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遼寧科技大學本科生畢業(yè)論文 第16頁
Digital Drive Crane Hoist Conversion
While working on the bridge of a crane, I remember feeling the intense heat of the speed reduction Resistors. I looked over the prints and tried to figure out how to reduce this energy loss. As I understood, heat is the product of energy lost (). I was new to crane maintenance in 1990 and, having an electrical/electronic background,
Crane panel manufacturers desired a novel method of crane control that combines new technology with some of the oldest. The new crane panel resulted in lower costs, increased productivity and reduced wear on components, as well as energy savings.
I believed new technology existed. Several of the newer devices needed alternating current input. SCRs, VFDs and PMWs were becoming common acronyms in newer plants. The possibility of upgrading our pre-existing 250 VDC distribution was cost-prohibitive, Various transistors could run DC, but not at the ampere demands we needed. With crane panel replacement under consideration, we challenged our panel suppliers to develop new crane control technology
Digital Hoist Conversion
Severstal North America Inc. is an integrated steel mill dating back to 1917, when Henry Ford built it to supply his Ford Motor Co. auto manufacturing enterprise. It was operated as Ford Steel Division ur~ti11982, when it became Rouge Steel Co. In 2004, OAt Severstal Steel purchased the assets of Rouge Industries and Rouge Steel.
Figure1.A digital drive controller was installed Figure2. Preliminary setup of DDC hoist panel
on this 135-ton-capacity slab-handling crane
The market price for steel was flat in the early part of the new millennium, forcing departmental groups to look for cost-saving improvements. One improvement was the installation of a new type of digital electronic control panel in 2003. This panel represented the introduction of DC electronic crane control to Rouge Steel and the largest duplex crane hoist controller (dual 200-hp) of its type in North America.
The original panels were built on a P&H 135-ton slab-handling crane having standard DC hoisting contactor controls. They were industrial and functional, designed to handle the loads of this crane in 1972. The loads are greater now with heavier slabs, runing the crane at maximum limits and higher production rates. This caused premature equipment failures and production down-time. With three aging cranes in this bay, maintenance costs were rising to new highs. Those involved in maintenance were finding that distributors and manufactures were downsizing or had gone out of business, making replacement parts costly or obsolete. The market drivers of today are forcing the change to newer technologies
Figure3. Digital panel installed on crane trolley deck Figure4.Prewired resistors reduced start-up time
A novel design approach was asked of the crane panel manufactures. They replied with a proposed partnership and an effort to add some of the newest technology to the oldest methods of crane controls. The result was high-current transistor switching with a 250 VDC input. The design was well-thought-out and included integrating the original motors, limits, switches and wiring. Now speeds are controlled by sending the motors only enough current to safely lift and lower the load. The motors are soft stopped (reverse plugged) before the brakes close. This saves wear on components, reduces costs and increases productivity. Without the need for reduction resistors, there is no energy wasted, maximizing the energy savings. The panel installation of the SY-4 crane was completed in 2003 and is still running. The results are smoother movements with little energy loss (heat).
The new panels were designed for installation on the trolley deck, as opposed to the bridge deck.. This aids in troubleshooting and reduces excessive wiring mainly at the weak point of the cable powertrack.. This allowed the time and ability to perform all setup work during mini-downturns without disabling the original hoist. The original panel was left in place as a backup, as failures could not be predicted. To date, the fail-safe panel has not been required.
The panels were pre-wired and pre-tested prior to crane installation, further reducing crane downtime. When the transfer day came, only the master switch, motors and limit leads needed to be rerouted to the new system. On-the-job tuning and monitoring were vital for the first couple of days. It was important to have crane operators involved for that “personal feel” and to obtain their buy-in to the project, to increase awareness and productivity. No-load and full-load current tests were run with great results.
An aded benefit to this control is the electrical current savings. Without reductin resistors for speed points, and with the added benefit of power produced when regenerative lowering, this single crane installation saves more than ＄25000 in electricity annually. This can be a very important consideration if substation power is near critical usage levels. The demand this system imposes is much less than a similar contactor system. With energy costs on the rise, this is a concern for every project considered. Figure 5 indicates an example of electrical current savings potential by comparing contactor panel loads(top) to digital drive loads(bottom).
