JP4091402B2

JP4091402B2 - Electric field relaxation material, electric field relaxation member using this material, and electromagnetic coil

Info

Publication number: JP4091402B2
Application number: JP2002328411A
Authority: JP
Inventors: 徹志岡本; 和哉瀬川; 誠河原; 利光山田; 浩幡野; 憲之岩田; 良之井上
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2002-11-12
Filing date: 2002-11-12
Publication date: 2008-05-28
Anticipated expiration: 2022-11-12
Also published as: JP2004165355A

Description

【０００１】
【発明の属する技術分野】
本発明は、安定した電気抵抗特性を有する電界緩和材料及びこの材料を用いた電界緩和部材並びに電磁コイルに関する。
【０００２】
【従来の技術】
従来、電界を和らげることを目的として、高電界を発生する導体端部、例えば電磁コイルのコイルエンド部に電界緩和材を設けることが知られている。
【０００３】
この電界緩和材としては、電界に対して非線形な抵抗を持つ炭化珪素（ＳｉＣ）と四三酸化鉄を組合せたものがある（例えば、特許文献１参照）。
【０００４】
図１４は、かかる電磁コイルのコイルエンド部を示す断面図である。
【０００５】
図１４において、１はコイル導体で、このコイル導体１の周囲部には絶縁層２が形成され、その外周面に電界緩和材として導電性塗料層３とＳｉＣ塗料層４を組合せて設けられている。
【０００６】
この材料は、優れた電界緩和効果を示すが、一方で周囲の状況、例えば製造時の温度条件や配合比のばらつきなどが変化した場合、それに伴って電界緩和能力が低下することがあった。
【０００７】
【特許文献１】
特公昭６１−３７７２１号公報
【０００８】
【発明が解決しようとする課題】
このように電界緩和材の特性が周囲の条件によりばらつくと、製品の性能低下につながる。特に機器の高電圧化が進む中、許容される特性のばらつきは狭くなってきている。
【０００９】
本発明は上記のような事情に鑑みてなされたもので、周囲条件の変化に対して鈍感な特性を持つ安定した且つ放電抑制特性に優れた電界緩和材料及びこの材料を用いた電界緩和部材並びに電磁コイルを提供することを目的とする。
【００１０】
【課題を解決するための手段】
本発明は上記の目的を達成するため、次のような電界緩和材料とするものである。
【００１１】
本発明は、非線形抵抗を持つ粒子と線形抵抗を示す粒子を樹脂中に分散してなる複合材料において、前記線形抵抗を示す粒子の体積比率が、前記非線形抵抗を持つ粒子を除く体積に対する線形抵抗を示す粒子の体積比率をｐとした場合に、非線形を示さない電界で測定した電気抵抗ρとｐの間にｌｏｇρ∝（ｐ−ｐｃ）^-k（ｋは正の整数）なる関係が示されるある体積比率ｐｃ以上である。
【００１２】
【発明の実施の形態】
以下本発明の実施の形態を図面を参照して説明する。
【００１３】
図１は、本発明の第１の実施形態における電界緩和材料の組成を示す模式図である。
【００１４】
本実施形態では、図１に示すように非線形抵抗を持つ粒子５と線形抵抗を示す粒子６の塊をバインダー樹脂７中に分散してなる複合材料において、線形抵抗を示す粒子５の体積比率が、非線形抵抗を持つ粒子を除く体積に対する線形抵抗を示す粒子の体積比率をｐとした場合に、非線形を示さない電界で測定した電気抵抗ρとｐとの間にｌｏｇρ∝（ｐ−ｐｃ）^-k（ｋは正の整数）なる関係が示されるある体積比率ｐｃ以上としたものである。
【００１５】
図２は、高密度ポリエチレン中にカーボン粒子を充填した材料の抵抗と配合比の関係を示したものである。
【００１６】
樹脂に金属粒子や導電性の粒子を分散させると、電気抵抗は２ヶ所の折れ曲がりを持つ曲線で示されることが知られている。この現象はパーコレーション理論により説明される。
【００１７】
これまでの研究で、特に高充填量側の折れ曲がる点は、パーコレーション閾値ｐｃであり、導電性粒子の体積比率ｐと抵抗ρの間には、ｌｏｇρ∝（ｐ−ｐｃ）^-k（ｋは正の整数）なる関係があることが示されている。
【００１８】
