PFCD to help house power quality?

[romeff00]

I got a question for you. Living in a country with 250 Volts elect, i got into a house that had weak lights from time to times, and the other some times couldn't turn on some appliances because of that, is there a device which would correct that?

I was thinking of a PFCD - The PFCD increases power factor, by reducing the amount of reactive power that the load draws, while providing surge protection.

What do you guys think??

 

[lorenb]

seems like the power company should be adjusting for any problems with reactive power.
but buildings are suppose stay within certain guidelines for their reactive power. Try talking with the power company, etc...

 

[romeff00]

Not an option. According to my sources the problem is in the power grid that is too old. Power company does not care. And i am not talking about USA.

 

[Bob S]

Power factor correction circuits only reduce the voltage, and are useful only for induction motors. The PFC uses a triac to control (delay) the turn-on phase, and reduce the output voltage.

Induction motors have a very low power factor when unloaded. I measured an unloaded 1/3 HP induction motor at 125 watts (real power) and 400 VA (total volt-amps), for example. At full load, the 275 VA of reactive power is unchanged but the real power watts increases to over 400 watts. By reducing the voltage with a PFC, the reactive VA decreases, and the real power remains nearly unchanged (the real current increases because the RPM changes very little), so the power factor increases.

If you want to increase the 250 volts ac by say 5%, get a standard power transformer with a 12.5-volt isolated secondary output, and wire the secondary (as an autotransformer) to boost the input voltage by 12.5 volts to 262.5 volts. The current rating of the secondary must meet or exceed your total current requirement at 262.5 volts.

Bob S

 

[romeff00]

i get what you saying, however we not talking about one motor i am talking about the entire house.
Taking into account how many small motors you got around the house i thought it would help if electricity wasnt being wasted

 

[romeff00]

My basic problem is that the power is weak and some of the motors in the house won't start.

 

[Bob S]

I assume you are using single-phase power, so your induction motors have starting coils. Is that right? You might consider changing motors. Capacitor-start induction motors have higher starting torque than split phase, and lower surge current drain. Even better are repulsion-start motors (but none have been manufactured after about 1940, to my knowledge). I have an old 1/2-HP repulsion-start motor that weighs at least 100 lbs (40 kg). You should also look into building the boost autotransformers (I mentioned above) for the motors. The PFC circuits are only useful if you want to save electricity - they will not boost the starting torque.

Bob S

 

[romeff00]

So basically in terms of generation of power the electrical company still produces the same amount of energy even if you have a PFC.
I was thinking does the PFC has the same ability than a capacitor bank the type that is use in big industrial places in order to help when you have extra load on your sistem?

 

[uart]

Power factor correction circuits only reduce the voltage, and are useful only for induction motors. The PFC uses a triac to control (delay) the turn-on phase, and reduce the output voltage.

Hi Bob. I think you're confusing "power factor correction" with "AC phase control".

Power factor correction may be achieved with either active circuits or passive circuits (eg simple capacitor bank) but the function is always to generate lagging VARS locally instead of relying on lagging VARS being supplied through the transmission lines / transformers etc from the power company.

Remember that lagging VARS (which basically just means the reactive power that a capacitor "generates" or equivalently, that which an inductor "consumes") contain no real power, so they can be generated pretty much for free.

In general if you generate your lagging VARS locally then you will raise your line voltage. So what the OP is suggesting may actually work. I'm just not sure if it will have enough of an effect to fully solve the problem. It really depends on the conditions of the power companies supply circuit, the nature of the nearby loads on this circuit and precisely why his voltage is dropping so much. What I'm saying is that depending on various factor that are probably external to the OP's premises, the PFC idea may either be effective or not so effective at boosting the voltage.

 

[Bob S]

Hi Bob. I think you're confusing "power factor correction" with "AC phase control"..

You are correct. The simple "PFC" circuits I was referring to used thyristor circuits to reduce the voltage applied to reactive loads to reduce the reactive power. The much larger power factor correction systems use additional reactive power generators to cancel a (usually inductive) power factor. The lab I used to work for had about 10,000 HP of motor-generator sets. Roughly half were induction motors, and the remaining were salient pole synchronous motors. Sometimes the synchronous motors were used as synchronous capacitors to correct the inductive power factor of the induction motors.

Bob S.

 

[sophiecentaur]

Why should power factor necessarily be the problem? Your lamps wouldn't notice a bit of phase difference and they are possibly just short of volts. Doesn't this call for a Voltage Regulator? Where I used to work, they had a transformer with a tap changer which used to whirr from time to time and adjust its output volts to be more or less level compared with what the company supplied. I think it was very elderly and quite expensive, though. It was installed in the days of valves and unregulated power supplies in equipment.

Perhaps you should complain to the supply company first. Then, if no joy from them(i.e. they won't step up your volts a bit), get yourself a step up transformer and give yourself an extra circuit in the house with a few more volts , for operating those fussy bits of equipment on.