肖項(xiàng)濤 郝亮亮 梁鄭秋 何 鵬 吳鵬飛
核電站控制棒電源系統(tǒng)發(fā)電機(jī)失磁故障解析
肖項(xiàng)濤1郝亮亮1梁鄭秋1何 鵬2吳鵬飛3
(1.北京交通大學(xué)電氣工程學(xué)院 北京 100044 2.遼寧紅沿河核電有限公司 大連 116001 3. 陽(yáng)江核電有限公司 陽(yáng)江 529599)
核電站控制棒電源(簡(jiǎn)稱棒控電源)是控制棒驅(qū)動(dòng)機(jī)構(gòu)的唯一供電系統(tǒng),確保該系統(tǒng)的安全可靠運(yùn)行對(duì)提高核電站安全性具有重大意義。實(shí)際運(yùn)行的棒控電源系統(tǒng)中發(fā)電機(jī)的失磁保護(hù)判據(jù)原理簡(jiǎn)單,現(xiàn)場(chǎng)發(fā)生了多起失磁保護(hù)失配事件,且棒控電源系統(tǒng)中發(fā)電機(jī)的運(yùn)行狀態(tài)不同于常規(guī)并網(wǎng)發(fā)電機(jī);為了有效解決失磁保護(hù)失配問(wèn)題,需對(duì)棒控電源系統(tǒng)中發(fā)電機(jī)的失磁故障進(jìn)行重新解析。首先,根據(jù)轉(zhuǎn)差率和功角特點(diǎn)將失磁發(fā)展歷程劃分為等功角階段、異步運(yùn)行階段和周期異步運(yùn)行階段;其次,以發(fā)電機(jī)等效電路及相量圖為基礎(chǔ),以q軸電動(dòng)勢(shì)為切入點(diǎn),結(jié)合發(fā)電機(jī)基本方程,由各階段q軸電動(dòng)勢(shì)的變化解析得到各電氣量穩(wěn)態(tài)表達(dá)式;最后,通過(guò)實(shí)際機(jī)組的失磁實(shí)驗(yàn)數(shù)據(jù)以及基于PSCAD平臺(tái)的失磁故障仿真,全面驗(yàn)證了解析結(jié)果的正確性。該文給出的失磁故障解析過(guò)程為棒控電源系統(tǒng)發(fā)電機(jī)失磁保護(hù)方案的制定奠定了理論基礎(chǔ)。
核電站控制棒電源系統(tǒng) 發(fā)電機(jī)失磁 故障解析 故障分段
圖1 完整棒控電源系統(tǒng)結(jié)構(gòu)圖
由于對(duì)RAM系統(tǒng)發(fā)電機(jī)的失磁過(guò)程認(rèn)識(shí)不清,工程實(shí)際中僅采用簡(jiǎn)單的轉(zhuǎn)子低電流作為保護(hù)判據(jù),導(dǎo)致現(xiàn)場(chǎng)發(fā)生多起保護(hù)失去選擇性而誤動(dòng)的事件。如2019年11月14日,某百萬(wàn)kW級(jí)核電站并列運(yùn)行的RAM系統(tǒng)中一列機(jī)組因故障導(dǎo)致失磁,進(jìn)而造成正常列過(guò)電流。由于當(dāng)前采用的轉(zhuǎn)子低電流判據(jù)適用性存在問(wèn)題,使得正常列過(guò)電流保護(hù)動(dòng)作將正常列切除,故障列失磁保護(hù)動(dòng)作將故障列切除,兩列系統(tǒng)全部失效,控制棒線圈失電落棒導(dǎo)致反應(yīng)堆停堆,給核電站造成了巨大的經(jīng)濟(jì)損失。
同步發(fā)電機(jī)失去勵(lì)磁是發(fā)電機(jī)勵(lì)磁回路常見的故障,發(fā)電機(jī)失磁不僅會(huì)影響自身安全,還可能會(huì)危及整個(gè)系統(tǒng)的穩(wěn)定運(yùn)行[2-6]。現(xiàn)有的失磁故障特征分析主要針對(duì)并網(wǎng)發(fā)電機(jī)。并網(wǎng)發(fā)電機(jī)發(fā)生失磁后,伴隨著失磁程度的加深,主要有發(fā)電機(jī)無(wú)功功率反向、系統(tǒng)電壓降低、定子過(guò)電流及轉(zhuǎn)子過(guò)熱等特點(diǎn),且發(fā)電機(jī)以低轉(zhuǎn)差率聯(lián)網(wǎng)運(yùn)行,輸出一定的有功功率[7-11]。
目前對(duì)并網(wǎng)發(fā)電機(jī)失磁研究,主要分為定性和定量分析兩方面。定性分析的技術(shù)路線為根據(jù)發(fā)電機(jī)失磁后的運(yùn)行狀態(tài)將整個(gè)失磁歷程分為等有功階段、異步運(yùn)行階段和穩(wěn)態(tài)異步運(yùn)行階段,并闡述了各階段電氣量變化規(guī)律;其中,文獻(xiàn)[3,7,12]基于Matlab對(duì)單機(jī)無(wú)窮大系統(tǒng)進(jìn)行失磁仿真,并按階段對(duì)電氣量變化規(guī)律進(jìn)行了說(shuō)明。定量分析主流技術(shù)路線為通過(guò)建立發(fā)電機(jī)數(shù)學(xué)模型,將失磁故障特征量化為方程,代入發(fā)電機(jī)數(shù)學(xué)模型求解,進(jìn)而得到定轉(zhuǎn)子側(cè)各電氣量的時(shí)域表達(dá)式[13-16]。
