Sceimhle Dearbhaíochta Aisteoireachta do 12kV Air-Insulated Ring Main Unit Isolating Gap chun Anéas Imtharraingt a Líomh

Leithis an tionscadal forbartha na tionscal cumhachta, tá an ciorcal iompair láidir, sábháilte agus comhshaoil go doimhne cruinnithe isteach sa dheidhmeas agus an tionscadal de shainleictreacha aonair. Is é an Ring Main Unit (RMU) údar oibre leictreach tábhachtach i lúiní roinnt. Is é sláinte, comhshaoil, ionsaitheacht, feidhmniúchán éifeachtach agus eacnamaíocht níos mó éimeartha i bhfeidhmíocht. Tá RMUt ar an gcaoi traidisiúnta SF6 gas-insulated RMUs. Mar gheall ar ard-leibhéal SF6 arc-extinguishing agus insuláid ard, tá siad tar éis a bheith cuireadh go forleathan. Ach, SF6 cuireann an tionscadal ghlas. Le meastachán rialtais ag dul suas ar ghaisceana ghlas, is é forbairt RMUs gas-insulated comhshaoil mar chuid den SF6 éimeartha.

Faoi láthair, tá RMUs gas-insulated comhshaoil ina measc nitrogen-insulated RMUs agus dry air-insulated RMUs. Tá na roghanna seo curtha amach sa litríocht. Comhfhreagras le insuláid SF6, is é insuláid nitrogen agus dry air ach trí nóiméad. Mar sin, is é a chinntiú nach mbeidh an insuláid RMU agus na scuabanna iontracha ina ndianchúlóid as an laghdú insuláid an méid, agus cothrom le dáta cabinet spás, go háirithe tábhachtach. Is é seo go príomha léirítear i dheidhmeas leictreach agus struchtúr insuláid. Is féidir a dhéanamh a dheighnéise leictreach agus struchtúr insuláid a chur chun cinn a chur chuige don insuláid an méid.

Is é an taighde seo a dhíríonn ar an bpoll insuláid i 12kV air-insulated RMU. Díríonn sé ar an réimse reatha agus a neamhionrach, measann insuláid an áit, agus déanann struchtúr optimalú chun an dóchas a laghdú agus insuláid a fheabhsú. Is é an aidhm atá ann a thabhairt amach a thabhairt a chur faoi deara do sheanraíocht insuláid na mbuill cosúil.

​1 Struchtúr an Air-Insulated RMU​

Tá an modh struchtúr 3D air-insulated RMU a staidéar sa phapier seo léirítear in Figure 1. Tá an struchtúr príomhchiorcal RMU ag cleachtadh scéim a chombhaint vacuum switch agus three-position switch. Tá an réimse ag cleachtadh scéim ina bhfuil three-position switch suite ar an busbar láthair, seachas, tá three-position switch suite ar an taobh uachtarach den RMU, agus tá an vacuum switch suite ar an taobh íochtarach trí pole solid-insulated.

Ós rud é go bhfuil an vacuum switch incapsulated laistigh den pole, tá a barrach agus insuláid epoxy resin. Is é an insuláid epoxy resin go leor níos fearr ná an aer, mar sin, chun insuláid riail a chur i bhfeidhm. Níos mó, tá an busbar ceangailte ag an taobh sealda pole solid-insulated ag cleachtadh rounded corners, designs curve, agus silicone rubber seal, solú freisin a dhéanamh partial discharge a fhadhb an áit. Tá an insuláid clearances idir busbars agus an talamh deartha de réir insuláid riail agus maolú.

Bhíonn an bláth insuláid three-position switch go hiomlán ag brath ar an gaol aer. Mar aon cheangailte gluaiseach, tá a struchtúr deartha ag cleachtadh cuid metal pin, springs, disc springs, agus retaining rings chun a chur faoi mhórdhromchla idir bláth insuláid. Ach, mar gheall ar an gcruth speisialta na cuid metal, is féidir leo a dhéanamh an réimse reatha go neamhionrach, ag cruthú partial discharge. Is é seo a chuir an tionscal a dhíbríú, ag cur isteach ar an insuláid an áit. Mar sin, is é an dearadh leictreach anseo go háirithe tábhachtach.

