DTT for small distribution generator 1

[JensenDrive]

I have a case of a small distribution generator that is sized larger then the minimum load on the line, so the generator has the ability to carry line load if the utility trips. The utility is saying a direct transfer trip (DTT) scheme will be needed to ensure the gen trips if the utility trips. So far the utility is not saying what technology is going to be needed. I have someone telling me unlicensed radio transceivers would be the way to go (SEL has a couple items), but I question whether the utility is going to buy using unlicensed radio for DTT. Might swing as this is a low risk application. Before I talk to the utility engineer, does anyone have any experience in low budget DTT? Running fiber from the substation to the customer of course is a nice idea, but it seems a major investment.

 

[QBplanner]

@Sn00ze
here is what happenedin the utility I work. For most of D-IPPs without DTTs. for any force outages, to allow crew to start work on the faulted feeder. control center will call IPP to go off line and open entrance disconnect switches. After that, PSSP worker will be sent to virtually confirm if the IPP disconnect switch is open. then crew will start to work if there are no other sources on that feeder.
For any scheduled outages, 5 days in advance notice to D-IPPs.

@waross
"In Canada the CEO of a company may be charged with a criminal offence in the event of the injury or death of a worker if it can be shown that accepted safety practices were not followed."
maybe in Canada 30 years ago when people were still caring about life and customers. and the utility I work, a few years ago one P&C tech. was killed during the work in a indoor sub.and his accompany even left him alone and went out for sth else. Nothing happened to the CEO. nothing happened to anybody. I appreciate your old school staff but what I learned here is completely different than what you experienced.
Give your a example, Here is what happening in the utility now, last year, a sub is supplied by 2 X 230kV lines, one line is under maintenance so the whole 230kV sub was supplied by one 230kV line and P&C tech wanted to wire checking on one of the two CBs for the remaining 230kV line. The work even got approved and during the work sth happened and mistakenly tripped the remaining 230kV line and lost 60000 customers. the number is correct, 60000 customers. what happened next is even more funny, the utility claimed that is trying hard to restore the power so the customer should appreciate it.
@davidbeach
P&C guy like you always think you save the world. I have no doubt about that the first person gets call when sth goes wrong will be P&C guys in any utility. Guess what in the utility I work when P&C guys could not figure it out what had happened because they checked everything out and nothing went wrong they either asked help from system planners to figure out from broader aspects other than the narrow P&C perspectives. or they start to blame system design.

When the system I designed energized successfully, I got a call from control center manager said thank you for the system you designed it works beautifully. I am not aware that P&C guy got the similar phone call to show appreciation. DO I need to mention the reason?
BTW,
I am not like you said only knows N-0,N-1,N-2. These are just some dummy new generation planners who work in a utility for a few years and want a manager position and who only know following NERC AND WECC standards. I was trained in the country I came from by the old timers and dealing with much more complicated network issues than here in North America. I came here was trying to learn from the best such as experts in BPA and the utility I work. What I learned quickly the facts is these experts I called they are either planning the system for God or retired long time ago. The people around me from manager to the manager's manager to the VP have no clues what the hell they are doing and they are not even electrical engineers. what a pity.

 

[crshears]

Although I do find QBPlanner's negativity and cynicism somewhat disheartening, I cannot completely disagree with him, either; ime [in my experience] utilities, and sometimes even the disparate geographic regions of a given utility, have varying levels of dysfunctionality. The eventual outcomes of court proceedings, criminal prosecutions, etc. can also be all over the map.

Within my utility, freewave communication media are becoming the comm path of choice; relatively inexpensive and generally quite reliable, although not universally so...and the instances where DG is tripped off due to loss of comm tends to replicate in specific schemes, iow there is some sort of problem with that particular comm path not being as line-of-sight as designed or constructed, vegetation behaviours not being taken into account, specific types of atmospheric conditions rendering that specific scheme's function sub-optimal at times, etc., etc., and where these situations occur the developers/investors/owners may not have deep enough pockets to afford the changes needed to correct the issues, threatening the viability of the entire project.

Hope this helps.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[HamburgerHelper]

Where I am at, P&C is at a loggerhead with planners. It is difficult to get good models for fault current. We have to check the models and sometimes are told why we don't create the model additions. I don't know why it is this way. It probably won't get fixed until an expensive mistake happens even though people have been complaining about it for awhile.

 

[davidbeach]

What I've found is that the planners are likely to have a model that is wider in extent, more of the relevant interconnection, but far shallower than the protection models. From what I've seen, planners live in a dull and boring world of positive sequence. The fault models allow entry in the vastly more interesting world where things also happen in the negative and zero sequences. The vast majority of faults cannot be looked at, with any real meaning, in just the positive sequence. Ground faults and zero sequence mutual coupling - that's where the fun can be found.

I once had a planner ask me what the impedance was for a ground fault at a certain bus. Seemed an odd question, as it obviously could anything one might want it to be from zero up, particularly the resistive component. No, that's not what he meant, he wanted the zero and negative sequence source impedances associated with that fault so that he could use them as the fault impedance to get the right positive sequence values. Yep, the positive sequence values were correct, but for what? No ground fault I've ever been aware of produces a balanced set of phase currents nor a balanced set of phase voltages. If your world is just the positive sequence it is apparently good enough, but seems to me to miss the entire point of running the fault in the first place. Most of the other planners seem to be much more in touch with how the system actually works.

 

[QBplanner]

@divadbeach
Maybe in the utility you r in that planners only know the positive sequence network. In the utility I am in we calculated SLG impedance by hand using positive, negative and zero sequence network impedances. Also when performing EMTP study, we have much complicated model than P&C planning has in Aspen. you may disagree.
NTW, positive, negative and zero just a mathematical models just like ABC to DQ0, there is nothing fancy and so simple.
Try double fourier transformation if you want to understand what is complicated.

 

[HamburgerHelper]

Modeling lines probably has to only be withing 10% for P&C with the margins we use. We still have a hard time getting them to put anything in the model because they don't have all the commitments or know all the construction details or something. I don't understand the whys completely. Per/mile values would probably be enough for all or most of the line modeling and that includes negative and zero sequence. Screwing up modeling a transformer can easily swing around the fault current by way more than 10% and that occasionally happens. We have mutual coupling modeled everywhere down to the 0.00001 PU. I think CYA engineering was made the priority on that one. 99% of our mutual coupling data serves no purpose other than someone can say everything is modeled.