Circuit breakers and disconnect box.

TeapopperTeapopper Registered Users Posts: 13
Hi all

Just won a wind turbine from an auction, this is a windmax 1000w 24v turbine with a charge controller box.
but as i am a total newbie i want to be secure with all the circuit breakers and disconnect box.

Im struggeling to understand the purpose of the circuit breakers and disconnect box, why do we need em ?, i have not found a good guide on theese, only that i need em and where to place em in a schematic.

i have tried to understand this schematic as i believe its something like this i have do connect.
https://plus.google.com/photos/103436312314613567107/albums/5478255887572895537/5478255974814853378?banner=pwa

Why so high amps on the breakers ?, and do i need 3 of em after the wind turbine if you look on the schematic in link ?
Is the 3 100 amp breakers also acting as a disconnect box in this type of setup ?
why is there a 200 amp circuit breaker behind the controller ? and why 200 amps and not 50 amps ?

Gosh, sorry if this is many questions but i just want to be safe before starting, thanx for a good forum.
Teapopper

Comments

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Circuit breakers and disconnect box.

    I think the 100 amp breakers are to protect each of the three windings in the windmill If one winding has a fault, the other two could supply it with more current than the faulted winding could handle. The 200 amp breaker is to protect you from a fault in the controller. When controllers fail they often short circuit the battery (which may explode under those circumstances).
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Circuit breakers and disconnect box.

    I wonder, does the turbine itself have some sort of built-in braking? I spend some time on a wind-power forum and they strongly recommend AGAINST breakers or fuses in the lines coming down from the turbine. Your dump load - what may be the last defense against overspeed and self-destruction in high winds - should ALWAYS be available to the turbine. If those breakers trip, the turbine suddenly has no load and will rapidly increase in speed, possibly to the point of destruction. I'd rather risk burning up the windings than have turbine blades fragment and start flying around.

    That said, some commercial turbines do have electronic braking built into the turbine itself but the ones I've seen that do that also rectify the power in the turbine, they don't have the "wild" 3-phase power coming down to a controller on the ground.

    THAT said, I'm no turbine expert! Just repeating the first thought in my head when I saw the schematic! :-)

    The 200A breaker on the battery side is mostly to protect the wiring / battery bank as vtmaps mentioned. If something in the controller shorts, you don't want the massive power available in the batteries to melt down the wiring and start a fire. If the charge controller will never exceed 1kW, then seems like you should be able to put a much smaller breaker there. Perhaps it has some ability to exceed normal "continuous" ratings like some AC inverters?
  • TeapopperTeapopper Registered Users Posts: 13
    Re: Circuit breakers and disconnect box.

    Thank you for answers.

    Yes the wind turbine has a electronic breaking built in.
    Is there something i can use instead of the 3 100 amp circuit breakers like 1 unit.
    Do i altso need a separate disconnect box for maintenance or can i just switch off the 3 100 amp circuit breakers ?

    Teapopper
  • BB.BB. Super Moderators, Administrators Posts: 31,068 admin
    Re: Circuit breakers and disconnect box.

    The breakers are there to protect the wiring... At 100 amps on the turbine side--That is way over the rated output current capabilities (I presume) of the turbine... And way over the 30 amp breaker recommendations for 10 AWG wire (per NEC--Although, 35-40 amps is technically feasible. The "fusing" rating for 10 AWG wire is around 333 amps.

    The other breaker is larger (and hopefully the wire too) because it is the vector sum of the wild three phase current from the turbine.

    I would agree that they are using the fuses/breakers as a last ditch safety measure to keep the turbine "safe" (over speed turbines tend to throw blades and even take down entire turbine nacels or even towers when their "brakes" fail).

    The entire electrical design is something I would not have been allowed to do with UL Registered systems I designed.

    If they were "forced" to do this to code--They would be looking at ~3-2 AWG wire minimum for 100 amp breakers. Doing things to code/best practices can get very expensive very quickly.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TeapopperTeapopper Registered Users Posts: 13
    Re: Circuit breakers and disconnect box.

    Ok, so if i go 2 AWG wire i wont be needing any Circuit breaker from wind turbine to charge controller ?
    The only purpose would then be to protect the wind turbine itself if the electrical brakes fails, but 100 amps would not save me as the turbine is rated for 50 amps and will likely blow up before it reaches 100 amps.
  • BB.BB. Super Moderators, Administrators Posts: 31,068 admin
    Re: Circuit breakers and disconnect box.