How it works in the circuit is not unique. The insulated gate bipolar transistor(IGBT) takes the place of the contactors and acceleration resistors. As the master switch is selected for greater speed, the circuitry triggers the transistor at a frequency(pulse width modulated) that allows current to flow through the IGBT. The current circulates in the standard series armature and series field along with the series brake. The longer the input is turned on, the higher the output average voltage (Figure 6). The higher the voltage, the higher the horsepower produced. This system can provide high torque with low currents(heat) as the result of motor regenerative properties. High speed with no load can also be accomplished. Much of this could not be achieved with the original panels.
Figure5.Example of energy saved during lowering sequence.
The difference is noticed when the IGBT is in its off cycle(Figure 7). In this instance, the motor acts as a generator, producing circulating currents through the flyback diode and maintaining self-induced motor currents. This effect reduces ripple and provides current that was not provided by the original power source. The reduction of current loads on system feeders and hardware further adds to the total savings package.
The following items are important considerations when determining if this system will work with an application.
IGBTs are the newest part of the design that makes this panel work with 250 volts DC. They combine the advantages of the bipolar transistor(high voltage and current) with the advantages of the metal oxide semiconductor field effect transistor(MOSFET)(low power consumtion and high switching). IGBTs are semiconductors that combine a high voltage and high current bipolar junction transistor(BJT) with a low-power and fast-switching MOSFET. Consequently, IGBTs provide faster speeds and better drive and output characteristics than power transistors and offer higher current capabilities than equivalent high-powered transistors.
Figure6.Hoist current flow when the IGBT is on
Figure7.Hoist continuing motor current flow when the IGBT is off.
Heat sinking, including consideration of air temperature and air flow, is essential to the proper operation of any solid-state reply. It is necessary to rovide an effective means of removing heat from the IGBT. The importance of using a proper heat sink cannot be overstressed, since it directly affects the maximum usable load current and maximum allowable ambient temperature. Up to 90 percent of the problems with transistors are directly related to heat. Lack of attention to this detail can result in improper switching(lockup) or even total destruction of the IGBT. If the device ever reaches an internal temperature of 105℃, it will be permanently destroyed. One of the problems encountered at Severstal NA was program temperature cutbacks due to excessive heating. When electrical current cutback does not control the drive, it will stop on software limits. Transistors develop heat as a result of a forward voltage drop through the junction of the IGBT. Beyond this point, heat will cause a reduction(software cutback) of the load current that can be handled. If the demand is too great, the program is designed to shut down.
Care must be taken when mounting solid-state relays(SSRs) in a confined area. SSRs should be mounted on individual heat sinks whenever possible. SSRs should never be operated without proper heat sinking or in free air, as they will thermally self-destruct under load. A simple way to monitor temperature is to slip a thermocouple under a mounting screw. If the base temperature does not exceed 45℃, the SSR is operating at its optimal level. Remember that the heatsink removes the heat from the SSR and transfers that heat to the air in the electrical enclosure. In turn, this air must circulate and transfer its heat to the outside ambient. Vents and forced ventilation are good ways to accomplish this. Semiconductor fuses are the only reliable way to protect SSRs. They are also referred to as current-limiting fuses, providing extremely fast opening while restricting let-through current far below the fault current that could destroy the semiconductor. This type of fuse tends to be expensive, but cheap by comparison to the damage that could occur, providing a means of fully protecting SSRs against high current overloads. An fuse rating is useful in aiding in the proper design of SSR fusing. This rating is the benchmark for an SSR's ability to handle a shorted output condition. Devices such as circuit breakers and slow blowfuses cannot react quickly enough to protect the SSR in a shorted condition and are not recommended. Every SSR has an rating. The idea is to select a fuse matching the capability of the solid-state relay for the same duration.
