Power Quality Audit (PQA) in Smart Grid

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In smart grid technology, the term Power Quality Audit refers to the process of assessment of technical aspects, efficiency, reliability, and safety of the electrical system.

Power quality audit is one of the important services to ensure optimized operation of equipment and systems in electrical grid. In this chapter, we will discuss about power quality audit in the context of smart grids.

What is Power Quality Audit?

Power quality audit is a service provided by an electrical support organization to assess the efficiency, reliability, and safety of an electrical system in an organization. It provides information about power quality issues in the electrical system.

Power quality audit helps in addressing issues like reliability and stability in advance before they actually affect the performance and operation of the system.

Power Quality Audit Checklist

A detailed power quality audit checklist includes all the tests and inspections that ensure electrical systems operate reliably, efficiently, and safely. The major power quality audit inspections and tests are explained below −

Facility Walkthrough

It is a visual inspection of the electrical system to identify major sources of power quality issues. During this inspection, the following checks are performed −

• Equipment condition
• Grounding system
• Wiring connections
• Surrounding environment
• Nearby sources of electromagnetic interference, etc.

Load Study

This inspection of electrical system is performed to analyze the load profile and to understand the power consumption patterns. This power quality audit activity involves the measurement and recording of following electrical parameters −

• System voltage
• Load current
• Power factor
• Harmonic distortions, etc.

Inter-Harmonics

Inter-harmonics are nothing but non-integer multiples of fundamental frequency. The main purpose of this power quality check is to identify the presence of inter-harmonics and their impact on the system. This power quality audit involves the following activities −

• Detection of inter-harmonics in the electrical system
• Analysis of inter-harmonics to understand their impacts on the sensitive electrical equipment.

Voltage and Current Harmonics

This power quality check is performed to measure and assess the total harmonic distortions of voltage and current in the electrical system. Under this audit, the total harmonic distortion is calculated to determine if it is exceeding the specified limit. This power quality audit helps in preventing overheating of power equipment of the system.

Earth-Pit Resistance Test (At Mains Transformer)

This test is performed to check the robustness and effectiveness of the earthing system. To perform this test, an earth resistance tester (megger) is used to measure the resistance of earth pit and verify its values are within the specified limits.

Reactive Power Analysis

This test is performed during power quality audit to determine the reactive power flow in the system. The reactive power analysis is important for maintaining power factor and reduce the energy losses and costs. This audit involves the following activities −

• Calculation of reactive power flow, both inductive and capacitive components.
• Recommend corrective actions for reactive power compensation and power factor improvement.

Power Parameters

This activity involves the analysis of important power parameters to ensure efficient, reliable, and stable operation of the electrical system. In this power quality audit, the following parameters are measured and analyzed to assess the health and performance of the system −

• Voltage and current levels
• Power factor
• Active and reactive power
• Apparent power

Line Disturbances (Transient, Sags, Swells at Main Transformer)

This power quality audit is performed to identify and reduce the voltage transients, sags, and swells in the electrical system. It is very important for preventing equipment from getting damaged. Under this audit, the following activities are performed −

• Monitoring and recording transient events at the main transformer using power quality analyzers.
• Provide recommendations to implement protection schemes.

Captive Power Assessment

Captive power assessment is performed to evaluate the reliability and performance of the captive or backup power systems like diesel generators, UPS, etc. Under this power quality audit, the backup power systems are tested to verify their capability to provide uninterrupted power supply during main power outage.

Load Distribution

Load distribution analysis is another important inspection performed during power quality audit. It is primarily meant for determining the distribution of electrical load across different phases and circuits of the system.

The main activities involved in this power quality audit include determination of load distribution patterns across the circuit and balance the loading if required.

Thermography

This test is performed to identify the points in electrical system that have faulty connections or insulation breakdown. In this test, thermal imaging cameras are used to take infrared images of electrical components. These images highlight those areas of the system that have abnormal temperature rise due to unwanted current flow.