針對(duì)發(fā)電機(jī)模型,文獻(xiàn)[17]給出了四種發(fā)電機(jī)失磁異步運(yùn)行的數(shù)學(xué)模型,包含傳統(tǒng)的Park模型、計(jì)及實(shí)心轉(zhuǎn)子渦流的定參數(shù)模型、計(jì)及實(shí)心轉(zhuǎn)子渦流的d軸三繞組變參數(shù)模型和計(jì)及實(shí)心轉(zhuǎn)子渦流的d軸兩繞組變參數(shù)模型,并通過(guò)失磁仿真,得出后兩種模型精度更高的結(jié)論。此外,文獻(xiàn)[18-19]從氣隙磁通密度諧波變化、轉(zhuǎn)子端部漏抗變化及渦流損耗計(jì)算角度出發(fā)考量發(fā)電機(jī)失磁后的動(dòng)態(tài)特性,并通過(guò)建立有限元模型求解,驗(yàn)證了方法的有效性。
明確失磁故障特征是制定保護(hù)方案的基礎(chǔ),因此對(duì)失磁過(guò)程的解析很關(guān)鍵。針對(duì)RAM系統(tǒng)發(fā)電機(jī)失磁故障解析,本文基于合理的假設(shè),由其等效電路與發(fā)電機(jī)數(shù)學(xué)模型,得到q軸電動(dòng)勢(shì)的一般表達(dá)式;按照發(fā)電機(jī)失磁后轉(zhuǎn)差率及功角特點(diǎn),將失磁發(fā)展歷程分為等功角階段、異步運(yùn)行階段及周期異步運(yùn)行階段;根據(jù)各階段q軸電動(dòng)勢(shì)表達(dá)式推導(dǎo)得到各電氣量的解析表達(dá)式,之后通過(guò)實(shí)際機(jī)組失磁實(shí)驗(yàn)數(shù)據(jù)和失磁仿真全面驗(yàn)證了解析結(jié)果的正確性。本文對(duì)RAM系統(tǒng)發(fā)電機(jī)失磁故障的解析為失磁保護(hù)方案的制定奠定了理論基礎(chǔ)。
為了突出RAM發(fā)電機(jī)失磁過(guò)程的主要規(guī)律,本文忽略次要因素,進(jìn)行以下假設(shè):
(1)認(rèn)為RAM機(jī)組具有足夠的無(wú)功支撐能力。當(dāng)對(duì)列具有足夠的無(wú)功供給能力,且忽略發(fā)電機(jī)磁飽和,則認(rèn)為母線出口電壓在故障發(fā)展過(guò)程中保持不變。
(2)忽略定、轉(zhuǎn)子間漏磁及阻尼繞組引起的次暫態(tài)過(guò)程。針對(duì)RAM系統(tǒng)失磁的研究最終要落實(shí)到保護(hù)優(yōu)化上,側(cè)重于失磁后各電氣量穩(wěn)態(tài)時(shí)的規(guī)律,因此忽略定轉(zhuǎn)子漏磁及阻尼繞組引起的次暫態(tài)變化過(guò)程。
圖2 單列RAM機(jī)組等效電路
圖3 RAM隱極發(fā)電機(jī)穩(wěn)態(tài)運(yùn)行dq軸等效電路
根據(jù)圖4所示相量圖可以得到穩(wěn)態(tài)時(shí)機(jī)端電流表達(dá)式為
輸出有功功率及無(wú)功功率分別為
發(fā)電機(jī)轉(zhuǎn)子運(yùn)動(dòng)方程為
發(fā)電機(jī)任意時(shí)刻都有轉(zhuǎn)子方程式(6)成立。
由圖4發(fā)電機(jī)相量圖可知有
式中,各量均采用瞬時(shí)值,在發(fā)電機(jī)失磁后,RAM機(jī)組有足夠的無(wú)功功率支撐使得機(jī)端電壓保持不變,則有
將式(11)代入式(9)有
根據(jù)發(fā)電機(jī)失磁后的功角及轉(zhuǎn)差率特點(diǎn),可將RAM發(fā)電機(jī)失磁發(fā)展歷程劃分為等功角階段、異步運(yùn)行階段和周期異步運(yùn)行階段三個(gè)階段,如圖5所示。
等功角階段:原動(dòng)機(jī)輸出機(jī)械功率不能突變,發(fā)電機(jī)輸出有功減小,由式(5)可得,故障列轉(zhuǎn)子有加速趨勢(shì),正常列機(jī)組有減速趨勢(shì);而電動(dòng)機(jī)與發(fā)電機(jī)同軸連接一慣性質(zhì)量大的飛輪,因此轉(zhuǎn)速不能突變,所以功角在失磁初始階段不變,稱之為等功角階段。RAM系統(tǒng)發(fā)生失磁導(dǎo)致故障列q軸電動(dòng)勢(shì)衰減,由式(1)和式(2)可知,輸出電流和有功功率減小,無(wú)功功率減小乃至反向。正常列機(jī)組通過(guò)增加勵(lì)磁來(lái)增加無(wú)功功率輸出,輸出有功功率、無(wú)功功率及電流增加。此階段故障列發(fā)電機(jī)基本可視為同步運(yùn)行。
圖5 RAM發(fā)電機(jī)失磁發(fā)展歷程分段
