发电机失磁保护的原理及整定计算

PRINCIPLE OF GENERATOR LOSS-OF-EXCITATION PROTECTION AND ITS SETTING CALCULATION

发电机失磁具有两大特征:发电机电势降低和导致静稳破坏。电势降低通常以系统电压或发电机机端电压降低来判断。静稳破坏的定子判据用静稳临界阻抗;转子判据用有功功率与转子电压的关系,对隐极机静稳临界阻抗是圆,UL-P是直线,对凸极机静稳临界阻抗不是圆,UL-P不是直线。分析了凸极机静稳临界曲线的凹凸性,证明了用圆拟合静稳临界曲线优于直线拟合。为了提高发电机电势降低判据的灵敏度,防止系统振荡造成的误动作,提出了发电机低电势判据。静稳阻抗和低电势阻抗采用正序阻抗,能有效地防止外部短路造成的误动作。在分析推导的过程中,给出了整定计算的公式和方法。

Two main characteristics of the generator loss-of-excitation are low generator voltage and loss of static stability. It is common in selecting the system voltage or the generator terminal voltage to estimate the low voltage. The stator criterion of static stability is a circle. The rotor criterion utilizes the relation between the active power and the rotor voltage. For the turbine synchronous generator, the critical static stability impedance is a circle and is a line. But for the salient-pole synchronous generator, the critical static stability impedance is no longer a circle and is no longer a line. This paper analyzes the idiosyncrasy of the static stability impedance of the salient-pole synchronous generator, thus testifies that it is better to apply a circle than a line. In order to improve the sensitivity of the low-voltage impedance and avoid mal-operating in the system swing, it gives a new criterion about generator low-voltage impedance. It uses the positive impedance in static stability and low-voltage impedance which can effectively prevent the mal-operation in external faults. It also gives out the method and formula about setting calculations.