矿热炉低压无功补偿
矿热炉低压无功补偿稳定运行须解决的七大特性问题
高谐波电气特性：变压器励磁及不平衡负载会产生3次谐波但其只在短网之间流动（三角形接法），并不反应到一次侧；同时电弧冶炼会产生5次谐波。因此在二次侧加装无功补偿，配备电抗率不小于12%和5.67%的铁芯电抗器，抑制和部分吸收3、5次谐波，对品质的影响是决定性的。
是否加装一定电抗率电抗器的判断依据是：谐波源负载是否大于总容量的20%而非谐波含量是否超标！
容性电气特性：国家关于容性负载的相关规定：即容性负载载流体的载流量须为额定电流的1.3～2.5倍。低压无功补偿一个单元的运行电流一般超过2000安培，必须通过增加载流体截面降低设备的发热，增加设备运行的稳定性。
虽然降低载流体的额定电流可以降低成本，但其带来的危害同样不可忽视。
浪涌电气特性：在投切时，容性负载会产生比感性负载更高的浪涌电流，如主回路无限流电抗器，严重情况投切涌流高达350 倍
所以大多数没有加装一定电抗率电抗器的设备，其投切元件只能采用过零投切方式，如采用真空投切，则会发生真空弧焊；看似先进，实则无奈之举。
强干扰电气特性：由于电弧冶炼的电流达到几万甚至十几万安培，现场会产生很强的交变磁场，它会使闭合导磁回路产生涡流效应，同时对电子开关的触发信号产生影响而导致误导通。
这就是很多采用晶闸管或可控硅作为投切元件经常烧损的原因，当然还有一点就是硅单晶过大（1V压降）的节点功耗。
振动物理特性：受冶炼电弧的反作用力及电磁影响，现场一直处于振动状态，对于低电压、大电流运行的低压无功补偿来说，振动对载流体连接的紧固程度产生影响，如不采取措施，振动会导致大电流连接处松动而打弧烧损。
很多载流体连接处的烧蚀或着火都是由于振动导致螺栓松动造成的，看似微小，实则破坏力极强。所以必须对连接处采用防松设计。
温度高物理特性：弧光辐射、电炉本体及烟罩散热会造成现场环境温度在夏天时会高达40℃以上，同时低压无功补偿设备本身运行发热，双重叠加，如不降低安装环境温度和设备运行温度，电容器的寿命会大大降低。
电容器薄膜的玻璃化（失效）温度为80℃。因此需采用综合措施降低电容器的工作温度和环境温度，除加装合适电抗率的电抗器、放大载流体截面、选择优质元件外，通风同样是必备手段。
粉尘物理特性：冶炼产生的部分细微粉尘漂浮、沉积在现场，对元器件特别是投切元件产生影响。因此低压无功补偿须采用无触点或真空接触器作为其投切元件。
投切元件只能采用真空或无触点开关；如采用无触点开关，其冷却方式亦只能采用水冷方式，如风冷，粉尘会覆盖在散热器表面，散热效果降低，导致晶闸管或可控硅烧损。
Low voltage reactive power compensation of ore furnace
The stable operation of low voltage reactive power compensation of
ore furnace must solve seven characteristic questions
High frequency electrical characteristics: Transformer excitation and unbalanced loads will produce harmonic 3 times but only flow between the busbar (a triangle connection method) and does not react to a side; at the same time arc smelting will generate harmonic five times. Therefore install the reactive power compensation in the secondary side, equipped with the iron core reactor with the reactance rate of not less than 12% and 5.67% to suppress and partially absorb the 3 and 5 harmonic. It has a decisive impact on the quality.
Capacitive electrical characteristics: the relevant provisions of the state on the capacitive load: that is, the load capacity of the capacitive load carrier fluid must be 1.3 ~ 2.5 times of the rated current. The operating current of the low voltage reactive power compensation of a unit is generally more than 2000 amps, so must reduce the equipment heat by increase the carrier fluid loading cross section to increase the operation stability of the equipment.
