Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Don Y Newsgroups: sci.electronics.design Subject: Re: The Spanish Grid Drop-out - recently released information. Date: Thu, 15 May 2025 15:34:08 -0700 Organization: A noiseless patient Spider Lines: 96 Message-ID: <1005q52$3bp75$1@dont-email.me> References:

<10032b6$2n0o4$1@dont-email.me> <1004nhq$34c0m$1@dont-email.me> <1004pin$34pes$1@dont-email.me> <1004reh$3541v$1@dont-email.me> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Fri, 16 May 2025 00:34:13 +0200 (CEST) Injection-Info: dont-email.me; posting-host="834da558340bebbe55849e087260a4f8"; logging-data="3532005"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18gH0qJPLpwJNVUCHymYeji" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:Rd/FbUGGLZWjdWsjZTkjXnxfCVo= Content-Language: en-US In-Reply-To: Bytes: 6794 On 5/15/2025 2:37 PM, Glen Walpert wrote: >>>>>> >>>>>> SCADA is used to monitor and control the grid, where control is done >>>>>> in real time by adjusting the set points for real and reactive power >>>>>> at all controlled power sources. A small percentage of sources >>>>>> being inaccessible degrades control by an insignificant amount. >>> >>> I'll believe it is used to monitor the parameters at key locations in >>> "realtime", update set points and try to reset tripped breakers. >> >> The 'S' in SCADA -- SUPERVISORY. Like deciding how fas the subway car >> will travel but not actually commutating the current in the motor. >> You want local control that reports status (Data Acquisition) >> and accepts control (Supervisory Control) from a higher level >> functionary. > > Right, I had a feeling I was misremembering but was too lazy to look it > up. Realtime depends on the application - SCADA signaling is fast > compared to the response times of large generators, realtime control of > the grid, not of the local inner loop generator controls (governor and > field exciter). Yes. I think Theo's notion was to provide a "reference signal" to the "network" (via RF) instead of letting the network itself supply that. Thinking, perhaps, that could better hold the network's individual cogenerators in closer "check" than allowing them to be semi-autonomous. >>> Indeed. And smaller generation systems can just get crushed like flies >>> if they try to stop a rampaging elephant as big GW systems drop >>> offline. >>> >>> If the system did fail due to local over voltage excursions somewhere >>> and then failed to become stable again after a few suppliers dropped >>> out then their network stability analysis must be appallingly bad. >> >> The problem is all of the distributed "residential" solar rivals "big GW >> systems". E.g., we have ~10GW of total solar, here -- but, of that, >> 300,000 individual residential systems in the 5KW (avg) power rating. >> So, 1.5GW whose location is varied and diverse BUT whose control is >> *likely* mandated by regulations/specifications created when solar was >> intended to be "the dog's tail" -- tracking an otherwise stable grid. >> >> And, if a residential cogenerator goes offline, the residence's LOAD is >> still there, no longer being supported by that "local" generation. > > Right, the first generation of solar inverters was like that, the second > generation of 'grid assist' inverters will assist in grid stabilization if > properly used. At least some of these require a local battery and limit > grid connected inverter output to 80% of stand-alone rating so there is > almost always some reserve for grid support. How are the "legacy" installations treated? Are they mandated to replace (or update) their controllers to comply with "new requirements"? Or, is the hope that their effects will be lost in the noise? (I'm thinking particularly about folks who paid for residential solar installation and might -- potentially -- be forced/coerced into having to do an equipment upgrade because of issues with "their version" of the hardware.) > BTW the reason for using reactive power setpoints to control grid voltage > can be illustrated by considering the connection of a generator to the > grid. The generator is brought up to slightly above synchronous speed > with the governor in droop mode (power output subtracts from speed > setpoint) and the field excitation will be in voltage regulation mode, > voltage set the same as the local grid connection. As soon as the output > breaker is closed (in phase!) the generator speed and voltage is locked to > the grid, local control is not possible. The governor will increase power > until the negative power feedback reduces the setpoint to exactly grid > speed, delivering a small amount of power to prevent the reverse power > relay from tripping; the governor speed knob now controls real power > output, not speed. > > At the instant the main breaker closes on the grid an aux contact switches > the field exciter to reactive power control mode, easily measured in a > balanced 3 phase system as Vac(-Ib), and initially set at 0. With > reactive power output at 0 the field exciter will provide as much field as > required for real power output as set by the governor. More excitation > than required for real power produces reactive power, less is a bad idea. > Small cogen may not get paid for or be required to provide reactive power > and won't for maximum efficiency, larger cogen will, and overall reactive > power supply must be balanced with load requirements by the grid > operator. Increasing reactive power set points above load requirements > will raise grid voltage with the excess field excitation, not enough > reduces voltage. > > Thus the requirement that grid support inverters deliver reactive power on > low grid voltage - it has a much larger effect on grid voltage than real > power, at least when there are enough rotating generators and induction > motors on it. Plus you can get quite a bit of it with a small reduction > in real power due to the sin-cos relationship. > > Glen >