Loss of Control Power on Protection Relays

[mbk2k3]

Hey guys,

Ive been reading through the manuals of multifunction protection relays and would like to confirm the following:

If I wanted to design a system where the system trips in the event of loss of control power to the protection relays (SEL/Beckwith/Multilin/etc), do I do so using the self-test contact available on these relays?

I know the self-test can be used for alarming, but can it also be used directly in the tripping circuit or does it normally go through an auxiliary relay?

I'm just wondering what the standard industry practice is in this regard.

Cheers.

 

[oldfieldguy]

The application varies from one manufacturer to the next, but many relays offer a "Fail-safe" mode, wherein a contact which must close to perform a trip function is held open by control power and absence of trip condition. If the relay loses control power (or, in some cases, fails its self-test) the contacts revert to shelf state and will trip the protected devices.

old field guy

 

[JG2828]

Some relays have jumper select-able NO/NC output contacts. You also need to invert the logic to that output when programming. ie. out101 = NOT TRIP or similar.

For example the SEL-351 relay manual says the following:
Figure 2.30, Figure 2.31, and Figure 2.32 show the exact location of jumpers
that determine output contact type (Form A or Form B). With a jumper in the
A position, the corresponding output contact is a Form A output contact. A
Form A output contact is open when the output contact coil is de-energized
and closed when the output contact coil is energized. With a jumper in the B
position, the corresponding output contact is a Form B output contact. A Form
B output contact is closed when the output contact coil is de-energized and
open when the output contact coil is energized. These jumpers are soldered in
place.
WARNING
The jumpers that determine if an
output is Form A or Form B are
soldered into the circuit board. Follow
proper desoldering and soldering
procedures when changing those
jumpers, or return the relay to the
factory to have the jumpers changed.

For a GE UR relay you could just order it with a form-C output module and wire to the NC contact. Module 6E or similar.