零线电流（零序谐波）

零线电流（零序谐波）

零序谐波的定义及特点

电力系统中零序谐波是三相电流或电压矢量方向相同的谐波电流或电压，由3次、6次、9次及3n（n=1、 2、3…）次谐波电流构成。由于它通常都往中性线流，

所以在三相平衡的三相四线电力系统中，中性线电流即为零序谐波电流。

零线电流产生的原因

1. The cause of zero line current occuring

根据国家标准GB17625.1-2003《电磁兼容 限值 谐波电流发射限值（设备每相输入电流≤16A）》限值要求，对以上设备谐波限值很低，造就产品3次谐波含量很大，由于3次谐波矢量方向角度一致，使用寿命次谐波向零线叠加，造成零线电流过大，。单体功率极少，单体而言，造成的危害可以忽略不计，但当相当多的单体一起使用时，零线电流大得惊人（严重时超过相线电流的两倍）

According to limit value stipulated by national standard GB17625.1-2003 “Electromagnetic compatibility--Limits--Limits for harmonic current emissions(equipment input current≤16A per phase)”, the harmonic current limit value regulated for above equipment stated under item 3 is very low, it makes the 3rd order harmonic current capacity large, also because the 3rd order harmonic current is consistent in vector, direction and angle, the working life of sub harmonic current overlay to zero line, these makes the current of zero line over flow. Power capacity of single equipment is low and we could ignore its damage, but when a great amount of equipments are used at the same time, current of zero line will be great (it will be more than twice of the phase line in serious situation).

零序谐波的危害

1. Harm Of Harmonic Current

l 正常情况下，零线线径为相线的1/3或1/2，而实际电流情况是零线电流高于相线电流的情况越来越多，使零线过载严重、发热严重，老化迅速，很容易由于短路造成火灾等一系列人身安全隐患；

l Normally the wire diameter of zero line is 1/3 or 1/2 of the phase line, in fact it becomes common that current of zero line is higher than phase line, these makes the zero line over load, serious heat and rapid aging, under such condition, fire and other safety loophole will be easily caused by short circuit.

l 由于零线电流过大，使变压器零序保护动作经常跳闸。

l Because the current of zero line over flow greatly, consequently the zero-sequence protection of transformer starts and trips frequently.

l 增加用电量，零线电流过大，零线发热消耗能量，谐波也会消耗能量

l The electricity consumption increase. Because the zero line over flow greatly, the zero line heat and consume energy and accordingly the harmonic current consume energy.

l 补偿功率因数的电容器过热，易损坏，寿命短，造成功率因数降低；

l The capacitor used to compensate power factor is overheating, under such condition, the capacitor is easy to be damaged and work shortly, and consequently the power factor decrease.

l 造成开关及误动作、失灵；设备精度下降、稳定性下降；

l It will lead to switch malfunction and out of work, consequently the accuracy and stability of equipment decreases.