?? 誤區1、使用變頻器都能節電

? ? 一些文(wen)獻宣(xuan)稱變頻(pin)調(diao)(diao)速(su)器(qi)(qi)(qi)是節(jie)電控(kong)(kong)制(zhi)產(chan)品(pin)，給人的感(gan)覺(jue)是只(zhi)要使(shi)用變頻(pin)調(diao)(diao)速(su)器(qi)(qi)(qi)都能節(jie)電，實際上(shang)，變頻(pin)調(diao)(diao)速(su)器(qi)(qi)(qi)之所(suo)以(yi)能夠節(jie)電，是因(yin)為其能對電動(dong)機進(jin)行調(diao)(diao)速(su)。如果說變頻(pin)調(diao)(diao)速(su)器(qi)(qi)(qi)是節(jie)電控(kong)(kong)制(zhi)產(chan)品(pin)的話，那么(me)所(suo)有(you)的調(diao)(diao)速(su)設備也(ye)都可以(yi)說是節(jie)電控(kong)(kong)制(zhi)產(chan)品(pin)。變頻(pin)調(diao)(diao)速(su)器(qi)(qi)(qi)只(zhi)不過(guo)比其它(ta)調(diao)(diao)速(su)設備效率(lv)(lv)和功率(lv)(lv)因(yin)數略(lve)高(gao)罷(ba)了。

? ? 變(bian)頻(pin)(pin)調(diao)(diao)速(su)(su)(su)(su)器能(neng)否實現節(jie)(jie)(jie)電(dian)(dian)，是由其負(fu)(fu)(fu)載的(de)(de)(de)(de)(de)(de)調(diao)(diao)速(su)(su)(su)(su)特性決定的(de)(de)(de)(de)(de)(de)。對(dui)于離心(xin)風機(ji)、離心(xin)水(shui)(shui)泵這(zhe)類(lei)負(fu)(fu)(fu)載，轉(zhuan)矩(ju)與轉(zhuan)速(su)(su)(su)(su)的(de)(de)(de)(de)(de)(de)平(ping)方成正比(bi)，功(gong)(gong)率(lv)與轉(zhuan)速(su)(su)(su)(su)的(de)(de)(de)(de)(de)(de)立方成正比(bi)。只要(yao)原來(lai)采用(yong)閥門(men)控制流量(liang)，且不是滿負(fu)(fu)(fu)荷工(gong)作，改為(wei)(wei)調(diao)(diao)速(su)(su)(su)(su)運(yun)行，均能(neng)實現節(jie)(jie)(jie)電(dian)(dian)。當轉(zhuan)速(su)(su)(su)(su)下(xia)降為(wei)(wei)原來(lai)的(de)(de)(de)(de)(de)(de)80%時，功(gong)(gong)率(lv)只有原來(lai)的(de)(de)(de)(de)(de)(de)51.2%。可見，變(bian)頻(pin)(pin)調(diao)(diao)速(su)(su)(su)(su)器在這(zhe)類(lei)負(fu)(fu)(fu)載中(zhong)的(de)(de)(de)(de)(de)(de)應(ying)用(yong)，節(jie)(jie)(jie)電(dian)(dian)效果最為(wei)(wei)明顯。對(dui)于羅(luo)茨風機(ji)這(zhe)類(lei)負(fu)(fu)(fu)載，轉(zhuan)矩(ju)與轉(zhuan)速(su)(su)(su)(su)的(de)(de)(de)(de)(de)(de)大(da)小無關(guan)，即恒(heng)(heng)(heng)轉(zhuan)矩(ju)負(fu)(fu)(fu)載。若(ruo)原來(lai)采用(yong)放(fang)風閥放(fang)走多(duo)(duo)余風量(liang)的(de)(de)(de)(de)(de)(de)方法調(diao)(diao)節(jie)(jie)(jie)風量(liang)，改為(wei)(wei)調(diao)(diao)速(su)(su)(su)(su)運(yun)行，也(ye)能(neng)實現節(jie)(jie)(jie)電(dian)(dian)。當轉(zhuan)速(su)(su)(su)(su)下(xia)降為(wei)(wei)原來(lai)的(de)(de)(de)(de)(de)(de)80%時，功(gong)(gong)率(lv)為(wei)(wei)原來(lai)的(de)(de)(de)(de)(de)(de)80%。比(bi)在離心(xin)風機(ji)、離心(xin)水(shui)(shui)泵中(zhong)的(de)(de)(de)(de)(de)(de)應(ying)用(yong)節(jie)(jie)(jie)電(dian)(dian)效果要(yao)小得多(duo)(duo)。對(dui)于恒(heng)(heng)(heng)功(gong)(gong)率(lv)負(fu)(fu)(fu)載，功(gong)(gong)率(lv)與轉(zhuan)速(su)(su)(su)(su)的(de)(de)(de)(de)(de)(de)大(da)小無關(guan)。水(shui)(shui)泥廠恒(heng)(heng)(heng)功(gong)(gong)率(lv)負(fu)(fu)(fu)載，如配料(liao)皮(pi)帶秤，在設定流量(liang)一定的(de)(de)(de)(de)(de)(de)條件(jian)下(xia)，當料(liao)層厚時，皮(pi)帶速(su)(su)(su)(su)度減慢；當料(liao)層薄時，皮(pi)帶速(su)(su)(su)(su)度加(jia)快。變(bian)頻(pin)(pin)調(diao)(diao)速(su)(su)(su)(su)器在這(zhe)類(lei)負(fu)(fu)(fu)載中(zhong)的(de)(de)(de)(de)(de)(de)應(ying)用(yong)，不能(neng)節(jie)(jie)(jie)電(dian)(dian)。

