Delta filter with an adaptive time window for protective relays
AssigneeSchweitzer Engineering Laboratories, Inc.
InventorsGabriel Benmouyal, Jeffrey B. Roberts
Life of this patent
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Abstract
A delta filter for use in a protective relay which includes an input circuit for receiving phasor signals representative of electrical signal quantities on the power line. A difference value, if any, is determined between the phasor signals at a present time and the phasor signals at a past point in time (delayed), the delay typically being one cycle. A first incremental output value is produced if there is a difference. When a power line disturbance is first noted by the recognition of a first incremental output value, the phasor signal value at the beginning of the disturbance is stored and then used as a reference value for comparison with subsequent present time phasor signals to determine continuing change in power system condition.
Claims9
A delta filter system for use in a protective relay for power systems, comprising:
- an input portion for receiving electrical signal values representative of selected electrical quantities present on a power line;
- a first comparison element for comparing said electrical signal values at a present point in time with said electrical signal values at a selected past point in time, each selected past point in time value being provided by a delay element and functioning as a first reference value;
- circuit means for providing a first incremental signal quantity output if the past and present values are different, the first incremental signal quantity indicative of a change in the power system condition;
- a memory for storing the present time electrical signal value following the appearance of said first incremental signal quantity output;
- and
- means using said stored electrical signal value as a fixed second reference value for future comparisons in a second comparison element beyond the point in time of the appearance of said first incremental signal quantity output to produce a second incremental signal quantity output if the power system continues to change.
Dependencies are inferred from the claim text.