Analysis of Power Grid Interference

There are various forms of interference on the public power grid. Except for noticeable power outages, the vast majority of interferences are not easily noticeable. However, it is precisely this imperceptible interference that poses a serious threat to the normal operation of electrical and electronic devices. For example, the interference induced by lightning on the power grid can cause a voltage of over 20000 volts, which can burn out electrical equipment on the grid.

The interference of high-order harmonics on the neutral line can seriously affect the operation of high-frequency communication equipment, causing misoperation of digital circuits and resulting in serious consequences such as communication interruption and system data loss.

Traditionally, power grid interference is divided into the following categories:

1、 Low frequency interference.

A. Overvoltage: Voltage continuously exceeding 10% of the rated value.

B. Undervoltage: Voltage continuously below 15% of rated value.

C. Power outage: Power interruption exceeding 300ms.

D. Interruption: Power supply interruption of less than 300ms.

E. Surge: Voltage exceeding 10% of the rated value for a duration of 1 to several cycles.

F. Frequency drift: ± 2% of the normal frequency offset.

2、 High frequency interference.

A. Peak: Short term overvoltage several times higher than the rated voltage, sometimes up to several thousand volts, with a duration of milliseconds.

B. Burr: Transient overvoltage several times higher than the rated voltage, sometimes up to tens of thousands of volts, with a duration of microseconds.

C. High order harmonics: Distortion of the power grid waveform caused by the nonlinearity of the load.

D. The main causes of low-frequency interference are: the on/off of large electrical appliances; Excessive changes in power grid load (overload or light load); Load short circuit, etc.

The main reasons for high-frequency interference are:

Nonlinear loads powered by the power grid; Radiation generated by equipment operating in high-frequency mode; Thunder and lightning; Electrical equipment on/off, etc. How to eliminate the impact of various interferences on electrical equipment and provide high-quality and pure power supply for electrical equipment? The current common practice is:

A. Enable UPS to have voltage and frequency stabilization functions, eliminating the effects of high or low voltage and frequency drift.

B. UPS comes with a built-in battery pack, which solves the problems of power grid failures and power outages.

C. Use harmonic filters to effectively filter out high-order harmonics.

D. Use radio frequency interference (RFI) filters to eliminate radio frequency interference.

E. Adopt good shielding measures.

(1) The EVADA UPS adopts DSP control technology for dual isolation online operation, which enables it to have stable voltage, frequency and anti-interference performance. The input voltage range of the IGBT rectifier can be as wide as ± 25% (usually ± 15% for UPS), and the output voltage is within the rated value within this range. Thus solving the problem of input voltage being too high or too low.