Omicron COMPANO 100 - User Manual

Application Note
Cable Impedance Measurement with COMPANO 100
Author
Josef Schmidbauer | josef.schmidbauer@omicronenergy.com
Date
Jan. 10, 2024
Related OMICRON Product
COMPANO 100
Application Area
Cable Impedance Measurements
Keywords
Cable Impedance, k-factor, Line Impedance
Version
v1.0
Document ID
ANS_23003_ENU
Abstract
This application note explains how the impedances and the k-factor of short power cables (up to 5 km) can
be measured with COMPANO 100. Such cables are very common in urban distribution networks and
industrial energy networks.
The results can be used for configuring protection relays, performing load calculations or for network
simulations.
For longer cables or overhead lines, use CPC 100 + CP CU 1.

Summary

Safety Instructions

Safety Accessories

Details on accessories for enhanced safety during test operations.

General Safety Precautions

General safety guidelines and precautions for operating the test equipment.

Operating the Measurement Setup

Procedures and safety measures for operating the measurement setup.

Handling Long Cables

Guidelines for safely handling long cables during measurements.

Orderly Measures

Administrative and procedural measures to ensure safe work practices.

Disclaimer

Statement regarding equipment usage and manufacturer liability.

Introduction to Cable Impedance Measurement

Safety Concept for Measurements

Explanation of the safety concept for protecting users and equipment.

Handling the CP GB1 Grounding Box

Instructions for the correct handling and maintenance of the CP GB1.

Measurement Method Explained

Description of the frequency selective method used for cable impedance measurement.

Connecting and Preparing for Measurement

First Criterion: Cable Length

Check for cable length less than 5 km as a primary criterion.

Second Criterion: Estimated Open-Cable Voltage

Procedure to estimate open-cable voltage for measurement preparation.

Third Criterion: Measured Open-Line Voltage

Steps to measure and verify the actual open-line voltage.

Fourth Criterion: Injected Test Current

Process for injecting the test current using COMPANO 100.

Performing and Evaluating Cable Impedance Measurements

Measurement Setup

Instructions for setting up the measurement environment and equipment.

Loading Configuration Templates

Guidance on loading predefined configuration profiles for measurements.

Performing the Measurement

Detailed steps for conducting the cable impedance measurement with different loops.

Evaluation of Measurement Results

How to evaluate the measurement results using an Excel spreadsheet.

Final Results and Interpretation

Final results and interpretation of physical model impedances and k-factors.

List of Literature

Overview

1. Function Description
2. Usage Features
3. Maintenance Features

The COMPANO 100, in conjunction with the CP GB1 Grounding Box, is a versatile and robust test system designed for precise cable impedance measurements, particularly on short power cables (up to 5 km) commonly found in urban distribution and industrial energy networks. This application note details its operation, safety protocols, and measurement methodology, ensuring accurate data collection for various electrical engineering applications.

Function Description

The primary function of the COMPANO 100 with CP GB1 is to measure the impedance and k-factors of power cables. These measurements are crucial for configuring protection relays, performing accurate load calculations, and conducting network simulations. The system employs a frequency-selective method to achieve high accuracy, even in the presence of mains frequency distortions or harmonics.

A test current is injected at specific frequencies (30 Hz and 70 Hz for 50 Hz systems, or 40 Hz and 80 Hz for 60 Hz systems). The voltage drop caused by this test current is then measured, also frequency-selectively, at the output frequency. This approach effectively filters out unwanted interference from the mains frequency or its harmonics, ensuring that the calculated resistance (R) and reactance (X) values are highly reliable. The R and X values obtained at these test frequencies are then linearly interpolated to determine the impedance at the mains frequency.

The measurement process involves repeating these tests for different current loops. The individual results are then combined and processed using a provided Excel Template to calculate the parameters of various line models and the k-factors. This comprehensive approach allows for a detailed characterization of the cable's electrical properties.

The CP GB1 Grounding Box plays a critical safety role by protecting the user from unexpected events on the cable, such as accidental energization or high fault currents from adjacent live systems. It is designed to divert high short-circuit currents to ground, safeguarding both the operator and the test equipment. The insulation of the COMPANO 100 is built to withstand voltages significantly higher than the CP GB1's surge arrestors can handle, further enhancing safety.