この考え方は、１種類の充填材を配合した材料に対して有効であることが知られていた。本発明者等は、この理論に関して２種類の充填材を含む系に拡大する研究を進めると共に、非線形抵抗を含む系に拡大する研究を進めた結果、非線形抵抗を示す炭化珪素と線形抵抗を持つ四三酸化鉄を充填した複合材料において、四三酸化鉄のパーコレーション閾値ｐｃ（Ｆｅ₃Ｏ₄）は、他方である炭化珪素粒子を除いた体積に対する体積比率ｐ（Ｆｅ₃Ｏ₄）と低電界の抵抗ρの間にｌｏｇρ∝（ｐ−ｐｃ）^-k（ｋは正の整数）なる関係が示されることを明らかにした。
【００１９】
すなわち、図１において、非線形抵抗を示す粒子５と線形抵抗を示す粒子６の塊をバインダー樹脂７中に分散した電界緩和材料を考えた場合、低電界領域の電気抵抗を決定する線形低抵抗を示す粒子が作る電気伝導路に注目する。このとき、パーコレーション閾値として、非線形抵抗を示す粒子を除いた体積に対して考えた場合の浸透現象を考えればよいことを編み出したものである。
【００２０】
図３は、非線形抵抗材料である炭化珪素粒子を全体量に対して２４．３ｖｏｌ％含んだポリブタジエン樹脂に線形抵抗材料である四三酸化鉄を分散した複合材料の低電界領域での体積抵抗率を示すもので、２つの折れ曲がり曲線を持つ曲線で描かれている。
【００２１】
このパーコレーション閾値直下の領域では、体積比率の変化量に対して電気抵抗が大きく変化する領域にあると考えることができるため、本発明者等は特にこのパーコレーション閾値以上の配合比に注目し、材料を製造することを考え出した。
【００２２】
図４は、炭化珪素と四三酸化鉄をポリブタジエン中に分散させた電界緩和材料をガラスクロステープに塗布し、乾燥させた後、溶解性の高い溶媒中に浸漬し、その後取り出して硬化させたテープ状サンプルの電気抵抗値を示している。
【００２３】
図４において、横軸が炭化珪素を除く樹脂分の体積に対する四三酸化鉄の体積比率を示している。
【００２４】
ここで、これらのテープ材料に対するパーコレーション閾値は、上述の式を用いて溶解性の高い溶媒中に浸漬せずに硬化させたテープ材料の低電界領域の電気抵抗と配合比の関係から、１２ｖｏｌ％であることが分かった。
【００２５】
本実施形態では、炭化珪素を除く樹脂分の体積に対する四三酸化鉄の体積比率が、パーコレーション閾値（１２ｖｏｌ％）以上であることが特徴であり、体積比率として１５ｖｏｌ％を採用した。
【００２６】
比較例として、炭化珪素を除く樹脂分の体積に対する四三酸化鉄の体積比率が、１０ｖｏｌ％と１１ｖｏｌ％のものを示すが、明らかに１２ｖｏｌ％以下ではばらつきが大きく、特性が不安定になることが示されている。
【００２７】
このように第１の実施形態では、非線形抵抗を持つ粒子５と線形抵抗を示す粒子６の塊をバインダー樹脂７中に分散してなる複合材料において、線形抵抗を示す粒子５の体積比率が、非線形抵抗を持つ粒子を除く体積に対する線形抵抗を示す粒子の体積比率をｐとした場合に、非線形抵抗を示さない電界で測定した電気抵抗ρとｐとの間にｌｏｇρ∝（ｐ−ｐｃ）^-k（ｋは正の整数）なる関係が示されるある体積比率ｐｃ以上とすることにより、電気抵抗特性の安定した電界緩和材料を得ることができる。
【００２８】
なお、非線形抵抗を示す粒子としては、炭化珪素のほかに酸化亜鉛が考えられる。
【００２９】
図５は、本発明の第２の実施形態における電界緩和材料の組成を示す模式図で、図１と同一要素には同一符号を付してその説明を省略し、ここでは異なる点について述べる。
【００３０】
第２の実施形態では、図５に示すように線形抵抗を示す粒子８の体積抵抗率が１０^7.25〜１０^10.5Ωｍとするものである。
【００３１】
非線形抵抗を示す粒子５と線形抵抗を示す粒子６を樹脂中に含む複合材料であるが、この線形抵抗６を示す粒子が１０^7.25〜１０^10.5Ωｍの抵抗を持つ。
【００３２】
図６は、コイル導体周囲にマイカ層による主絶縁を形成し、その周囲に電界緩和層を設けると共に、中心部に電極を設け、この中心部をアース電位として、コイル導体に高電圧を印加した場合の沿面放電破壊電圧と電界緩和層の電気抵抗率の関係を示したものである。
【００３３】
沿面放電破壊電圧は、電気抵抗率に対して凸の形状を呈している。ここで、回転電機のコイルは、定格電圧をＥとして、３×ＥＶの耐圧試験に合格する必要がある。図６に示したコイルは、２３ｋＶ級コイルであるため、破壊電圧として６９ｋＶ以上の値を示す必要がある。この観点から、電界緩和材料として、１０^7.25〜１０^10.5Ωｍの抵抗を持つことが好ましい。
