RTUs - Trip/Close vs. Raise/Lower

[amurray]

Could someone explain the difference between a Trip/Close control & a Raise/Lower in a RTU? This came up in a GE RTU, but believe most RTUs have these different control types.

I understand you would use a T/C for circuit breaker or other device you want to open & close & that the R/L would be more for pulsing up or down something (tap changers etc) but would both these just be a contact close pulse for a certain time? Why are these two types of controls wired differenlty on an RTU control board & programmed differently in the RTU & SCADA software?

Thanks in advance.
Andy

 

[petetheswift]

Hi,First post so bear with me.
I have been involved with SCADA systems for some time so I will try to explain the differences between Trip/close and Raise/lower functions as implemented in the system I worked on.
Trip/Close is as expected a momentary contact used to operate items such as circuit breakers. The implementation we use is a pair of relays one of which is the Trip function and the second is the Close function. In the system we use controls are grouped in 12 output relays per card so one can wire 6 trip/Close pairs per card.
The contact closure is timed to be about 2 seconds (usual) and this would apply to all Trip/Close pairs on a card.

The Raise/Lower function is similarly organized but the operation is somewhat different.
The purpose of this function was originally to control governors on steam turbines etc.
The operation of the Raise control is to close the relay contact for a programmed number of pulses for a programmed time. (i.e 5 pulses of 5 seconds each). The same applies to the Lower control.
Each Raise/Lower pair can have different timings.
I hope that helps.
rgds

 

[amurray]

Thanks for the reply. Do raise/lower commands usually have an analog value associated as a control confirmation method? I am familar with using a breaker contact as feedback for a trip/close command & wonder if R/L has a similar setup?

Andy

 

[petetheswift]

Hi,
Haven't used Raise/Lower for some time but no, I don't remember that it has a analog value as feedback. It's a matter of operator seeing the result and also "tuning" the system to provide a known response to the R/L signals.
The systems we used had a "two pass" control whereby when a command was issued (T/C etc)a signal was sent to the RTU with appropriate addressing and function details and this was then "confirmed" back to master station before a "command excute" was sent. This happened automatically and if no confirmation was received no control occured and an error was flagged.