Medium voltage Vaccum Breakers?

Status
Not open for further replies.
Mike01

Mike01

Senior Member
Location
MidWest
What makes a medium voltage circuit breaker trip??
Do you have to have a electronic trip device (ex. digitrip)
When looking at a coordination curve is there a breaker curve or is it just the settings of the electronic relays that activate the breaker?
 
Mike01 said:
What makes a medium voltage circuit breaker trip??
Do you have to have a electronic trip device (ex. digitrip)
When looking at a coordination curve is there a breaker curve or is it just the settings of the electronic relays that activate the breaker?
Click to expand...
Every one I've seen, the vacuum CB is a vacuum contactor with an electronic trip unit. The coordination curve is set by the trip unit programming.

carl
 
coulter said:
Every one I've seen, the vacuum CB is a vacuum contactor with an electronic trip unit. The coordination curve is set by the trip unit programming.

carl
Click to expand...
You can still buy breakers with electro mechanical relays in them .
We bought a few last year .
 
Just to nit pick, there is technically a difference between the vacuum bottles used in a vacuum breaker and a vacuum contactor. Vacuum breakers use cheaper bottles and may exhibit "chop" when used to open and close repeatedly as a contactor would be. vacuum breakers are only meant to be opened under fault conditions, contactors are made to be opened under normal loads.

But as to the trip mechanisms; most are electronic, but they do still have "trip curves" associated with them nonetheless.
 
Jraef, thats not nitpicking at all, using a contactor or breaker for the right application is vital to the proper operation of the system, however you can upgrade your vacuum bottles if necessary but it is best to use the right device for the appliaction needed. Going thru this right now with a client who was using VCB's for motor starting and is having all sorts of problems.
 
Curve type?

Curve type?

What other types of circuit breakers would be available on medium voltage all I have seen is vacuum circuit breakers, and regarding the relays it appears (from some of my own investigation) that there are three distinct curve types each with up to 4 curve types most relays allow you to select the type of protection you want, either Thermal, ANSI, or IEC curves each category with sub categories like I2t, I4t, inverse, very inverse, what is the true advantage to one style (thermal, ansi, iec) over the other? I know the IEEE Blue Book refers to the application of Low Voltage Circuit Breakers, but is there any IEEE Color Book that refers to the application of medium voltage C.B.?s? How would you know what type to select and then what sub, type below that? Or is this something usually left to the coordination end of the project??
 
Air breakers were commonly used for up to 15kV, but are mostly outdated. Oil Breakers were used for all voltages and again are outdated.

Nowdays MV is all VCB's and SF6.
 
Mike01 said:
What other types of circuit breakers would be available on medium voltage all I have seen is vacuum circuit breakers, and regarding the relays it appears (from some of my own investigation) that there are three distinct curve types each with up to 4 curve types most relays allow you to select the type of protection you want, either Thermal, ANSI, or IEC curves each category with sub categories like I2t, I4t, inverse, very inverse, what is the true advantage to one style (thermal, ansi, iec) over the other? I know the IEEE Blue Book refers to the application of Low Voltage Circuit Breakers, but is there any IEEE Color Book that refers to the application of medium voltage C.B.?s? How would you know what type to select and then what sub, type below that? Or is this something usually left to the coordination end of the project??
Click to expand...
The type of curve is normally determined to match other protection that it has to coordinate with. ANSI curves will coordinate easier with other ANSI curves.
 
Relays

Relays

Most medium voltage circuit breakers are "dump." They have trip and close coils, and auxillary contacts. The protection features are provided my relays. Older systems use electro-mechanical type realys. It took one relay for each protection element (overcurrent, over/under voltage, over/under frequency, etc.) Today, everyones uses multifunction relays (MFR), which provide many elements into one device...and they are programable (like plc's) and can communicate data to a network. You can also use one MFR for multiple circuit breakers. Very powerful!
 
jghrist said:
The type of curve is normally determined to match other protection that it has to coordinate with. ANSI curves will coordinate easier with other ANSI curves.
Click to expand...

