What is the device that disconnects your solar when power is cut from the grid - Page 1
Forum section: electronics / projects

author: drakejest
author_rank: Regular Contributor
timestamp: November 17, 2020, 09:13:42 pm
content: What do you call the device that is being used in solar panel system where it disconnects the connection of the grid to the inverter when grid power goes out?Is it just a magnetic contactor or it has a much more specialized name?

author: Phoenix
author_rank: Frequent Contributor
timestamp: November 18, 2020, 02:13:51 am
content: For a domestic solar system it is a regular old relay internal to the inverter. (It will likely be a special model of relay with larger contact gap to meet the requirements of IEC 62109-2.)It does have many names depending on the standard you refer to...AS/NZS 4777.2 "Disconnection device"VDE-AR-N 4105 "Interface switch"

author: bdunham7
author_rank: Super Contributor
timestamp: November 18, 2020, 02:21:51 am
content: There typically isn't a separate device and how an inverter implements the grid-loss shutdown will vary by design. In my case, there is no disconnect at all--the inverters simply cease operating.

author: Phoenix
author_rank: Frequent Contributor
timestamp: November 18, 2020, 02:31:17 am
content: Quote from: bdunham7 on November 18, 2020, 02:21:51 amWhat model inverters do you have? I'd be very surprised if there was no internal relays for this.In Au/NZ and EU there is a mandatory requirement for mechanical disconnection between the utility grid and DC source for microgeneration inverters. (Though I can't find the specific clause about it in UL or IEEE for US).

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 18, 2020, 03:38:51 am
content: Quote from: Phoenix on November 18, 2020, 02:31:17 amI have never seen a microinverter with a relay to disconnect the mains, that would be an extra failure point.For string inverters, there's a good reason to have a relay and that's adding the capability to provide backup power. Only a few manufacturers implement it in a way that does not require batteries to work, but it's becoming more common as the value is becoming apparent.

author: bdunham7
author_rank: Super Contributor
timestamp: November 18, 2020, 04:33:00 am
content: Quote from: Phoenix on November 18, 2020, 02:31:17 amEnphase M210. Is that mandatory requirement for a mechanical disconnect in case of a power outage or just a requirement for a manual disconnect? The first would seem silly, the second I have. The inverters themselves don't need to be disconnected.

author: Berni
author_rank: Super Contributor
timestamp: November 18, 2020, 06:52:27 am
content: If it is a grid tie inverter for sending power back out to the grid then there are strict requirements for these inverters to shut down if the voltage on any of the phases gets too low or too high. This means the inverter was disconnected from the grid and must stop operation to avoid pushing power out on the power poles outside of your property, the power may have been shut off for maintenance work, so pushing power out could injure a maintenance worker.Almost everywhere it is illegal to connect a grid tie inverter without this functionality.As for a manual disconnect, those are called circuit breakers. Separate breakers on the mains side of the inverter (and ganged together if its 3 phase) are most likely mandatory for the case that the inverter blows up and shorts out the mains. You want those anyway to make servicing easier by making disconnecting it from the mains easy.

author: sandalcandal
author_rank: Unknown
timestamp: November 18, 2020, 07:23:23 am
content: I think you're talking about an "anti-islanding" function which in AS 4777.2 is part of the "Automatic Disconnection Device". The anti-islanding functionality is built into most grid-tie inverter systems."protection against islanding" and "Islanding Protection" are equivalent terms used in IEC standards.https://en.wikipedia.org/wiki/Islanding

author: Phoenix
author_rank: Frequent Contributor
timestamp: November 18, 2020, 09:51:41 am
content: Quote from: bdunham7 on November 18, 2020, 04:33:00 amIn every other region I am familiar with (Europe, Aus/NZ) the inverter requires a mechanical relay type switch (in every phase and neutral) that automatically opens to prevent islanding (upon detection of over voltage/under voltage/over freq/under freq/plus usually a form of active anti-islanding). The purpose is to protect linesmen from electric shock due to accidental islanding.In fact for non-isolated topologies (most solar inverters these days) they require two redundant relays. Plus in either isolated or non-isolated the relays need to be tested for welding each time before the inverter operates. That's how serious they are about what may "seem silly" to you.Maybe the US is the exception to the rule as I can't find anything in UL1741 or IEEE1547 regarding this requirement. Justcease to energise.For the case of Enphase microinverters they make a device called the Q Relay which is designed to act as the disconnect. They also make other products to act as disconnects depending on the rest of the system. It makes sense here to have a single external disconnect than several internal ones.https://enphase.com/sites/default/files/downloads/support/Q-Relay-QIG-EN-INT.pdf

