System and method for island detection

• US 6,850,074 B2
• Filed: 08/05/2002
• Issued: 02/01/2005
• Est. Priority Date: 08/05/2002
• Status: Expired due to Fees

• Current Assignee: Primary Integration - Encorp, LLC
• Original Assignee: Encorp, Inc.
• Inventors: Pope, Jeffrey G., Adams, Larry L.
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): NATALINI, JEFF WILLIAM
• Application Number:
  US10/211,281
• Publication Number:
  US 20040021470A1
• Time in Patent Office: 911 Days
• Field of Search: 324133-134, 324527-528, 324/76.74, 324/508, 324/512, 702/60, 307/43, 307/31, 307/11
• US Class Current: 324/527
• CPC Class Codes: G01R 31/086 in power transmission or distribution networks, i.e. with interconnected conductors
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02J 3/388 Islanding, i.e. disconnection of local power supply from the network
• CPC Class Codes: Y04S 10/52 Outage or fault management, e.g. fault detection or location

Abstract

A system and method is provided for detecting an island condition using active detection. The active detection involves biasing the voltage, frequency, current or phase of a distributed resource connected to a utility network. Biasing the distributed resource involves inducing a change of voltage, frequency, current or phases above or below the normal operating values. The impact of this biasing on the system operating parameters can then be measure to determine if an island condition exists. Once an island condition has been detected, the system can initiate an anti-islanding procedure to remove the distributed resource from the utility network such as opening a breaker connecting the distributed resource to the network. Additionally, the system and method can include a passive element for detecting frequency and voltage (or other parameters) shifts above certain points.

Claims

1. A method of island detection for a distributed resource connected to a network having a load and a utility source, comprising:

energizing the distributed resource to supply power to the network;

operating the distributed resource at normal system parameters;

inducing a change in at least one operating parameter of the distributed resource; and

monitoring at least one of the system parameters,

wherein inducing a change includes;

adding a positive ramped value to a frequency bias output of the distributed resource;

adding a negative ramped value to the frequency bias output;

monitoring the frequency bias output; and

detecting an island event based on the monitored frequency bias output.

2. The method of island detection according to claim 1, further comprising:

setting a short df/dt setpoint;

setting a long df/dt setpoint;

monitoring a rate of change of a frequency of a voltage; and

detecting the island event based on the monitored rate of change of the frequency of the voltage.

3. The method of island detection according to claim 2, wherein the island event is detected when the rate of change of the frequency exceeds the long df/dt setpoint, the rate of change of the frequency is determined by averaging the frequency over 60 sampling periods and comparing the average to an average of a previous 60 sampling periods.

4. The method of island detection according to claim 3, wherein the long df/dt setpoint is set for approximately 50% of a maximum frequency shift expected by an active detection frequency bias in a one second period.

5. The method of island detection according to claim 2, wherein the island event is detected when the rate of change of the frequency exceeds the short df/dt setpoint, the rate of change of the frequency is determined by averaging the frequency over three sampling periods and comparing the average to an average of a previous three sampling periods.

6. A system for detecting an island condition in an utility network, comprising:

a distributed resource connected to the utility network through a feeder line;

an active detection module monitoring the distributed resource; and

a biasing device connected to the distributed resource, wherein the biasing device is configured to induce a change in at least one operating parameter of the distributed resource by adding a positive ramped value and a negative ramped value to the at least one operating parameter of the distributed resource, and wherein the active detection module is configured to monitor the at least one operating parameter.

7. The system of claim 6, wherein the active detection module is connected to the feeder line for monitoring system parameters of the utility network and the biasing device is a controller for controlling an operation of the distributed resource.

8. The system of claim 7, wherein the active detection module is connected to the biasing device for sending a biasing signal to the biasing device.

9. The system of claim 8, wherein the biasing signal causes the biasing device to induce the change in the at least one operating parameters of the distributed resource.

10. The system of claim 9, wherein the change in the at least one operating parameters is one of a change in a frequency, a voltage, a current, a phase of the voltage and a phase of the current.

11. The system of claim 9, wherein the active detection module detects the island condition based on a change in the monitored system parameters.

12. The system of claim 11, wherein the change in the monitored system parameters is caused by the induced change in the at least one operating parameters of the distributed resource.

13. The system of claim 12, wherein the active detection module includes an over voltage relay, an under voltage relay, an over frequency relay, and an under frequency relay.

14. A method of system and unit island detection using a detection module for a distributed resource connected to a network having a load and a utility source, comprising:

setting the detection module for one of a unit detection and a system detection;

monitoring a circuit breaker of the distributed resource when the detection module is set for unit detection;

monitoring a circuit breaker of the utility source when the detection module is set for system detection;

detecting an island event based on the monitored circuit breaker, wherein detecting an island event includes adding a positive ramped value and a negative ramped value to an output of the distributed resource and monitoring the output; and

initiating an anti-islanding procedure when the island event is detected.

15. The method of claim 14, wherein the output of the distributed resource is one of a frequency, a voltage, a current, a phase of the voltage, and a phase of the current.