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通过三相线电压计算得出三相不对称非正弦状态下负载侧等效相电压,并利用三相瞬时功率理论来测量三相异步电机的输入功率。只需要两组电压电流传感器即可以精确测量三相三线制不对称非正弦状态下的异步电机有功功率和无功功率。测试算法可以普遍应用于三相三线制不对称非正弦电路功率测量。 相似文献
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该文用文中约定的简略表达式分别给出了对称线电压下,三相三线负载电压或电流对称时的导纳或阻抗条件,它们是:相电压负载时相电压对称的条件a~-(Y)=0相电压负载时电流对称的条件a~+(Z)=0线电压负载时线电流对称的条件a~+(Y)=0式中 相似文献
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本文通过对三相三线电路中有功电能的计量分析得到,在具有独立员荷的三相三线电路中,只有当B相接地的两线一地供电方式才能用标准接线的三相三线有功电度表正确计量有功电能(即这时有功电度表一元件采用线电压UAB和线电流i A,二元件采用线电压UCB和线电流I c)。而当其它相接地时,则要相应改变电度表的接线方式。 相似文献
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中点不接零线的星接负载,如三相负载不平衡,则会引起中点偏移。这时,虽然负载的线电压相等,但相电压不等,负载大的一相电压低,负载小的一相电压高。负载严重不对称时,将使负载不能正常工作,甚至烧坏。例:一房内安装了一只三相铁壳开关,总零线接在电线管的接地螺钉上,负载端电线管与总零线用一根约4mm~2的裸铜线连接,负载零线接在负载端电线管上。房内装几只日光灯和一台电瓶充电机。这些负载分别接在三相电源上,工作正常,充电机充电电流40A。突然,充电机充电电流下落到3A,日光灯发红继而烧坏。切断所有负载,测量电源线电压和相电压,都正常。再打开电灯,开启充电机,测量电源的线电压都相等,而相电压不相等,分别为150、300、 相似文献
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1.三相三线有功电度表的接线如图1。在接线正常情况下,其相量图如图2。由此可见三相三线式电度表测得电能,其中:U_1、I_1分别为线电压和线电流,ρ为功率因数角。三相四线式电度表为三组旋转元件,每组元件上加的电压为相电压,通过电流为相电流。 相似文献
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三相电路中功率现象的解释及无功功率的分类 总被引:10,自引:8,他引:10
该文对三相电路的功率现象进行了详细的物理分析,并指出:三相瞬时有功功率之和不为常数是电源电压为非正弦及不对称所必须付出的代价;提出了在非正弦及不对称电路中,三相电路(包括三相三线制和三相四线制)中不仅存在相间无功流动,而且可能存在电源与负载间的无功流动的观点,并在通用瞬时功率理论的基础},给出了基于最小能量传输损失的三相相间流动的无功功率、三相电源与三相负载间流动的无功功率定义。文中所定义的相间流动的无功电流、三相电源与三相负载间流动的无功电流以及有功电流之间具有两两正交的关系。如果忽略电源与负载间的无功流动,则通用瞬时功率理论与赤木泰文瞬时无功理论一致。 相似文献
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The definition of apparent power for unbalanced or non-sinusoidal three-phase systems is still a controversial issue. Two schools of thought are prevalent at this moment. Both schools define the apparent power as the maximum active power that can be delivered to the load while adjusting or maintaining unchanged certain equivalent values of load voltages and currents unchanged. However, one definition uses a pure mathematical approach that leads to a condition where negative and zero-sequence currents may be present. The second definition is based on a practical engineering concept based on assumption that unity power factor implies a perfectly balanced system with pure positive-sequence voltages and currents, (neutral current nil). This paper starts with the theoretical analysis of the most general case when both the network and the load are unbalanced. Comparison among the results obtained by using the two methods indicate minor differences, nevertheless the unity power factor requirement for symmetrical and balanced condition seems to be the better approach for the apparent power definition. 相似文献
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并联型有源电力滤波器在非理想电源电压下的控制 总被引:32,自引:8,他引:32
首先提出了并联型有源电力滤波器在不对称、非正弦电源电压情况下补偿电流指令的准确计算方法。该方法基于同时对三相电压、电流进行旋转坐标变换和投影变换。所求得的补偿电流指令为非线性负载电流中除了基波正序有功分量之外的全部电流分量。应用于三相三线制电路时,该方法可以计算任意次谐波电流的瞬时值。进一步提出了在不对称、非正弦电源电压情况下,并联型有源电力滤波器产生补偿电流的无差拍控制法。理论分析、仿真及实验结果表明了所提出的计算和控制方法的有效性,从而为并联型有源电力滤波器在非理想电源电压条件下的正确控制提供了一条有效途径。所提出的方法对其它类型有源电力滤波器的控制也有借鉴意义。 相似文献
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根据三相四线制发电机整流桥系统的等效电路,应用状态空间平均法推导了四线制二极管整流桥在连续导通模式下的动态平均值模型,给出了换相角的解析表达式.分别应用整流桥的开关模型在Matlab/Simulink软件环境中对平均值模型进行了仿真验证,并应用发电机三相四线制二极管整流桥负载系统对平均值模型进行了实验验证.仿真与实验结果表明,文中的平均值模型能够描述整流桥的主要稳态和瞬态特征,相应直流电压的误差较小,从而验证了模型的有效性.文中给出的平均值模型可以用于此类发电机(变压器)整流桥系统的建模、阻抗特性分析及小扰动下稳定性分析. 相似文献
