Practical Maintenance Guide for Power Factor Correction Systems: Capacitor Bank Inspection, Reactors Verification and Controller Calibration

1. Scope and Purpose

This practical guide details the essential preventive and corrective maintenance procedures for Power Factor Correction Systems (SCFP) installed in industrial environments, focusing on capacitor banks, harmonic filter reactors and their respective controllers. The application of these guidelines aims to ensure energy efficiency, the quality of electrical energy and extend the useful life of components, minimizing operational interruptions.

Regular maintenance of an SCFP is critical for:

• Maintain the power factor within regulatory limits (e.g., minimum of 0.92 capacitive, according to ANEEL in Brazil), avoiding fines for reactive energy consumption.
• Reduce energy losses in the internal electrical network, optimizing the capacity of transformers and cables.
• Protect sensitive equipment against harmonic distortions and overvoltages.
• Prevent premature failures of components, such as capacitors and reactors, which can result in unplanned production stops.

This procedure must be carried out as part of the plant's predictive and preventive maintenance plan, especially after identification of low power factor, overheating of components or failures of equipment connected to the network.

2. Safety Precautions

SAFETY ALERT: MANDATORY DE-ENERGIZATION
Before starting any intervention on the SCFP, it is mandatory that the system is completely de-energized. Implement the Lockout and Tagout procedure (LOTO - Lockout/Tagout) in accordance with Regulatory Standard NR-10. Make sure that all electrical power points on the SCFP panel are properly blocked and marked.

SAFETY ALERT: RESIDUAL ENERGY IN CAPACITORS
Capacitors store electrical charge even after the system is de-energized. It is essential to wait a minimum period of 5 minutes for the natural discharge of the internal resistors, and then manually discharge each capacitor using an appropriate discharger with an insulated rod, checking the absence of voltage with a voltmeter before any touch. Failure to discharge capacitors may result in fatal electric shock.

SAFETY ALERT: PERSONAL PROTECTIVE EQUIPMENT (PPE)
The use of appropriate PPE is non-negotiable throughout the intervention. Use: insulating gloves (Class 00 or higher, according to NR-10 and working voltage), safety glasses with side protection, face shield, flame retardant clothing (flame retardant), and dielectric safety shoes. Check the validity and integrity of all PPE before use.

3. Tools and Materials Required

The following table lists the tools and materials essential for carrying out this maintenance.

4. Pre-Maintenance Inspection Checklist

Before detailed intervention, carry out this visual and functional inspection to identify obvious problems or risks.

5. Step by Step Procedure

5.1. De-energization and Safety

1. Activate the Main Circuit Breaker: Locate and activate the SCFP's general power circuit breaker to the “OFF” position. Common error: Not correctly identifying the circuit and de-energizing the wrong panel. Always consult the updated electrical diagrams.
2. LOTO Procedure: Apply Lock and Tag (LOTO) padlocks and tags to the general circuit breaker, as per the unit standard. The block must be nominal and non-transferable. Common mistake: Relying only on visual signaling. Physical blocking is mandatory by NR-10.
3. Lack of Voltage Check: Using a True-RMS digital voltmeter with insulated test leads, check the absence of voltage between phases and between phase and ground on all input and output terminals of the SCFP panel. The reading should be 0 Vac. Common error: Not testing the voltmeter before and after measuring on a known voltage source.
4. Capacitor Discharge:
   1. SAFETY ALERT: Wait a minimum of 5 minutes after de-energization for the natural discharge of the capacitors through their internal discharge resistors. This time may vary depending on the manufacturer.
   2. With the insulated rod capacitor discharger, connect the discharger terminals to the terminals of each capacitor, phase to phase and phase to ground, until there are no more sparks or readings on the voltmeter coupled to the discharger. The final reading of each capacitor should be 0 Vcc.
   3. Repeat the process for all capacitors in the bank. Common error: Not discharging all capacitors individually or not checking the absence of voltage after discharging.

5.2. Detailed Visual Inspection and Internal Cleaning

5. Capacitor Inspection: Observe each capacitor individually. Look for:
   • Casing padding (indicates internal failure or overpressure).
   • Leakage of dielectric oil (oil capacitors) or electrolyte (dry capacitors).
   • Deformations, cracks or darkened areas on the surface.
   • Corroded or overheated terminals (discoloration).
   Visually, a capacitor in good condition must have an intact housing, without deformation and free of leaks. Common error: Ignoring small changes to the housing. These may be the first signs of imminent failure.
6. Inspection of Reactors (Inductors): Check harmonic filter or current limiting reactors.
   • Deformation or breakage of the casing (if applicable).
   • Signs of overheating in the coil (discoloration, dry insulation or burning smell).
   • Loose or corroded terminal connections.
   • Excessive noise or vibration (if detected before de-energization).
   The coil must be intact and without signs of visible overheating.
7. Internal Panel Cleaning: Use the industrial vacuum cleaner and soft bristle brush to remove dust, debris and dirt accumulated on all components, busbars and insulators. Apply electrical contact cleaner to specific points, if necessary, and remove excess with a microfiber cloth. Common mistake: Using compressed air carelessly, which can spread dirt to sensitive areas or damage components.

5.3. Checking Electrical Connections and Torques

8. Checking and Retightening Terminals: Using the torque wrench, check and retighten all electrical connections, including capacitor terminals, reactors, contactors, circuit breakers, terminals and buses. Follow the manufacturers' recommended torque values.