異步運(yùn)行階段:隨著失磁程度加深,機(jī)組轉(zhuǎn)速突破飛輪限制出現(xiàn)緩慢變化。故障列功角和轉(zhuǎn)差率開始增加,與正常機(jī)組不同步,進(jìn)入異步運(yùn)行階段。故障機(jī)組定轉(zhuǎn)子之間出現(xiàn)相對(duì)運(yùn)動(dòng),在轉(zhuǎn)子上產(chǎn)生感應(yīng)電勢(shì),減緩了勵(lì)磁的衰減;隨著轉(zhuǎn)差率及功角增大,發(fā)電機(jī)輸出異步有功功率及從對(duì)列吸收無(wú)功功率增大;反向無(wú)功的增大及定子上的感應(yīng)電動(dòng)勢(shì)使得定子電流增加。在此階段中,正常列機(jī)組仍然基本為同步運(yùn)行。
1)等功角階段
對(duì)式(13)進(jìn)行積分求解,結(jié)合初始條件,有
根據(jù)式(1)~式(4)可得此階段故障機(jī)組輸出有功、無(wú)功及電流為
2)異步運(yùn)行階段
對(duì)式(20)進(jìn)行求解得
由于故障機(jī)組定子電壓仍是對(duì)稱三相交流電,因此產(chǎn)生的磁場(chǎng)為圓形旋轉(zhuǎn)磁場(chǎng),轉(zhuǎn)子相對(duì)于定子磁場(chǎng)的轉(zhuǎn)速為(為正常機(jī)組轉(zhuǎn)速),進(jìn)而在轉(zhuǎn)子側(cè)各繞組中感應(yīng)出頻率為(為正常機(jī)組頻率)的單相電流。此電流產(chǎn)生的功率是發(fā)電機(jī)異步運(yùn)行輸出有功的主要成分。
將式(22)代入式(3)中,可得縱軸方向勵(lì)磁繞組磁通與定子磁場(chǎng)作用產(chǎn)生的異步有功功率為
同理可得此階段輸出無(wú)功功率平均值為
定子電流變化規(guī)律可由有功功率、無(wú)功功率及機(jī)端電壓求出,即
3)周期異步運(yùn)行階段
電動(dòng)機(jī)參數(shù)見表1,發(fā)電機(jī)參數(shù)見表2。
表1 電動(dòng)機(jī)參數(shù)
Tab.1 Motor parameters
表2 發(fā)電機(jī)參數(shù)
Tab.2 Generator parameters
RAM系統(tǒng)電動(dòng)機(jī)、飛輪、發(fā)電機(jī)同軸連接,且電動(dòng)機(jī)無(wú)調(diào)速器。建模時(shí)將飛輪轉(zhuǎn)動(dòng)慣量等效進(jìn)電動(dòng)機(jī)慣量中,M-G機(jī)組耦合原理如圖6所示。電動(dòng)機(jī)運(yùn)行在轉(zhuǎn)矩控制模式,發(fā)電機(jī)運(yùn)行在轉(zhuǎn)速控制模式。將電動(dòng)機(jī)-發(fā)電機(jī)視為一個(gè)面向負(fù)荷的整體,由機(jī)組整體與負(fù)荷實(shí)現(xiàn)功率與轉(zhuǎn)矩的平衡;在機(jī)組內(nèi)部,發(fā)電機(jī)將對(duì)應(yīng)負(fù)荷條件下所需的電磁功率傳遞給電動(dòng)機(jī),由電動(dòng)機(jī)實(shí)現(xiàn)相應(yīng)功率下的轉(zhuǎn)速要求,并將此轉(zhuǎn)速傳遞至發(fā)電機(jī),使兩者運(yùn)行在同一轉(zhuǎn)速。
圖6 M-G機(jī)組耦合原理
由于PSCAD中發(fā)電機(jī)和電動(dòng)機(jī)模型的轉(zhuǎn)矩輸入輸出采取標(biāo)幺值,該標(biāo)幺值均以各自的額定轉(zhuǎn)矩作為基準(zhǔn)值。而系統(tǒng)中的電動(dòng)機(jī)和發(fā)電機(jī)的額定轉(zhuǎn)矩不同,本文將發(fā)電機(jī)額定電磁轉(zhuǎn)矩與電動(dòng)機(jī)額定電磁轉(zhuǎn)矩之比定義為轉(zhuǎn)矩耦合系數(shù),由該系數(shù)來(lái)實(shí)現(xiàn)兩者轉(zhuǎn)矩的匹配。
由于發(fā)電機(jī)電樞繞組電阻很小,忽略電樞繞組上產(chǎn)生的損耗,有
發(fā)電機(jī)額定電磁轉(zhuǎn)矩為
電動(dòng)機(jī)額定轉(zhuǎn)矩計(jì)算公式為
因此由式(27)可得轉(zhuǎn)矩耦合系數(shù)為
圖7 失磁機(jī)組波形對(duì)比
圖8 正常機(jī)組波形對(duì)比
兩機(jī)組勵(lì)磁電流實(shí)際錄波值與仿真值對(duì)比如圖9所示。為便于對(duì)比,已將仿真波形時(shí)間與錄波時(shí)間對(duì)齊。
圖9 勵(lì)磁電流仿真值與錄波值對(duì)比