【００３４】
本発明者等は、非線形抵抗特性を示す炭化珪素素子と線形抵抗を示す四三酸化鉄の複合材料の非線形抵抗特性を様々な配合比に対して測定し、これらの複合材料の非線形抵抗特性は、図７に示す非線形抵抗を示す炭化珪素粒子からなる伝導路に起因する非線形抵抗９と線形抵抗を示す四三酸化鉄からなる伝導路に起因する線形抵抗１０の平行回路によって説明できることを明らかにした。
【００３５】
すなわち、低電界領域の抵抗値は線形抵抗を示す粒子の体積抵抗率に依存して変化する。しかも、線形抵抗を示す粒子の配合比が非線形抵抗を持つ粒子を除く体積に対する線形抵抗を示す粒子の体積で考えた場合のパーコレーション閾値以上であれば、材料の物性は線形抵抗を示す粒子の抵抗と極めて近づいた値になるからである。
【００３６】
そこで、線形抵抗を示す粒子の電気抵抗率が１０^7.25〜１０^10.5Ωｍであれば、極めて安定した、優れた放電抑制特性を持つ電界緩和材を得ることができる。
【００３７】
このような材料として、酸化錫を用いた試験を行った。非線形抵抗を示す粒子として酸化珪素を用い、線形抵抗を示す粒子として酸化錫を用いて、エポキシ樹脂中に混練し、しかる後硬化させて作成した板材料の体積抵抗率を測定した。酸化錫は高電界で弱い非線形を示すが、炭化珪素と比較して弱いため、線形と同様の動きになる。
【００３８】
図８は、この材料の体積抵抗率の電界依存性を示すグラフである。低電界の体積抵抗が１０⁸Ωｍであり、適した非線形抵抗を得ることができた。また、公知文献１にも記載されているように、１ｋｖ／ｃｍの電界での表面抵抗率は１０⁸Ωｍ以下であることが好ましい。
【００３９】
通常電界緩和層の厚みは、１mm程度であることから、体積抵抗率に換算すると１０⁵Ωｍである。図８から明らかなように、この材料はいずれの特性も満足する。
【００４０】
このように第２の実施形態では、線形抵抗を示す粒子８の体積抵抗率を１０^7.25〜１０^10.5Ωｍとすることにより、電気抵抗特性が安定し、且つ電界緩和能力の高い非線形抵抗材料を得ることができる。
【００４１】
なお、線形抵抗を示す粒子としては、酸化錫のほかに酸化クロム、酸化チタンなどが挙げられる。
【００４２】
図９は、本発明の第３の実施形態における電界緩和部材を示す斜視図である。
【００４３】
第３の実施形態では、図９に示すように前述した第１又は第２の実施形態で得られた電界緩和材料をシート状に成形して電界緩和部材１１を構成したものである。
【００４４】
第１又は第２の実施形態で得られた電界緩和材は電気抵抗性に優れた材料であり、この材料を塗料として用いることも可能であるが、例えば電磁コイルのコイルエンド部に塗布して使用する場合、斑になることがあり、その結果抵抗値にばらつきが発生するため、抵抗が低下してしまうことがある。
【００４５】
そこで、予め本電界緩和材をシート状に加工することにより安定した特性を得ることができる。
【００４６】
また、図１０に示すように電界緩和材料１３をクロスに塗布してテープ状にすることも可能である。この方法によれば、柔軟性が高く、電界緩和を行う対象物に密着しやすい構成を得ることができる。これらの塗料を塗布又は含浸する基材は、ポリエステルテープやコロナ侵食に強いガラス繊維の紡績、貼り合わせ、ロービング材を用いることが望ましい。
【００４７】
このように第３の実施形態では、第１又は第２の実施形態で得られた電界緩和材料をシート状又はテープ状に成形して電界緩和部材を構成することにより、作業性に優れ、電気抵抗が安定し、且つ優れた放電抑制特性を持たせることができる。
【００４８】
図１１は、本発明の第４の実施形態を示すコイルエンド部の斜視図である。
【００４９】
第４の実施形態は、図１１に示すように第３の実施形態で得られたテープ状の電界緩和部材１１をコイルエンド部に巻き付け、電界緩和層を形成するようにしたものである。
【００５０】
本実施形態では、回転機器の電磁コイルを対象として、絶縁を施した導体を束ねた後に主絶縁層であるマイカ層を巻回し、しかる後第３の実施形態で得られたテープ状の電界緩和部材１１を巻回し、樹脂含浸した後、押え板にてコイルの周囲を押え、スプリングにて保持した後、加温して硬化させて試験コイルを製作した。この場合、含浸レジンとしてバインダー樹脂と相溶性の高い溶剤を用いた。
【００５１】
このコイルの周囲にギャップ長１０mmの電極を銀ペーストにて設けて電気抵抗を測定した。
【００５２】
表１は、低電界での抵抗値及び抵抗値のばらつきを示している。
【００５３】
【表１】

