What is Anti-Islanding? | BCJ Controls | Solar Relay

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What Is Anti-Islanding?

• Why do we need Anti-Islanding Protection?

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What is Anti-Islanding?

• Anti-Islanding is a type of electrical protection
  for embedded generators such as grid connected
  solar, wind or diesel. It ensures the generator
  disconnects electrical supply to the grid in the
  event of a blackout. Anti-Islanding protection
  exists to protect personnel and equipment
  connected the grid in the occurrence of a fault
  or maintenance.

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Why do we need Anti-Islanding Protection?

• Islanding can be dangerous to utility workers,
  who may not realize that a circuit is energized,
  and it may prevent automatic re-connection of
  devices. For that reason, inverters must detect
  islanding and immediately stop producing power
  this is referred to as anti-islanding protection.

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Why do we need Anti-Islanding Protection?

• The most common example of islanding is a grid
  supply that has solar panels attached to it. In
  the case of a blackout, the solar panels will
  continue to deliver power as long as the sun is
  shining. In this case, the supply line is an
  island with power, surrounded by a sea, or
  void of unpowered lines.

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Why do we need Anti-Islanding Protection?

• For this reason, solar inverters that are
  designed to supply power to the grid are
  generally required to have some sort of automatic
  anti-islanding protection in them. In intentional
  islanding, the installation disconnects from the
  grid, and forces the inverter to power the local
  circuit. This is often used as a backup system.

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How to detect Islanding?

• Grid-interactive inverters are required to
  produce AC power that matches the existing power
  presented on the grid. In particular, the
  voltage, frequency and synchronize phases of the
  feed it connects to.

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How to detect Islanding?

• An installation with an array of solar panels and
  inverters attached convert the varying DC current
  provided by the panels into AC power that matches
  the grid supply. If the grid is disconnected, the
  voltage on the grid line would be expected to
  drop to zero, a clear indication of a service
  interruption.

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How to detect Islanding?

• However, when the houses load matches the output
  of the panels at the instant of the grid
  interruption, the panels can continue supplying
  power, which is used up by the houses load. In
  this case there is no obvious indication of an
  interruption.

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How to detect Islanding?

• Even when usage and production are matched, the
  failure of the grid will result in additional
  transient signals, there will almost always be a
  short decrease in line voltage, which will
  indicate a potential fault. Such events can also
  be caused by normal events, like the DOL (Direct
  On-Line) starting of a large electric motor.

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How to detect Islanding?

• Ways to detect islanding without a large number
  of false trips is the subject of considerable
  research. Each way has some threshold that needs
  to be met before a state is considered to be a
  signal of grid interruption, which leads to a
  protection blind spot in the range of conditions
  where a real grid failure will be filtered out.

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