由圖9可知,在失磁后的1.2s內(nèi),隨著失磁列機(jī)組勵(lì)磁電流從0.8(pu)降至0.2(pu),正常列機(jī)組的勵(lì)磁電流從1.2(pu)升高至2.1(pu);由圖7及圖8可知,整個(gè)失磁過(guò)程中機(jī)端電壓穩(wěn)定在1(pu);失磁機(jī)組因從對(duì)列吸取無(wú)功功率,導(dǎo)致機(jī)端電流增大,而正常機(jī)組增發(fā)無(wú)功功率導(dǎo)致機(jī)端電流增大。
由圖7~圖9可知,仿真模型中的機(jī)端電壓、電流和勵(lì)磁電流變化情況與原始錄波數(shù)據(jù)基本吻合,進(jìn)一步驗(yàn)證了模型的正確性。因此,仿真模型可以正確模擬出實(shí)際機(jī)組中各電氣量變化過(guò)程,對(duì)于實(shí)驗(yàn)過(guò)程中無(wú)法測(cè)取的發(fā)電機(jī)功角和轉(zhuǎn)差率以及更多工況和時(shí)間尺度的數(shù)據(jù)可采用仿真值進(jìn)行分析。失磁過(guò)程中功角及轉(zhuǎn)差率的仿真波形如圖10所示。
圖10 功角及轉(zhuǎn)差率波形
本文所推導(dǎo)出的等功角階段q軸電動(dòng)勢(shì)變化規(guī)律如式(15)所示,則由本次失磁實(shí)驗(yàn)及對(duì)圖9a中曲線進(jìn)行擬合可得失磁機(jī)組q軸電動(dòng)勢(shì)變化規(guī)律為
由式(16)和式(17)可知,失磁機(jī)組輸出有功功率和無(wú)功功率分別為
經(jīng)由式(33)和式(34)計(jì)算得到的功率解析值與實(shí)際仿真值對(duì)比如圖11所示。
由圖11對(duì)比結(jié)果可知,等功角階段解析結(jié)果與仿真結(jié)果相吻合,驗(yàn)證了解析過(guò)程的正確性。隨著失磁程度加深,功角及轉(zhuǎn)差增大,機(jī)組進(jìn)入異步運(yùn)行階段,即失磁機(jī)組相對(duì)正常機(jī)組異步運(yùn)行。而本次實(shí)驗(yàn)出于安全考慮,只進(jìn)行了較短時(shí)間內(nèi)輕負(fù)載水平下發(fā)生部分失磁的實(shí)驗(yàn),因此實(shí)驗(yàn)數(shù)據(jù)無(wú)法對(duì)異步運(yùn)行階段及周期異步運(yùn)行階段進(jìn)行驗(yàn)證。
3.3.1 等功角階段
圖12 等功角階段功角及勵(lì)磁電流波形
圖13 等功角階段其余各電氣量波形
由圖12b可知,實(shí)際勵(lì)磁電流失磁后的衰減規(guī)律與理論一致,均呈指數(shù)規(guī)律變化。之所以實(shí)際衰減值高于理論值,是因?yàn)樵诘裙请A段,兩列機(jī)組功角仍出現(xiàn)了較小差別,進(jìn)而在轉(zhuǎn)子繞組上產(chǎn)生感應(yīng)電動(dòng)勢(shì),減緩了勵(lì)磁電流的衰減。
故障機(jī)組發(fā)生失磁,需要從相鄰機(jī)組吸取無(wú)功來(lái)維持自身磁場(chǎng),而正常列有足夠的無(wú)功支撐能力,因此可以維持出口母線電壓在整個(gè)失磁階段內(nèi)維持不變。
3.3.2 異步運(yùn)行階段
圖14 異步運(yùn)行階段各電氣量波形
3.3.3 周期異步運(yùn)行階段
圖15 周期異步運(yùn)行階段各電氣量波形
將上述RAM系統(tǒng)發(fā)電機(jī)失磁過(guò)程與并網(wǎng)發(fā)電機(jī)失磁過(guò)程進(jìn)行對(duì)比總結(jié),見表3。
表3 失磁過(guò)程總結(jié)
Tab.3 Summary of demagnetization process
由表3明顯得知,RAM系統(tǒng)發(fā)電機(jī)的失磁過(guò)程與并網(wǎng)發(fā)電機(jī)有顯著差異。
本文以核電站RAM系統(tǒng)為研究對(duì)象,對(duì)RAM發(fā)電機(jī)失磁故障特征展開了定性分析和定量解析。定性分析為根據(jù)失磁后功角及轉(zhuǎn)差率特點(diǎn),將整個(gè)失磁發(fā)展歷程分為等功角階段、異步運(yùn)行階段和周期異步運(yùn)行階段。定量分析為根據(jù)各階段q軸電動(dòng)勢(shì)的變化,解析得到各階段電氣量一般表達(dá)式,并通過(guò)失磁實(shí)驗(yàn)錄波數(shù)據(jù)和失磁仿真全面驗(yàn)證了解析結(jié)果的正確性。上述失磁故障解析工作為制定失磁保護(hù)方案及提高核電站的安全穩(wěn)定運(yùn)行提供了依據(jù)。本文并未對(duì)RAM系統(tǒng)失磁保護(hù)方案進(jìn)行討論,需要進(jìn)一步研究。
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Analysis of Generator Loss of Field Fault in Nuclear Power Plant Control Rod Power System