【００５４】
この表より明らかなように四三酸化鉄の配合比がパーコレーション閾値直下のサンプルはばらつきが大きく、本実施形態はいずれも抵抗が安定していることが分かる。
【００５５】
このように本実施形態では、第３の実施形態で得られたテープ状の電界緩和部材１１をコイルエンド部に巻き付けて電界緩和層を形成することにより、安定した沿面放電特性を持つ電磁コイルを得ることができる。
【００５６】
図１２は、本発明の第５の実施形態を示す電磁コイルの構成図である。
【００５７】
本実施形態は、図１２に示すようにコイル１６の導体に第１又は第２の実施形態で得られた電界緩和材料による電界緩和層１８と低電界の電気抵抗率が非線形抵抗を示す充填材の固有抵抗以上である電界緩和材料による電界緩和層１９を２段階にして設けるようにしたものである。
【００５８】
電界緩和層の最も重要な特性は、コイルエンド部の沿面放電を抑制する点にある。図１１に示すように導体外周に施されている主絶縁層１５の外周には、固定子鉄心内部の放電防止用の導電性層が形成され、且つこの導電性層端に電気的に接触させて本実施形態の電界緩和層を設ける。
【００５９】
ここで、電界緩和層の電気抵抗としては、高すぎると導電性層と電界緩和層のつなぎ目部に高い電界が生じてしまうため、このつなぎ目部に放電が発生し易くなる。また、抵抗が低すぎるとコイルに与える電圧が高い場合には、電界緩和層端においても十分な電位上昇ができず、電界緩和層端にて放電を生じる。
【００６０】
そこで、第２の実施形態で得られた電界緩和材料を用いれば、最適な電界緩和を行うことができる。また、電圧の高いコイルの放電を抑制する方法として、抵抗の異なる電界緩和層を２段階に分けて用いる方法がある。
【００６１】
図１２において、電界緩和層１８は、非線形抵抗を示す充填材として炭化珪素を４０ｖｏｌ％、線形抵抗を示す充填材として四三酸化鉄を炭化珪素を除く体積に対して１５ｖｏｌ％をポリブタジエンに混練して形成したもので、第１の実施形態と同様の材料である。
【００６２】
また、電界緩和層１９は、非線形抵抗を示す炭化珪素を４０ｖｏｌ％、線形抵抗を示す充填材として四三酸化鉄を炭化珪素を除く体積に対して５ｖｏｌ％をポリブタジエンに混練して形成したもので、第１の実施形態で述べたように電気抵抗率は、配合比に対して２つの変極点を持つ曲線で描かれる。
【００６３】
高充填側の変極点にあたるパーコレーション閾値以上の領域では、電気抵抗率が安定することは既に述べた。同様に低充填側の変極点以下の領域でも電気抵抗が安定することが期待される。低充填側の変極点とは、図７に示した等価回路において、線形抵抗が存在しない状態、すなわち非線形抵抗を示す粒子の抵抗にのみ規定される領域であると判断できる。つまり、低電界の電気抵抗率が非線形抵抗を示す充填材の固有抵抗以上である材料を作ることによって安定した特性の材料が得られる。
【００６４】
図４に示したように四三酸化鉄の量が少なく、溶剤に浸漬する前の低電界の電気抵抗率が炭化珪素の低電界の固有抵抗率より高い材料は、浸漬後の抵抗値が安定していることが分かる。
【００６５】
しかしながら、図６に示したようにかかる高い抵抗値を持つ材料は、単独では十分な放電抑制能力を持たないことが分かる。そこで、図１２に示したような構成が考えられる。
【００６６】
電界緩和層１８の体積抵抗率は、１０⁶Ωｍ程度であり、電界緩和層１９の体積抵抗率は１０¹¹Ωｍ程度であった。これら単独では良い特性が得られないと考えられる。
【００６７】
図１３は、電界緩和層１８と電界緩和層１９及びこれらを２段階で組合せた場合の可視レベルでの沿面放電開始開始電圧及び沿面破壊電圧を示している。
【００６８】
従って、両者を組合せることにより、高い放電抑制能力を得ることができる。
【００６９】
このように本実施形態によれば、第１又は第２の実施形態で得られる電界緩和材料と低電界の電気抵抗率が非線形抵抗を示す充填材の固有抵抗以上である電界緩和材料を２段階にして設けることにより、安定して且つ沿面放電破壊電圧が高い電磁コイルを得ることができる。
【００７０】
【発明の効果】
以上述べたように本発明によれば、電気抵抗特性が安定し、且つ優れた放電抑制特性を持つ電界緩和材料及びこの材料を用いた電界緩和部材並びに電磁コイルを提供することができる。
【図面の簡単な説明】
【図１】本発明の第１の実施形態における電界緩和材料の組成を示す模式図。
【図２】同実施形態において、高密度ポリエチレン中にカーボン粒子を充填した材料の抵抗と配合比の関係を示図。
【図３】同実施形態において、炭化珪素、四三酸化鉄と樹脂の複合材料の体積抵抗率及び配合比の関係を示す曲線図。
【図４】同実施形態において、溶剤に浸漬したときの抵抗のばらつきを示す図。
【図５】本発明の第２の実施形態における電界緩和材料の組成を示す模式図。
【図６】同実施形態において、沿面破壊電圧と抵抗の関係を示す図。
【図７】同実施形態において、非線形抵抗材料の特性を示す等価回路図。
【図８】同実施形態において、酸化錫、炭化珪素と樹脂の複合材料の体積抵抗率の電界依存性を示す図。
【図９】本発明の第３の実施形態における電界緩和部材を示す斜視図。
【図１０】同実施形態において、ガラスクロスに塗布して構成される電界緩和部材を示す図。
【図１１】本発明の第４の実施形態を示すコイルエンド部の斜視図。
【図１２】本発明の第５の実施形態を示す電磁コイルの構成図。
【図１３】同実施形態において、沿面破壊電圧と比較例との比較を示す図。
【図１４】従来の電界緩和部材を施したコイル導体を示す断面図。
【符号の説明】
５……非線形素子
６……線形抵抗粒子の塊
７……バインダー樹脂
８……線形抵抗素子
９……非線形抵抗
１０……線形抵抗
１１……電界緩和部材
１２……線形抵抗
１３……電界緩和材料
１４……コイル導体
１５……主絶縁層
１６……コイル
１７……低抵抗塗料
１８．１９……電界緩和層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric field relaxation material having stable electric resistance characteristics, an electric field relaxation member using the material, and an electromagnetic coil.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, it is known to provide an electric field relaxation material at a conductor end portion that generates a high electric field, for example, a coil end portion of an electromagnetic coil, in order to soften the electric field.
[0003]
As this electric field relaxation material, there is a combination of silicon carbide (SiC) having a non-linear resistance to an electric field and triiron tetroxide (see, for example, Patent Document 1).
[0004]
FIG. 14 is a cross-sectional view showing a coil end portion of the electromagnetic coil.
[0005]
In FIG. 14, reference numeral 1 denotes a coil conductor, and an insulating layer 2 is formed around the coil conductor 1, and a conductive paint layer 3 and a SiC paint layer 4 are provided on the outer peripheral surface in combination as an electric field relaxation material. Yes.
[0006]
Although this material exhibits an excellent electric field relaxation effect, on the other hand, when the surrounding conditions, for example, temperature conditions at the time of manufacture and variations in the blending ratio change, the electric field relaxation ability may be lowered accordingly.
[0007]
[Patent Document 1]
Japanese Patent Publication No. 61-37721 [0008]
[Problems to be solved by the invention]
Thus, if the characteristics of the electric field relaxation material vary depending on the surrounding conditions, the performance of the product is degraded. In particular, the variation in allowable characteristics is becoming narrower as the voltage of devices is increased.
[0009]
The present invention has been made in view of the above circumstances, and has a stable electric field relaxation material having insensitive characteristics to changes in ambient conditions and excellent discharge suppression characteristics, and an electric field relaxation member using this material, and An object is to provide an electromagnetic coil.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides the following electric field relaxation material.
[0011]
The present invention provides a composite material in which particles having nonlinear resistance and particles having linear resistance are dispersed in a resin, wherein the volume ratio of the particles having linear resistance is linear resistance to the volume excluding the particles having nonlinear resistance. When the volume ratio of the particles indicating p is p, a relationship of log ρ∝ (p−pc) ^−k (k is a positive integer) is shown between the electric resistances ρ and p measured with an electric field that does not exhibit nonlinearity. It is more than a certain volume ratio pc.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
FIG. 1 is a schematic diagram showing the composition of the electric field relaxation material in the first embodiment of the present invention.
[0014]
In the present embodiment, as shown in FIG. 1, in a composite material in which a mass of particles 5 having nonlinear resistance and particles 6 showing linear resistance are dispersed in a binder resin 7, the volume ratio of particles 5 showing linear resistance is Log p∝ (p−pc) ⁻ between the electric resistances ρ and p measured with an electric field not showing non-linearity, where p is the volume ratio of particles showing linear resistance to the volume excluding particles having non-linear resistance. ^The volume ratio pc is greater than or equal to a certain relationship ^k (k is a positive integer).
