output voltage crowbar

[Jasonz in MO]

Has anyone developed a circuit to monitor the output voltage and kill the generator if it varies outside of preset limits?

I'm concerned about using MEP-003 to power my house and then have a VR failure which fries all my expensive loads.

I'm thinking of an external circuit which monitors the voltage and using a relay to open the DC buss if it varies beyond voltage limits.

I realize governor/frequency control would also cause havoc but I tend to think the mechanical governor will wear/fail gradually. Where as the electrical components in the VR circuit can fail immediately.

Anyone have any ideas or is this really not a concern now that I have it repaired?

 

[Jimc]

i dont have an answer but have been wondering the same thing as you. i have alot of expensive electronic components in the house.

 

[Isaac-1]

There are a variety of industrial safety units that should provide input to a relay to do what you want, take a look at time mark power monitors (you can often find cheap used ones one ebay, etc.)

Ike

 

[Triple Jim]

Very interesting idea, Jason. You could wire a relay in the line with the oil pressure switch and simply stop the engine if a voltage out of range occurs. As far as expensive electronics go, I try to have all of mine on UPSs. They sense both over and under voltage and come on for either condition. Generators are not the only source of overvoltage conditions.

Now you also have me thinking of adding voltage metering to my indoor generator load current meter box.

 

[Jimc]

this is great info. i was just on time-mark's website. looks like model 260 or even the 160 might be the ticket and jim that is a super idea on how to shut down the gen. the whole time i was looking at the specs i was trying to think of a simple way to get that integrated. they are simple 8 pin socket and are small. they could be mounted right inside the control box with ease. found a few on ebay for $20 and under. very cheap insurance. i believe you would need 2 of them. one to monitor each leg.

 

[3dAngus]

It would be way to late in the game if you wanted to shut off the gen. Your best bet is a power conditioner, where the power conditioner shut down, rather then the generator. They are on sale at GL and have alarms and monitoring for all three phase voltages, current, load, voltages, etc. The occasional transients are filters and capped, cleaned, and there is no impact to the interior electronics. The overvoltage conditions are clamped until there is a hazard, and the Power Conditioner, or Power Distribution Unit shuts down so a human can get involved and troubleshoot and/or repair the problem, whether it be with the incoming power from the gen set, the power company, or output from the PDU.

If it trips based on a trigger, they happen more often then you would think, especially from a generator, and by the time the generator ran the voltage up there then went though the shutdown process, it would not be much protection at all. The used PDUs are very reasonable for what they do.

Shutting off the output voltage switch from the generator would be a much faster response then shutting down the engine.

 

[Jasonz in MO]

I think this would be perfect. Monitors voltage and frequency provides a digital display and and be wired to kill the generator if either moves outside of specs.

http://www.bender.org/voltage_relays.aspx#Description

 

[Jimc]

yes basically same thing i guess but more fancy. angus is right though as far as tying it in. the power would spike and shutting down the engine would take too long. it would need to be tied in to simply cut electrical power output.

 

[Isaac-1]

Voltage is going to drop as the engine looses rpms though

 

[Jimc]

True but it will only take a fraction of a second to fry some electronics. If all we had to worry about were electric motors, refridgerators, etc then i think killing the engine would work

 

[Triple Jim]

3dAngus' point is a good one. I was assuming that loads sensitive to spikes spikes and brief overvoltages were already protected. Shutting off the generator engine in my case would be to protect things like refrigerator motors and lighting, and possibly the generator itself.

 

[Jimc]

I guess another good question would be if an 003 were to spike in voltage, how high could it spike? I assume it can only put out so much.

 

[Triple Jim]

When I did my measurement of regulator current while idling the engine on my 003A recently, I disconnected the regulator output briefly with the generator at 1800 RPM, and the output voltage was right around 160 on each 120 leg. When the regulator is disconnected, the transformer that supplies exciter field current has no current through its control windings, so it supplies full output to the exciter field. This should be a worst case failure, since if the transformer itself fails, or the rectifier it's connected to fails, it's unlikely the failure would increase field voltage.

 

[Jimc]

Well every electrical component in our homes is engineered differently so hard to tell how long a computer for instance could handle 160volts. Really that doesnt seem like a huge overvoltage. For extended periods absolutely. For a couple seconds until a diesel engine shut down??? Hard to tell and im only guessing really. In any case i would definately prefer to hook up a voltage sensing relay to shut down the elec output of the gen like the way angus said. That would be my first choice anyway.

 

[Triple Jim]

Doing both would probably be a good idea, since stopping the engine could prevent additional damage to the generator or control circuitry. It would be easy enough to have a 2-pole relay do both things. In any case, there's not much point to having the engine continue running after the output of the generator is turned off.

 

[storeman]

I believe Angus's power conditioners are all 3-phase.

 

[Jimc]

Couldnt agree more jim.

Yeah i looked at those jerry and they appear to be. Also looked them up on grainger and your lookin at $1500-$2000.

 

[storeman]

Yup.

 

[Jasonz in MO]

I agree concerning the time delay shutdown to really protect the loads. I don't yet understand the main breaker shunt circuit but wondering if a simple relay circuit could be used to force the main to trip. I haven't studied this idea at all, just a thought.

Regarding what power leg to monitor. If developing the original idea and not moving to a power conditioner then I don't think it really matters. The frequency is controlled by the rpm of the engine so affects all legs equally. Voltage of all outputs are also controlled by a single device, the voltage regulator. A VR failure will affect the output voltage of all the legs equally.

 

[LuckyDog]

Yea - What Jason said...

Ooops, I just repeated Jason's post...

What about using the power monitor for tripping the main output circuit breaker?

Looking at the schematic (fig 1-7) In the Upper Left corner is the connections for CB1 monitoring circuit. I haven't looked real close to it, but if the current out is too high (or R3 is mis-adjusted) the CB trips.

Wire an output from the voltage monitor to one of the legs on CB1 (1, 9, or 5). I haven't looked into the details. I don't know what kind of voltages you need to apply, just that there is the logical place, If you want a fast voltage shutdown due to Freq or Voltage Out-of-tolerance condition. That is where I would shut it down. You could also shut down the engine, but killing the voltage fast is what will save electronics.

Ask me how I know about brown out problems?