Problem Investigation

The main aim of problem investigation is to analyze the power quality issues in the electrical system identified during the audit process or reported by the stakeholders. Under this check, the root causes of power quality issues like equipment failure, voltage fluctuations, harmonic distortion, etc. are diagnosed.

PQA Report

This report is prepared for stakeholders to provide a comprehensive study on findings, measurements, and analysis of audit. The power quality audit report contains detailed descriptions of identified issues, results of data analysis, and recommendations for corrective actions.

Power Quality Problems Covered in PQA

The following are some major power quality problems that covered in the power quality audit −

• Voltage sags and swells
• Spikes and surges
• Frequency variations
• Switching transients
• Equipment failure
• Low power factor
• Harmonic resonance or distortions
• Load unbalancing
• Electrical line noise
• Transformer overheating
• Blackouts
• Wastage of electricity, etc.

Why Power Quality Audit is Important?

Power quality audit in a modern electrical grid or smart grid is important for the following reasons −

• To ensure continuity of power supply i.e., power quality audit ensures that the power in the network is available on a regular basis.
• To maintain quality of voltage i.e., power quality audit is important for avoiding voltage disturbances in the network.

Power Quality Audit Stages

The power quality audit is completed in the following major stages −

Stage 1: Pre Call Audit

At this stage, the following activities are carried out −

• Pre-call audit on all blocks from point of common coupling to user end.
• Study of electrical layouts and schematics.
• Identification of points of measurements.
• Study of domain process and schedules.
• Preparation of line schematic for measurement audit.

Stage 2: Site Survey and Measurements

This stage of power quality audit involves the following major activities −

• Checkups of panels, meters, cables, switchgears, protection, distribution equipment.
• Compliance checkup as per statutory.
• Identification of bottlenecks.
• Measurements like snaps, trend records, data, graphs, events, and alarms.
• Test and analysis as per standards.

Stage 3: Analysis and Solution

The major activities performed during this stage of power quality audit are as follows −

• Detailed analysis of data, snaps, trend records, events, alarms, and other measurements.
• Quandary data analysis.
• Power quality and reliability measurements.
• Power quality aberration forecast.
• Cost analysis of power quality problems.
• Solution formation in options.

Stage 4: Report and Presentation

At this stage, the following power quality audit activities are performed −

• Preparation of records.
• Report preparation on observations.
• Cause analysis.
• Evaluation and comparison.
• Report on regulatory adherence.
• Recommendations.

These four stages of power quality audit are represented in the following block diagram.

Flow Chart of an Example Power Quality Audit

The following figure shows a flow chart of an example power quality audit and different activities.

Why Power Quality Audit is Required?

The following are some major reasons that make the power quality audit an important task in smart grids −

• It helps in improving system power factor and efficiency.
• It plays a significant role in preventing breakdowns and interruptions in the electrical power supply.
• It helps in avoiding excess energy consumption and energy losses.
• PQA also helps in removing transients, surges, and harmonics from the electrical grid.
• PQA prevents the voltage and frequency fluctuations in the network.
• It helps in avoiding transformer overheating, unwanted trips, and capacitor bursts.
• PQA also reduces the kVA demand and energy losses and helps in reducing the electricity bills.
• PQA is also important for better quality and production rate in power industry.
• It improves the life cycle of the electrical grid and equipment.
• PQA maximizes the distribution capacity of the plant.

Conclusion

Power quality audit is an important task in smart grid to determine power quality issues in the electrical system. It helps in addressing the major issues that can disturb the operation of electrical systems and compromise its efficiency, reliability, and safety.

Power quality audit is an important practice to avoid the degradation of performance of the electrical network in an organization. In practice, power quality audit services are generally provided by government or private technical support organization. These auditing entities check and assess the health and performance of organizations electrical system and provides detailed analysis reports and recommendations for corrective actions.