@MBrooke . Correct. Also, most of our clients preference to disable by removing the internal wiring for the manual push button in the MOD cabinet to avoid "human error". so it only opens/close from the control module or SCADA
Gained would be that there is not a switching agent standing generally somewhere underneath the device being manually operated that might be subjected to a rain of molten copper if something goes agley...and who must depend upon personal protective equipment as a last line of defense against such occurrences. The likelihood of this happening is of course a function of the quality, age and condition of the equipment being operated.
The down side is that there is more equipment to maintain.
As for switching from remote locations: as long as Work Protection is not a consideration, we as controllers/operators will commonly use as many tools as are at our disposal to confirm that equipment is operating or has operated correctly. The more ways we can verify that something is working the way it's supposed to, the more we like it. Switch position check-back is the primary information source; potential indicating devices are a close second, although which source or piece of equipment these are connected to will sometimes impose limits on how we can use them.
When switching transformers out of service, we don't like to remove them from potential without an agent there to confirm the three phases of the primary disconnect open; we would only contemplate doing such in the presence of three-phase transformer bushing potential devices to confirm proper switch operation such that the transformer is not being single-phased...and even then, there is no guarantee that if the switch has a problem and we close it back in that all three phases will close, and we don't want to be the ones on the hook if a bank gets damaged from such causes...single-phasing a circuit or cable doesn't carry the same risk of damage.
Spoken from an operations standpoint only, as I'm not an engineer, just a lowly operator...hopefully somewhat redeemed by years of experience and having worked with many, many different types of equipment...
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
For new work we use MODs at 500kV due to the high phase-phase spacing and manual disconnects everywhere else. The old 57 and 115kV MODs have a huge variety of failure modes we'd just as soon be rid of that we won't (presently) consider MODs in lieu of manual switches.
@Davidbeach: Including 345kv? I am really curious about the failure mods of these MODs. How old are they and what is being encountered?
While this video does not reflect IEEE/ANSI equipment, 1:56 and 5:52 onward demonstrates a potential benefit in using MODs when it comes to worker safety:
We don't have any 345, so that's moot. Ideally a disconnect is used to drop/pick up the charging current between the switch location and the adjacent breaker. We use MODs on 500kV simply because the phase spacing becomes to larger for a single handle manually operated switch. Others do various fancy automatic MOD operations following breaker trips, we don't; they're isolation devices. Older installations still use MODs where we'd only consider circuit switchers today.
I checked and it is possible to get away with MODs at 345kv (some utilities choose not to have them at that level). In fact Id say many utilities share your philosophy and its probably 50/50.
As for the the failures you experience, they are within the operator itself?
Use of motor operated disconnects (MOD) is largely a customer preference. I know of utilities that utilize MODs for all 345 kV and above equipment and others that prefer manual operation. Even if a MOD is operated locally (at the switch) time delays can be built into the operator to allow personnel to get clear of the switch before it is is operated.
Depending on the P&C (Protection & Control) employed the motor operator can be easily interlocked to eliminated improper operation.
The motor operators I am familiar with are designed such that you can uncouple them from the switch and lock out. They also do no allow for getting them out of sync (switch is closed but indicate an open switch)
The majority of the 345 kV and above switches I see are MODs but again not always. The splits is ~75/25.
Even if you choose to employ MODs at a HV station, it isn't a good idea to operate them remotely without having boots on the ground to verify correct operation.
Sometimes you may want to initiate a DS operation via protection, ie: automatically, so in that case you will need MODs.
Whatever equipment you choose, it's important to know that operating practices need to reflect what equipment has been installed.
Thanks, it really is a preference based on pros and cons. One utility I know of only has MODs directly on the outgoing lines and all the remaining disconnects within the station being manual. Personally I think that might be the best route for me. Anyone have any idea of how long a MOD lasts versions a standard manual operating means?
I am not sure if there is a definite answer on life expectancy of a MOD, however if there was, I'd assume it was based
on what kind of maintenance philosophy was applied and how often it was operated. I often see spare arcing horns available in the substation, which leads me to believe these are components that are likely to wear over time.
Like any disconnect switch, proper setup and adjustment are critical. As far as the motor drive unit, proper sealing and heating are critical. Most internal components are not all that different that what one would find in a breaker cabinet (limit switches, terminal blocks, control switches, indicating lamps). Of course, one get what one pays for in terms of quality and component selection.
I was at a generating station this week and there were MOD's on all 3 345 kV lines and 3 GSU connections. I asked the staff about MOD issues and none were reported since installation in 2005. All 6 MOD's had the external shaft coupled auxiliary switches (52a & 52b connected). Additionally the lines were connected to an auto reset 86 (or 94L) when the line was opened after a fault to allow the ring bus to be closed up after a permanent fault.
In our case, wasps seemed to like the the control cabinets - always something to look out for!
Id argue thats because they were never opened (assuming no line faults) in the first place. I've heard of switches that just failed when called upon 20 years latter for the first time. But now that you mention it I have been thinking about setting an auto open for bay MODs after a line trip.
Switches that fail to close properly seem to love following me around. It seems that 40% of the time I am doing work (P&C upgrades, etc), when it's time to switch back in, we have issues. Its funny watching all of the associated crew members making that call / text to the wife (It may be a long day). Last January, after a transformer replacement, we went to close the 138kV breaker disconnects (40+ year old switch) and the porcelain separated from the base on one phase. That phase fell towards, but did not touch the adjacent phase. Manually operated switch with a low profile bus.