Figure8.IGBT and components mounted on heat Figure9.External mounted fans removed IGBT heat
Figure10. Panel fans removed internal heat buildup Figure11. Semiconductor fuses provide the best protection for solid-state relays
Motor switching and dynamic loads, such as motors and solenoids, can create special problems for SSPs. High initial surge current is drawn because its star t-up impedance is usually very low. As a motor rotates, it develops a counter electromotive force (CEMF) that resists the flow of currenL This CEMF can also add to the applied line voltage and create over-voltage conditions during turn-off and regenerative times. It should be noted that over-voltage caused by inductive voltage doubling or CEMF from the motor cannot be effectively dealt with by adding voltage-transient suppressors. Suppressors such as metal oxide varistors (MOVs) are typically designed for brief high-voltage spikes and may be destroyed by sustained hlgh-energy conduction. Voltage dump resistors may be needed in extreme cases and should be engineered to meet a system's demand, It is therefore important that SSRa are chosen to withstand the highest expected sustained voltage.
Problems encountered while running the200-hp dual drive were few hut worth mentioning. The program allows for setdng many variables (i.e., speed, currents, brake-open voltage). Most of these are detrimental to the drive or motor if set incorrectly. Although staying within the drive specifications is safe, this may not produce the desired actions. Ambient temperatures must also be considered, since most useful application are near higher-temperature areas. Following are several problems(and solutions) observed during installation and trials:
l Problem 1:The first problem presented itself when applying excessive brake-open curent. The direction contactors were flashed and pitted. Also, the emergency brake contactor appears bluish from high heat. Reducing brake-open current and power-on time to a shorter duration solved the problem.
l Problem 2:Hall effect transistors and IGBT were thought to be faulty parts and/or wiring, but this could not be duplicated. Many suspect parts were replaced, but it was determined that internal panel ambient temperature was the problem. This was solved with cooling fans on the doors and on the IGBT cooling fins.
l Problem 3:Temperature cutbacks usually led to errors. It was found that a new crane operator did not like operating the hoist at full speed. Longer run time and higher IGBT cycles caused unnecessary heating in panels. Reducing field current settings eased this problem. This increased the lowering speeds but greatly reduced the IGBT voltage drop, in turn reducing its heat dissipation. Cooling fans eliminated the problem.
l Problem 4:All power must be disconnected from the line because all lines feed from a common bus capacitive filtering system. This means that the typical way of “pulling motor disconnect and running the controls only” to troubleshoot does not work. The panel diagnostics and troubleshooting information provided is very helpful.
l Problem 5:Lack of electronic knowledge by the electricians is a concern. When production downtime is critical, the time to troubleshoot is a high-priced commodity. This ultimately puts pressure on the electricians, causing frustration. The solutions was to ensure that the crew is involved Mth project design and installation. Training is vital. If the maintenance team is nat up to speed with the technology, failure is probable. Two training classes were held for all electrical team members.
After one year, the actual materials maintenance and labor savings were calculated, with a payback of 6.2 months. Cost savings and efficiency gains were greater than expected. This led the way to the next drive conversion, which was scheduled for 2006. With a cooperative effort by salespersons, manufacturers, engineers and end-users, Severstal NA vastly improved its ability to compete successfully.
Acknowledgments
The author would like to acknowledge the efforts of former general supervisor Fred Schwartz and the crew at Severstal North America. Without their help, the project may never have gotten this far.
References
1. Creech, R., 'Energy Savings -- DC Digital and DC Contactor Hoist Control System," Iron ~ Steel Technotogg, May 2005, pp. 225-228.