? ? 與直(zhi)流(liu)(liu)調速系統比(bi)(bi)(bi)較(jiao)，直(zhi)流(liu)(liu)電動(dong)機比(bi)(bi)(bi)交流(liu)(liu)電動(dong)機效率(lv)高(gao)、功率(lv)因數(shu)高(gao)，數(shu)字(zi)直(zhi)流(liu)(liu)調速器與變頻(pin)調速器效率(lv)不(bu)相上下，甚至數(shu)字(zi)直(zhi)流(liu)(liu)調速器比(bi)(bi)(bi)變頻(pin)調速器效率(lv)略高(gao)。所以，宣稱使用(yong)交流(liu)(liu)異步電動(dong)機和變頻(pin)調速器比(bi)(bi)(bi)使用(yong)直(zhi)流(liu)(liu)電動(dong)機和直(zhi)流(liu)(liu)調速器要(yao)節電，理論(lun)和實(shi)踐(jian)證明，這是(shi)不(bu)正確的。

? ??誤區2、變頻器的容量選擇以電動機額定功率為依據

? ? 相對于(yu)電動(dong)機來說(shuo)，變(bian)頻(pin)調(diao)速(su)(su)器的(de)(de)價格較貴，因此在(zai)保證安全可靠運行(xing)的(de)(de)前提下(xia)，合理地降低變(bian)頻(pin)調(diao)速(su)(su)器的(de)(de)容量就顯(xian)得十分有意義(yi)。變(bian)頻(pin)調(diao)速(su)(su)器的(de)(de)功率指的(de)(de)是(shi)它適用的(de)(de)4極交流異步電動(dong)機的(de)(de)功率。

? ? 由于同(tong)容(rong)(rong)量電(dian)(dian)動(dong)(dong)機，其(qi)極(ji)(ji)數(shu)不同(tong)，電(dian)(dian)動(dong)(dong)機額(e)定(ding)電(dian)(dian)流(liu)(liu)不同(tong)。隨著電(dian)(dian)動(dong)(dong)機極(ji)(ji)數(shu)的(de)(de)(de)增多，電(dian)(dian)動(dong)(dong)機額(e)定(ding)電(dian)(dian)流(liu)(liu)增大(da)。變(bian)頻調速(su)器(qi)的(de)(de)(de)容(rong)(rong)量選(xuan)擇不能(neng)以電(dian)(dian)動(dong)(dong)機額(e)定(ding)功率為(wei)(wei)依據。同(tong)時，對于原(yuan)來未采用(yong)變(bian)頻器(qi)的(de)(de)(de)改造項(xiang)目，變(bian)頻調速(su)器(qi)的(de)(de)(de)容(rong)(rong)量選(xuan)擇也(ye)不能(neng)以電(dian)(dian)動(dong)(dong)機額(e)定(ding)電(dian)(dian)流(liu)(liu)為(wei)(wei)依據。這(zhe)是因(yin)為(wei)(wei)，電(dian)(dian)動(dong)(dong)機的(de)(de)(de)容(rong)(rong)量選(xuan)擇要考慮最大(da)負荷(he)、富裕(yu)系數(shu)、電(dian)(dian)動(dong)(dong)機規格等因(yin)素，往往富裕(yu)量較大(da)，工業用(yong)電(dian)(dian)動(dong)(dong)機常常在50%～60%額(e)定(ding)負荷(he)下(xia)運行。若以電(dian)(dian)動(dong)(dong)機額(e)定(ding)電(dian)(dian)流(liu)(liu)為(wei)(wei)依據來選(xuan)擇變(bian)頻調速(su)器(qi)的(de)(de)(de)容(rong)(rong)量，留有(you)富裕(yu)量太(tai)大(da)，造成經濟(ji)上的(de)(de)(de)浪費，而可靠性(xing)并(bing)沒有(you)因(yin)此得到提高。

? ? 對于鼠(shu)籠式(shi)電(dian)(dian)(dian)動(dong)機(ji)(ji)，變(bian)頻調(diao)速(su)器(qi)的(de)容量(liang)選擇應(ying)以變(bian)頻器(qi)的(de)額定電(dian)(dian)(dian)流大(da)于或等于電(dian)(dian)(dian)動(dong)機(ji)(ji)的(de)最大(da)正常(chang)工作電(dian)(dian)(dian)流1.1倍為原則，這樣(yang)可以最大(da)限度地節(jie)約資金(jin)。對于重載起動(dong)、高溫環境、繞線(xian)式(shi)電(dian)(dian)(dian)動(dong)機(ji)(ji)、同步電(dian)(dian)(dian)動(dong)機(ji)(ji)等條件(jian)下，變(bian)頻調(diao)速(su)器(qi)的(de)容量(liang)應(ying)適當加(jia)大(da)。

? ? 對于一(yi)開始就采用變頻器(qi)(qi)的設(she)(she)計中，變頻器(qi)(qi)容(rong)量的選擇(ze)以電動(dong)機額定電流為(wei)依(yi)據無可厚非。這(zhe)是因為(wei)此時(shi)變頻器(qi)(qi)容(rong)量不(bu)能以實際運(yun)行(xing)情況來(lai)選擇(ze)。當(dang)然(ran)，為(wei)了減少投資，在有些場合(he)，也可先不(bu)確定變頻器(qi)(qi)的容(rong)量，等設(she)(she)備實際運(yun)轉(zhuan)一(yi)段時(shi)間后，再根(gen)據實際電流進行(xing)選擇(ze)。

