What Does DC Current do to AC Only Devices

If the building people can not fix there equipment. I would be installing isolation transformers with proper fusing to open the circuit when the DC current rush came in.

If its equipment that needs to operate I would look into power conditioning UPS supplies.

Others on CR4 may have more info.

To your question, I think the surge protector most likely will not help. The surge protectors work more on the quick higher voltage of a surge "mostly DC" If the DC pulse is not much more than the RMS of the AC I don't think it will work very well. But it might it all depends on the duration of the DC.

A side note, the building generator electronic control should not engage the output until the AC has stabilized.Or there system is not appropriate for its use.

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Thanks RAMConsulant, ya beat me to the punch GA.

First, the generator , if it is an AC generator, it will only generate AC, I cannot imagine how a AC generator will generate DC during start up !

Second, some AC powered device such as computers (or those with switching power dupply) will be able to run from either AC or DC supply as long as the supply voltage does not exceed voltage rating. Some AC powered devices, such as those with a input step down transformer will be immediately damaged if you plug it into DC supply.

An AC urge protector will also protect against DC surge if it is within voltage rating.

To sum up what everyone else is saying, THERE CAN BE NO INTERMITTENT DC VOLTAGE FROM A GENERATOR. PERIOD. Either the building engineer is lying to you or he is totally incompetent.

The principle of surge protector is to protect your equipment against voltage spikes. Surge protectors have energy dissipation capability. As long as the energy dissipated is within the rating of the protector, the protector must allow supply removing the voltage spikes without any damage to itself.

As far as the load is concerned, It is not clear whether the load will be able to withstand the DC current. It may depend on the nature of the load.

What DC current?

The heading says DC Current do to AC Only Devices???

Surge arresters in AC for example are not meant to provide protection only against AC voltage.

The OP has no idea but is repeating what some clown told them

You are wrongly informed by your incompetent engineer.

All generators are made AC, no DC. Typical for building set-up, you have right there an ATS-Automatic Transfer Switch. Once there is an interuption, it switches automatically shifted from local electric provider to your generator.

As the generator receives the signal to power-on, a DC current from the battery rushes to the starter of the engine(isolated)--NOT to the main supply lines.

Once the shaft of the generator turns, AC current will be induced not DC, so no DC in the main lines of your building.

Just to answer your question "what if the AC equipment be plug in to DC or change type of power- AC to DC" ---So long as your DC Voltage is less or equal AC Voltage rating, your equipment wont be affected/burn.

Most electrical equipment has a transformer on it that works only with AC type of supply. Plugging a DC on it wont effect to induction of current. So your electrical equipment wont work.

As pointed out above a DC voltage supplied to a transformer will FRY it!

A DC voltage supplied to an induction motor will make it act as a break! A generator connected to an electric motor with lots of inertia will produce lots of voltage spikes on the line and mechanical spikes to the motor load. The bigger the motor and load the bigger the spikes and surges on the line till the generator and motor synchronize.

The spike protectors (MOV) are designed to conduct any voltage over 150VAC(±212VDC) or 300VAC(±424VDC).

Perhaps, you wouldn't mind showing me equation why should it fry. You cant just say things you cant justify. A transformer is not a motor nonetheless yes, they have same working basics "electromagnetism" but different functions.

Basic Equations like Ohms Law Power= (Voltage x Amperage)_dc= (Voltage x Amperage x PF)_ac

All settles down to the power rating of the transformer so long as it is not loaded excessively than its capacity rating either it be DC or AC-> it should not burn, do you get it now?

Inductive impedance (X_L) = ωL. If ω = 0 = DC what is your impedance? With that impedance what is your current? How much current can the conductors in your transformer handle? Maybe your fuse will blow or your breaker will trip first but something will go.

"As pointed out above a DC voltage supplied to a transformer will FRY it!"

Well to be fair, not ANY DC voltage applied to a transformer will fry it. There is SOME resistance in the windings, so if the DC voltage is low enough, it will have a heating effect and if lower enough again, a negligible one.

"A DC voltage supplied to an induction motor will make it act as a break!"

Well again, to be fair, a DC voltage applied to a ROTATING motor will make it act as a brake, but once it stops, it's just a heater.

"A generator connected to an electric motor with lots of inertia will produce lots of voltage spikes on the line and mechanical spikes to the motor load. The bigger the motor and load the bigger the spikes and surges on the line till the generator and motor synchronize."

Not to be pedantic, but the spikes, however real, are only going to be there for the first few cycles. After that the motor field is synchronized and it just goes right along as normal from then on. Assuming everything survives of course, because you are right that those first few cycles can create horrendous spikes, in theory up to 2200% of mormal current in the motor, and I have seen the resultant torque spike twist the shaft off of a 500HP motor.

I beg to differ with the following statement of yours;
"All generators are made AC, no DC." ?? Not quite correct! There are AC as well as DC generators. It will all depend on how the motor is built and terminated. Generators found in automotive applications is a good example, they are either AC or the DC type.
"Plugging a DC on it wont effect to induction of current." Depending on the magnitude of the DC fed on a transformer, may cause winding saturate which may blow any protective fusing for the device.

The BS alarms are going off. Get your boots on.

"That must be some ancient generator. Back in the very early seventies we did have generators on board that sent a low DC current through the power wiring to sense if a load such as a light was switched on. "

You just jogged my memory on something similar! We used to call it a "toe-in-the-water" circuit on large soft starters, because we would send out the low DC votlage pulses and watch the rate of rise in current to see if there was a dead short before gating the SCRs full on into the load. I don't think anyone does that any longer though.