To be more accurate and simpler; the two main function of curve fitting is to follow the protected equipment, cable, etc. thermal damage curve as closely as possible, and to allow the inrush current at startup. Obviously selective coordination then requires the upstream breakers to ccordinate with the downstream ones, act as a backup, but never to trip before the downstream devices.
 
djohns6 said:
You can still buy breakers with electro mechanical relays in them .
We bought a few last year .
Click to expand...
I didn't know that. I've never seen a vacuum CB or SF6 with mechanical relays.

carl
 
Jraef said:
Just to nit pick, there is technically a difference between the vacuum bottles used in a vacuum breaker and a vacuum contactor. Vacuum breakers use cheaper bottles and may exhibit "chop" when used to open and close repeatedly as a contactor would be. vacuum breakers are only meant to be opened under fault conditions, contactors are made to be opened under normal loads. ...
Click to expand...
Didn't know that. Thanks. Apparently I haven't spent much time looking at the mechanical end of the devices:confused:

carl
 
Last edited:
coulter said:
I didn't know that. I've never seen a vacuum CB or SF6 with mechanical relays.

carl
Click to expand...

Yep , G.E. makes them and I think ABB as well . Just about everything we buy now has SEL microprocessor relays . I don't know why they bought those other dinosaurs . They used them in some some low tech applications . I don't forsee them getting any more .
 
Why electro-mechanical relays with MV breaker?

Why electro-mechanical relays with MV breaker?

A electro-mechnical overcurrent relay does not need control power. Couple the relays with a breaker that has a capacitor trip device to store the tripping power and you have a substation feeder breaker that doesn't need a battery system to trip.

A belt and suspenders engineer might use this method on a second trip coil as backup disaster protection in a remote substation.

There are some interesting videos of substations burning down when they lost DC control power and a fault occurred but the breaker couldn't trip.
 
rcwilson said:
A electro-mechnical overcurrent relay does not need control power. Couple the relays with a breaker that has a capacitor trip device to store the tripping power and you have a substation feeder breaker that doesn't need a battery system to trip.

A belt and suspenders engineer might use this method on a second trip coil as backup disaster protection in a remote substation.

There are some interesting videos of substations burning down when they lost DC control power and a fault occurred but the breaker couldn't trip.
Click to expand...

We are phasing out all of our Cap. trip devices . I have done a boatload of
retrofits on our distribution breakers to convert them to station battery .
The 125 volt system is already in place for other devices and for SCADA , so it made sense . Some of those Cap. trip devices are putting out 300 volts and are not compatible with our new RTU's .
 
rcwilson said:
A electro-mechnical overcurrent relay does not need control power. Couple the relays with a breaker that has a capacitor trip device to store the tripping power and you have a substation feeder breaker that doesn't need a battery system to trip.

A belt and suspenders engineer might use this method on a second trip coil as backup disaster protection in a remote substation.

There are some interesting videos of substations burning down when they lost DC control power and a fault occurred but the breaker couldn't trip.
Click to expand...

So is the capacitor tripping device more reliable than a UPS with batteries or supplied by two independent control power sources. Or for DC, using two independent power supplies with diode auctioneering?
 
dont have the data to back it up but I would guess a battery system with a remote alarm on the charger is the most reliable system for your money
 
zog said:
dont have the data to back it up but I would guess a battery system with a remote alarm on the charger is the most reliable system for your money
Click to expand...

Add a redundant battery bank and Cellwatch to that system and you will be right.

In battery banks all the batteries are connected in series so the failure of any one of the cells will take the whole bank out. (Eg. higher the voltage the more cells you have. 48VDC vs 125VDC argument.) Most common failure of a single cell is the open cell under load where the voltage appears normal until load is applied.
 
Status
Not open for further replies.
Top