    Noooo... Not quite saying that. What I was trying to say is that a 100 Amp breaker on a 10 AWG wire is WAY TOO HIGH of rating. If there was something approaching 100 amps going through that wiring, it would cook the insulation and may cause a short/fire.

    IF they wanted to use a 100 amp breaker, per NEC, they would need a minimum of 3-2 AWG wiring to support that size of breaker.

    In the end, you need to look at your energy sources and what can fail--For the most part, we only design for single point of failure (and subsequent issues/failures).

    So--Look at the Wind Turbine as an energy source--if a couple of the three phase wires shorted together--would the turbine be capable of providing > 30 amps (damage to 10 AWG wiring). If not, then a breaker/fuse is not required there.

    Next, look at the other end of the cable. If the rectifier/charge controller shorted, could excessive current flow. Technically, you may be able to drive >30 amps backup to the turbine (and its windings)--But not >100 amps (just pure guessing, not even a SWAG at this point--You would need to know the source voltage and resistance of the various wire runs and turbine windings). Note this is a single fault situation. If you were doing double faults (shorted rectifier and shorted 10 AWG tower wiring), then the answer would probably be different (i.e., you would absolutely need a 30 amp fuse in the 10 AWG wiring).

    And, the same thing back to the battery bank from the charge controller... There, the high current source is your DC battery bank, which can output 1,000's to 10,000's of amperes into a dead short. So--An appropriately sized breaker located close to the battery (current source) and appropriate wiring make this one a definite requirement for protection against over current.

    The problem is that wind turbines are electro/mechanical devices that are subjected to weather, water, ice, vibration, and various failures. One of the biggest issues is that engineers can easily design to support a maximum known Wind Loading (for example). However, it is rare that anyone knows the actual 100 or 500 year wind through their neighborhood--let alone at their site. And because the power in wind goes with the cube of the velocity (power is proportional to V3)--it can quickly eat through the "typical" factor of 10 safety used for most "non aerospace" applications (i.e., a gust that is 2.2x the design limit is over 10x the amount of energy the engineer designed for).

    Add to this that turbine components wear/fail over time (vibration, temperature cycling, lubrication failures, screw-ups, etc.--Actually everything fails over time)... The cost that somebody wants to put into a system is, more or less, based on how much money they wish to spend to reduce the risk of failure and what would happen if it failed (the picture below of a commercial turbine failing is in an open field--Much different if that was a residential/near to home setting).

    Attachment not found.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TeapopperTeapopper Registered Users Posts: 13
    Re: Circuit breakers and disconnect box.

    Thank you BB for the explanation, i will be able to sleep tonight :).
  • PolaracoPolaraco Solar Expert Posts: 102 ✭✭✭✭
    Re: Circuit breakers and disconnect box.

    Why NEC is calling for a 100 Amp Breaker on a 42 amp generator is beyond me. For years I have questioned NEC's policies on some things. 100 Amps would be if that was a motor of some kind. They must be thinking there may be a surge like there is on a motor starting up. If the turbine went wild, you would want to have it protected to trip sooner. With no loadon them though, they will run wild. You could use #6 welding cable which is pretty easy to pull, bend and connect for wire. Technically, to do it right, it should be a 3 pole breaker. Not 3 single poles. The reason for the 3 breakers is because it is 3 phase AC. If one pole tripped, you have a potential of the other parts of the field to generate enough to burn it up.

    The controller is probably nothing more than a buck Boost rectifier setup. To protect from fire, you should have short circuit protection before and after the controller. Fuses work just as well and are more cost effective. Technically, you can use 3 of those solar panel fuses if you want too. You'd need a way of mounting them and still need a switch of some sort.

    I only breezed BB's last comment, but #10 THHN wire is only rated for 30 Amps. You need to run at least #8 wire to cover the 42 amps safely. Wind generators have a high pulse rate. The frequency varies with the speed. It all depends on the windings and rotors.

    Can you use the breaker box as a disconnect box? Most definitely. NEC mandates the disconnect is supposed to be in site of the motor. Not sure what they are saying about the turbines. Given the fact they have battery voltage going to the turbine, it would make sense to have the same.
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