This standard specifies limits, calculation, and measurement and evaluation method of three-phase voltage unbalance.
This standard is applicable to voltage unbalance of point of common coupling caused by negative sequence fundamental component with the normal operation mode of AC power system with a nominal frequency of 50Hz and voltage unbalance of point of common coupling caused by zero sequence fundamental component of the low-pressure system.
Voltage unbalance factor and permissible value of negative phase sequence current of rated condition of the electrical apparatus shall be specified by the respective standard, for example, rotating motors shall meet the requirements in GB 755.
Instantaneous and momentary unbalance problem are not applicable to this standard.
2 Normative References
The following documents contain provisions which, through reference in this standard, constitute provisions of this standard. For dated reference, subsequent amendments to (excluding correction contents), any of these publications do not apply. However, parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. For undated references, the latest edition of the normative document is applicable to this standard.
GB/T 156-2007 "Standard Voltage" (IEC 60038:2002, MOD)
GB/T 12325 "Power Quality-Deviation of Supply Voltage"
3 Terms and Definitions
The following terms and definitions apply in this standard.
3.1
Voltage unbalance
Three-phase voltage is different in amplitude or (and) the phase difference is not 120°.
3.2
Unbalance factor
It refers to the unbalanced degree of three-phase in the three phase power system and shall be represented by voltage, current, negative sequence fundamental component or the percentage between the zero sequence fundamental component and root mean square value of positive sequence fundamental component. Voltage, negative sequence unbalance factor of the current and zero sequence unbalance factor shall be respectively represented by , , and .
3.3
Positive-sequence component
It is the component of the positive sequence symmetric system, when the electric quantity of the balanced three phase system is decomposed according to the symmetrical component method.
3.4
Negative-sequence component
It is the component of the negative sequence symmetric system, when the electric quantity of the balanced three phase system is decomposed according to the symmetrical component method.
3.5
Zero-sequence component
It is the component of the zero sequence symmetric system, when the electric quantity of the balanced three phase system is decomposed according to the symmetrical component method.
3.6
Point of common coupling
It refers to the joint of more then one users in power system.
3.7
Instantantaneous
It is a modifier used to quantify variation duration time in a short time and the time scope is power frequency 0.5 cycles~30 cycles.
3.8
Momentary
It is a modifier used to quantify variation duration time in a short time and the time scope is power frequency 30 cycles~3s.
3.9
Temporary
It is a modifier used to quantify variation duration time in a short time and the time scope is power frequency 3s~1 min.