author: Phoenix
author_rank: Frequent Contributor
timestamp: November 18, 2020, 10:04:13 am
content: Quote from: Berni on November 18, 2020, 06:52:27 amThis is a topic that may be hard to generalise across countries/regions as they have their own installation requirements. I'm most familiar with Australia's installation requirements (AS/NZS 4777.1).Here you require a lockable manual isolation switch (on both AC and the PV side) located near your inverter. You also require a circuit breaker in the fuse box (obviously, to protect the final circuit cable). The fuse box circuit breaker can act as the manual AC isolation switch if close enough and visible. Just to be more annoying we also require DC isolators on the rooftop near the panels - for some reason.The nearby isolators are required for electricians and less electrically skilled people (like emergency services) to isolate the inverter in an emergency. The lockout is to allow an authority to lockout/disable the system if the need arises.[Note that circuit breakers trip on overcurrent, isolators do not].

author: Berni
author_rank: Super Contributor
timestamp: November 18, 2020, 11:59:32 am
content: Quote from: Phoenix on November 18, 2020, 10:04:13 amYep the exact requirements vary a lot from country to country. Over here upon putting in the paperwork to set you up to receive compensation for the power you give to the grid will also require the inverter to be inspected by a certain certified person. If you don't have things done by the book you don't get the paperwork.In terms of actual requirements here things are similar, they want a disconnect close to the inverter for both the AC and DC side. No such requirement for having isolators up on the roof, but the particular system we use has "optimizer modules" on the panels that can bypass shaded panels, monitor each panel but also short them out if told so to make the array safe.

author: bdunham7
author_rank: Super Contributor
timestamp: November 18, 2020, 06:43:08 pm
content: Quote from: Phoenix on November 18, 2020, 09:51:41 amWas this regulation in response to any actual incident or was it a bunch of people dreaming up what-if scenarios? In a system like mine, islanding would be functionally impossible and has never, ever happened AFAIK with many, many inverters installed.QuoteNo automatic relay or disconnect was required when installing my system and the mechanical disconnect is a circuit breaker. That is for a grid-tied systemincapableof islanding. Newer Enphase systems are capable of islanding and even include battery storage, so a separate anti-islanding disconnect is now obviously needed. I don't know about non-US requirements, but microinverters are not that common AFAIK outside the US.

author: Phoenix
author_rank: Frequent Contributor
timestamp: November 18, 2020, 10:02:09 pm
content: Quote from: bdunham7 on November 18, 2020, 06:43:08 pmI'm afraid I'm simply regurgitating the requirement on this one. I can speculate that they want to maintain isolation of the (continuously energised) PV from the mains, even under catastrophic failure of the inverter hardware.Interestingly, the latest US standard UL 1741:2020 requires what's called PVRSS (PV Rapid Shutdown) - which involves boxes on every solar panel to reduce each ones individual hazard below a certain level upon shutdown. Microinverters are allowed perform this function. I don't know that much about these because I don't deal specifically in PV anymore.QuoteMicroinverters are everywhere. Enphase is big enough in Australia and has European and other certs.

author: drakejest
author_rank: Regular Contributor
timestamp: November 22, 2020, 04:24:00 pm
content: Quote from: Phoenix on November 18, 2020, 02:31:17 amThere actually is an internal relay or this, but it wont harm if i place another one right?

author: drakejest
author_rank: Regular Contributor
timestamp: November 22, 2020, 04:32:27 pm
content: Quote from: Phoenix on November 18, 2020, 10:04:13 amI do not live in the areas you have mentioned but we share the same requirements. Breakers on each battery pack, breakers on the PV near the inverter and near the panels. breakers in the grid input the inverter output ( usually this will be the master breaker of the existing house). and finally this anti-Islanding device (although my inveter has one i would still like to place a good quality one). There are many names which makes it a bit hard to look for it online.