? ??誤區3、用視在功率計算無功補償節能收益

? ? 用視在功率(lv)計(ji)算無功補償節能(neng)效果(guo)。如(ru)某文獻：原系(xi)統風機工(gong)頻滿(man)載工(gong)作(zuo)時，電(dian)動機運行電(dian)流為289A，采用變(bian)頻調速時，50Hz滿(man)載運行時的(de)功率(lv)因(yin)數約為0.99，電(dian)流是257A，這是由于(yu)變(bian)頻器內部(bu)濾波電(dian)容產生(sheng)改善功率(lv)因(yin)數的(de)作(zuo)用，其節能(neng)計(ji)算如(ru)下：

? ? ΔS=UI=×380×(289－257)=21kVA

? ? 因此該文認為(wei)(wei)其節能效果(guo)約為(wei)(wei)單機容量的11%左右(you)。

? ? 實際(ji)(ji)分(fen)析：S即(ji)表示視在(zai)(zai)(zai)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)，即(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)與(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)乘積，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)相同時，視在(zai)(zai)(zai)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)節約(yue)百(bai)(bai)分(fen)比與(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)節約(yue)百(bai)(bai)分(fen)比是(shi)(shi)(shi)一(yi)(yi)回事。在(zai)(zai)(zai)有(you)(you)(you)(you)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)抗的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路中，視在(zai)(zai)(zai)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)只(zhi)是(shi)(shi)(shi)反映了(le)配(pei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)系統的(de)(de)(de)(de)允許最大輸(shu)出能力，而不能反映電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)動機(ji)實際(ji)(ji)消耗(hao)(hao)(hao)的(de)(de)(de)(de)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)動機(ji)實際(ji)(ji)消耗(hao)(hao)(hao)的(de)(de)(de)(de)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)只(zhi)能用有(you)(you)(you)(you)功(gong)(gong)(gong)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)表示。在(zai)(zai)(zai)該(gai)例中，雖用實際(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)計(ji)算，但計(ji)算的(de)(de)(de)(de)是(shi)(shi)(shi)視在(zai)(zai)(zai)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)，而不是(shi)(shi)(shi)有(you)(you)(you)(you)功(gong)(gong)(gong)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)。我們知(zhi)道，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)動機(ji)實際(ji)(ji)消耗(hao)(hao)(hao)的(de)(de)(de)(de)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)是(shi)(shi)(shi)由風(feng)機(ji)及其負載(zai)決定(ding)(ding)的(de)(de)(de)(de)。功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)因(yin)數的(de)(de)(de)(de)提高(gao)并沒(mei)(mei)有(you)(you)(you)(you)改變(bian)(bian)(bian)風(feng)機(ji)的(de)(de)(de)(de)負載(zai)，也沒(mei)(mei)有(you)(you)(you)(you)提高(gao)風(feng)機(ji)的(de)(de)(de)(de)效率(lv)(lv)(lv)(lv)，風(feng)機(ji)實際(ji)(ji)消耗(hao)(hao)(hao)的(de)(de)(de)(de)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)沒(mei)(mei)有(you)(you)(you)(you)減(jian)(jian)少(shao)(shao)。功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)因(yin)數提高(gao)后，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)動機(ji)運(yun)行狀態也沒(mei)(mei)有(you)(you)(you)(you)改變(bian)(bian)(bian)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)動機(ji)定(ding)(ding)子電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)并沒(mei)(mei)有(you)(you)(you)(you)減(jian)(jian)少(shao)(shao)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)動機(ji)消耗(hao)(hao)(hao)的(de)(de)(de)(de)有(you)(you)(you)(you)功(gong)(gong)(gong)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)和無功(gong)(gong)(gong)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)都沒(mei)(mei)有(you)(you)(you)(you)改變(bian)(bian)(bian)。功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)因(yin)數提高(gao)的(de)(de)(de)(de)原因(yin)是(shi)(shi)(shi)變(bian)(bian)(bian)頻(pin)器(qi)內部濾波電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容產生無功(gong)(gong)(gong)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)供(gong)給(gei)了(le)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)動機(ji)消耗(hao)(hao)(hao)。隨(sui)著功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)因(yin)數提高(gao)，變(bian)(bian)(bian)頻(pin)器(qi)的(de)(de)(de)(de)實際(ji)(ji)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)減(jian)(jian)少(shao)(shao)，從而減(jian)(jian)少(shao)(shao)了(le)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)網至變(bian)(bian)(bian)頻(pin)器(qi)之(zhi)間的(de)(de)(de)(de)線(xian)損(sun)(sun)(sun)和變(bian)(bian)(bian)壓(ya)器(qi)的(de)(de)(de)(de)銅耗(hao)(hao)(hao)。同時，負荷電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)減(jian)(jian)小(xiao)，給(gei)變(bian)(bian)(bian)頻(pin)器(qi)供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)變(bian)(bian)(bian)壓(ya)器(qi)、開關、接(jie)觸器(qi)、導線(xian)等配(pei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)設備可(ke)以帶更多的(de)(de)(de)(de)負載(zai)。需要指出的(de)(de)(de)(de)是(shi)(shi)(shi)，如果象該(gai)例一(yi)(yi)樣不考慮(lv)線(xian)損(sun)(sun)(sun)和變(bian)(bian)(bian)壓(ya)器(qi)銅耗(hao)(hao)(hao)的(de)(de)(de)(de)節約(yue)，而考慮(lv)變(bian)(bian)(bian)頻(pin)器(qi)的(de)(de)(de)(de)損(sun)(sun)(sun)耗(hao)(hao)(hao)，變(bian)(bian)(bian)頻(pin)器(qi)在(zai)(zai)(zai)50Hz滿載(zai)運(yun)行時，不僅沒(mei)(mei)有(you)(you)(you)(you)節能，而且還(huan)費電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。因(yin)此，用視在(zai)(zai)(zai)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)計(ji)算節能效果是(shi)(shi)(shi)不對的(de)(de)(de)(de)。