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In this paper a new configuration for an active line conditioner is proposed to correct dynamically voltage unbalances in a three-phase AC system. In the proposed system it is shown that the injection of a correction voltage Vinj in one phase is sufficient to nullify the negative sequence voltage component in the incoming three phase supply. The resulting three phase voltages at the load terminals are essentially positive sequence voltages and hence are balanced. It is further shown that the kVA requirement of the proposed active line conditioner is small, typically 3% for a ten percentage unbalance in the input supply. The dynamic cancellation of the negative sequence voltage component by the proposed scheme drastically improves the performance of induction motor loads connected to a weak AC system. A thorough analysis of the scheme along with the suitable design guides are presented. Finally selected experimental results on a laboratory prototype active line conditioner are detailed 相似文献
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一种用80C196KC单片机控制的新型全自动化功率因数补偿器系统,能对各相负载分别进行补偿,以提高功率因数,尤为适用于三相不对称负载的电力用户。通过键盘能完成对电力参数的设定。同时,还具有各相电流值和功率因数分时显示等特点。 相似文献
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电力系统中非线性元件的急剧增加,造成电流电压波形的畸变和不对称日益严重。尽管非正弦波形下有功功率的定义已确定无疑,但视在功率的定义存在争议,导致功率因数的差异。对工业界广泛使用的算术视在功率和矢量视在功率与IEEE1459-2000试行标准中有效视在功率的定义进行了对比分析,通过线损和视在功率的关系证明了传统定义的局限性和有效视在功率定义的科学性;以三相不对称的牵引电力网为例,根据德昌牵引变电所实测数据进行了仿真试验,通过计算结果的分析,证实了有效视在功率在实际应用中的现实意义。 相似文献
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三相四线制系统下电流谐波和无功功率的检测与补偿 总被引:10,自引:0,他引:10
本文提出了一种三相四线制系统下电流谐波和无功功率的补偿方法,给出了αβ0坐标系下广义瞬时电流的定义,分析了瞬时无功功率在三相四线制系统下的物理意义,并给出了该系统下谐波电流和无功功率补偿电路,基于此电路的仿真结果表明该补偿方法能有效消除电流谐波及无功功率。 相似文献
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In the literature, it is well known that transformers and cables have excessive losses or overheating under non-sinusoidal current conditions. Accordingly, they have reduced current carrying capabilities (or loading capabilities) for that kind of conditions. This paper aims to employ passive filters for the effective utilization of the cables and transformers in the non-sinusoidal systems. Consequently, an optimal passive filter design approach is provided to maximize the power factor expression, which takes into account frequency-dependent line losses, under non-sinusoidal background voltage and line current conditions. The individual and total harmonic distortion limits placed in IEEE standard 519 are taken into account as constraints for the proposed approach. Besides, keeping the load’s displacement power factor at an adequate range is desired by the proposed approach. The proposed approach and the traditional optimal passive filter design approach, which aims to maximize the classical power factor expression, are comparatively evaluated for an industrial power system with a group of linear and non-linear loads, overhead transmission lines, cables and a transformer. Numerical results show that the proposed one has a considerable advantage in the improvement of the total supply line loss and the transformer’s loading capability under non-sinusoidal conditions when compared to the traditional one. On the other hand, for the simulated system cases, both approaches lead to almost the same current carrying capability value of the cables. 相似文献