Now that the FLAK has subsided I would like to give some comments.
ISLAND = GRID TIED external power source feeding POWER to the GRID.
The regulations for ISLAND protection is due to several reasons in the use of multiple ISLANDS in a single large branch of a GRID section.
GRID section, like a 1000 KVA, may have several sub-branches, in a short condition, the circuitry may order a power OFF for a down line of the GRID section,or under a manual disconnection the circuitry includes, as well, opening the lines in the sub-branches for easy re-connection that is done in segments to avoid initial ON very high peak currents.
If a section or a sub-branch may have several connected ISLANDs that may have enough power to feed power to that sub-branch, the power stays up sometimes with good wave form because some of the ISLANDS may have sine wave form capabilities, specially if they have higher power capabilities and the effective Q, in the whole section or sub-branch, is greater than the damping effects of the loads .
If the loads are greater than the capabilities of one or more ISLANDs the power dies down with certain limitations, like around 100 cycles or so.
The regulations have some age, when the electronics available were in their infancy, but with the present available technology a GRID connected Inverter does not need to supply a wave form, but to supply a AC current that is determined by the incoming sine wave of the GRID.
The AC Current level is defined by the available power source and if the source is variable, the AC Current will be as well variable -- the Incoming AC Sine Wave defines the AC Current along the Sine Wave slope which in a sense represent the reverse behavior of a resistor as a load.
There are several forms to produce a GRID tied power source -- power source to indicate that it may not be a totally electronic piece of equipment, it could be one like such (most commonly available for higher efficiency) - BUT there are other methods, like :
- Wind Mill feeding a DC/AC GRID tied Inverter.
- Wind mill feeding a battery bank and this feeding a DC/AC GRID tied inverter
- Wind mill feeding a DC motor feeding an AC Induction Motor as generator ( Grid biasing)
- Wind mill with an Induction Motor as generator with electronics to connect/disconnect the GRID as the motor is within the GRID frequency, sometimes with a dynamic load for longer connection time.
- Wind mill with a 3 phase induction motor, as an Induction Generator with additional capabilities to make use of the 3 phase to supply energy to the GRID in single phase configuration.
- & 2) types require a DC/AC electronic Inverter -- highest efficiency around 90+ %
- the easiest for the "experimenter " to play with, because the controlling requirements may be low to implement, simple electronic controller is needed . Efficiency around 45 to 55 %
- A bit more complicated because a micro controller is needed with additional loads and electric - fluid brakes ( like in a car) with limited time -- over all efficiency around 40 %
- A MICROPROCESSOR is required and as well a not-too-complicated electronic to convert the 2 additional phases to the primary phase EFFICIENCY around 80 to 85 %
Other ideas are available, but is sufficient for now.
Nando