Back in the early days of grid tied PV, most utilities were encouraged/forced to create "short form" or expedited interconnect rules for grid tied PV. as their rules were written for industrial power and were quite complex and expensive to obtain. Normal interconnected generation needed approved protective relaying (Sort of a complex version of UL 1741), a T-1 line to a Normally Open Relay that they could remotely shut down grid feeding (small PV does not have this) and finally a lockable disconnect switch accessible 24/7 by the power company that they could with no notice open at any time and lock out. The lock out switch made it into many early grid tied PV systems including my original 660 watt array. If the utility did not like the looks of your grid tied PV system they could and would open the switch and lock it out until they were happy with the install. In some cases the local unions in southern CA didnt want non union installations and were locking out systems that they perceived did not meet code as they were installed by unqualfied people.
In theory if the utility was working on the distribution they could shut off and lock out any legal backfeed sources. The problem with that is that Joe homeowner trying to keep warm during a power outage with a generator and suicide cord is not a legal interconnect and that generator is just as likely to zap a lineman than a PV system so now the lines are grounded before any work starts. The requirement for a lockable disconnect is no more in most most utilities.
The T-1 line permissive to operate is somewhat back optionally for UL 1741 SA inverters that unlike an older 1741 unit can optionally be controlled remotely by the utility as those units, dependent on configuration and permitting can stay on the grid to reinforce it until it goes outside a far greater range of grid limits than the old 1741.
The thing is, stuff happens when lines are energized and deenergized, power factor capacitors can fire and other odd crap happens. It is probably good to be disconnected from the grid during that transition as frequently that is when surges and droops happen.
War story time, the last project I was involved with was a very old 1920s power system in very large old industrial facility that occupied a couple of city blocks. Much of the plant was built before the grid was installed in the 1800s. It was a critical industry pre and during WW2 and they could not afford to lose power so it was fed from 3 different 13.8 KV utility circuits with 14 primary local feeder circuits split between two incoming utility circuits with a spare utility circuit that could be toggled between either side. In addition, they had a backpressure turbine with a generator on it hanging off primary circuit. They also could feed all the local feeders from any one circuit. This could be done completely independent of the utility with zero logic involved just big vacublast breakers. That meant that someone in the plant could backfeed any of the three utility circuits from the other two. No interconnect protective relays. When we proposed the project, the utility rep told us that they were really really interested in working with us to clean up that mess. They did a whole lot of upgrading on their side and the client ended up with one primary circuit with a backup circuit remote controlled by a utility owned breaker/transfer switch in a utility vault with only one circuit going into the client site. We had installed a 5 MW generator with synchronization inside the plant so if the utility could not supply the power, they could go off grid and run off the generator. BTW we still needed the TI permissive to operate and a lockable disconnect accessible to the utility even with their upgrade. The only guy who understood the plant electrical system was 70 and worked as a consultant to the plant. They had no one trained to replace him.
or some kids walking down the road.
