...

In the UK you have to hold a MV ticket to carry out testing/switching operations on MV, then every three years a refresher for legislation update course is needed to hold on to your ticket.

The first course I went on was MV system management, I’d rather put my hand in a food mincer than go though that again!

 

[mivey]

Those MV panels with polymer insulators developed corona discharges and were damaged, when heater stopped working.

So pretty much if the equipment fails and maintenance is not done then trouble will follow. Got it.

 

[Sahib]

So pretty much if the equipment fails and maintenance is not done then trouble will follow. Got it.

A LV panel would not fail that way if under the same circumstances.

 

[mivey]

I'd rather be close to a MV distribution fault in open air than inside a switchgear with a 277/480V fault. Just me, though.

Space for the energy and heat to go other than all in my direction and anything to deflect what can come in my direction is what I look for in either case.

If it is just standing slightly to the side, or hiding behind a cabinet, or opening the door while behind it rather than eagerly sticking your face in, close your eyes/turn your head when switching: always look for ways to reduce your exposure.

And always keep an open path to the substation gate when possible...and don't lean on the fence or equipment...the list goes on but common sense is the key.

 

[mivey]

A LV panel would not fail that way if under the same circumstances.

LV panels are different than MV panels so I would not expect them to behave the same way.

 

[Sahib]

LV panels are different than MV panels so I would not expect them to behave the same way.

Iam not talking about the constructional differences between LV and MV panels. It is about nature of LV and MV voltages: corona damages in MV and not in LV, for example.
May be because of that, code included up to 1000V in LV category?

 

[mbrooke]

Iam not talking about the constructional differences between LV and MV panels. It is about nature of LV and MV voltages: corona damages in MV and not in LV, for example.
May be because of that, code included up to 1000V in LV category?

Yes- but one can have other problems in LV not seen in MV.

 

[mivey]

Iam not talking about the constructional differences between LV and MV panels. It is about nature of LV and MV voltages: corona damages in MV and not in LV, for example.
May be because of that, code included up to 1000V in LV category?

They are constructed different because their natures are different.

mbrooke's point to keep the heater running was valid. They were included for a reason.

 

[Sahib]

Yes- but one can have other problems in LV not seen in MV.

Such as?