Testing of static distance protection relay using Relay Testing Kit

 

Testing of Static Distance Protection Relay Using Relay Testing Kit

Distance protection relays are essential in the protection of transmission lines. These relays operate by measuring the impedance (or apparent impedance) between the relay location and the fault point. A static distance protection relay uses digital or electronic components to evaluate the impedance of the line and provides protection based on this measurement. The relay detects faults such as short circuits or ground faults by calculating the impedance between the fault and the relay.

In this lab, we will use a Relay Testing Kit to test a Static Distance Protection Relay and assess its performance by simulating fault conditions and verifying its response.

Objective:

To test the Static Distance Protection Relay using the Relay Testing Kit and evaluate its correct operation by simulating faults and verifying its ability to detect various types of faults (e.g., short-circuit, earth faults) at different distances along the transmission line.

Equipment/Materials Required:

1. Static Distance Protection Relay (the device under test)
2. Relay Testing Kit (for injecting test currents and voltages)
3. Test Panel or Relay Test Setup (for connecting the relay and testing equipment)
4. Power Supply (for supplying the required voltages and currents)
5. Ammeter (for measuring the test current)
6. Voltmeter (for measuring voltage)
7. Impedance Simulation Unit (part of the relay testing kit, which simulates different fault conditions and distances)
8. Data Logger/Time Counter (optional, for recording test data)
9. Test Leads and Connectors
10. Safety Equipment (Gloves, goggles, etc.)

Theory of Operation:

A static distance protection relay uses the principle of measuring the impedance of the line to detect faults. The relay calculates the impedance $Z$ between the relay location and the fault point using the following relation:

$$Z = \frac{V}{I}$$

Where:

• $Z$ is the impedance.
• $V$ is the voltage at the relay point.
• $I$ is the current flowing through the circuit.

When a fault occurs, the impedance changes. The relay compares this measured impedance with the pre-set impedance values corresponding to different fault conditions, such as line-to-ground, line-to-line, or three-phase faults.

Distance Protection Zones:

• Zone 1: Primary protection zone, typically set to cover 80-90% of the line length. It trips instantly for faults.
• Zone 2: Backup protection zone, typically set to cover the entire line length. It has a time delay to coordinate with Zone 1 protection.
• Zone 3: Extended backup protection, covering the area beyond the line to protect the system.

Key Characteristics of Static Distance Relays:

• Impedance Measurement: Based on the ratio of voltage and current.
• Operating Time: Varies depending on the impedance value and fault location.
• Settings: Adjustable reach, time delay, and fault type.

Procedure for Testing the Static Distance Protection Relay:

1. Setup the Relay Testing Kit:

1. Power Supply Configuration:

   • Connect the relay testing kit to a suitable power supply, ensuring that the voltage and current levels correspond to the operating voltage and current of the relay.

2. Relay Connection:

   • Connect the distance protection relay to the relay testing kit, making sure to connect the voltage and current inputs from the test equipment to the corresponding terminals on the relay.
   • Ensure the proper connection of the relay’s voltage and current sensing circuits.

3. Impedance Simulation:

   • The relay testing kit should be able to simulate various fault conditions along the transmission line. Use the impedance simulation module to set different fault conditions by adjusting the values of voltage, current, and impedance.

2. Set the Test Parameters:

• Set the Relay Settings:
  • Adjust the reach setting (impedance value) of the relay for Zone 1, Zone 2, and Zone 3.
  • Set the time delay for Zone 2 and Zone 3 protections (if applicable).
  • Adjust the fault characteristics, such as the fault type (line-to-ground, line-to-line, three-phase fault).

3. Simulate Faults and Test the Relay Response:

Test 1: Simulate a Fault Near the Relay (Zone 1)

• Simulate a fault close to the relay location (within Zone 1).
• Apply a fault current using the relay testing kit, ensuring that the impedance between the relay and the fault point corresponds to a value within Zone 1’s reach setting.
• The relay should trip instantly when the fault is within Zone 1, as the impedance is within the preset trip zone.
• Record the time it takes for the relay to trip (the trip time should be minimal).

Test 2: Simulate a Fault at an Intermediate Distance (Zone 2)

• Simulate a fault at a location further from the relay, but within Zone 2’s reach setting.
• Increase the fault impedance (increase the distance from the relay) until it falls within Zone 2’s range.
• The relay should trip with a time delay, as Zone 2 typically has a time delay to coordinate with Zone 1.
• Record the trip time. It should be greater than the time recorded in Zone 1.

Test 3: Simulate a Fault at the Maximum Reach (Zone 3)

• Simulate a fault at the maximum distance that falls within Zone 3.
• Apply the fault current so that the impedance corresponds to the maximum reach.
• The relay should trip with an extended time delay, as Zone 3 provides backup protection.
• Record the trip time. The time should be the highest for Zone 3 as it is typically used as a backup protection zone.

Test 4: Simulate a Line-to-Ground Fault

• Simulate a fault in which one phase of the line is shorted to ground.
• The relay should detect the fault and trip if it falls within the designated zone.
• This can be tested for each zone (Zone 1, Zone 2, Zone 3).

4. Plot the Distance-Operating Time Characteristics:

• Plot the impedance values (X-axis) against the relay trip time (Y-axis) for each fault type (line-to-line, line-to-ground, etc.).
• You should plot different curves for each zone (Zone 1, Zone 2, Zone 3), showing the inverse relationship between impedance and trip time.

5. Monitor for Accuracy:

• Ensure that the relay trips when the impedance crosses the set threshold for each zone.
• Verify that the relay responds accurately to the test conditions and provides the correct trip time according to the settings.

Documentation:

• Record the test data in a table format for each fault condition:
  • Fault Type: (e.g., Line-to-Ground, Three-Phase Fault, etc.)
  • Fault Distance: (Impedance value corresponding to the fault distance)
  • Zone: (Zone 1, Zone 2, or Zone 3)
  • Time to Trip: (Measured time)
• Plot the impedance vs. time characteristics for each zone to confirm that the relay is operating according to its inverse characteristic.

Precautions:

1. Safety First: Always ensure that proper safety protocols are followed when handling high voltages and currents.
2. Check the Relay Settings: Ensure that the relay’s settings (reach, time delay) are properly configured before starting the tests.
3. Ensure Proper Connections: Make sure the relay testing kit is properly connected to avoid incorrect readings or accidental faults.
4. Verify Trip Times: Verify that the trip times and relay responses are consistent with the relay’s specifications.

Conclusion:

Testing the Static Distance Protection Relay using the Relay Testing Kit allows for an in-depth analysis of the relay's performance in detecting faults at various distances along the transmission line. By simulating fault conditions and plotting the impedance vs. trip time characteristics, we can confirm that the relay operates as expected, providing effective protection against faults and ensuring proper coordination between protection zones.