Usage Features

The COMPANO 100 is designed for ease of use, with clear instructions and safety protocols to guide the operator through the measurement process.

• Safety Concept: A rigorous safety concept is integrated into the system's design and operation. This includes mandatory grounding procedures for both the COMPANO 100 and CP GB1, the use of specific measurement leads (at least 10 m / 30 ft in length) to limit transients, and the establishment of a danger zone around the CP GB1. Operators are explicitly warned about potential hazards such as high voltage/current and mechanical impact from fault currents.
• Pre-Measurement Checks: Before initiating any measurement, several criteria must be checked:
  • Line Length: The cable under test must be less than 5 km (3 miles) long. For longer cables or overhead lines, the CPC 100 + CP CU1 system is recommended due to the COMPANO 100's output power limitations.
  • Estimated Open-Cable Voltage: This involves measuring the circular current caused by interference from parallel systems. Both ends of the cable must be grounded to allow for circular current flow. A grounding set is used to measure the current in each of the three phases. An estimated open-line voltage is then calculated. If this estimated voltage exceeds 20 V, the measurement cannot be performed with COMPANO 100, and alternative solutions or interference reduction methods must be considered.
  • Measured Open-Line Voltage: After connecting the CP GB1 to the cable, the actual open-line voltage is measured using a voltmeter. This step verifies the initial estimation and confirms that the voltage is within safe limits (below 20 V) for COMPANO 100 operation.
  • Injected Test Current: The COMPANO 100 is connected to the CP GB1, and a test current (e.g., 5 A at 70 Hz for 50 Hz systems) is injected. The system indicates if the current can be successfully injected or if an overload occurs due to high cable impedance, requiring a reduction in the test current.
• Measurement Loops: The measurement process involves performing seven distinct measurement loops, each with different current paths (e.g., L1-L2, L1-E, L1+L2+L3-E). For each loop, the Kelvin clamps are connected to specific studs on the CP GB1, and the COMPANO 100's output is started. The device automatically stops after a few seconds, and the results are stored on a USB flash drive.
• Configuration Profiles: The system utilizes pre-defined configuration profiles (e.g., CABLE-50.occp for 50 Hz systems) that can be loaded from a USB flash drive. These profiles set the test current and frequencies, simplifying the setup process for common scenarios.
• Data Evaluation: An Excel report spreadsheet (COMPANO-Template-Cable-Impedance-Measurement-2023-ENU.xlsm) is provided for evaluating the measurement results. Operators fill in basic cable information and then load the XML result files from the COMPANO 100 into the spreadsheet. The R and X values from each measurement loop are copied into the template, which then calculates physical model impedances, symmetrical components, line model parameters, and k-factors. An error calculation section helps validate the measurements.

Maintenance Features

While the document primarily focuses on operational aspects, it implicitly highlights several maintenance considerations:

• Regular Inspection of Grounding Components: The importance of ensuring that grounding studs are in good condition, clean, and free of oxidation is repeatedly emphasized. This suggests that regular inspection and cleaning of these critical safety components are necessary to maintain effective grounding.
• Proper Cable Handling: Instructions on handling measurement leads and grounding cables, including ensuring proper cross-section and secure connections, imply that these cables should be regularly checked for wear and tear. Damaged cables could compromise safety and measurement accuracy.
• Adherence to Manuals: The document stresses that the application note must be used in conjunction with relevant product manuals (COMPANO 100 User Manual and CP CU1 User Manual). These manuals likely contain detailed information on routine maintenance, calibration, and troubleshooting procedures for the devices.
• No Unauthorized Modifications: Users are explicitly warned not to open the CP GB1's housing or to repair, modify, extend, or adapt COMPANO 100, CP GB1, or any accessories. This underscores the need for professional servicing and the use of original OMICRON accessories to ensure the integrity and safety of the equipment.
• Environmental Considerations: The recommendation to place cables as close as possible to ground level to minimize electric and magnetic coupling, and to avoid unauthorized human entry into the measurement environment, suggests that maintaining a controlled and safe testing environment is an ongoing responsibility.

Omicron COMPANO 100 Specifications