Mains overvoltage transients and inductance of the mains

Hello
How do we assess which value of mains wiring inductance to use for our investigation of mains transients on our outdoor electric lights?
(The schematic and LTspice simulation of our situation is as attached.)

The following says that impedance of the mains in UK is 0.25+j0.23 ohms
http://www.acoustica.org.uk/other/mains_Z.html
That means that the mains inductance depends on the frequency. So which value do we use?

Consider that here in Italy, you have a short circuiti current of 6 kA for house electrical installation, with a mains nominal voltage of 230 Vac, you have an impedance of 0,038 Ohm.

Nothing is said about real and imaginary part; the only information I have is that the cos fi is 0,7 with that short circuit current
Mandi

Thansk, are some Mains Overvoltage transients caused by inverters of all the wind turbines and solar panels switching into the mains and creating a short overvoltage spike on the mains?

Overvoltage transients are much higher than 230 Vac like 1kv and above. Wind turbines and solar panel systems can cause harmonics but individual harmonic components are quite small. For example 1% level is 23 Vac.

Thanks, though i am not speaking about harmonics.
I am speaking about a remote generator suddenly switching into the national grid, and the voltage of the grid suddenly going up because the grid is not loaded sufficiently to take the energy from the remopte generator, and the remote generator's feedback loop is not quick enough to staunch its energy flow into the grid, so an overvoltage spike results.

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Overvoltage transients are much higher than 230 Vac like 1kv and above

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Thanks, small overvoltage transients, as you know, less than 1kV, also occur.
Some spikes on the mains supply voltage just go up to say 450V. Some as you say, are higher than that.

Hi,

I'm currently monitoring our mains voltage.
It is nominally 230V RMS sine.
With about 10kSmpl/s the peak value was less than 330V.

With a pure 230V sine the peak should be 325.3V.
Most of the time we have about 228V RMS with about 318V peak (the top of the sine is a bit flttened)

Klaus

Thanks Klaus.
Thats a good sample rate, 1 sample every 100usec...so you shouldnt miss transients.
I must admit, i work for a company that has shipped 1000's of outdoor mains connected items with very limited mains transient protection, and yet the failure rate is under 1% after 2 years.
We are beginning to wonder if all the alarm about mains transients is really for real.
We do have a TMOV, but that voltage goes up to 900V as it clamps, so our 450V vdd pin of our offline controller would not be protected adequately by the TMOV, but they have survived in great numbers. We dont even have a mains filter.

Hi,

I don't think the transients often are not the problem when continously connected to a low impedance stable mains grid.
In my location most of the grid cabling is undergroung with earh shielded high voltage cables.

While this shielding is installed mainly because of safety reasons... it adds a lot of capacitance.
The whole grid is more capacitive and we need to add inductance for power factor compensation.
This capacitance act like a HF filter.
Additionally earth cables are less critical with thunderstorms.

About 40 years before we had free air cabling, the grid was more inductive and we had to add capacitors for PF compenfation.

A current pulse at an inductive grid causes a lot of voltage spikes ...with a capacitive grid we don't have that high spikes.

******
But you should prepare your application fir high voltage transients.
* other regions have higher impedace grid for transients
* disconnecting the application from grid may cause spikes, especially when there are other devices still connected with your application
* consider that your application may be operated from other power sources (inverter, motor generator, island operated..) here you have completely different conditions.
* consider thunderstorms..

****
Actually I'm wating for a heavy thunderstorm in our location to monitor the voltage spikes...maybe even a power down of the grid.
But we have a power off maybe once in three years for a couple of minutes. Currently I generate 1GByte of data every 3 days....

Added:
"1 sample every 100us"
Indeed I use a sigma delta ADC with 128 oversampling rate...so I surely will detect spikes with 2us of, but for sure I'm not able to detect it's amplitude correctely. Only a small part of the true amplitude...but my resulution is in the mV range.

Klaus

Generators are synchronized to the grid and no spikes occur. Spikes can occur during short circuits and also during normal swiching operations. Lighting strikes often cause overvoltage transients.

Hello,
We want to buy a Mains transient protection unit for our outdoor electrical products. We want it to prevent the mains going above 450V peak.
Do you know of any?
We searched Schneider, Hager, ABB , WJ Furse, etc etc but none limit to 450Vpk.

By their construction, the mains suppressors with a lightning current can have a maximum voltage of 1200 v across the terminals.
and thios is the same for all the companies.
personally I use the OBO V20C for household protection; no problem, sometimes you have to change the discharger because the window turns to red or black due the intervention.

Mandi

I presume you are worried about the safety of the electronic components attached to the mains line. I understand your concern but I differ in the approach.

Your input is sensitive to a high voltage (breakdown failure) but the total power is also important. I hope your instrument can survive a 10kV pulse for 1 ns. With 1 ohm as input impedance, this can deliver a max power of 0.1J. Fortunately these high voltage short duration transients do not propagate far- they quickly get integrated in the line capacitance and inductance. Such spikes do occur in lightning strikes close to the home and they affect only a few nearby places.

More common are 1-5kV pulses that last upto 1us. They are the silent killers. They propagate further and most electronics are designed to be protected against these spikes: about 10% (I do not have the numbers right now) die under this assault.

The problems are particularly tough with respect to SMPS because it is easy to have input-output coupling at relatively high frequency.

My personal suggestion is to use a twisted wire feed for the mains; that will both increase the capacitance and inductance that will integrate any fast rising pulses. If possible, do not ground the circuit- use two wire connection only.

If possible, do not ground the circuit- use two wire connection only.

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Thanks, is that because lightning pulses are with respect to earth ground?

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More common are 1-5kV pulses that last upto 1us. They are the silent killers.

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Thanks, i wonder what casues them?
Probably malfunctioning equipment?
I mean , surely any equipment that produced such things in normal operation would surley be illegal?