[0015]
FIG. 2 shows the relationship between the resistance and the compounding ratio of a material in which carbon particles are filled in high-density polyethylene.
[0016]
It is known that when metal particles or conductive particles are dispersed in a resin, the electric resistance is indicated by a curved line having two bends. This phenomenon is explained by percolation theory.
[0017]
In the previous research, the bending point on the high filling amount side is the percolation threshold value pc, and log ρ∝ (p−pc) ^−k (k is positive) between the volume ratio p of the conductive particles and the resistance ρ. (Integer).
[0018]
This concept has been known to be effective for materials containing one type of filler. The inventors of the present invention have advanced research to expand to a system including two kinds of fillers with respect to this theory, and have advanced research to expand to a system including nonlinear resistance. As a result, the present inventors have a linear resistance and silicon carbide exhibiting nonlinear resistance. In the composite material filled with triiron tetroxide, the percolation threshold value pc (Fe ₃ O ₄ ) of triiron tetroxide is a volume ratio p (Fe ₃ O ₄ ) to the volume excluding silicon carbide particles, which is the other, and a low electric field. It has been clarified that a relationship of log ρ∝ (p−pc) ^−k (k is a positive integer) is shown between the resistances ρ.
[0019]
That is, in FIG. 1, when considering an electric field relaxation material in which a lump of particles 5 exhibiting nonlinear resistance and particles 6 exhibiting linear resistance are dispersed in a binder resin 7, a linear low resistance that determines the electric resistance in a low electric field region is shown. Focus on the electrical conduction path created by the particles shown. At this time, it has been devised that the percolation threshold should be considered as a percolation threshold when the volume excluding particles exhibiting nonlinear resistance is considered.
[0020]
FIG. 3 shows a volume resistivity in a low electric field region of a composite material in which iron carbide tetraoxide as a linear resistance material is dispersed in a polybutadiene resin containing 24.3 vol% of silicon carbide particles as a non-linear resistance material. It is drawn with a curve having two bent curves.
[0021]
Since the region immediately below the percolation threshold can be considered to be in a region where the electric resistance greatly changes with respect to the change amount of the volume ratio, the present inventors pay particular attention to the blending ratio above the percolation threshold, and the material Figured out to manufacture.
[0022]
FIG. 4 shows an electric field relaxation material in which silicon carbide and iron tetroxide dispersed in polybutadiene are applied to a glass cloth tape, dried, dipped in a highly soluble solvent, and then taken out and cured. The electric resistance value of the tape-shaped sample is shown.
[0023]
In FIG. 4, the horizontal axis represents the volume ratio of iron trioxide to the volume of the resin component excluding silicon carbide.
[0024]
Here, the percolation threshold for these tape materials is 12 vol% based on the relationship between the electrical resistance in the low electric field region and the compounding ratio of the tape material cured without being immersed in a highly soluble solvent using the above formula. It turns out that.
[0025]
The present embodiment is characterized in that the volume ratio of iron tetroxide to the volume of the resin component excluding silicon carbide is not less than the percolation threshold (12 vol%), and 15 vol% is adopted as the volume ratio.
[0026]
As a comparative example, the volume ratio of ferric tetroxide to the volume of the resin component excluding silicon carbide is 10 vol% and 11 vol%, but obviously the variation is large at 12 vol% or less, and the characteristics become unstable. It is shown.
[0027]
Thus, in the first embodiment, in a composite material in which a mass of particles 5 having nonlinear resistance and particles 6 showing linear resistance are dispersed in a binder resin 7, the volume ratio of particles 5 showing linear resistance is: When the volume ratio of particles exhibiting linear resistance to the volume excluding particles having nonlinear resistance is p, log ρ∝ (p−pc) ⁻ between the electric resistances ρ and p measured with an electric field that does not exhibit nonlinear resistance. ^{By making} the volume ratio pc or more that shows the relationship ^k (k is a positive integer), an electric field relaxation material having stable electric resistance characteristics can be obtained.
[0028]
In addition, as a particle | grains which show nonlinear resistance, zinc oxide other than silicon carbide can be considered.
[0029]
FIG. 5 is a schematic diagram showing the composition of the electric field relaxation material in the second embodiment of the present invention. The same elements as those in FIG. 1 are denoted by the same reference numerals and the description thereof is omitted, and different points will be described here.
[0030]
In the second embodiment, as shown in FIG. 5, the volume resistivity of the particles 8 exhibiting linear resistance is set to 10 ^7.25 to 10 ^10.5 Ωm.
[0031]
The composite material includes particles 5 exhibiting non-linear resistance and particles 6 exhibiting linear resistance in a resin, and the particles exhibiting linear resistance 6 have a resistance of 10 ^7.25 to 10 ^10.5 Ωm.
[0032]
FIG. 6 shows that a main insulation is formed by a mica layer around the coil conductor, an electric field relaxation layer is provided around the coil conductor, an electrode is provided at the center, and a high voltage is applied to the coil conductor with the center as the ground potential. The relationship between the creeping discharge breakdown voltage and the electric resistivity of the electric field relaxation layer is shown.
[0033]
