Relay Coordination for a Distribution System!!

Background

The utility company, operates a medium-voltage distribution system supplying power to a residential area. The distribution system includes multiple substations, feeders, transformers, and customer connections. The company has experienced an increase in fault occurrences, leading to frequent outages and equipment damage. They decided to conduct a relay coordination study to address these issues and improve the system’s reliability.

Objectives
  1. Minimize outage duration by ensuring the selective operation of protective relays.
  2. Reduce equipment damage by swiftly isolating faulted sections.
  3. Improve system reliability and safety for customers and utility personnel.
Approach

The Company hired Elegrow Technology to conduct the relay coordination study. We followed these steps:

1. Data Collection

The team collected detailed information about the distribution system, including single-line diagrams, protection settings, relay coordination curves, and historical fault data. For this study, the following data was considered:

  • Substations: Substation A, Substation B, and Substation C
  • Feeders: Feeder 1, Feeder 2, and Feeder 3
  • Fault Currents: Based on short circuit analysis, fault currents at various locations are determined.
2. System Modeling

The engineers developed a detailed model of the distribution system using specialized software, including all equipment, protection devices, and interconnections.

3. Load Flow and Short Circuit Analysis

Perform load flow and short circuit studies to determine fault current magnitudes and fault locations. The fault data is as follows:

Location
Fault Current (kA)

Feeder 1

5.8

Feeder 2

3.2

Feeder 3

4.5

Substation A

12.0

Substation B

9.5

Substation C

11.2

4. Pre-Coordination Settings

Reviewed existing protection relay settings to identify any existing issues or improper coordination. Adjusted settings as necessary to ensure proper coordination between protection devices.

5. Time-Current Coordination Analysis

Plotted time-current curves for each relay in the system. The coordination curves for Feeder 1 are shown below (time in seconds):

Relay
0.1
0.2
0.5
1.0
2.0
3.0

Relay at A

0.005

0.015

0.050

0.200

1.000

2.000

Relay at B

0.010

0.030

0.100

0.400

2.000

3.000

Relay at C

0.030

0.100

0.300

1.500

5.000

7.000

6. Sensitivity Analysis

Analyzed the effects of load variations and possible system expansions on the relay coordination and Ensured that the coordination remains effective under different operating conditions.

7. Verification and Validation

Simulated various fault scenarios using the coordinated relay settings and verified that the relays operate selectively to isolate faults while maintaining service to healthy parts of the system.

Results and Recommendations:

Based on the relay coordination study, Elegrow Technology provided the following recommendations to the client.:

  1. Revised relay settings had been implemented to achieve selective coordination and faster fault isolation.
  2. By adjusting the relay settings, the client can now minimize the impact of faults and reduce outage durations, thus improving system reliability.
  3. The coordinated protection scheme ensures safer operation for both utility personnel and customers, as it efficiently isolates faulted sections.
  4. The sensitivity analysis shows that the coordination remains effective under various load and system expansion scenarios.

In conclusion, the relay coordination study has helped the client. enhance the reliability and safety of their distribution system, ultimately leading to improved service for their customers.

 

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