2. http://ray.eeel.nist.gov/modval/database/contents/reports/igbt.html
3. http://web.ece.umr.edu/computing/unix/software/matlab/toolbox/powersys/igbt.html
4. http://www.fujisemiconductor.com/old_pdf/app_ notes/r_ipm.pdf
5. http://www.mathworks.com/access/helpdesk_r13/help/toolbox/physmod/powersys/igbt.html
數(shù)字機起重機提升轉換
雖然工作在橋上的吊車，我記得感覺酷熱的速度減少電阻.我看著圖紙，并試圖弄清楚如何減少這種能源損失.正如我的理解一樣，熱是產(chǎn)品的能源損失（ ） 。我是新來起重機維修工于1990年，并在電氣/電子背景下，我認為新技術是存在的.一些較新的設備需要交流電輸送.在新工廠，SCRs ， VFDs andPMWs已成為常用縮寫詞。在新的可能性下，提升我們的預先分配現(xiàn)有的250伏直流電是成本過高.各種晶體管可以運行直流，但不能以安培的要求，.現(xiàn)在起重機小組正在考慮向我們的面板供應商提出制定新的起重機控制技術。
起重機面板制造商設計了一個新的起重機控制方法，那就是把新技術和最老的技術結合起來。這個新的起重機面板導致了降低成本，提高生產(chǎn)力和減少磨損的部件，以及節(jié)約能源的效果。
數(shù)字提升轉換
韋爾北美公司是一家綜合鋼廠可以追溯到1917年，當亨利福特建立它提供了福特汽車公司生產(chǎn)企業(yè). 在1982年之前，這是作為福特鋼司，之后改名為高棉鋼公司。在2004年，俄羅斯謝韋爾鋼收購了高棉鋼鐵工業(yè)和高棉鋼公司。
在新的千年年初，鋼鐵的市場價格持平，迫使部門團體尋求節(jié)省成本的改進。在2003年，一個改進的方法是安裝一種新型的數(shù)字式電子控制面板，這個小組代表介紹，在北美，直流電子起重機控制高棉最大的鋼鐵和全雙工起重機吊重機控制器（雙200馬力）的類型。
圖1.數(shù)字硬盤控制器被安裝在這臺有 圖2.初步安裝DDC的提升小組
135噸板坯處理能力的起重機上
原來的面板上建立了一個P&H公司135噸板坯處理起重機在吊裝標準直流接觸器控制。它們的工業(yè)功能被設計用于處理負載的這臺于1972生產(chǎn)的起重機。在保證最高限額和更高的生產(chǎn)速度之下，運行起重機的負載更大了就好比加了巨大的石板。這就造成早產(chǎn)和生產(chǎn)設備故障停機時間加大。三老化起重機在這灣，維修費用上升到新高。那些參與維修的人發(fā)現(xiàn)，分銷商和制造商縮編或已停業(yè)，使備件昂貴或過時。市場驅動的今天，迫使改變新技術。
起重機面板制造商被要求需要一種新的設計方法。他們回應在最基本的起重機控制上努力增加一些最新的技術。其結果是高電流晶體管開關的250伏直流電輸入。設計是經(jīng)過深思熟慮的，其中包括整合原汽車，限制，交換機和擰?，F(xiàn)在速度控制發(fā)送只夠目前的汽車安全升降機及降低負荷。電機軟停止（反向插入）前剎車密切。這樣可以節(jié)省的磨損部件，降低成本和提高生產(chǎn)效率。而不需要減少電阻，沒有能源浪費，最大限度地節(jié)約能源。小組安裝系統(tǒng)- 4起重機于2003年完成，目前仍在運行。結果表明，幾乎沒有順暢流動的能量損失（熱）。
圖3.數(shù)字面板安裝在起重機小車甲板上 圖4.預置電阻減少啟動時間
新的面板設計為安裝在甲板上的小車，而不是橋面。這個故障排除和減少過多的電線主要是在于電纜的薄弱。在稍微衰退而停用原來的起重機，在這允許的時間和能力內(nèi)來執(zhí)行所有的安裝工作。原來的面板留在地方作為備用，失敗是無法預測的。迄今為止，面板沒有達到萬無一失要求。