Surge electrical characteristics: in the switching, the capacitive load will produce surge current higher than the inductive load. If the main circuit has no current limiting reactor, the current surge can up to 350 times for serious situation
Strong electrical interference characteristics: since the smelting electric arc current reaches tens of thousands or even hundreds of amperes. The scene will generate a strong alternating magnetic field. It will make the closed magnetic circuit produce eddy current effect. It will have an influence on the trigger signal of the electronic switch and leads to wrong conduction.
Physical characteristics of vibration: due to the reaction force of arc smelting and electromagnetic effects, the site has been in vibration. For operating low voltage reactive power compensation with low voltage, large current, vibration will have effect on fastening degree of the carrier fluid connection. If we do not take measures, the vibration will induce loose connections of high current and arc burning.
High temperature physical characteristics: the arc radiation, the furnace body and smoke cover heat radiation will cause the site environment temperature in summer will be as high as over 40t; at the same time low-voltage reactive power compensation equipment device itself will heat in its operation, double stack. If you don’t reduce the installation environment temperature and the operating temperature of the device, the lifetime of the capacitor will be greatly reduced.
Physical characteristics of dust: some fine dust produced by smelting floats and deposits in the field, which will have effect on, especially for the switching components, the components. Therefore the low voltage reactive power compensation should use contactless or vacuum contactor as the switching components.
The judgment of whether to install a certain reactance rate reactor is based on: whether the harmonic source load is greater than 20% of the total capacity not the harmonic content is beyond the standard!
Although reduce the rated current of the carrier fluid can reduce costs, its hazards can not be ignored.
So most of the equipment is not equipped with a certain reactance rate reactor, and its switching components can only use the way of zero switching. If vacuum cast is used, it will produce a vacuum arc welding; it is seemingly advanced, but in reality it is a helpless move.
This is why the thyristor or silicon control is used as switching components often burned. Of course it is also because of too large (IV drop)of silicon single crystal of power consumption of the nodes.
A lot of ablation or fire at the connection of the carrier fluid is caused because vibration causes loose bolts. It is seemingly small, actually has strong destroy. So we must use the anti loose design at the connection.
The glass (failure) temperature of the capacitor film is 80C. Therefore, it is necessary to adopt comprehensive measures to reduce the working temperature and environmental temperature of the capacitor. In addition to install the reactor with a suitable reactance rate, to enlarge the fluid section and select the high quality components, ventilation is also a necessary means.
Switching components only use vacuum or contactless switch; in case of the use of contactless switch, the cooling mode only uses water cooling. If wind cooling is used, dust will cover on the surface of the radiator, so the heat dissipation effect is decreased, which eventually leading to the thyristor or silicon control burning.
低压无功补偿的特点
The characteristics of Low voltage reactive power compensation
回路双隔离
gG级熔断保护
机械式自保持真空投切及计数
自动、手动、检修三状态控制
单体电容器接地保护及故障处理
纯干式充气银锌覆膜电容器
电容器温升小于10K
14%、7%低噪音铁芯电抗器（F级绝缘）
操作过电压特性保护
载流体放大处理
隔磁框架
紧固螺栓防松设计
超压、超温自动控制
自动循环投切控制
自放电时间保护控制
设备运行温度自动控制
| Double isolation circuit
GG grade fuse protection
Mechanical self holding vacuum switching and counting
Automatic, manual, overhaul three state control
Grounding protection and fault treatment of single capacitor
Pure dry air filled silver zinc peritoneal capacitor
The temperature rise of the capacitor less than 10K
14%， 7% low noise iron core reactor (class F insulation)
Operating over voltage protection
Fluid amplification treatment
Magnetic isolation frame
Fastening bolt anti loose design
Automatic control of over pressure, over temperature
Automatic cycle switching control
Self discharging time protection control
Automatic control of equipment operating temperature |
