Electrical switching apparatus with digital trip unit and automatic frequency selection
First Claim
1. Electrical apparatus for connecting a load to either of a 50 Hz power source and 60 Hz power source, said apparatus comprising:
- separable contacts selectively connecting said load to the power source when closed and disconnecting the load from the power source when open;
sensing means sensing current flowing through said separable contacts to the load when said contacts are closed;
digital control means including digitizing means digitally sampling said current sensed by said sensing means at a selectable time interval to generate digital current signals, means responsive to predetermined values of said digital current signals to generate a trip signal, and means responsive to said digital current signals to set said selectable time interval for use by said digitizing means to digitally sample said currents a common number of samples per cycle for both a 50 Hz power source and a 60 HZ power source; and
means responsive to said trip signal to open said contacts.
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Accused Products
Abstract
A microprocessor based switch such as a circuit breaker generates digital rms representations of analog load currents from n samples of the analog currents per cycle synchronized to the line frequency, where n is an odd integer equal to a selected highest order harmonic to be detected plus 2. A routine determines whether the power system is 50 or 60 Hz, and automatically sets the sampling interval to provide exactly n samples per cycle for the connected source. Terminals for rapidly resetting an analog memory for calibration and field testing of a long delay trip are hidden behind a removable rating plug.
46 Citations
9 Claims
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1. Electrical apparatus for connecting a load to either of a 50 Hz power source and 60 Hz power source, said apparatus comprising:
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separable contacts selectively connecting said load to the power source when closed and disconnecting the load from the power source when open; sensing means sensing current flowing through said separable contacts to the load when said contacts are closed; digital control means including digitizing means digitally sampling said current sensed by said sensing means at a selectable time interval to generate digital current signals, means responsive to predetermined values of said digital current signals to generate a trip signal, and means responsive to said digital current signals to set said selectable time interval for use by said digitizing means to digitally sample said currents a common number of samples per cycle for both a 50 Hz power source and a 60 HZ power source; and means responsive to said trip signal to open said contacts. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification