Controller for controlling operation of at least one electrical load operating on an AC supply, and a method thereof

A controller for controlling operation of at least one electrical load operating on an AC supply having a typical frequency, said AC supply being provided via power transformers by an electrical power distribution grid, said controller being associated with said at least one load and comprising:

• an input interface including input terminals for connection to said grid, and an output for producing a signal representative of said AC supply and having the same frequency;
• frequency detecting means for detecting the frequency of said AC supply, said frequency detecting means having an input connected to said output of the interface, and an output for producing a signal indicative of said frequency;
• memory means for storing preprogrammed commands;
• frequency monitoring means connected to the output of said frequency detecting means, for reading the signal indicative of said frequency and producing frequency data derived thereof;
• selecting means connected to said frequency monitoring means and said memory means, for selecting at least one of said preprogrammed commands with respect to said frequency data, said selecting means comprising:
• means for detecting a substantial drop in the frequency of said AC supply below a threshold value and, on detection of said drop, selecting a first group of said commands for achieving a disconnection of said at least one load from said grid for a first predetermined time period;
• means for detecting whether a variation in the frequency of said AC supply exceeds a predetermined level and, on detection of said variation exceeding said level, selecting a second group of said commands for achieving a disconnection of said at least one load from said grid for said first predetermined time period;
• means for detecting an absence of said AC supply and, on detection of said absence, selecting a third group of said commands for achieving a disconnection of said at least one load from said grid for a second time period longer than the first time period;
• and clock and timer means for timing operations performed by said selecting means;
• control means having an output for producing at least one command signal representative of the at least one of said preprogrammed commands selected by said selecting means;
• and
• an output interface including an input connected to said output of the control means, and an output for connection to said at least one load, said output interface including means responsive to the command signal for controlling said at least one load;
• whereby said at least one load can be controlled by means of said controller depending on the frequency of said AC supply.