Field discharge and overvoltage protective device for large-sized generator rotor

Abstract

The invention discloses a field discharge and overvoltage protective device for a large-sized generator rotor, and relates to a new scheme for field discharge and overvoltage protective devices for large-sized generator rotors. According to the characteristics of high voltage and high field discharge capacity of large-sized generator rotors and respective characteristics of silicon carbide (SiC) nonlinear resistors widely applied abroad and zinc oxide (ZnO) nonlinear resistors 7 widely applied domestically, the silicon carbide nonlinear resistors and the zinc oxide nonlinear resistors are innovatively applied to a same system simultaneously and used for field discharge and positive overvoltage protection respectively, and a traditional field discharge and overvoltage protective device which only employs one type of resistors for both field discharge and positive overvoltage protection is replaced. The novel field discharge and overvoltage protective device not only has the advantages of safety, reliability, quickness and stability of the silicon carbide resistors in field discharge but also has the advantages of quickness in automatic shutoff of the zinc oxide nonlinear resistors 7 after overvoltage protection, and thereby the problem that large-sized generator rotors are bound to shut down after overvoltage protection is solved.

Description

technical field [0001] The invention relates to a large generator rotor demagnetization and overvoltage protection device. Background technique [0002] At present, the capacity of large-scale generator sets is increasing continuously, the excitation current of the rotor is also increasing, and the magnetic field energy stored in the rotor winding is also increasing. The safe and stable operation of the generator set plays a decisive role. At present, the demagnetization resistors of the core components of the conventional generator rotor demagnetization and overvoltage protection devices use linear resistors or nonlinear resistors. Commonly used, the linear demagnetization resistor is stable and reliable, and the cost is low, but the demagnetization time is long, which is not conducive to rapid demagnetization during emergency shutdown. The nonlinear demagnetization resistor can greatly shorten the demagnetization time. Generally, zinc oxide (ZnO) or silicon carbide ( SiC)...

AI Technical Summary

Problems solved by technology

[0002] At present, the capacity of large-scale generator sets is increasing continuously, the excitation current of the rotor is also increasing, and the magnetic field energy stored in the rotor winding is also increasing. The safe and stable operation of the generator set plays a decisive role. At present, the demagnetization resistors of the core components of the conventional generator rotor demagnetization and overvoltage protection devices use linear resistors or nonlinear resistors. Commonly used, the linear demagnetization resistor is stable and reliable, and the cost is low, but the demagnetization time is long, which is not conducive to rapid demagnetization during emergency shutdown. The nonlinear demagnetization resistor can greatly shorten the demagnetization time. Generally, zinc oxide (ZnO) or silicon carbide ( SiC) material non-linear resistors, zinc oxide resistors have switching characteristics, small leakage current, can be directly connected in parallel at both ends of the rotor winding, using zinc oxide resistors for demagnetization and overvoltage protection devices, demagnetization is rapid and effective, after the overvoltage disappears When the voltage is lower than the threshold value, the circuit can be shut off automatically, but the characteristics of the zinc oxide resistance change greatly with the extension of time, and it will be in a short circuit state after damage, which also poses a threat to the safe operation of the generator. It is difficult to choose a zinc oxide resistor with a matching high voltage threshold when it is increased. The volt-ampere characteristic of the silicon carbide resistor is between the linear resistor and the zinc oxide resistor, and its demagnetization time is also between the two. The strengths of the two are stable characteristics, and silicon carbide resistors have no obvious threshold voltage. Large-scale units increasingly choose silicon carbide demagnetization resistors, but the leakage current of silicon carbide resistors is large. When used as overvoltage protection resistors, After the positive overvoltage disappears, the circuit cannot realize self-shutoff, and the generator can only stop, which is unacceptable to domestic power plant users

[0003] In this way, in the existing generator de-excitation and overvoltage protection devices commonly used at home and abroad, the selection of the de-excitation resistor is faced with the need to quickly de-excite, ensure that the circuit can be automatically shut down after the overvoltage is restored, and at the same time need to de-excite The magnetic resistance characteristics are stable and reliable, which can ensure the safe operation of the generator

Images