Why Monitoring Accuracy Matters in Power Quality Systems
The Critical Role of Monitoring Accuracy in Power Quality Online Devices
The measurement accuracy of online power quality monitoring devices is the core of the power system’s “perception capability,” directly determining the safety, economy, stability, and reliability of power supply to users. Inadequate accuracy leads to misjudgment, incorrect control, and flawed decision-making—potentially causing equipment damage, economic losses, or even grid failures. Conversely, high accuracy enables precise fault identification, optimized dispatching, and reliable power supply, forming the foundation for intelligent operation and maintenance.
Below is an in-depth analysis of its impact across five key dimensions:
1. Impact on Grid Dispatching: Determines “Ability to Maintain System Balance”
Grid dispatching relies on real-time data from monitoring devices to balance generation, transmission, and distribution—ensuring three-phase balance, frequency stability, and acceptable voltage levels. Inaccurate data leads directly to flawed dispatch decisions.
Risks of Low Accuracy
Misjudging Three-Phase Imbalance: If a device’s measurement error for negative-sequence voltage unbalance exceeds ±0.5% (e.g., actual ε₂% = 2.5%, measured as 1.8%), the control center may wrongly assume balance, failing to adjust single-phase loads or inverter outputs. This allows imbalance to worsen, causing transformer overheating (10–20% increased losses), elevated zero-sequence currents, and even protective tripping.
Missing Harmonic Overlimits: If 5th harmonic measurement error exceeds ±1% (actual 5%, measured as 4.2%), the system may miss a harmonic violation (GB limit: 4%), allowing harmonic accumulation that disrupts relay protection (maloperation) and distorts communication signals.
Value of High Accuracy
Precise Dispatching: Class A devices (voltage unbalance error ≤ ±0.1%) can detect changes as small as 0.1%, enabling dispatchers to proactively adjust generator excitation or switch compensation devices, keeping ε₂% within the 2% national standard.
Efficient Renewable Integration: ±0.5% accuracy in harmonic monitoring (2–50th orders) for wind and solar ensures compliant grid connection, reducing grid fluctuations and improving renewable utilization (e.g., cutting curtailment by 2–3%).
2. Impact on Equipment Protection: Determines “Ability to Prevent Fault Escalation”
Protection devices (e.g., circuit breakers, surge arresters) rely on transient parameters (e.g., voltage sag magnitude and duration) from monitoring systems. Inaccurate data causes maloperation (false tripping) or failure to operate (missed tripping), risking equipment damage.
Risks of Low Accuracy
Incorrect Sag Duration Measurement: A ±40ms error (actual 100ms, measured as 140ms) may cause over-tripping—disconnecting healthy lines instead of only the faulted branch—leading to widespread outages (costing industrial users tens of thousands per incident).
Short-Circuit Current Misjudgment: A ±1% current measurement error (actual 20kA, measured as 19.8kA) may prevent breaker tripping, allowing faults to persist and destroy transformers or cables (replacement cost for a 110kV transformer exceeds one million RMB).
Value of High Accuracy
Accurate Protection: Class A devices (sag duration error ≤ ±20ms) capture 10ms-level transients precisely, enabling protection systems to isolate only the fault point—minimizing outage scope and reducing equipment damage by over 80%.
Fault Tracing: High-precision phase and amplitude data (phase error ≤ ±0.5°) help locate faults (e.g., short-circuit positions), reducing repair time from 4 hours to under 1 hour.
3. Impact on Energy Metering: Determines “Economic Fairness Between Generators and Consumers”
Energy billing relies on accurate voltage, current, and power measurements—especially at grid interconnection points (power plant-grid, grid-user). Measurement errors directly cause financial imbalance.
Risks of Low Accuracy
Metering Deviation at Gateways: A Class A device with >±0.1% voltage error (actual 220V, measured as 220.22V) for a 1000MW unit at ¥0.3/kWh would overcharge by ~¥51,840 monthly—leading to long-term financial disputes.
