By sion932 
As a core national standard in China’s power industry, GB/T 12325-2008 “Power Quality – Deviation of Supply Voltage” plays a pivotal role in regulating the quality of power supply, ensuring the safe and stable operation of electrical equipment, and promoting the efficient and reliable operation of the power system. Issued on June 18, 2008, and implemented on May 1, 2009, this standard replaces the previous GB/T 12325-2003 version, incorporating updated technical requirements and practical operational guidelines to adapt to the evolving needs of the power industry.
1. Scope and Normative References
GB/T 12325-2008 specifies the limits, measurement methods, and qualification rate statistics of supply voltage deviation. It applies to the deviation of supply voltage from the nominal system voltage under normal operating conditions in 50 Hz AC power systems. This scope ensures that the standard covers the majority of power supply scenarios in China, providing uniform technical criteria for power supply enterprises, power users, and relevant research and design institutions.
The standard incorporates normative references to GB/T 156-2007 “Standard Voltages” (modifed from IEC 60038:2002). Clauses from the referenced documents become integral parts of this standard. For dated references, subsequent amendments (excluding errata) or revisions do not apply; however, parties agreeing to use this standard are encouraged to consider the latest versions. For undated references, the latest versions shall apply.
2. Key Terms and Definitions
To ensure consistent understanding and implementation, GB/T 12325-2008 defines several core terms, aligning the first three with GB/T 156-2007 for better coordination across standards:
- Nominal System Voltage: A specified value used to mark or identify the system voltage, serving as the reference for evaluating voltage deviation.
- Supply Terminals: The connection point between the power supply department’s distribution system and the user’s electrical system, which is the key location for measuring supply voltage.
- Supply Voltage: The line voltage or phase voltage at the supply terminals, representing the actual voltage provided to the user.
- Voltage Deviation: The relative value of the deviation between the actual operating voltage and the nominal system voltage, expressed as a percentage. This is the core indicator regulated by the standard.
- Voltage Qualification Rate: The percentage of the total operating time during which the actual voltage deviation remains within the specified limits. This indicator reflects the overall quality of power supply over a period.
Notably, compared to the 2003 version, the 2008 standard revises the definition of “voltage deviation” and adds the term “voltage qualification rate,” enhancing the standard’s practicality and operability.
3. Limits of Supply Voltage Deviation
One of the core contents of GB/T 12325-2008 is the clear specification of voltage deviation limits for different voltage levels and supply types, ensuring that the power quality meets the needs of various electrical equipment and users:
- For supply voltages of 35 kV and above, the sum of the absolute values of positive and negative deviations shall not exceed 10% of the nominal voltage. If the upper and lower deviations have the same sign (both positive or both negative), the larger absolute deviation shall be used as the evaluation criterion.
- For three-phase supply voltages of 20 kV and below, the deviation shall be ±7% of the nominal voltage. This addition of the 20 kV voltage level limit (compared to the 2003 version) addresses the technical requirements of the emerging 20 kV power distribution system, expanding the standard’s applicability.
- For single-phase 220 V supply voltage, the deviation shall be +7% and -10% of the nominal voltage. This asymmetric limit considers the characteristics of single-phase loads (such as household electrical appliances) and balances the requirements of power supply stability and user equipment protection.
- For users with small short-circuit capacity at the supply terminals, long power supply distances, or special requirements for voltage deviation, the limits shall be determined through negotiation between the power supply and user parties. This flexible provision accommodates special operating conditions, ensuring the standard’s adaptability.
4. Measurement of Supply Voltage Deviation
To enhance the operability of the standard, GB/T 12325-2008 adds a dedicated chapter on the measurement of supply voltage deviation, specifying instrument performance classifications and measurement methods:
4.1 Classification of Measuring Instrument Performance
Measuring instruments are classified into two performance grades based on application requirements:
- Grade A Performance: Suitable for scenarios requiring high-precision measurements, such as contract arbitration and dispute resolution. Instruments of this grade ensure the accuracy and authority of measurement results, providing a reliable basis for legal and commercial disputes.
- Grade B Performance: Applicable for investigation and statistics, fault diagnosis, and other scenarios where high precision is not required. This classification optimizes the cost-effectiveness of measurement practices, allowing for flexible selection based on actual needs.
4.2 Measurement Methods
The basic measurement time window for obtaining the effective value of voltage shall be 10 cycles. Each measurement window shall be adjacent to the next without overlap. Continuous measurements are performed to calculate the average value of the voltage effective value, and the supply voltage deviation is derived from this average. This standardized measurement method ensures the consistency and comparability of measurement results across different regions and institutions.
5. Informative Appendices
GB/T 12325-2008 includes two informative appendices to support practical implementation: Appendix A “Statistics of Voltage Qualification Rate” and Appendix B “Monitoring of Power Grid Voltage and Statistics of Regional Grid Voltage Qualification Rate”. These appendices provide detailed guidelines for statistical methods, data processing, and monitoring practices, helping power supply enterprises effectively evaluate the quality of power supply and identify areas for improvement. Although informative (non-mandatory), the appendices significantly enhance the standard’s practical value by bridging the gap between technical requirements and on-site operations.
6. Significance and Impact
The implementation of GB/T 12325-2008 has far-reaching significance for China’s power industry. Firstly, it standardizes the management of supply voltage deviation, reducing equipment failures and operational risks caused by voltage fluctuations, thereby improving the reliability of the power system. Secondly, the clear and graded voltage limits cater to the diverse needs of different users, promoting the rational utilization of power resources. Thirdly, the standardized measurement methods and qualification rate statistics facilitate the supervision and evaluation of power supply quality, encouraging power supply enterprises to continuously improve their service levels.
Compared to the 2003 version, the 2008 update reflects the development of China’s power industry, addressing new technical issues and practical challenges. The addition of the 20 kV voltage level, the refinement of measurement requirements, and the inclusion of informative appendices make the standard more comprehensive, scientific, and operable. It not only aligns with domestic industry development but also draws on international experience (through referenced IEC standards), contributing to the modernization and globalization of China’s power quality management system.
GB/T 12325-2008 “Power Quality – Deviation of Supply Voltage” is an indispensable technical benchmark in China’s power supply sector. By defining clear limits, standardized measurement methods, and scientific statistical criteria for supply voltage deviation, the standard ensures the stability and reliability of power supply, protects the interests of both power supply enterprises and users, and supports the healthy development of the power industry. As the power industry continues to evolve with new technologies such as smart grids and renewable energy integration, GB/T 12325-2008 will remain a foundational standard, guiding the continuous improvement of power quality management in China.
References
[1] General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, Standardization Administration of the People’s Republic of China. GB/T 12325-2008 Power Quality – Deviation of Supply Voltage[S]. 2008.
[2] State Grid Jiangsu Electric Power Co., Ltd. GB/T 12325-2008 Power Quality – Deviation of Supply Voltage[P]. 2024.
[3] Pinghu Municipal People’s Government. GB/T 12325-2008 Power Quality – Deviation of Supply Voltage[P]. 2022.
[4] Chinese Standard. Translated English Version of GB/T 12325-2008[P]. 2025.
[5] Haiyan County People’s Government. GB/T 12325-2008 Power Quality – Deviation of Supply Voltage[P].