breaker operation frying surge protector? 3

[bytebyte]

My supervisor is complaining that the utility's substation breaker operations fried the surge protector on our 480V line. Is that possible? If so, what are our options in mitigating it? Thanks.

 

[ScottyUK]

Yeah, definitely possible. Better to kill the protector rather than wipe out your load, in which case it did its job - MOV type arresors are a finite life item so you should expect them to need replacement from time to time.

As for mitigation, well the arrestor did its job. The utility won't stop switching their network so if you have a sensitive load which you are protecting then your options are to continue to protect it using a reasonably cheap solution or save the cost of the arrestor and wait until loads start dying.



----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[PHovnanian]

Replace the protector you've got with one having a higher energy rating.

 

[Tscott8201]

I am going to plead ignorance here and ask a question. All the substation breaker does is open and close the circuit. How could this cause a surge arrestor to fail? The voltage before and after the breaker operation should be the same correct?

Tom

 

[dpc]

Due to the inductance and capacitance in the system, the switching operation can generate short-lived surges and voltage transients.



"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

 

[itsmoked]

Depending on the size of the inductance and the current at the time it could be a very high voltage spike.

The surge suppressor essentially shorts the spike and is faced with doing this until the voltage drops to below the trigger level. Depending on just where the suppressor is located, impedance wise, in the circuit, controls how much of the energy in the spike actually is dropped inside the spike suppressor. This is why they all have energy ratings.

If you are toasting suppressors you need to either get one with a higher energy rating or interpose some resistance between the suppressor and the source of the voltage spikes.

There are two places you can add resistance. If you add in series with just the suppressor and its connection to the network being protected, you essentially protect the suppressor while reducing protection of the network. You must balance this with the fact that the more the resistance the higher the voltage the protected area will experence.

Alternatively you can instead add resistance to the network. Again this will cause the suppressor to see less energy during an event but it also helps the protected area of the system too. This is the method used most effectively with smaller devices like a TV. The spike suppressor is on the device's side of the zip cord supplying the device's power. When the suppressor is tripped the 6 feet of zip cord becomes the series resistance that dissipates most of the transient's energy. The normal power load is not hampered with this zip cord resistance during normal operation.

In large power systems this "source resistance" can result in substantial heating or power waste and is sometimes problematic. Often though it is fine and you even get transformers and such helping with the same issue and in the same way as the zip cord.

If the transient is being caused inside the system and nearby, then it gets harder to use interposing resistance as a helper. Hence add a larger energy capacity suppressor and if you hit the maximum size available then you have to provide some form of interposing resistance.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[PHovnanian]

Thinking about this a bit more:

It would be interesting to see how this surge protector is connected in relation to distribution transformers, your incoming service, any contactors in your facilities, other loads, etc.

It strikes me as odd that you'd be suffering from inordinate amounts of inductive kick. Normally, you see big spikes when you open the supply to an inductive load sitting on a circuit all by itself. But on a utility distribution circuit, there are normally lots of other loads that remain in parallel with the inductor and would serve as a low impedance path for decaying currents.

 

[steelerfan28655]

What is your line distance from the utility breaker? What size is the utility conductor? What size is the utility transformer that steps down to the 480 volts? What is the primary voltage to the transformer?

I am just trying to get an idea to see if there are any limiting factors on the utility side that they may be able to help with. The utility should be able to supply you with the max fault currents for your location, the line distance, cumulative x/r ratios... etc. There may be a small change on the utility side that would limit the amount of in rushing current after the blink.

Have you contacted the utility to see if they may be able/willing to help?

Happiness is a way of travel, not a destination.

 

[steelerfan28655]

One more thing, are your arrestors connected Phase to ground, or phase to phase?

Happiness is a way of travel, not a destination.

 

[jghrist]

Switching surges at distribution voltages are not nearly as severe as lightning disturbances. I doubt that switching surges from distribution circuit breakers caused the problem.

 

[rbulsara]

You may want to verify if the utility co. is closing a breaker or fuse cutouts? If the fuse cutouts, then ferroresonance is a strong possibility.

Especially if there is a relatively long overhead line combined with some underground cable and lightly loaded transformer.




Rafiq Bulsara

http://www.srengineersct.com

 

[steelerfan28655]

I think the utility should be involved if this is a re-occuring problem. They should be able to tell you if the breaker operations are due to normal switching, or if there have been fault situations on their lines.
Bulsara brings up a good point about the fused cutouts. Typically they are thrown in one at a time with a few seconds of single phasing while the second and third cutouts are closed.
How many times have you lost your arrestors?

Happiness is a way of travel, not a destination.

 

[bytebyte]

The arresters are connected line to ground and I don't think the arresters operated. The utility monitored our service for a different issue in April and it showed that there was a 20% increase in voltage on one of the phases. We don't know when our surge protector was damaged so don't know whether it was a result of the voltage swell or not. I suppose we will never know, but at least we know that the surge protector did its job. Thanks everyone for your input!