Load shed module
A load shed module configured to be connected in series between a power supply and a load is disclosed. A separate load shed module is connected in series between each load and the power supply. The load shed module determines the frequency of the voltage supplied from the power supply. Based on the frequency, the load shed module determines if utility power is connected or if a generator is connected. If the generator is connected and the frequency of the voltage goes outside of a desired operating range for a preset time, the load shed module disconnects the load from the power supply. Each load shed module includes a priority setting and reconnects its corresponding load after a predetermined time corresponding to the priority setting.
1. A method of connecting a load to a power source in a power distribution system, comprising the steps of:
determining whether electrical power supplied at an input of a load shed module is from a utility power source or from a backup generator in response to a frequency of the electrical power and when the electrical power is from the backup generator, conducting the additional steps of:
monitoring a voltage and a frequency of the voltage with a controller in the load shed module at the input of the load shed module;
comparing the frequency to a threshold frequency;
generating a control signal with the controller to open a switch connected in series between the input and an output of the load shed module when the frequency of the voltage at the input is outside of the threshold frequency for a first predetermined time, wherein the output of the load shed module is connected to the load;
determining a priority level of the load shed module; and
generating the control signal with the controller to close the switch connected in series between the input and the output of the load shed module after a second predetermined time when the frequency of the voltage is within the threshold frequency, wherein the second predetermined time is a function of the priority level of the load shed module.
2. A method of connecting a load to a power source in a power distribution system, comprising the steps of:
reading a feedback signal corresponding to a voltage received at an input of a load shed module from the power source;
determining a frequency of the voltage from the feedback signal with a controller in the load shed module;
determining whether the voltage at the input of the load shed module is from a utility power source or from a backup generator as a function of the frequency of the voltage;
comparing the frequency to a threshold frequency;
generating a control signal with the controller to open a switch connected in series between the input and an output of the load shed module when the frequency of the voltage at the input is outside of the threshold frequency for a first predetermined time, wherein the output of the load shed module is connected to the load;
determining a priority level of the load shed module; and
generating the control signal with the controller to close the switch connected in series between the input and the output of the load shed module after a second predetermined time when the frequency of the voltage is within the threshold frequency, wherein the second predetermined time is a function of the priority level of the load shed module.
3. The method of claim 1 wherein:
the load shed module is operable in a first operating mode and in a second operating mode,
the first predetermined time is a first duration in the first operating mode,
the first predetermined time is a second duration in the second operating mode, and
the first duration is longer than the second duration.
4. A method of connecting a load to a power source in a power distribution system, comprising the steps of:
reading a feedback signal corresponding to a voltage received at an input of a load shed module from the power source, the load shed module being operable in a first operating mode and in a second operating mode;
determining a frequency of the voltage from the feedback signal with a controller in the load shed module;
comparing the frequency to a threshold frequency;
generating a control signal with the controller to open a switch connected in series between the input and an output of the load shed module when the frequency of the voltage at the input is outside of the threshold frequency for a first predetermined time, wherein the output of the load shed module is connected to the load;
determining a priority level of the load shed module;
generating the control signal with the controller to close the switch connected in series between the input and the output of the load shed module after a second predetermined time when the frequency of the voltage is within the threshold frequency, wherein the second predetermined time is a function of the priority level of the load shed module; and
entering a lock out operating mode when the frequency of the voltage at the input is outside of the threshold frequency for the first predetermined time during the second operating mode;
wherein:
the first predetermined time is a first duration in the first operating mode,
the first predetermined time is a second duration in the second operating mode, and
the first duration is longer than the second duration.
5. The method of claim 1 further comprising the steps of:
determining a minimum frequency of the voltage at the input of the load shed module with the controller;
determining a maximum frequency of the voltage at the input of the load shed module with the controller;
determining a difference between the minimum frequency and the maximum frequency with the controller, wherein the threshold frequency is a maximum difference between the minimum frequency and the maximum frequency, and
generating the control signal to open the switch when the difference exceeds the maximum difference for the first predetermined time.
6. The method of claim 1 further comprising the steps of:
determining a difference between the frequency of the voltage present at the input and an expected frequency of the voltage present at the input, wherein the threshold is a maximum difference between the frequency of the voltage present at the input and the expected frequency of the voltage present at the input, and
generating the control signal to open the switch when the difference exceeds the maximum difference for the first predetermined time.