? ??誤區4、變頻器輸出側不能加裝接觸器

? ? 幾乎(hu)所有變(bian)頻調(diao)速(su)器(qi)使用說(shuo)明書(shu)都指出(chu)(chu)，變(bian)頻調(diao)速(su)器(qi)輸(shu)(shu)出(chu)(chu)側不能(neng)加(jia)裝接觸器(qi)。如日本安川變(bian)頻器(qi)說(shuo)明書(shu)就規定“切勿在(zai)輸(shu)(shu)出(chu)(chu)回路連接電(dian)(dian)磁開關(guan)、電(dian)(dian)磁接觸器(qi)”。

? ? 廠(chang)家的規定(ding)是為了防(fang)止(zhi)在(zai)(zai)(zai)變(bian)頻(pin)(pin)(pin)調(diao)速(su)(su)器(qi)有(you)(you)(you)輸(shu)出時(shi)接(jie)(jie)觸(chu)(chu)器(qi)動(dong)(dong)(dong)作。變(bian)頻(pin)(pin)(pin)器(qi)在(zai)(zai)(zai)運行中連接(jie)(jie)負載，會由(you)于漏電流(liu)而使過電流(liu)保(bao)護(hu)回路動(dong)(dong)(dong)作。那(nei)么，只要在(zai)(zai)(zai)變(bian)頻(pin)(pin)(pin)調(diao)速(su)(su)器(qi)輸(shu)出與接(jie)(jie)觸(chu)(chu)器(qi)動(dong)(dong)(dong)作之(zhi)間，加(jia)以必要的控制聯(lian)鎖(suo)，保(bao)證(zheng)只有(you)(you)(you)在(zai)(zai)(zai)變(bian)頻(pin)(pin)(pin)調(diao)速(su)(su)器(qi)無輸(shu)出時(shi)，接(jie)(jie)觸(chu)(chu)器(qi)才能動(dong)(dong)(dong)作，變(bian)頻(pin)(pin)(pin)調(diao)速(su)(su)器(qi)輸(shu)出側就可(ke)以加(jia)裝接(jie)(jie)觸(chu)(chu)器(qi)。這種方(fang)案對于只有(you)(you)(you)1臺(tai)變(bian)頻(pin)(pin)(pin)調(diao)速(su)(su)器(qi)，2臺(tai)電動(dong)(dong)(dong)機(ji)(ji)(1臺(tai)電動(dong)(dong)(dong)機(ji)(ji)運行，1臺(tai)電動(dong)(dong)(dong)機(ji)(ji)備(bei)(bei)用(yong))的場合，具有(you)(you)(you)重要的意義。當(dang)運行的電動(dong)(dong)(dong)機(ji)(ji)出現(xian)故障時(shi)，可(ke)以很方(fang)便地將變(bian)頻(pin)(pin)(pin)器(qi)切換到備(bei)(bei)用(yong)電動(dong)(dong)(dong)機(ji)(ji)，經過延時(shi)使變(bian)頻(pin)(pin)(pin)器(qi)運行，實(shi)現(xian)備(bei)(bei)用(yong)電動(dong)(dong)(dong)機(ji)(ji)自動(dong)(dong)(dong)投入變(bian)頻(pin)(pin)(pin)運行。并且還(huan)可(ke)以很方(fang)便地實(shi)現(xian)2臺(tai)電動(dong)(dong)(dong)機(ji)(ji)的互(hu)為備(bei)(bei)用(yong)。

? ??誤區5、變頻調速器在離心風機中的應用，可完全取代風機的調節閥門

? ? 采用變頻調(diao)速器(qi)(qi)對(dui)離心風(feng)(feng)(feng)(feng)機進行調(diao)速來控制風(feng)(feng)(feng)(feng)量，與調(diao)節(jie)閥門控制風(feng)(feng)(feng)(feng)量相(xiang)比,具有明顯的(de)節(jie)電(dian)效果。但在有些場合，變頻調(diao)速器(qi)(qi)不能完全(quan)取代風(feng)(feng)(feng)(feng)機的(de)閥門，在設計(ji)中要引起特(te)別注意。為了說明這(zhe)個(ge)問題，我們先從其節(jie)電(dian)原理談起。離心風(feng)(feng)(feng)(feng)機的(de)風(feng)(feng)(feng)(feng)量與轉(zhuan)速的(de)一(yi)次方(fang)成(cheng)正比，風(feng)(feng)(feng)(feng)壓與轉(zhuan)速的(de)平(ping)方(fang)成(cheng)正比，軸功率與轉(zhuan)速的(de)立方(fang)成(cheng)正比。