De réir riail dearadh na tuairisc, caithfidh an poll insuláid a choinnigh rated short-time power-frequency withstand voltage 50kV. Tá an electrical clearance íosta poll insuláid deartha mar 100mm. Ag smaoineamh ar an gcruinneas struchtúr bláth insuláid, gradings shields cuireadh ar an da thaobh den bláth insuláid chun a fheabhsú an réimse reatha ionrach agus a laghdú partial discharge. Tá an modh 3D three-position switch léirítear in Figure 2. De réir sin, déanann an taighde seo anailís reatha simuláid ar an poll insuláid.

Bhí software finite element ag cleachtadh an reatha simuláid RMU, ag anailís an reatha intinsity distribution across the isolating gap faoi 50kV rated short-time power-frequency withstand voltage. Bhí dhá scénario reatha simuláid electrostatic curtha amach:

• ​Scénario 1:​​ Busbar láthair (láthair le bláth insuláid static contact seat) ceangailte le íosta potential (0V), line láthair (láthair le bláth insuláid head) ceangailte le hard potential (50kV).
• ​Scénario 2:​​ Busbar láthair (láthair le bláth insuláid static contact seat) ceangailte le hard potential (50kV), line láthair (láthair le bláth insuláid head) ceangailte le íosta potential (0V).

Bhí an reatha distributions ag an áit reatha intinsity íosta san poll insuláid do dhá scénario fuarthas ón simuláid. Tá an reatha intinsity distribution ag an bláth insuláid head do Scénario 1 léirítear in Figure 3, agus sin ag an bláth insuláid static contact seat do Scénario 2 léirítear in Figure 4. Tá an reatha intinsity íosta in Scénario 1 ag an deireadh gradings shield, measuring 7.07 kV/mm. Tá an reatha intinsity íosta in Scénario 2 ag an chamfer bláth insuláid static contact seat, measuring 4.90 kV/mm.

Is é an critical breakdown reatha strength air faoi choinníllí standard go minic 3 kV/mm. Léiríonn Figures 3 agus 4 go dtí go raibh áiteanna áitiúla san poll insuláid os cionn 3 kV/mm, an reatha intinsity i réimsí eile fós thíos an teorainn, mar sin, is é an tionscal a dhíbríú neamhdhírbhíoch. Ach, beidh partial discharge ag cruthú sa áiteanna áitiúla ina bhfuil an reatha intinsity os cionn 3 kV/mm.

Nuair a athraíonn aer ó driobhach go mearbhallach, laghdóidh a insuláid capability. Is é an critical breakdown reatha strength faoi choinníllí uniform field faoi 3 kV/mm. Níos mó, is é an reatha distribution go neamhionrach go minic cuireann síos an critical breakdown reatha strength air. Dhá facht is éard a chuiríonn an dóchas agus an tionscal a dhíbríú. Chun a laghdú an tionchar de choinníllí comhshaoil, agus a fheabhsú an coefficient ionrach reatha, is é an aidhm atá ann a thabhairt amach a chur faoi deara do degree of ionrach reatha distribution agus an withstand voltage value of the gap. Is é seo a chur faoi deara chun a fheabhsú an insuláid capability of the isolating gap.

​3 Carachtair Insuláid Aer​

​3.1 Meastachán Coefficient Reatha Neamhionrach​

Níl reatha fields ionrach go hiomlán i bhfeidhm; go leor reatha fields is é neamhionrach. De réir an coefficient neamhionrach f, reatha fields is é dhá chineál: slightly neamhionrach reatha fields nuair f ≤ 4; agus go minic neamhionrach reatha fields nuair f > 4. Is é an coefficient reatha neamhionrach f a chur chun cinn de réir f = E_max / E_avg, áit a E_max is é an local reatha intinsity íosta, fuarthas ón simuláid results, agus E_avg is é an average reatha intinsity, a chur chun cinn de réir an applied voltage roinnte ar an electrical clearance íosta.

De réir Figure 3, E_max = 7.07 kV/mm agus E_avg = 0.5 kV/mm (50kV / 100mm). Mar sin, is é an coefficient neamhionrach poll insuláid f = 14.14 > 4, classifying it as an extremely non-uniform field. Stable partial discharge phenomena can form near extremely non-uniform fields. The greater the degree of non-uniformity, the more pronounced the partial discharge, and the larger the discharge magnitude. For a 12kV RMU, the requirement is that the total partial discharge of the entire cabinet should be less than 20pC. Reducing the non-uniformity coefficient f is beneficial for decreasing partial discharge magnitude.

