# US 2019/0245347 A1 · Coordinated frequency load shedding protection method using distributed electrical protection devices

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- Number: US 2019/0245347 A1
- Document ID: US20190245347A1
- Status: Published application
- Kind: A1
- Application number: 16/164,401
- Filed: 2018-10-18
- Published: 2019-08-08
- Earliest claimed: 2018-02-03
- Assignees: S&C Electric Company
- Applicants: S&C Electric Company
- Inventors: Joseph Matamoros
- Web page: https://patentgrep.com/patent/US20190245347A1

## CPC

- H02H 3/46: responsive to frequency deviations
- G01R 19/02: Measuring effective values, i.e. root-mean-square values
- G01R 19/16528: {using digital techniques or performing arithmetic operations (using digital techniques to measure a voltage or a current, see G01R19/25)}
- G01R 19/2506: {Arrangements for conditioning or analysing measured signals, e.g. for indicating peak values (G01R19/003 takes precedence); Details concerning sampling, digitizing or waveform capturing (displaying waveforms G01R13/00; analog sampling G01R19/0053)}
- G01R 19/2513: {Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging}
- G01R 31/08: Locating faults in cables, transmission lines, or networks
- H02H 1/0007: {concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445)}
- H02H 3/42: responsive to product of voltage and current
- H02H 7/26: Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured (locating faults in cables G01R31/08)
- H02H 7/28: for meshed systems
- H02J 3/00: Circuit arrangements for AC mains or AC distribution networks
- H02J 3/14: by switching loads on to, or off from, the networks, e.g. progressively balanced loading
- H02J 13/182: the equipment comprising loads connected to the power network
- H02H 1/0092: {concerning the data processing means, e.g. expert systems, neural networks}
- H02J 3/381: {Dispersed generators}
- H02J 2101/24: Photovoltaics
- H02J 2101/28: Wind energy
- H02J 2105/12: supplying households or buildings
- H02J 2105/42: Home appliances
- H02J 2105/52: for limitation of the power consumption in the networks or in one section of the networks, e.g. load shedding or peak shaving
- Y02B 70/3225: Demand response systems, e.g. load shedding, peak shaving
- Y02E 10/56: Power conversion systems, e.g. maximum power point trackers
- Y04S 20/222: Demand response systems, e.g. load shedding, peak shaving
- H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y04S: SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS

## Abstract

A method for providing frequency load shedding in a power distribution network. The network includes a number of distributed switch-gear assemblies that control whether AC power is provided to groups of loads. The distributed switch-gear assemblies monitor the frequency of the AC signal to determine if a frequency event is occurring and also determine the direction of the power flow at the time of the event. The switch-gear assembly may open in an underfrequency event only if the loads are drawing power from the network, and the switch-gear assembly may open in an overfrequency event only if there is reverse power flow during the event. In addition, the order of operation of which switch-gear assemblies may open first in response to the frequency event is determined in advance by the location of the switch-gear assembly in the network and a corresponding time delay and coordinated frequency set-points.

## Claims

### Claim 1

A method for shedding load in response to an underfrequency event in an electrical power distribution network, wherein an AC power signal from a power source flows on at least one electrical line through a plurality of switch-gear assemblies to a plurality of groups of loads provided among and between the switch-gear assemblies, each group of loads including a plurality of individual loads that may combine to be drawing power from the network or providing power to the network at any particular point in time, the method comprising:
assigning a time delay value and a frequency set-point to each switch-gear assembly that are coordinated and calibrated relative to each other, where switch-gear assemblies that are farther downstream from the power source relative to the AC power signal flow will have shorter time delay values than other upstream switch-gear assemblies;
monitoring a frequency of the AC power signal flowing on the at least one electrical line at each switch-gear assembly;
determining that the underfrequency event is occurring if the frequency of the AC power signal falls below a predetermined minimum frequency; and
opening a first one of the switch-gear assemblies having a shortest time delay value in response to the underfrequency event so as to prevent at least one of the groups of loads from drawing power from the network.

### Claim 2 (depends on 1)

The method according to claim 1 further comprising determining a direction of the AC power signal flow through each switch-gear assembly and preventing the first one of the switch-gear assemblies from opening in response to the underfrequency event if the direction of the AC power signal flow through the first one of the switch-gear assemblies indicates that the at least one of the groups of loads is providing power to the network.

### Claim 3 (depends on 2)

The method according to claim 2 further comprising opening a second one of the switch-gear assemblies having a next shortest time delay value in response to the underfrequency event so as to prevent at least one other of the groups of loads from drawing power from the network if the at least one of the groups of loads is providing power to the network.

### Claim 4 (depends on 1)

The method according to claim 1 further comprising determining that an overfrequency event is occurring if the frequency of the AC power signal rises above a predetermined maximum frequency and opening the first one of the switch-gear assemblies in response to the overfrequency event so as to prevent the at least one of the groups of loads from providing power to the network.

### Claim 5 (depends on 4)

The method according to claim 4 further comprising determining a direction of the AC power signal flow through each switch-gear assembly and preventing the first one of the switch-gear assemblies from opening in response to the overfrequency event if the direction of the AC power signal flow through the first one of the switch-gear assemblies indicates that the at least one of the groups of loads is drawing power from the network.