Overbilling Industrial Users: An S-class device with >±0.5% current error (actual 1000A, measured as 1005A) could cause a steel plant to overpay ~¥142,000 monthly, increasing operational costs.
Value of High Accuracy
Fair Settlements: Class A devices (voltage/current error ≤ ±0.1%) ensure gateway metering accuracy within ±0.2% (per GB/T 19862-2016), preventing disputes and ensuring fairness among generators, grid operators, and consumers.
Cost Optimization: High-precision monitoring (power factor error ≤ ±0.001) allows industrial users to fine-tune reactive compensation, improving power factor from 0.85 to 0.95 and reducing penalty fees by 5–10% monthly.
4. Impact on Renewable Integration: Determines “Ability to Safely Absorb Clean Energy”
The variability of wind and solar power introduces harmonics, DC offset, and voltage fluctuations. Low monitoring accuracy allows non-compliant devices to connect, threatening grid safety. High accuracy ensures “friendly grid integration.”
Risks of Low Accuracy
Harmonic Overlimit Connection: A ±0.5% error in measuring 5th harmonic from a PV inverter (actual 5%, measured as 4.3%) may falsely pass compliance (GB limit: 4%), injecting harmful harmonics that disrupt sensitive equipment (e.g., MRI machines, lithography tools) or trigger resonance.
Missing DC Offset: A ±0.1% measurement error in DC content from a wind converter (actual: 0.3%, measured: 0.18%) may fail to detect excessive DC offset, leading to transformer DC bias, a 30% increase in losses, and a 50% reduction in lifespan.
Value of High Accuracy
Compliant Connection: Class A devices (harmonic error ≤ ±0.1%, DC offset error ≤ ±0.05%) accurately identify non-compliant renewables, requiring fixes before connection—reducing grid faults from renewable integration by over 30%.
Optimized Dispatch: High-precision power fluctuation data (1-minute error ≤ ±0.5%) helps predict renewable output, enabling better coordination with thermal or storage units and reducing curtailment (e.g., boosting PV utilization to over 98%).
5. Impact on Power Supply to Users: Determines “Ability to Meet Sensitive Load Demands”
Modern industries (e.g., semiconductors, electronics, pharmaceuticals) demand high power quality (e.g., voltage fluctuation ≤ ±0.5%, sag duration ≤ 50ms). Low monitoring accuracy leads to undetected quality issues and production losses.
Risks of Low Accuracy
Production Accidents: A ±0.3% error in voltage fluctuation measurement (actual: 0.8%, measured: 0.4%) may fail to detect excessive fluctuations, leading to wafer scrap (worth tens of thousands of RMB per piece) or production line shutdowns (daily losses exceeding one million RMB).
Failed Sag Alerts: A ±1% error in sag magnitude (actual 70% Un, measured as 71.2% Un) may misclassify a B-level sag as A-level, failing to trigger UPS switching—resulting in spoiled vaccines or production halts.
Value of High Accuracy
Early Warning: Class A devices (voltage fluctuation error ≤ ±0.1%) detect 0.2% changes, providing 10–30 seconds of advance warning—allowing users to switch to backup power and avoid losses (reducing incidents by over 90%).
Customized Power Supply: High-precision user load data enables tailored services (e.g., dedicated lines, harmonic filtering), improving product yield (e.g., from 95% to 99% in electronics plants).
Conclusion: Monitoring Accuracy is the “Nervous System” of the Power Grid
The accuracy of online power quality monitoring devices reflects the power system’s “perception capability.” Poor accuracy blinds the system, making it unable to detect risks or make sound decisions. High accuracy enables “predictive maintenance, precise dispatching, friendly integration, and premium power supply.”
In the long term, high-accuracy monitoring supports reliable grid planning (e.g., line upgrades, substation construction), avoiding blind investments and reducing redundant retrofitting costs by 20–30%. It is the foundational cornerstone for building a modern power system dominated by renewables and serving highly sensitive users.