? ? 如圖1所示(shi)，曲(qu)線(xian)(xian)(xian)(1)為(wei)風(feng)機在恒速下(xia)(xia)，風(feng)壓－風(feng)量(H－Q)特(te)(te)性(xing)；曲(qu)線(xian)(xian)(xian)(2)為(wei)管網風(feng)阻特(te)(te)性(xing)(閥(fa)門(men)開度(du)全(quan)開)。風(feng)機工(gong)(gong)作在A點(dian)時(shi)輸出風(feng)量為(wei)Q1，此時(shi)軸(zhou)功率(lv)N1與Q1、H1的乘積(ji)面積(ji)(AH1OQ1)成(cheng)正(zheng)比(bi)。當(dang)風(feng)量從Q1減少到(dao)Q2，如采用調節(jie)閥(fa)門(men)方法，使管網阻力特(te)(te)性(xing)變(bian)到(dao)曲(qu)線(xian)(xian)(xian)(3)。系統由(you)原來的工(gong)(gong)況點(dian)A變(bian)到(dao)新的工(gong)(gong)況點(dian)B運行，風(feng)壓反而增加(jia)，軸(zhou)功率(lv)N2與面積(ji)(BH2OQ2)成(cheng)正(zheng)比(bi)，N1與N2相差(cha)不多。如果采用調速控制方式，風(feng)機轉速由(you)n1降到(dao)n2,則風(feng)壓－風(feng)量(H－Q)特(te)(te)性(xing)如曲(qu)線(xian)(xian)(xian)(4)所示(shi)，在滿足同樣風(feng)量Q2的情況下(xia)(xia)，風(feng)壓H3大幅度(du)降低(di)，功率(lv)N3(相當(dang)于面積(ji)CH3OQ2)隨著(zhu)顯著(zhu)減少，節(jie)能效果十分顯著(zhu)。

? ? 從上(shang)面的(de)(de)分(fen)析還可以(yi)看出，調(diao)(diao)(diao)(diao)節閥門控(kong)制(zhi)風(feng)(feng)(feng)量(liang)(liang)，隨著風(feng)(feng)(feng)量(liang)(liang)的(de)(de)減(jian)少，風(feng)(feng)(feng)壓(ya)反而(er)增加；而(er)采用(yong)變(bian)(bian)(bian)頻調(diao)(diao)(diao)(diao)速(su)(su)器調(diao)(diao)(diao)(diao)速(su)(su)來控(kong)制(zhi)風(feng)(feng)(feng)量(liang)(liang)，隨著風(feng)(feng)(feng)量(liang)(liang)的(de)(de)減(jian)少，風(feng)(feng)(feng)壓(ya)大(da)幅度下降(jiang)。風(feng)(feng)(feng)壓(ya)下降(jiang)太多，有(you)可能(neng)(neng)滿(man)足不了(le)工(gong)藝要(yao)求(qiu)(qiu)。即如果工(gong)況點在(zai)曲(qu)線(1)、曲(qu)線(2)、H軸所圍(wei)區域內(nei)部，單純地(di)依靠(kao)(kao)變(bian)(bian)(bian)頻調(diao)(diao)(diao)(diao)速(su)(su)器調(diao)(diao)(diao)(diao)速(su)(su)將無法滿(man)足工(gong)藝要(yao)求(qiu)(qiu)，需要(yao)和(he)(he)閥門調(diao)(diao)(diao)(diao)節結合才能(neng)(neng)滿(man)足工(gong)藝要(yao)求(qiu)(qiu)。某廠引進(jin)的(de)(de)變(bian)(bian)(bian)頻調(diao)(diao)(diao)(diao)速(su)(su)器，在(zai)離(li)心風(feng)(feng)(feng)機中的(de)(de)應用(yong)中，因(yin)沒有(you)設計閥門，單純地(di)依靠(kao)(kao)變(bian)(bian)(bian)頻調(diao)(diao)(diao)(diao)速(su)(su)器調(diao)(diao)(diao)(diao)速(su)(su)來改變(bian)(bian)(bian)風(feng)(feng)(feng)機工(gong)況點，吃盡了(le)苦(ku)頭。要(yao)么轉(zhuan)速(su)(su)太高，風(feng)(feng)(feng)量(liang)(liang)太大(da)；若降(jiang)低轉(zhuan)速(su)(su)，風(feng)(feng)(feng)壓(ya)又滿(man)足不了(le)工(gong)藝要(yao)求(qiu)(qiu)，吹(chui)不進(jin)風(feng)(feng)(feng)。因(yin)此離(li)心風(feng)(feng)(feng)機在(zai)使用(yong)變(bian)(bian)(bian)頻調(diao)(diao)(diao)(diao)速(su)(su)器調(diao)(diao)(diao)(diao)速(su)(su)節電時，要(yao)兼顧(gu)風(feng)(feng)(feng)量(liang)(liang)和(he)(he)風(feng)(feng)(feng)壓(ya)這2個指(zhi)標，否(fou)則(ze)會(hui)帶來不良的(de)(de)后(hou)果。

??? 誤區6、通用電動機只能在其額定轉速以下采用變頻調速器降速運行

? ? 經典理論認(ren)為(wei)，通(tong)用(yong)電(dian)(dian)(dian)(dian)動(dong)機(ji)(ji)頻(pin)(pin)(pin)(pin)率上(shang)限為(wei)55Hz。這(zhe)(zhe)是因為(wei)當電(dian)(dian)(dian)(dian)動(dong)機(ji)(ji)轉(zhuan)(zhuan)速(su)需要調(diao)到額定(ding)轉(zhuan)(zhuan)速(su)以上(shang)運行時(shi)，定(ding)子(zi)頻(pin)(pin)(pin)(pin)率將(jiang)(jiang)(jiang)增加到高(gao)于額定(ding)頻(pin)(pin)(pin)(pin)率(50Hz)。這(zhe)(zhe)時(shi)，若仍按恒轉(zhuan)(zhuan)矩(ju)原則控制，則定(ding)子(zi)電(dian)(dian)(dian)(dian)壓將(jiang)(jiang)(jiang)升(sheng)高(gao)超過額定(ding)電(dian)(dian)(dian)(dian)壓。那么(me)，當調(diao)速(su)范圍高(gao)于額定(ding)轉(zhuan)(zhuan)速(su)時(shi),須保(bao)持定(ding)子(zi)電(dian)(dian)(dian)(dian)壓為(wei)額定(ding)電(dian)(dian)(dian)(dian)壓不變(bian)。這(zhe)(zhe)時(shi)，隨著轉(zhuan)(zhuan)速(su)/頻(pin)(pin)(pin)(pin)率的(de)上(shang)升(sheng)，磁通(tong)將(jiang)(jiang)(jiang)減少，因此在同一定(ding)子(zi)電(dian)(dian)(dian)(dian)流(liu)下的(de)轉(zhuan)(zhuan)矩(ju)將(jiang)(jiang)(jiang)減小，機(ji)(ji)械特性(xing)變(bian)軟，電(dian)(dian)(dian)(dian)動(dong)機(ji)(ji)的(de)過載能力大幅度減少。