該小組的前有線和預先測試前，起重機安裝，進一步降低起重機停機。當一天的轉讓中，只有總開關，汽車和限制導致需要轉移至新系統(tǒng)。在職調(diào)整和監(jiān)測至關重要的第一幾天。這是非常重要的吊機操作員參與的“個人感覺” ，并獲得他們的買進該項目，以提高認識和生產(chǎn)力?？蛰d和滿負荷運行試驗，目前取得極大的結果。
一個附加的好處是這個控制電流儲蓄。沒有電阻減少的速度點和再生降低時，功率產(chǎn)生的附加的好處，這種單一的起重機安裝每年節(jié)省超過25000美元的電費。這是一個非常重要的事情是附近變電站電力使用水平的關鍵。在實行這一制度的需求遠低于類似的聯(lián)系人制度。隨著能源成本上升，圖5顯示的一個例子電流儲蓄潛力比較接觸小組負載（頂部）到數(shù)字驅動負載（下）。
如何運作的電路并不是獨一無二的。絕緣柵雙極晶體管（ IGBT ）取代電流接觸器和加速度電阻。作為主開關是選擇更大的速度，晶體管電路觸發(fā)的頻率（ 脈寬調(diào)制） ，使電流流過IGBT的。目前流通中的標準系列電樞和一系列領域隨著一系列制動。投入的時間越長，，輸出更高的平均電壓（圖6 ） 。高的電壓保證高馬力生產(chǎn)。此系統(tǒng)可以提供高扭矩，低電流（熱）由于電機再生的緣故。高速無負載時也可以完成。這在很大程度上是不可能實現(xiàn)的在原來的面板上。
圖5.節(jié)省能源降低序列
所不同的是發(fā)現(xiàn)時的IGBT是在其起飛周期（圖7 ） 。在這種情況下，電機作為發(fā)電機，產(chǎn)生循環(huán)電流通過反激式二極管和維護自誘導電動機電流。這種效應降低了紋波，并規(guī)定這是目前所無法提供的原始動力源。減少電流負載饋線系統(tǒng)和硬件進一步增加了總儲蓄封裝。
下列項目是重要的考慮因素當確定是否該系統(tǒng)將與應用程序一起運作。
IGBT是最新的部分設計，使得面板在250伏特直流下工作。他們結合了雙極型晶體管（高電壓和電流）的優(yōu)勢，金屬氧化物半導體場效應晶體管（ MOSFET ）的電源（低功耗和高開關） 。 IGBT是半導體，結合高電壓和高電流雙極型晶體管（雙極晶體管）的低功耗和快速開關的MOSFET 。因此， IGBT提供更快的速度和更好的驅動器和輸出特性比功率晶體管，并提供更高的電流能力比同等高功率晶體管。
圖6.IGBT開啟時提升了電流
散熱，包括考慮空氣溫度和空氣流通，是必不可少的正常運作的任何固態(tài)繼電器。有必要提供一種有效的手段，消除熱的IGBT 。必要時，使用適當?shù)纳崞膊贿^分，因為它直接影響最大可用負載電流和最高允許環(huán)境溫度。高達百分之九十的問題晶體管是直接相關的熱量。沒有注意這個細節(jié)可能會導致不適當?shù)拈_關（鎖定） ，甚至完全破壞IGBT 。如果該設備以往的內(nèi)部溫度達到105攝氏度 ，這將是永久摧毀。一個韋爾北美公司遇到的問題，那是程序溫度在降低由于過度的熱量。當電流減少到不能控制驅動器，它將會停止對軟件的限制。晶體管開發(fā)熱而導致的正向壓降通過路口的IGBT。除了這一點，將導致熱量減少（軟件削減）的負載電流可處理。如果需求過大，該計劃旨在關閉。
圖7.IGBT關閉時電機電流在繼續(xù)提升
當安裝固態(tài)繼電器（序列）在一個封閉的地區(qū)時，應當十分小心。只要有可能，固態(tài)繼電器應安裝在單獨的散熱片上。序列不應該沒有適當?shù)牟僮骰蛏嶙杂煽諝?，因為它們將在這個負荷下自毀。一個簡單的方法來監(jiān)測溫度就是將在熱電偶下安裝螺釘。如果基溫度不超過45攝氏度，是操作系統(tǒng)的SSR在其最佳水平。請記住，移除SSR的熱量和轉讓熱空氣中的電器附件。反過來，這必須空氣流通和轉讓其熱量到外面。噴口和強制通風良好這一途徑來實現(xiàn)這個目標。
圖8. IGBT和元件安裝在散熱片上 圖9.在IGBT的外部安裝風扇散熱
半導體引信是唯一可靠的方式來保護序列。他們也被稱為限流熔斷器，提供極快的開放，同時限制讓通過遠低于目前的故障電流，可以摧毀半導體。這種類型的導火索往往是昂貴的，但比較便宜的損害可能發(fā)生，提供了一個手段，充分保護序列對高電流超載。一個保險絲評價是有用的幫助在適當?shù)脑O計，SSR的能力是處理短路輸出條件。設備，如斷路器和熔斷器緩慢打擊不能作出迅速反應，足以保護SSR在短路條件和不推薦。每一個SSR有一個類別。這樣做是為了選擇一個引信匹配的能力，固態(tài)繼電器的同一時間。