Xiao Xiangtao1Hao Liangliang1Liang Zhengqiu1He Peng2Wu Pengfei3
(1. School of Electrical Engineering Beijing Jiaotong University Beijing 100044 China 2.Liaoning Hongyanhe Nuclear Power Co. Ltd Dalian 116001 China 3. Yangjiang Nuclear Power Co. Ltd Yangjiang 529599 China)
Nuclear power plant control rod power is the only power supply system of control rod drive mechanism, to ensure the safe and reliable operation of this system is of great significance to improve the safety of nuclear power plants. The principle of loss of field protection is simple, and many mismatch events of loss of field(LOF) protection have occurred on site; the operation state of the control rod power system generator is different from that of the conventional grid-connected generator; In order to effectively solve the loss of field protection mismatch problem, this paper has carried out the qualitative analysis and quantitative analysis of the loss of field fault of the generator in control rod power system.
Firstly, it is assumed that the RAM unit has sufficient reactive power support capacity and ignores the magnetic leakage between stator and rotor and the sub transient process caused by damping winding, and the general expression of longitudinal potential is obtained on the basis of the equivalent circuit of RAM system and the mathematical model of generator. Since the variation quantity of power angle of fault-unit essentially reflects the accumulation of the speed difference between two units in time dimension, the loss of field development process is divided into equal power angle phase, asynchronous operation phase and periodic asynchronous operation phase according to the slip rate and power angle characteristics. Fault-unit generator can be regarded as synchronous operation in equal power angle phase, while normal-unit generator can be regarded as synchronous operation in asynchronous operation phase and periodic asynchronous operation phase.
