Solar unlimited – The ATS

What is a ATS?

An Automatic Transfer Switch (ATS) is an intelligent electrical device that plays a crucial role in ensuring continuous power supply to critical loads. Let’s delve into the details:

1. Purpose and Function:
   • The primary purpose of an ATS is to automatically switch the power source for a connected load circuit (which includes electrical equipment like lights, motors, and computers) from one of two power sources.
   • When the normal power source (such as utility service) fails or experiences abnormal conditions, the ATS ensures a seamless transition to an alternate power source (such as standby generators or uninterruptible power supplies).
2. Operational Characteristics:
   • Robustness: The ATS must operate as intended even under abnormal power system conditions, without human intervention.
   • Decision-Making: It determines when to transfer power and when not to, based on system conditions.
   • Control: The ATS operates switchgear (transfer circuit breakers) and signals the alternate power source (e.g., starting a generator).
   • Status Inputs: It receives status inputs from breakers (e.g., undervoltage and negative sequence voltage relays).
   • Frequency Monitoring: ATS monitors the frequency of the alternate power source.
   • User Interface: Allows adjustment of operating parameters and provides system status updates.
3. Modes of Operation:
   • An ATS must support different modes of operation, responding differently to changing system conditions.
   • For example, it can be set to transfer power immediately upon detecting a fault or delay the transfer based on specific criteria.
4. Example System Description:
   • Consider a main-main topology arrangement with an ATS: !ATS System
   • The ATS logic controls transfer circuit breakers, receives status inputs, and initiates generator startup.
   • Voltage transformers step down system voltages for relays.
   • The user interface allows adjustments and provides system status information.

With a transfer switch you can “off grid” your home for much less than parallel inverters.
With inverters Working in Parallel with the Grid:
When a grid-tied inverter operates in parallel with the grid, it synchronizes its AC output voltage and frequency with the grid’s voltage and frequency.
During normal grid operation, the inverter feeds power into the grid, supplementing the overall electricity supply.
If the grid experiences a power outage or abnormal conditions, the inverter must disconnect from the grid to ensure safety and prevent back-feeding into a potentially unstable grid.

Inverters in parallel must comply with UK Regulations and G98/G99 Type Testing:
In the UK, grid-tied inverters must comply with specific regulations to ensure safe and reliable operation.
G98 and G99 refer to the connection standards for grid-tied generators (including solar PV systems) in the UK.
Here’s what you need to know:
G98:
Applies to small-scale generators (up to 16A per phase) commissioned before 27th April 2019.
These generators must comply with G98 standards.
Exemptions exist for units contracted before 17th May 2018 and notified to the distribution network operator (DNO) by 17th November 2018.
G99:
Applies to all new and existing generators commissioned on or after 27th April 2019.
All generation operating in parallel with the distribution system must comply with G99 unless exempted.
Exemptions may apply based on specific criteria.
Type Testing:
Grid-tied inverters must undergo type testing to ensure compliance with G83, G59, G98, and G99 standards.
The basic design capacity of each piece of equipment (including inverters) should be 32A or less.
Manufacturers register their products in the type test register, indicating compliance with G98, G99, or G100 requirements, you cannot install an unregistered inverter working in parallel with the grid.

Why would you use a ATS inverter?

All ( mostly) inverters can work stand alone and you have probably seen or used one. The grid parallel inverters need the grid to work, when the grid down your down too. Not helpful during a power cut .
A “normal” inverter is “grid forming” so it is always on.

A grid-forming inverter is a critical component in the operation and stability of electrical power grids. Let’s explore its key characteristics:

1. Purpose and Function:
   • A grid-forming inverter serves as a controllable voltage source that connects renewable energy sources (such as solar panels or wind turbines) to the grid.
   • Unlike conventional inverters (which follow the grid), grid-forming inverters have the unique ability to restart the grid independently after a blackout or disturbance.
2. How It Works:
   • Imagine a scenario where the grid experiences a blackout. In this situation:
     • Conventional inverters would shut off power to renewable energy sources and wait for a signal from the rest of the grid to restart.
     • Grid-forming inverters, on the other hand, take the initiative to restart the grid without relying on external signals.
   • These inverters provide tightly controlled alternating current (AC) waves from solar or wind generation, ensuring a stable grid restoration.
3. Challenges and Opportunities:
   • As wind and solar contribute more to the overall electricity supply, relying solely on the rest of the grid to manage disturbances becomes impractical.
   • Researchers and industry stakeholders are exploring innovations in grid-forming inverter technology.
   • Challenges include creating new hardware, software, and controls, redesigning regulatory standards, and developing advanced modeling techniques.
   • The goal is to integrate grid-forming inverters into electric grids of increasing size and complexity over the next 10–30 years.
4. Benefits:
   • Grid-forming inverters enhance grid reliability and stability during rapid deployment of renewable technologies.
   • They allow for greater integration of solar, wind, and battery storage resources while maintaining system performance.

Having a Grid forming inverter with a ATS allows you to have power without the paper work and having to meet the regulations, a simpler installation is the short answer, the grid remains as back up power should you not produce enough solar or the battery is running low.

The ATS switches from the inverter to the grid when required, or the other way, care has to be taken in the choice of inverter due to “ground bonding” – in short, it creates a short in normal house wiring.
These are DIFFERENT from GRID ATTACHED inverter systems.

A grid attached system has a grid connection as a pass though, it also uses the grid to charge the battery while maintaining a “live” connection that is available with the grid at all times.