? ? 由此可見，通(tong)用電動機頻率上限為55Hz是有前提條件的：

? ? 1、定(ding)子電壓不能超過額定(ding)電壓；

? ? 2、電動(dong)機在額定(ding)功率運行；

? ? 3、恒轉矩負載。

? ? 上述情況下(xia)，理論和試驗(yan)證明，若頻率(lv)超過55Hz，將使電動機轉矩(ju)變小，機械特性變軟(ruan)，過載能力下(xia)降，鐵耗急增，發(fa)熱(re)嚴重。

? ? 筆者認(ren)為，電動機實際(ji)運(yun)(yun)行(xing)狀況(kuang)表(biao)明，通用電動機可以通過變頻調速(su)器進行(xing)提(ti)(ti)速(su)運(yun)(yun)行(xing)。能(neng)否(fou)變頻提(ti)(ti)速(su)?能(neng)提(ti)(ti)多少(shao)?主要(yao)是由電動機拖(tuo)動的(de)負(fu)載來決(jue)定的(de)。首先，要(yao)弄清(qing)負(fu)荷率是多少(shao)?其次(ci)，要(yao)搞清(qing)楚負(fu)載特性，根據負(fu)載的(de)具體情況(kuang)，進行(xing)推算(suan)。簡單(dan)分析如下：

? ? 1、事(shi)實上，對于(yu)380V通用電動(dong)機，定(ding)子(zi)(zi)電壓超過(guo)額定(ding)電壓10%長期(qi)運行是可以的，對電動(dong)機絕緣及壽命(ming)沒有(you)影響。定(ding)子(zi)(zi)電壓提高，轉矩顯(xian)著增大，定(ding)子(zi)(zi)電流減(jian)少，繞組溫度下降。

? ? 2、電動(dong)機負荷率通常(chang)為50%～60%

? ? 一般情況下(xia)，工業(ye)用(yong)電(dian)(dian)(dian)動(dong)(dong)機(ji)通(tong)常在50%～60%額(e)定(ding)功(gong)率下(xia)工作(zuo)。經推算，電(dian)(dian)(dian)動(dong)(dong)機(ji)輸(shu)出功(gong)率為70%額(e)定(ding)功(gong)率，定(ding)子(zi)(zi)電(dian)(dian)(dian)壓(ya)提(ti)(ti)高(gao)(gao)7%時，定(ding)子(zi)(zi)電(dian)(dian)(dian)流下(xia)降(jiang)26.4%，此(ci)時，即使是(shi)恒(heng)轉矩控制，采用(yong)變(bian)頻調速(su)器提(ti)(ti)高(gao)(gao)電(dian)(dian)(dian)動(dong)(dong)機(ji)轉速(su)20%，定(ding)子(zi)(zi)電(dian)(dian)(dian)流也不(bu)但不(bu)會上升(sheng)，反而(er)(er)會下(xia)降(jiang)。盡管提(ti)(ti)高(gao)(gao)頻率后，電(dian)(dian)(dian)動(dong)(dong)機(ji)鐵耗急增(zeng)，但由其產(chan)生的(de)熱量與定(ding)子(zi)(zi)電(dian)(dian)(dian)流下(xia)降(jiang)而(er)(er)減少的(de)熱量相比甚(shen)微。因此(ci)，電(dian)(dian)(dian)動(dong)(dong)機(ji)繞(rao)組溫度也將明顯下(xia)降(jiang)。

? ? 3、負載特性(xing)各(ge)種各(ge)樣

? ? 電動(dong)機(ji)(ji)拖動(dong)系統是為(wei)負載服務的(de)，不(bu)同(tong)的(de)負載，機(ji)(ji)械特性不(bu)同(tong)。電動(dong)機(ji)(ji)在提速后必須滿(man)足負載機(ji)(ji)械特性的(de)要求(qiu)。經推算(suan)恒(heng)轉(zhuan)矩(ju)負載不(bu)同(tong)負荷(he)率(lv)(lv)(lv)(k)時(shi)的(de)允許(xu)最(zui)高運行頻(pin)率(lv)(lv)(lv)(fmax)與負荷(he)率(lv)(lv)(lv)成反比，即fmax=fe/k，其中(zhong)fe為(wei)額定工頻(pin)。對恒(heng)功率(lv)(lv)(lv)負載，通用電動(dong)機(ji)(ji)的(de)允許(xu)最(zui)高工作頻(pin)率(lv)(lv)(lv)主要受電動(dong)機(ji)(ji)轉(zhuan)子和轉(zhuan)軸(zhou)的(de)機(ji)(ji)械強度限制(zhi)，筆者認(ren)為(wei)一般限制(zhi)在100Hz以(yi)內為(wei)宜。