### Claim 6 (depends on 1)

The method according to claim 1 wherein the individual loads may be providing power to the network from an electrical source selected from the group consisting of energy storage systems, solar arrays and wind turbines.

### Claim 7 (depends on 1)

The method according to claim 1 wherein the at least one electrical line includes feeder lines and lateral lines, where the plurality of loads are coupled to the lateral lines, and where the switch-gear assemblies are provided on both the feeder lines and the lateral lines.

### Claim 8 (depends on 1)

The method according to claim 1 wherein the power source is an electrical substation.

### Claim 9

A method for shedding load in response to an underfrequency event in an electrical power distribution network, wherein an AC power signal from a substation flows on a feeder or lateral electrical line through a plurality of switch-gear assemblies to a plurality of groups of loads provided among and between the switch-gear assemblies, each group of loads including a plurality of individual loads that may combine to be drawing power from the network or providing power to the network at any particular point in time, the method comprising:
assigning a time delay value and a frequency set-point to each switch-gear assembly that are coordinated and calibrated relative to each other, where switch-gear assemblies that are farther downstream from the power source relative to the AC power signal flow will have shorter time delay values than other upstream switch-gear assemblies;
monitoring a frequency of the AC power signal flowing on the electrical line at each switch-gear assembly;
determining a direction of the AC power signal flow through each switch-gear assembly;
determining that the underfrequency event is occurring if the frequency of the AC power signal falls below a predetermined minimum frequency;
opening a first one of the switch-gear assemblies having a shortest time delay value in response to the underfrequency event so as to prevent at least one of the groups of loads from drawing power from the network; and
preventing the first one of the switch-gear assemblies from opening in response to the underfrequency event if the direction of the AC power signal flow through the first one of the switch-gear assemblies indicates that the at least one of the groups of loads is providing power to the network.

### Claim 10 (depends on 9)

The method according to claim 9 further comprising opening a second one of the switch-gear assemblies having a next shortest time delay value in response to the underfrequency event so as to prevent at least one other of the groups of loads from drawing power from the network if the at least one of the groups of loads is providing power to the network.

### Claim 11 (depends on 9)

The method according to claim 9 further comprising determining that an overfrequency event is occurring if the frequency of the AC power signal rises above a predetermined maximum frequency and opening the first one of the switch-gear assemblies in response to the overfrequency event so as to prevent the at least one of the groups of loads from providing power to the network.

### Claim 12 (depends on 11)

The method according to claim 11 further comprising determining a direction of the AC power signal flow through each switch-gear assembly and preventing the first one of the switch-gear assemblies from opening in response to the overfrequency event if the direction of the AC power signal flow through the first one of the switch-gear assemblies indicates that the at least one of the groups of loads is drawing power from the network.

### Claim 13

A method for shedding load in response to an underfrequency event in an electrical power distribution network, wherein an AC power signal from a power source flow on at least one electrical line through a plurality of switch-gear assemblies to a plurality of groups of loads provided among and between the switch-gear assemblies, the method comprising:
monitoring a frequency of the AC power signal flowing on the at least one electrical line at each switch-gear assembly;
determining that the underfrequency event is occurring if the frequency of the AC power signal falls below a predetermined minimum frequency; and
opening a first one of the switch-gear assemblies at a remote location relative to the power source in response to the underfrequency event so as to remove at least one of the groups of loads from the network.

### Claim 14 (depends on 13)

The method according to claim 13 wherein each group of loads includes a plurality of individual loads that may combine to be drawing power from the network or providing power to the network at any particular point in time, and wherein the first one of the switch-gear assemblies is only opened if the at least one of the groups of loads is drawing power from the network.

### Claim 15 (depends on 13)

The method according to claim 13 further comprising assigning a time delay value to each switch-gear assembly that are calibrated relative to each other, where the switch-gear assemblies that are farther downstream from the power source relative to the AC power signal flow will have shorter time delay values than other upstream switch-gear assemblies, and wherein opening a first one of the switch-gear assemblies includes opening a switch-gear assembly having a shortest time delay value.

### Claim 16 (depends on 15)

The method according to claim 15 further comprising opening a second one of the switch-gear assemblies having a next shortest time delay value in response to the underfrequency event so as to prevent at least one other of the groups of loads from drawing power from the network if the at least one of the groups of loads is providing power to the network.

### Claim 17 (depends on 13)

The method according to claim 13 further comprising determining that an overfrequency event is occurring if the frequency of the AC power signal rises above a predetermined maximum frequency and opening the first one of the switch-gear assemblies in response to the overfrequency event so as to prevent the at least one of the groups of loads from providing power to the network.

### Claim 18 (depends on 17)

The method according to claim 17 further comprising determining a direction of the AC power signal flow through each switch-gear assembly and preventing the first one of the switch-gear assemblies from opening in response to the overfrequency event if the direction of the AC power signal flow through the first one of the switch-gear assemblies indicates that the at least one of the groups of loads is drawing power from the network.

### Claim 19 (depends on 13)

The method according to claim 13 wherein the at least one electrical line includes feeder lines and lateral lines, where the plurality of loads are coupled to the lateral lines, and where the switch-gear assemblies are provided on both the feeder lines and the lateral lines.

### Claim 20 (depends on 13)

The method according to claim 13 wherein the power source is an electrical substation.