After that, according to the segmentation method of the loss of field process of RAM units and taking the longitudinal potential as the starting point, the analytical expressions of electrical quantities in each phase are obtained from the longitudinal potential variation law in each stage and the basic equation of generator. The specific analytical process is given by taking the sudden complete loss of field voltage of RAM system as an example.
In order to fully verify the correctness of the analytical results of loss of field, experimental verification and simulation verification are carried out respectively.
Through the experimental data of partial loss of field in an actual nuclear power plant under light load level and combined with correct simulation model, the actual simulation values of active power and reactive power of the field loss unit are compared with the theoretical analysis values and the results are found to be very consistent, which verifies the correctness of analytical results of equal power angle phase after loss of field.
Furthermore, the simulation model verified by the experiment is used to simulate the fault of complete loss of field under two-generator parallel operation and full load level, and the simulation parameter settings are that total simulation duration is 100s and one RAM unit loses field voltage at 20s. The results show that, the variation of electrical quantities in each phase is consistent with theoretical analysis, and the loss of field process of RAM system generator is significantly different from that of grid-connected generator.
The analytical process of loss of field fault lays a theoretical foundation for the formulation of generator loss of field protection plan of the control rod power system.
Nuclear power plant control rod power system, generator loss of field, fault analysis, fault block
10.19595/j.cnki.1000-6753.tces.211667
TM341
中廣核集團(tuán)公司科技項(xiàng)目(3100077013)和中央高?;究蒲袠I(yè)務(wù)費(fèi)項(xiàng)目(2020JBM070)資助。
2021-10-20
2022-01-20
肖項(xiàng)濤 男,1996年生,碩士,研究方向?yàn)殡娏ο到y(tǒng)主設(shè)備故障分析及保護(hù)。E-mail:19121511@bjtu.edu.cn
郝亮亮 男,1985年生,副教授,博士生導(dǎo)師,研究方向?yàn)殡娏ο到y(tǒng)主設(shè)備故障分析及保護(hù)、直流輸電控制與保護(hù)、勵(lì)磁控制。E-mail:llhao@bjtu.edu.cn(通信作者)
(編輯 郭麗軍)