??? 誤區7、忽視變頻器的自身特點

? ? 變(bian)(bian)頻(pin)(pin)調(diao)速器的調(diao)試工作(zuo)一般(ban)由(you)經銷(xiao)廠家來(lai)完(wan)成，不會出現什(shen)么(me)問題。變(bian)(bian)頻(pin)(pin)調(diao)速器的安(an)裝工作(zuo)較簡單(dan)，一般(ban)由(you)用(yong)戶來(lai)完(wan)成。一些用(yong)戶不認真閱讀變(bian)(bian)頻(pin)(pin)調(diao)速器的使用(yong)說明(ming)書，不嚴(yan)格按照技術要求進行施工，忽視變(bian)(bian)頻(pin)(pin)器自身特點,將其等同于一般(ban)電氣(qi)器件,憑想當然和經驗辦事，為(wei)故(gu)障和事故(gu)埋下了隱患。

? ? 根據變(bian)頻(pin)(pin)調(diao)速(su)器(qi)的(de)(de)(de)(de)(de)使用(yong)(yong)說明書的(de)(de)(de)(de)(de)要求，接(jie)(jie)到(dao)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)應(ying)采(cai)用(yong)(yong)屏(ping)蔽(bi)電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)或(huo)(huo)鎧裝電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)，最好穿金屬管(guan)敷設(she)(she)(she)。截斷電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)的(de)(de)(de)(de)(de)端(duan)頭應(ying)盡可(ke)能(neng)整齊，未屏(ping)蔽(bi)的(de)(de)(de)(de)(de)線(xian)(xian)段盡可(ke)能(neng)短(duan)，電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)長度不宜超過一定的(de)(de)(de)(de)(de)距離（一般為(wei)50m）。當變(bian)頻(pin)(pin)調(diao)速(su)器(qi)與(yu)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)間(jian)的(de)(de)(de)(de)(de)接(jie)(jie)線(xian)(xian)距離較長時(shi)(shi)(shi)，來(lai)自電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)的(de)(de)(de)(de)(de)高諧波漏電(dian)(dian)(dian)(dian)流會(hui)對變(bian)頻(pin)(pin)調(diao)速(su)器(qi)和周邊(bian)設(she)(she)(she)備(bei)產(chan)生(sheng)不利影響(xiang)。從變(bian)頻(pin)(pin)器(qi)控(kong)制(zhi)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)返回的(de)(de)(de)(de)(de)接(jie)(jie)地線(xian)(xian)，應(ying)直接(jie)(jie)連到(dao)變(bian)頻(pin)(pin)器(qi)相(xiang)應(ying)的(de)(de)(de)(de)(de)接(jie)(jie)地端(duan)子上。變(bian)頻(pin)(pin)器(qi)的(de)(de)(de)(de)(de)接(jie)(jie)地線(xian)(xian)切勿與(yu)焊機(ji)及(ji)動(dong)(dong)(dong)力設(she)(she)(she)備(bei)共用(yong)(yong)，且盡可(ke)能(neng)短(duan)。由于變(bian)頻(pin)(pin)器(qi)產(chan)生(sheng)漏電(dian)(dian)(dian)(dian)流，與(yu)接(jie)(jie)地點(dian)太遠則接(jie)(jie)地端(duan)子的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)位不穩定。變(bian)頻(pin)(pin)器(qi)的(de)(de)(de)(de)(de)接(jie)(jie)地線(xian)(xian)的(de)(de)(de)(de)(de)最小截面積必(bi)須(xu)大于或(huo)(huo)等于供電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)的(de)(de)(de)(de)(de)截面積。為(wei)了防(fang)止干擾(rao)而引(yin)起的(de)(de)(de)(de)(de)誤動(dong)(dong)(dong)作，控(kong)制(zhi)電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)應(ying)使用(yong)(yong)絞合屏(ping)蔽(bi)線(xian)(xian)或(huo)(huo)雙股屏(ping)蔽(bi)線(xian)(xian)。同(tong)時(shi)(shi)(shi)要注(zhu)意切勿將屏(ping)蔽(bi)網線(xian)(xian)接(jie)(jie)觸到(dao)其它信(xin)號線(xian)(xian)及(ji)設(she)(she)(she)備(bei)外殼，用(yong)(yong)絕緣(yuan)膠帶纏包起來(lai)。為(wei)了避免其受到(dao)噪聲(sheng)的(de)(de)(de)(de)(de)影響(xiang)，控(kong)制(zhi)電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)長度不宜超過50m。控(kong)制(zhi)電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)和電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)必(bi)須(xu)分開敷設(she)(she)(she)，使用(yong)(yong)單獨的(de)(de)(de)(de)(de)走線(xian)(xian)槽(cao)，并(bing)盡可(ke)能(neng)遠離。當二者必(bi)須(xu)交(jiao)叉時(shi)(shi)(shi)，應(ying)采(cai)取垂直交(jiao)叉。千(qian)萬不能(neng)將它們放(fang)在(zai)同(tong)一個管(guan)道或(huo)(huo)電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)槽(cao)中。而一些用(yong)(yong)戶(hu)在(zai)進(jin)行(xing)電(dian)(dian)(dian)(dian)纜(lan)(lan)(lan)(lan)敷設(she)(she)(she)時(shi)(shi)(shi)，沒有嚴(yan)格按照(zhao)上述要求進(jin)行(xing)施工，導致(zhi)在(zai)單獨調(diao)試(shi)時(shi)(shi)(shi)設(she)(she)(she)備(bei)運(yun)轉(zhuan)正常，正常生(sheng)產(chan)時(shi)(shi)(shi)卻干擾(rao)嚴(yan)重，以致(zhi)不能(neng)運(yun)行(xing)。

