Protective relays and methods

A protective relay for use in an electrical power system having electrical conductors which are energizable with an AC voltage, the protective relay comprising:

• means for sensing the AC voltage to produce an AC output that has zero crossings and a time period between zero crossings;
• means for supplying an electrical signal representing a preselected pickup value of volts-per-Hertz for the relay;
• and
• means responsive to the AC output and to the electrical signal for generating an electrical level as a function of both the time period between zero crossings and the pickup value and for producing an output signal for the relay when the AC output exceeds the electrical level to indicate that a volts-per-Hertz value of the AC voltage exceeds the preselected pickup value of volts-per-Hertz for the relay.

A protective relay for use in an electrical power system with a circuit breaker for connecting and disconnecting first and second electrical conductors which are energizable with an AC voltage, the protective relay comprising:

• means for sensing the AC voltage to produce an AC output that has zero crossings;
• means for supplying an electrical signal representing a pickup value of volts-per-Hertz for the relay;
• and
• means responsive to the AC output and to the electrical signal for generating an electrical level as a function of both the pickup value and a first time period between a pair of the zero crossings, for measuring a second time period during which the AC output exceeds the electrical level, and for generating a second electrical signal as a function of the first and second time periods so that the second electrical signal represents a ratio of volts-per-Hertz of the AC voltage to the pickup value of volts-per-Hertz. Hertz.

A protective relay for use in an electrical power system with a circuit breaker for connecting and disconnecting first and second electrical conductors which are energizable with an AC voltage that has a value of actual volts-per-Hertz, and with means for sensing the AC voltage to produce an AC output, the protective relay comprising:

• means for supplying a first electrical signal representing a preselected pickup value of volts-per-Hertz for the relay;
• means responsive to the AC output and to the electrical signal for generating a second electrical signal which increases in magnitude during the time when the value of actual volts-per-Hertz exceeds the pickup value of volts-per-Hertz for the relay and the second electrical signal decreases in magnitude during the time when the value of actual volts-per-Hertz is less than the pickup value of volts-per-Hertz;
• and
• means for producing a display indicative of the magnitude of the second electrical signal as it increases and decreases in magnitude.

A protective relay for use in an electrical power system with a circuit breaker for connecting and disconnecting first and second electrical conductors which are energizable with an AC voltage that has a value of actual volts-per-Hertz, the protective relay comprising:

• means for sensing the AC voltage to produce an AC output;
• means responsive to the AC output for generating an electrical signal that increases in magnitude from an initial value to an accumulated value when the actual volts-per-Hertz exceeds a preselected pickup level of volts-per-Hertz for the relay;
• and
• means for supplying a reset control signal representative of a reset rate parameter for the relay, said generating means including means responsive to the reset control signal for decreasing the magnitude of the electrical signal from its accumulated value to the initial value in a reset time interval which varies directly with the accumulated value if the value of actual volts-per-Hertz is less than the pickup level of volts-per-Hertz throughout the reset time interval.

A protective relaying method for use in an electrical power system with a circuit breaker for connecting and disconnecting first and second electrical conductors which are energizable with an AC voltage, the method comprising the steps of:

• sensing the AC voltage to produce an AC output that has zero crossings and a time period between zero crossings;
• supplying an electrical signal representing a preselected pickup value of volts-per-Hertz;
• generating an electrical level as a function of both the time period and the pickup value;
• and
• producing an output signal when the AC output exceeds the electrical level so that the output signal is produced when a volts-per-Hertz value of the AC voltage is in excess of the preselected pickup value of volts-per-Hertz.

A protective relaying method for use in an electrical power system with a circuit breaker for connecting and disconnecting first and second electrical conductors which are energizable with an AC voltage that has a value of actual volts-per-Hertz, and with means for sensing the AC voltage to produce an AC output, the method comprising the steps of:

• supplying a first electrical signal representing a preselected pickup value of volts-per-Hertz;
• generating a second electrical signal which increases in magnitude during the time when the value of actual volts-per-Hertz exceeds the pickup value of volts-per-Hertz for the relay and the second electrical signal decreases in magnitude during the time when the value of actual volts-per-Hertz is less than the pickup value of volts-per-Hertz;
• and
• producing a display indicative of the magnitude of the second electrical signal as it increases and decreases in magnitude.

A protective relaying method for use in an electrical power system with a circuit breaker for connecting and disconnecting first and second electrical conductors which are energizable with an AC voltage that has a value of actual volts-per-Hertz, the method comprising the steps of:

• generating an electrical signal that increases in magnitude from an initial value to an accumulated value when the actual volts-per-Hertz exceeds a preselected pickup level of volts-per-Hertz;
• supplying a reset control signal representative of a reset rate parameter;
• and
• decreasing the magnitude of the electrical signal from its accumulated value to the initial value in a reset time interval which varies directly with the accumulated value if the value of actual volts-per-Hertz is less than the pickup level of volts-per-Hertz throughout the reset time interval.

A protective relaying method for use in an electrical power system with electrical apparatus to be protected having a thermal time constant, and with a circuit breaker for connecting and, in response to an electrical trip, disconnecting the electrical apparatus which is energizable with an AC voltage that has a value of actual volts-per-Hertz, the method comprising the steps of:

• generating an elecrrical signal in response to the AC voltage so that the electrical signal changes in magnitude from an initial value to an accumulated value generally representative of heating of the apparatus to be protected when the actual volts-per-Hertz exceeds a preselected pickup level of volts-per-Hertz;
• producing an electrical trip for the circuit breaker when the accumulated value reaches a predetermined amount;
• and
• upon an occurrence of the electrical trip, returning the electrical signal from its accumulated value during a reset tire interval related to the thermal time constant of the apparatus to be protected to allow cooling of the apparatus, the electrical signal generally representing the cooling during the reset time interval.

A protective relay for use with electrical apparatus to be protected that is energizable with an AC voltage that has a varying value of actual volts-per-Hertz, and for use with a circuit breaker for connecting and, in response to an electrical trip, disconnecting the electrical apparatus, and with means for sensing the AC voltage to produce an AC output, the protective relay comprising:

• means responsive to the AC output for generating an electrical signal that begins at an initial value and changes in value generally representing heating of the apparatus to be protected when the actual volts-per-Hertz exceeds a preselected pickup level of volts-per-Hertz for the relay and for generating a trip output for initiating the electrical trip when the electrical signal reaches a predetermined value;
• and
• means for supplying a reset control signal, said means for generating including means responsive to the reset control signal before a trip output occurs for resetting the electrical signal in value over a first reset time period provided the value of actual volts-per-Hertz becomes and remains less than the pickup level of volts-per-Hertz until the initial value is reached, and responsive to the reset control signal upon an occurrence of the trip output for resetting the electrical signal to the initial value over a second reset time period which exceeds the first reset time period in length.