TRANSFER SW [RE-wrenches]

[Pagan.MacKay at traceengineering.com]

Hi Drake,

If the contactor failed it would be possible that the inverters might 
attempt to SELL to the generator which would likely cause damage to the 
generator. This would be dependent on the type of generator; however, 
we're not able to determine exactly what would happen in a specific 
case. Given the possibility the inverters would succeed in selling to 
the the generator it would be a good idea to install a contactor 
isolating AC IN 1. Using two contactors in series as a fail safe would 
be a good way of ensuring possible damage to the generator is minimized. 
And, yes, the contactors should be "motor rated" to protect against 
possible inductive currents that might cause damage to the contactors.

The only other thing you might want to think about is what the generator 
behaviour is when the utility comes back on line. If you want to get 
into this in more detail, contact me offline and I'll put you in touch 
with someone in Applications Engineering.

Best,

Pagan


Drake Chamberlin - Electrical Energy wrote:
> Hi Wrenches,
> 
> We are setting up a transfer switch to run a house on a diesel generator 
> in 
> the event of a blackout.  The house now has a backup system consisting 
> of 
> two Trace 4048 inverters feeding an AC OUT backup panel.
> 
> The inverters AC 1 IN connections are fed from a breaker panel, that 
> will 
> get fed from the generator in the event that the transfer switch is 
> thrown.
> 
> The generator now feeds the AC IN 2 terminals, and the grid feeds the AC 
> IN 
> 1.  The inverters are in the SELL mode.  In the event of a transfer, the 
> 
> generator would want to feed AC IN 1 from the breaker panel, while the 
> generator would still be connected to AC IN 2 as well.
> 
> The inverters would preferentially connect to AC IN 1.  But still we 
> could 
> have excess PV input trying to sell to a generator.
> 
> My solution is to have a contactor open the circuit to AC IN 1 whenever 
> the 
> generator is on,  so that the generator could only connect to AC in 2, 
> which has no sell back issues.
> 
> My questions are:
> 
> 1) What would happen if the contactor isolating AC IN 1 failed?    What 
> would happen if the inverters tried to SELL power to the generator.  
> Should 
> we use two contactors in series as a fail safe?
> 
> 2) Being that the generator will take over loads,  does the contactor 
> need 
> to be motor rated?
> 
> 3) Does anyone find any problems I've missed.
> 
> Thanks for your help.
> 
> Drake
> 
> 
> 

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