? ? 在變(bian)頻(pin)(pin)調(diao)速器(qi)(qi)的(de)(de)日常維(wei)(wei)護中也要(yao)特別小心。有的(de)(de)電(dian)(dian)工(gong)一(yi)(yi)發(fa)現變(bian)頻(pin)(pin)器(qi)(qi)故(gu)障跳停(ting)，就(jiu)立即打開(kai)變(bian)頻(pin)(pin)器(qi)(qi)進(jin)(jin)(jin)行(xing)維(wei)(wei)修(xiu)。這樣做是(shi)(shi)很危(wei)險(xian)的(de)(de)，有可(ke)能(neng)(neng)(neng)發(fa)生人身觸電(dian)(dian)事故(gu)。這是(shi)(shi)因(yin)為即使(shi)變(bian)頻(pin)(pin)器(qi)(qi)不處(chu)于(yu)運行(xing)狀態，甚(shen)至電(dian)(dian)源已經切斷(duan)(duan)(duan)，由于(yu)其中的(de)(de)電(dian)(dian)容器(qi)(qi)的(de)(de)存(cun)在，變(bian)頻(pin)(pin)器(qi)(qi)的(de)(de)電(dian)(dian)源輸入線、直(zhi)流端(duan)子(zi)和電(dian)(dian)動(dong)機端(duan)子(zi)上仍(reng)然可(ke)能(neng)(neng)(neng)帶(dai)有電(dian)(dian)壓。斷(duan)(duan)(duan)開(kai)開(kai)關后(hou)(hou)，必須(xu)等待幾分鐘后(hou)(hou)，使(shi)變(bian)頻(pin)(pin)器(qi)(qi)放電(dian)(dian)完畢，才能(neng)(neng)(neng)開(kai)始(shi)工(gong)作。還有的(de)(de)電(dian)(dian)工(gong)習(xi)慣于(yu)一(yi)(yi)發(fa)現變(bian)頻(pin)(pin)調(diao)速系統跳停(ting)，就(jiu)立即用搖表對變(bian)頻(pin)(pin)器(qi)(qi)拖動(dong)的(de)(de)電(dian)(dian)動(dong)機進(jin)(jin)(jin)行(xing)絕緣(yuan)測(ce)試(shi)，從而判斷(duan)(duan)(duan)電(dian)(dian)動(dong)機是(shi)(shi)否燒(shao)毀。這也是(shi)(shi)很危(wei)險(xian)的(de)(de)，易使(shi)變(bian)頻(pin)(pin)器(qi)(qi)被燒(shao)。因(yin)此(ci)，在電(dian)(dian)動(dong)機與變(bian)頻(pin)(pin)器(qi)(qi)之間的(de)(de)電(dian)(dian)纜未斷(duan)(duan)(duan)開(kai)前，絕對不能(neng)(neng)(neng)對電(dian)(dian)動(dong)機進(jin)(jin)(jin)行(xing)絕緣(yuan)測(ce)試(shi)，也不能(neng)(neng)(neng)對已連接到變(bian)頻(pin)(pin)器(qi)(qi)的(de)(de)電(dian)(dian)纜進(jin)(jin)(jin)行(xing)絕緣(yuan)測(ce)試(shi)。

? ? 對變頻(pin)器(qi)的輸(shu)出參數(shu)進行測(ce)(ce)量(liang)(liang)時(shi)(shi)(shi)也(ye)要(yao)特別注(zhu)意。由于變頻(pin)器(qi)的輸(shu)出為PWM波(bo)(bo)形，含有(you)高次諧(xie)波(bo)(bo)，而(er)電動機(ji)轉矩主要(yao)依賴(lai)于基波(bo)(bo)電壓(ya)有(you)效值(zhi)，故(gu)測(ce)(ce)量(liang)(liang)輸(shu)出電壓(ya)時(shi)(shi)(shi)，主要(yao)是測(ce)(ce)量(liang)(liang)基波(bo)(bo)電壓(ya)值(zhi)，使用(yong)(yong)整流式(shi)電壓(ya)表(biao)，其測(ce)(ce)量(liang)(liang)結果最接近數(shu)字(zi)(zi)頻(pin)譜分析儀測(ce)(ce)量(liang)(liang)值(zhi)，而(er)且(qie)與(yu)變頻(pin)器(qi)的輸(shu)出頻(pin)率有(you)極好(hao)的線性關系。若需進一步提高測(ce)(ce)量(liang)(liang)精度，可以采用(yong)(yong)阻(zu)容濾波(bo)(bo)器(qi)。數(shu)字(zi)(zi)萬(wan)用(yong)(yong)表(biao)容易受干擾，測(ce)(ce)量(liang)(liang)有(you)較大的誤差。輸(shu)出電流需要(yao)測(ce)(ce)量(liang)(liang)包括(kuo)基波(bo)(bo)和其他高次諧(xie)波(bo)(bo)在(zai)內的總有(you)效值(zhi)，因此常用(yong)(yong)的儀表(biao)是動圈(quan)式(shi)電流表(biao)（在(zai)電動機(ji)負(fu)載(zai)時(shi)(shi)(shi)，基波(bo)(bo)電流有(you)效值(zhi)和總電流有(you)效值(zhi)差別不大）。當考(kao)慮(lv)到測(ce)(ce)量(liang)(liang)方便而(er)采用(yong)(yong)電流互感器(qi)時(shi)(shi)(shi)，在(zai)低(di)頻(pin)情況下電流互感器(qi)可能飽和，所以，必須選擇適當容量(liang)(liang)的電