電機開關和動態(tài)載荷，如汽車和螺線管，可以建立特殊問題的序列。要注意高初始浪涌電流，因為它的啟動阻抗通常很低。作為電機轉動時，它開發(fā)了一個反電動勢（ CEMF ）來抵制流動的電流。這CEMF也可以添加到線電壓的應用，并創(chuàng)造過電壓條件在關閉和再生次。應當指出的是，過電壓引起的感應電壓一倍或CEMF從電機不能得到有效處理，增加電壓瞬態(tài)抑制器。抑制器，如金屬氧化物變阻器（ MOVs ）通常是專為簡短的高電壓尖峰，并可能被摧毀的持續(xù)高能量傳導。電壓轉儲電阻可能需要在極端的情況下，應設計，以滿足系統(tǒng)的需求。因此，重要的是序列中選出能承受的最高預期持續(xù)的電壓。
圖10.面板風扇散去內(nèi)部熱量積聚 圖11.安森美半導體提供最好的熔斷器保護固態(tài)繼電器
遇到的問題，同時運行的200馬力的雙驅動器很少，但值得一提。該計劃允許設置許多變量（即，速度，電流，制動初始電壓） 。大多數(shù)這些不利于驅動器或電機如果設置不正確。雖然留在驅動器的規(guī)格是安全的，這可能不會產(chǎn)生預期的行動。環(huán)境溫度也必須加以考慮，因為最有用的應用是近高溫度區(qū)。以下是幾個問題（和解決方案）觀察在安裝過程中和試驗：
(1)第一個問題出現(xiàn)當提出過度制動初始電流。接觸了方向閃現(xiàn)和進站。此外，緊急制動接觸出現(xiàn)高熱量。減少制動初始電流和功率上的時間更短的時間解決了這個問題。
(2)霍爾效應晶體管和IGBT被認為是錯誤的部分和/或線路系統(tǒng)，但這無法復制的。許多人懷疑部分取代，但它的內(nèi)部面板確定，環(huán)境溫度是這個問題。這是解決散熱風扇的入口和IGBT的散熱片的方法。
(3)溫度削減通常導致錯誤。結果發(fā)現(xiàn)，一個新的起重機操作員不喜歡經(jīng)營提升全速。長遠來說，時間和更高的IGBT周期中造成不必要的加熱板。減少外地當前設置來緩解這一問題。這增加了降低速度，但大大降低了IGBT的電壓下降，反過來又減少其散熱。冷卻風扇來消除這個問題。
(4)一切功能必須同線路分開，因為所有線路由一個共同的電容過濾系統(tǒng)提供。這意味著，典型的方式“拉電機斷開和運行控制只有”排查不工作。該小組的診斷和故障排除提供的信息是非常有幫助的。
(5)缺乏電子知識的電工是一個關切的問題。當生產(chǎn)停工是至關重要的，解決的時間是一個高價位的商品。這最終對電工造成壓力，造成挫折。該解決方案是確保工作人員是參與項目的設計和安裝的工作中。培訓是至關重要的。如果維修人員不是提高維修技術的速度，失敗是有可能的。兩個所有電氣團隊成員的培訓班被成立了。
一年后，維修的實際材料和勞動力節(jié)省了計算，回收期為6.2個月。節(jié)約成本和提高效率大于預期。這導致了下一個驅動器轉換，這是定于2006年。與合作努力的銷售商，制造商，工程師和終端用戶， 韋爾北美公司那大大改善其競爭能力為競爭成功。
致謝
作者要感謝前總務主管弗雷德施瓦茲和韋爾北美公司全體工作人員的努力。沒有他們的幫助，該項目可能永遠不會走到這么遠的地步。
參考資料
1 克里奇，河， “節(jié)能---直流數(shù)字和直流接觸器提升機控制系統(tǒng)， ”鋼鐵學院， 2005年5月， 225-228頁。
2 http://ray.eeel.nist.gov/modval/database/contents/reports/igbt.html
3 http://web.ece.umr.edu/computing/unix/software/matlab/toolbox/powersys/igbt.html
4 http://www.fujisemiconductor.com/old_pdf/app_notes/r_ipm.pdf
5 http://www.mathworks.com/access/helpdesk_r13/help/toolbox/physmod/powersys/igbt.html