   Component	Screw Size	Recommended Torque (Nm)
   Capacitor Terminals	M8/M10	20 - 25 Nm
   Copper Busbars	M10/M12	35 - 45 Nm
   Contactor/Circuit Breaker Terminals	M4/M6	8 - 15 Nm
   Control Wiring Connections	M3	1.5 - 2.5 Nm

   Common error: Not using a torque wrench, resulting in insufficient (increases resistance and heat) or excessive (damages the terminals) tightening.
9. Inspection for Signs of Overheating: Observe the color of the busbars and cables. Darkened areas, dry insulation, or brown/blue coloring indicate chronic overheating due to loose connections or overload. Correct the problem before re-energizing. Busbars and cables must have their original color, without signs of discoloration or degradation.

5.4. Electrical Testing of Components

10. Individual Capacitance Measurement (Capacitors):
    1. Using a multimeter with a capacitance function, measure the value of each capacitor individually. Disconnect at least one terminal to ensure accurate measurement of the isolated component.
    2. Compare the measured value with the nominal value specified on the capacitor nameplate. The acceptable value must be within a tolerance of ±5% to ±10% of the nominal value (check the manufacturer's datasheet).
    3. Capacitors outside this range must be replaced. A 50 kvar, 480V capacitor must have a capacitance corresponding to its nominal capacitive reactance value.
    4. Common error: Not disconnecting the capacitor from the network for measurement, which can lead to false readings due to parallel circuits.
11. Insulation Resistance Measurement:
    1. With the megger, measure the insulation resistance between the terminals of each capacitor and the housing (ground), and between the terminals. Apply the recommended test voltage (usually 500V or 1000V).
    2. The minimum acceptable insulation resistance is 100 MΩ. Values ​​below may indicate dielectric degradation or contamination.
    3. Common error: Performing the test with the capacitor still connected, which could damage the megger or adjacent components.
12. Reactor Inspection and Measurement:
    1. Physically inspect coils for signs of overheating, cracked insulation, or varnish leaks.
    2. If possible and with suitable equipment (LCR meter), measure the inductance of each reactor and compare it with the nominal value. Disconnect the ballast for this measurement. Tolerance is typically ±5%.
    3. Common error: Not considering the ambient temperature when measuring inductance, as inductance can vary slightly with temperature.

5.5. Power Factor Controller Check and Calibration

13. Parameter Check: Access the controller configuration menu and check that the parameters are correct according to the original installation or the current needs of the plant. Critical parameters include:
    • Target Power Factor (e.g., 0.98 inductive).
    • Stage Switching Time (e.g., 20 to 60 seconds to avoid overloads and oscillations).
    • Nominal values ​​of capacitors (in kvar) and reactors (if programmable).
    • Type of control (automatic, semi-automatic).
    The parameters must correspond to those of the electrical project and the characteristics of the installed capacitors. Common error: Changing parameters without in-depth technical knowledge, which can cause instability in the system.
14. Calibration of Current Sensors (CTs - Current Transformers):
    1. Check the connections of the CTs to the controller. Confirm the polarity (P1/P2 and S1/S2) and the direction of the current.
    2. If the controller has a CT self-calibration function, activate it. Otherwise, manually check the transformation ratio and secondary current.
    3. With the system energized (after all safety steps), measure the current in the CT phase with the clamp meter and compare it with the reading indicated on the controller display. They must be in direct proportion to the TC ratio. Deviations greater than 5% require calibration.
    4. Common error: Inverted CT connection, leading to incorrect power factor readings.

5.6. Maintenance of Fans and Filters

15. Cleaning/Replacing Filters: Remove the panel ventilation filters and clean them carefully with compressed air or wash them (washing and complete drying if permitted). If they are damaged or excessively saturated, replace them with new ones.
16. Fan Operation Test: With the system de-energized and before re-energizing, manually rotate the fan blades to check for any obstructions or mechanical noise. After re-energizing, confirm proper operation. Fans must operate smoothly and quietly, without excessive vibrations.

5.7. Reenergization and Monitoring

17. LOTO Removal: After all work is completed and safety confirmed, remove the Lockout and Tagout (LOTO).
18. Gradual Reenergization: Turn on the SCFP main circuit breaker. Monitor the panel for unusual noises, smells or smoke.
19. Initial Monitoring: Use the clamp meter and voltmeter to measure:
    • Line currents (must be balanced, maximum variation of 10% between phases).
    • Line and phase-to-ground voltages (must be within the nominal range of the installation, e.g., 380Vac ±5%).
    • Power factor (on the controller and with external equipment).
    • Temperature of components (capacitors and reactors with infrared thermometer). Ideal temperatures for capacitors below 50°C, for reactors below 70°C.
    The system must operate stably, with the power factor corrected to the target value and without overheating.

6. Post-Maintenance Verification Checklist

After re-energization and a period of stabilization, confirm SCFP performance.

7. Troubleshooting Guide

This table presents common symptoms, their probable causes and corrective actions to assist the technician in the field.

8. Recommended Maintenance Table

A predictive and preventive maintenance schedule is crucial to the durability of the SCFP.

9. Spare Parts Reference

The availability of spare parts is an essential factor for efficient maintenance. See the UNITEC-D catalog for specifications and compatible models.

For detailed information and purchase of these and other parts, visit the UNITEC-D electronic catalog: www.unitecd.com/e-catalog/

10. References

• ABNT NBR 5410: Low Voltage Electrical Installations.
• ABNT NBR 14039: Medium Voltage Electrical Installations, from 1.0 kV to 36.2 kV.
• NR-10: Safety in Electricity Installations and Services - Ministry of Labor and Employment.
• Operation and Maintenance Manuals from component manufacturers (capacitors, reactors, controllers, contactors).
• IEEE Std 18-2012: Standard for Shunt Power Capacitors.
• IEC 60831-1/2: Shunt power capacitors of the self-healing type for a.c. systems having a rated voltage up to and including 1000 V.