The creeping discharge breakdown voltage has a convex shape with respect to the electrical resistivity. Here, the coil of the rotating electrical machine needs to pass a 3 × EV withstand voltage test with a rated voltage of E. Since the coil shown in FIG. 6 is a 23 kV class coil, it is necessary to show a value of 69 kV or more as the breakdown voltage. From this viewpoint, the electric field relaxation material preferably has a resistance of 10 ^7.25 to 10 ^10.5 Ωm.
[0034]
The inventors measured the non-linear resistance characteristics of silicon carbide elements exhibiting non-linear resistance characteristics and the composite materials of iron tetroxide exhibiting linear resistance with respect to various compounding ratios, and the non-linear resistance characteristics of these composite materials were FIG. 7 clearly shows that it can be explained by the parallel circuit of the non-linear resistance 9 caused by the conduction path made of silicon carbide particles exhibiting non-linear resistance and the linear resistance 10 caused by the conduction path made of iron trioxide showing linear resistance. did.
[0035]
That is, the resistance value in the low electric field region varies depending on the volume resistivity of particles exhibiting linear resistance. Moreover, if the mixing ratio of particles exhibiting linear resistance is equal to or greater than the percolation threshold when considering the volume of particles exhibiting linear resistance relative to the volume excluding particles having non-linear resistance, the material properties are the resistance of particles exhibiting linear resistance. This is because the values are very close.
[0036]
Therefore, if the electrical resistivity of particles exhibiting linear resistance is 10 ^7.25 to 10 ^10.5 Ωm, an extremely stable electric field relaxation material having excellent discharge suppression characteristics can be obtained.
[0037]
As such a material, a test using tin oxide was performed. Using silicon oxide as particles exhibiting non-linear resistance and tin oxide as particles exhibiting linear resistance, the volume resistivity of a plate material prepared by kneading in an epoxy resin and then curing was measured. Tin oxide exhibits a weak non-linearity at a high electric field, but since it is weaker than silicon carbide, it behaves in the same manner as linear.
[0038]
FIG. 8 is a graph showing the electric field dependence of the volume resistivity of this material. The volume resistance of the low electric field was 10 ⁸ Ωm, and a suitable non-linear resistance could be obtained. Further, as described in the known document 1, the surface resistivity at an electric field of 1 kv / cm is preferably 10 ⁸ Ωm or less.
[0039]
Since the thickness of the electric field relaxation layer is usually about 1 mm, it is 10 ⁵ Ωm in terms of volume resistivity. As is apparent from FIG. 8, this material satisfies both properties.
[0040]
As described above, in the second embodiment, by setting the volume resistivity of the particle 8 exhibiting linear resistance to 10 ^7.25 to 10 ^10.5 Ωm, a nonlinear resistance material having stable electric resistance characteristics and high electric field relaxation capability is obtained. be able to.
[0041]
Examples of the particles exhibiting linear resistance include chromium oxide and titanium oxide in addition to tin oxide.
[0042]
FIG. 9 is a perspective view showing an electric field relaxation member according to the third embodiment of the present invention.
[0043]
In the third embodiment, as shown in FIG. 9, the electric field relaxation member 11 is configured by molding the electric field relaxation material obtained in the first or second embodiment described above into a sheet shape.
[0044]
The electric field relaxation material obtained in the first or second embodiment is a material having excellent electrical resistance, and this material can be used as a paint. For example, it can be applied to the coil end portion of an electromagnetic coil. When used, it may become uneven, resulting in variations in resistance values, which may reduce the resistance.
[0045]
Therefore, stable characteristics can be obtained by processing the electric field relaxation material into a sheet in advance.
[0046]
Further, as shown in FIG. 10, the electric field relaxation material 13 can be applied to a cloth to form a tape shape. According to this method, it is possible to obtain a configuration that is highly flexible and easily adheres to an object to be subjected to electric field relaxation. As a base material on which these paints are applied or impregnated, it is desirable to use spinning, bonding, or roving materials of polyester fiber or glass fiber resistant to corona erosion.
[0047]
Thus, in the third embodiment, by forming the electric field relaxation member by forming the electric field relaxation material obtained in the first or second embodiment into a sheet shape or a tape shape, the workability is excellent, The resistance is stable and excellent discharge suppression characteristics can be provided.
[0048]
FIG. 11 is a perspective view of a coil end portion showing a fourth embodiment of the present invention.
[0049]
In the fourth embodiment, as shown in FIG. 11, the tape-like electric field relaxation member 11 obtained in the third embodiment is wound around a coil end portion to form an electric field relaxation layer.
[0050]
In this embodiment, the mica layer, which is the main insulating layer, is wound after bundling insulated conductors for the electromagnetic coil of the rotating device, and then the tape-shaped electric field relaxation obtained in the third embodiment is performed. After the member 11 was wound and impregnated with resin, the periphery of the coil was pressed with a holding plate and held with a spring, and then heated and cured to produce a test coil. In this case, a solvent having high compatibility with the binder resin was used as the impregnation resin.
[0051]
An electrode having a gap length of 10 mm was provided with silver paste around the coil, and the electrical resistance was measured.
[0052]
Table 1 shows resistance values and variations in resistance values in a low electric field.
[0053]
[Table 1]