​3.2 Meastachán Withstand Voltage Aer​

Tá an coefficient neamhionrach tionchar a chur ar an withstand voltage dry air. Nuair a bhíonn an reatha slightly neamhionrach, is é an withstand voltage:
​Fómhar (1)​​

Áit:

• U is the withstand voltage.
• d is the minimum electrical clearance between electrodes.
• k is a reliability factor, typically ranging from 1.2 to 1.5 based on experience.
• E₀ is the gas breakdown electric field strength. In practice, this value relates to the electrode structure. The air breakdown field strength varies under different electrode structures and clearances. For comparative analysis in this paper, E₀ = 3 kV/mm is tentatively set.

De réir Fómhar (1), is féidir a chur chun cinn an electrical clearance íosta d or a laghdú an coefficient neamhionrach f chun a fheabhsú an withstand voltage air. Nuair a bhíonn an reatha go minic neamhionrach, for electrodes with a minimum clearance d around 100mm, is é an withstand voltage a chur chun cinn de réir:
​Fómhar (2)​​

Áit is the lightning impulse 50% breakdown voltage for the electrode with an electrical clearance of d. In extremely non-uniform fields, breakdown voltage exhibits significant dispersion and a long discharge time delay, making it highly unstable.

In engineering practice, U_50%(d) is determined through multiple lightning impulse tests: the applied voltage at which breakdown occurs with a 50% probability is defined as U_50%(d). This value depends on the product structure and the degree of field uniformity. It is established that a lower non-uniformity coefficient results in smaller breakdown voltage dispersion, higher breakdown voltage, and consequently, a higher withstand voltage. Therefore, reducing the non-uniformity coefficient f improves the withstand voltage of the isolating gap.

​4 Structural Optimization​

To improve the uniformity of the electric field around the isolating blade head and reduce the non-uniformity coefficient, the grading shield structure was optimized.

Compared to the original design, the optimized grading shield features a thickened end with a rounded corner design. The fillet radius was increased from 0.75mm to 4mm, enhancing the curvature radius in this area, which benefits achieving more uniform field distribution. The electric field intensity distribution at the optimized isolating blade head is shown in Figure 7. The figure shows the maximum electric field intensity at this location is now 3.66 kV/mm, approximately half of the value before optimization, indicating significant improvement.

Based on the formula f = E_max / E_avg, the electric field non-uniformity coefficient after optimization is 7.32. Compared to the pre-optimization state, this value is reduced to about half. The uniformity of the electric field near the isolating blade head has also significantly improved, demonstrating the reasonableness of the structural optimization.

The optimized grading shield structure indeed reduces the risk of breakdown discharge across the isolating gap. However, the electric field across the gap remains extremely non-uniform, and its withstand voltage is still determined by U_50%(d). The extent to which the withstand voltage can be increased needs to be determined through subsequent field tests.

​5 Conclusion​

Through electric field analysis of the isolating gap in a 12kV air-insulated RMU, this paper reached the following conclusions:

1. Due to the inferior insulation capability of air compared to SF6, using air for insulation in the three-position switch within RMUs requires improving electric field distribution to enhance insulation capability.
2. Due to the structural complexity of moving parts (the isolating blade) within the three-position switch of air-insulated RMUs, the electric field intensity distribution at localized positions can become highly non-uniform. To reduce non-uniformity, grading shields can be added on both sides of the isolating blade to shield the electric field intensity near the ends of the blade connectors, shifting the maximum local field intensity to the ends of the grading shields. This paper increased the curvature radius of the grading shield end from 0.75mm to 4mm. This reduced both the maximum local electric field intensity and the non-uniformity coefficient to approximately half their original values, achieving the desired effect.
3. The degree of electric field uniformity, or the non-uniformity coefficient, significantly impacts partial discharge and breakdown discharge. Extremely non-uniform fields easily lead to stable partial discharge (corona discharge). For both slightly and extremely non-uniform fields, a higher non-uniformity coefficient corresponds to a lower withstand voltage between the two electrodes.