中性點(diǎn)直接接地系統(tǒng)基波諧振抑制措施研究.pdf

1、鐵磁諧振過電壓是電力系統(tǒng)中的一種內(nèi)部過電壓,嚴(yán)重威脅著電力系統(tǒng)的安全穩(wěn)定運(yùn)行。經(jīng)過長(zhǎng)時(shí)間的研究,目前已得出了眾多的消諧措施,但由于電網(wǎng)接線復(fù)雜,不同電網(wǎng)中的鐵磁諧振性質(zhì)也不同,消諧措施并不能通用。而且中性點(diǎn)直接接地系統(tǒng)鐵磁諧振通常發(fā)生在高壓側(cè),對(duì)電網(wǎng)的危害更大,根據(jù)以往的運(yùn)行經(jīng)驗(yàn),中性點(diǎn)直接接地系統(tǒng)中最容易發(fā)生基波諧振,因此本文僅對(duì)中性點(diǎn)直接接地系統(tǒng)中的基波諧振進(jìn)行研究。
　　本文對(duì)鐵磁諧振產(chǎn)生的基本原理進(jìn)行了分析,求取了基本諧振

2、回路的約束方程。對(duì)鐵磁諧振中的跳躍現(xiàn)象進(jìn)行了闡述,確定了鐵磁諧振發(fā)生需要滿足的條件。分析中采用非線性電感的工頻勵(lì)磁特性,為準(zhǔn)確分析基波諧振,對(duì)工頻勵(lì)磁特性的表達(dá)式進(jìn)行了推導(dǎo)。在 EMTP仿真模型中,電壓互感器采用非線性電感并聯(lián)線性電阻的模型,并利用EMTP的子程序SATURATION將實(shí)測(cè)的電壓-電流特性轉(zhuǎn)換成了電流-磁通特性。
　　在理論分析方面,根據(jù)得到的工頻勵(lì)磁特性,結(jié)合戴維南電源伏安特性對(duì)工頻諧振判據(jù)進(jìn)行了推導(dǎo),得到臨界阻

3、尼電阻的表達(dá)式。然后就典型諧振變電站接線圖分別在斷開斷路器和打開隔離刀閘兩種情況下諧振的發(fā)生情況,以及在互感器二次側(cè)星形繞組兩端并聯(lián)消諧電阻和退出消諧電阻兩種情況進(jìn)行了理論分析。并在EMTP中建立110kV典型諧振變電站的仿真模型,對(duì)以上理論分析逐一仿真,驗(yàn)證了理論分析的正確性。
　　經(jīng)過理論分析和仿真驗(yàn)證,雖然消諧電阻消諧的方法可以有效的抑制諧振發(fā)生,但是,退出消諧電阻時(shí)依然可能產(chǎn)生諧振,所以結(jié)合阻容消諧的方法對(duì)消諧電阻消諧進(jìn)行

4、了改進(jìn),在并聯(lián)消諧電阻的同時(shí),經(jīng)全橋整流電路并聯(lián)一個(gè)大電解電容,不僅可以吸收諧振產(chǎn)生的能量,而且可以防止電容電壓對(duì)系統(tǒng)產(chǎn)生影響。并用EMTP對(duì)打開斷路器和退出消諧電阻時(shí)的情況進(jìn)行了仿真,得到了良好的消諧效果。
　　Ferroresonance is an internal overvoltage in power system.It is a huge threat to the safety and operational st

5、ability of power system.Many useful measures to inhibit ferroresonance had been obtained after the long time research.But because of the complex of grid connection, the characters in different grids wouldn’t be the same.

6、And the measure to eliminate ferroresonance cannot be used general.And the ferroresonance in neutral-grounded system usually happened at the high voltage side.It’s more harmful.According to the running experience, the fu

7、ndamental ferroresonance in neutral-grounded system had happened most.So, this thesis only discussed the fundamental resonance to prevent and inhibit fundamental resonance.
　　This thesis analyzed the basic theories of

8、 ferroresonance, and then induced the constraint equation of the circuit.Then introduced the characteristic of jump phenomena, confirmed the necessary conditions of ferroresonance.This thesis adopts power-frequency excit

9、ation characteristic of non-linear inductance to analyze fundamental resonance, and deduced the expression of power-frequency excitation characteristic.Take a non-linear inductance paralleling a linear resistance as the

10、model of PT in EMTP.And then the U-I characteristic had been converted into i-φ characteristic with the program SATURATION in EMTP.
　　In the area of theory study, according to power-frequency excitation characteristic

11、, this thesis induced the criterion for fundamental ferroresonance, obtained equation of the critical damping resistance.Then it took the wiring diagram of the ferroresonance substation for example to analyses the two co

12、nditions that open the breaker and open the isolation breaker to judge whether the ferroresonance would happen, and then to analyses another two conditions that paralleling a small resistance on the Y windings of transfo

13、rm secondary side and cut down the resistance in theoretically.Next it built the simulation model of110kV system by using EMTP for checking above analysis one by one.
　　Through the Theory analyses and simulation check

14、ed, although it can inhibitferroresonance effectively by using the method that paralleling small resistance.But when cut it down, ferroresonance would happen again.So, this thesis had improved the method by add a electro

15、lytic capacitors after a full bridge rectifier circuit.It can absorb the power of resonance, and also can prevent the capacitor voltage to influence the system.Then two situations that open the break and cut off the resi