5 replies to this topic

[papaya]

Hi, been getting abit confused with AC and DC power generation. I know big power plants use AC Currents because it has less voltage drop for power transfer via long distances. However I would like to know more when it comes to local power generations, is Alternators or DC Generators more prefered? Is there any difference between the power generation efficiency? What are the considerations?

For example, car electronic uses DC current, however modern cars use Alternators and then use rectifiers to convert it to DC for use and charging batteries, wouldn't it be better to use a DC Generator instead, seeing AC requires Rectifier while DC Generators uses a Commutator. Or would the loss of AC rectified to DC still be smaller than a DC Generators?

Trying to do some research online but it's getting more and more confusing...

[djack77494]

papaya,
Being a chemical engineer, there is not a lot of help I can provide regarding electrical questions. I can say, however, that about the only place I see DC power being used is in situations where batteries are employed. No batteries = No DC power pretty much, except perhaps for some small low power electronic devices. Certainly, all commercial power transmission that I know of is 100% AC power. That also applies to anything other than very small low power consumers.

Regarding power generation, I believe AC power generation is more reliable/durable than DC. In conjunction with that, rectifiers are highly reliable solid state devices that easily and reliably accomplish the transformation of AC to DC where needed. There is also the safety aspect - AC electricity is much safer to be around than comparable DC power.
HTH,
Doug

[papaya]

papaya,
Being a chemical engineer, there is not a lot of help I can provide regarding electrical questions. I can say, however, that about the only place I see DC power being used is in situations where batteries are employed. No batteries = No DC power pretty much, except perhaps for some small low power electronic devices. Certainly, all commercial power transmission that I know of is 100% AC power. That also applies to anything other than very small low power consumers.

Regarding power generation, I believe AC power generation is more reliable/durable than DC. In conjunction with that, rectifiers are highly reliable solid state devices that easily and reliably accomplish the transformation of AC to DC where needed. There is also the safety aspect - AC electricity is much safer to be around than comparable DC power.
HTH,
Doug

Thanks for the explanation. However I would also like to know from the efficiency point of view whether AC power generation + Rectifier to convert to DC current is more efficient than DC power generation.

Also I though AC normally has higher voltage than DC thus is more dangerous? Normal AC would be 120/240Vac, but still it would be much higher than 12/24Vdc.

How about offshore oil platforms, do they prefer AC or DC generation, seeing that most of their powerful equipment like pump & compressors are powered by fuel and only require electrical power from batteries during start-up, and most of the electronics require DC current. Not sure about the air conditioning though.

[djack77494]

I would also like to know from the efficiency point of view whether AC power generation + Rectifier to convert to DC current is more efficient than DC power generation.

I don't know the answer to this specific question but believe that the overall cycle of generation, (optional) rectification, distribution, and consumption is more efficient for AC relative for larger power users.

AC normally has higher voltage than DC thus is more dangerous? Normal AC would be 120/240Vac, but still it would be much higher than 12/24Vdc.

What you say is true, but you're not comparing "apples to apples". Most DC users are very low power and the inefficiencies of using power at these low voltages is not an issue. AC users tend to be much larger, and for practical (efficiency) reasons, higher voltages are used. I have heard said, and believe that this is true, that if you come into contact with a DC power source, your muscles will contract and you will "freeze" in contact with the power source. For example, your hand muscles would contract around the power wire. In contrast, the alternating nature of AC power would tend to "throw you" away from contact with the power line.

How about offshore oil platforms, do they prefer AC or DC generation, seeing that most of their powerful equipment like pump & compressors are powered by fuel and only require electrical power from batteries during start-up, and most of the electronics require DC current. Not sure about the air conditioning though.

I'll tell you that you can neglect the electronics and even lighting and air conditioning systems. The biggest power consumers by far will be your equipment. Most pumps, compressors, and other big equipment I've seen offshore is electric (AC) powered.
Regards,
Doug

[papaya]

I would also like to know from the efficiency point of view whether AC power generation + Rectifier to convert to DC current is more efficient than DC power generation.

Doug

Great explanation. But I'd like to know why AC and DC reacts differently to human bodies.

[djack77494]

Great explanation. But I'd like to know why AC and DC reacts differently to human bodies.

Sorry. You just moved beyond my area of expertise. Hope someone else can supply an answer.
Doug