[0054]
As is apparent from this table, the samples in which the mixing ratio of iron tetroxide is directly below the percolation threshold varies greatly, and it can be seen that the resistance is stable in all of the present embodiments.
[0055]
As described above, in this embodiment, an electromagnetic coil having stable creeping discharge characteristics is obtained by forming the electric field relaxation layer by winding the tape-shaped electric field relaxation member 11 obtained in the third embodiment around the coil end portion. Obtainable.
[0056]
FIG. 12 is a configuration diagram of an electromagnetic coil showing a fifth embodiment of the present invention.
[0057]
In the present embodiment, as shown in FIG. 12, the conductor of the coil 16 is filled with the electric field relaxation layer 18 made of the electric field relaxation material obtained in the first or second embodiment, and the electric field resistivity of the low electric field exhibits nonlinear resistance. An electric field relaxation layer 19 made of an electric field relaxation material having a specific resistance or higher is provided in two stages.
[0058]
The most important characteristic of the electric field relaxation layer is to suppress creeping discharge at the coil end portion. As shown in FIG. 11, a conductive layer for preventing discharge inside the stator core is formed on the outer periphery of the main insulating layer 15 provided on the outer periphery of the conductor, and is electrically brought into contact with the end of the conductive layer. The electric field relaxation layer of this embodiment is provided.
[0059]
Here, if the electric resistance of the electric field relaxation layer is too high, a high electric field is generated at the joint portion between the conductive layer and the electric field relaxation layer, and thus discharge is likely to occur at the joint portion. On the other hand, if the resistance is too low, if the voltage applied to the coil is high, the potential cannot be sufficiently increased at the end of the electric field relaxation layer, and discharge occurs at the end of the electric field relaxation layer.
[0060]
Therefore, if the electric field relaxation material obtained in the second embodiment is used, optimal electric field relaxation can be performed. Further, as a method for suppressing the discharge of a coil having a high voltage, there is a method in which electric field relaxation layers having different resistances are used in two stages.
[0061]
In FIG. 12, the electric field relaxation layer 18 is obtained by kneading 40 vol% of silicon carbide as a filler exhibiting nonlinear resistance and 15 vol% of triiron tetroxide as a filler showing linear resistance into polybutadiene with respect to the volume excluding silicon carbide. The material is the same as that of the first embodiment.
[0062]
The electric field relaxation layer 19 is formed by kneading 40 vol% of silicon carbide exhibiting non-linear resistance and 5 vol% of triiron tetroxide as a filler exhibiting linear resistance with polybutadiene in a volume excluding silicon carbide. As described in the first embodiment, the electrical resistivity is drawn as a curve having two inflection points with respect to the blending ratio.
[0063]
It has already been described that the electrical resistivity is stable in the region above the percolation threshold corresponding to the inflection point on the high filling side. Similarly, it is expected that the electric resistance is stabilized even in the region below the inflection point on the low filling side. The inflection point on the low filling side can be determined to be a region defined only in the state where no linear resistance exists, that is, the resistance of particles exhibiting non-linear resistance in the equivalent circuit shown in FIG. In other words, a material having stable characteristics can be obtained by making a material having an electric resistivity of a low electric field equal to or higher than the specific resistance of the filler exhibiting nonlinear resistance.
[0064]
As shown in FIG. 4, a material having a small amount of triiron tetroxide and having a low electric field resistivity before dipping in a solvent is higher than the low electric field resistivity of silicon carbide has a stable resistance value after dipping. You can see that
[0065]
However, it can be seen that a material having such a high resistance value as shown in FIG. 6 does not have sufficient discharge suppression capability by itself. Therefore, a configuration as shown in FIG. 12 can be considered.
[0066]
The volume resistivity of the electric field relaxation layer 18 was about 10 ⁶ Ωm, and the volume resistivity of the electric field relaxation layer 19 was about 10 ¹¹ Ωm. It is thought that good characteristics cannot be obtained by these alone.
[0067]
FIG. 13 shows a creeping discharge start voltage and a creeping breakdown voltage at a visible level when the electric field relaxation layer 18 and the electric field relaxation layer 19 are combined in two stages.
[0068]
Therefore, a high discharge suppression capability can be obtained by combining both.
[0069]
As described above, according to the present embodiment, the electric field relaxation material obtained in the first or second embodiment and the electric field relaxation material in which the electric resistivity of the low electric field is equal to or higher than the specific resistance of the filler exhibiting nonlinear resistance are divided into two stages. Thus, an electromagnetic coil having a stable and high creepage breakdown voltage can be obtained.
[0070]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an electric field relaxation material having stable electric resistance characteristics and excellent discharge suppression characteristics, an electric field relaxation member using this material, and an electromagnetic coil.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a composition of an electric field relaxation material in a first embodiment of the present invention.
FIG. 2 is a view showing the relationship between the resistance and the compounding ratio of a material in which carbon particles are filled in high-density polyethylene in the same embodiment.
FIG. 3 is a curve diagram showing a relationship between a volume resistivity and a blending ratio of a composite material of silicon carbide, iron tetroxide and resin in the same embodiment.
FIG. 4 is a view showing variation in resistance when immersed in a solvent in the embodiment.
FIG. 5 is a schematic diagram showing a composition of an electric field relaxation material in a second embodiment of the present invention.
FIG. 6 is a view showing a relationship between a creeping breakdown voltage and resistance in the embodiment.
FIG. 7 is an equivalent circuit diagram showing characteristics of the nonlinear resistance material in the embodiment.
FIG. 8 is a graph showing the electric field dependence of the volume resistivity of a composite material of tin oxide, silicon carbide and resin in the same embodiment.
FIG. 9 is a perspective view showing an electric field relaxation member according to a third embodiment of the present invention.
FIG. 10 is a view showing an electric field relaxation member configured by being applied to a glass cloth in the embodiment.
FIG. 11 is a perspective view of a coil end portion showing a fourth embodiment of the present invention.
FIG. 12 is a configuration diagram of an electromagnetic coil showing a fifth embodiment of the present invention.
FIG. 13 is a diagram showing a comparison between a creeping breakdown voltage and a comparative example in the embodiment.
FIG. 14 is a cross-sectional view showing a coil conductor provided with a conventional electric field relaxation member.
[Explanation of symbols]
5 ... Nonlinear element 6 ... Linear resistance particle lump 7 ... Binder resin 8 ... Linear resistance element 9 ... Nonlinear resistance 10 ... Linear resistance 11 ... Electric field relaxation member 12 ... Linear resistance 13 ... Electric field relaxation Material 14 ... Coil conductor 15 ... Main insulation layer 16 ... Coil 17 ... Low resistance paint 18.19 ... Electric field relaxation layer

Claims

In a composite material in which particles having nonlinear resistance and particles showing linear resistance are dispersed in a resin,
When the volume ratio of particles exhibiting linear resistance is p and the volume ratio of particles exhibiting linear resistance to the volume excluding the particles having nonlinear resistance is p, the electrical resistances ρ and p measured by an electric field that does not exhibit nonlinearity An electric field relaxation material having a volume ratio pc or more in which a relation of log ρ∝ (p−pc) ^−k (k is a positive integer) is shown therebetween.

2. The electric field relaxation material according to claim 1, wherein the particles exhibiting non-linear resistance are silicon carbide.

2. The electric field relaxation material according to claim 1, wherein the material exhibiting linear resistance is triiron tetroxide or tin oxide.

2. The electric field relaxation material according to claim 1, wherein the particles exhibiting non-linear resistance are silicon carbide, and the particles exhibiting linear resistance are triiron tetroxide or tin oxide.

5. The electric field relaxation material according to claim 1, wherein the volume resistivity of particles exhibiting linear resistance is 10 ^7.25 to 10 ^10.5 Ωm.

An electric field relaxation member, wherein the electric field relaxation material according to any one of claims 1 to 5 is formed into a tape shape or a sheet shape.

An electric field relaxation member obtained by applying or impregnating the electric field relaxation material according to any one of claims 1 to 6 to a substrate such as a glass cloth or a polyester cloth.

An electromagnetic coil, wherein the electric field relaxation material according to claim 1 is applied to a coil portion to form an electric field relaxation layer.

An electromagnetic coil, wherein an electromagnetic relaxation layer is formed by winding the electric field relaxation member according to claim 6 around a coil portion.

The electric field relaxation material according to any one of claims 1 to 5 and the electric field relaxation material in which the electric resistivity of the low electric field is equal to or higher than the specific resistance at a low electric field of the filler exhibiting nonlinear resistance is provided in two stages. An electromagnetic coil characterized by that.