Exporting to the power grid

Hello wlhaynes

If the intention that the wind-generated power is to exported, then a basic requirement is an import/export meter.

If power amounts are "Large", then a specially calibrated import/export meter is used, normally run from Current Transformers placed in the connecting phases.

Because of the importance of the calibration, such a meter is normally carefully checked for accuracy by the Supply Authority to which you intend connecting, and their Test Laboratory will "seal the Meter", so that it may not be "adjusted' later, by others.

Sometimes there are two import/export meters, one owned by customer, one by Supply Authority, and both are read each month, both meters should, of course, read exactly the same at all times.

Out of interest, your 100,000kW = 1 MW and that is not a "large amount" of power.

If you are planning a "Wind Farm" of turbine/alternators, it is very important to do the study carefully, before any ordering or installation commences.

If you are planning to lease part of your property to a "Wind Farm Operator", ensure that you don't have some onerous conditions placed upon you.

Kind Regards....

Thanks, Sparky, for the advice. Import/export meters will probably be used for my connections. I suspect the power company will charge me for the cost of their equipment on their side of the meters.

Wally

I haven't found any real specific information about voltages and hertz when introducing power to the grid and if you have the time I have a couple questions.

What I think I understand is that the power already in the line will pull the introduced power into phase????? Is this true? Sounds tricky and dangerous.

Windmills produce power at 60 hertz only? Single or poly phase?

Inverters aren't used are they? If they are, aren't they a little dirty?

I appreciate any input about this.

In North America, the windmills have to produce 60Hz to connect to the network. The generator has to also control the voltage, power and power factor. This is not easy.

Depending on the type of generators you use, and the control strategy, an inverter might be needed. Various technologies are available without inverters. The inverter gives you more operation flexibility but add a few percents in losses.

The most important is to work with the utility company to make sure that the islanding phenomenon and the line protections are taken care of. One cannot safely connect to the line and start selling power. There are many aspects to consider to avoid de-stabilising the network especially when we are talking about many MW.

Sorry but you made a "small" mistake when you wrote:

"Out of interest, your 100,000kW = 1 MW and that is not a "large amount" of power."

It is actually 100MW. This is not small for a wind mill.

I agree with the rest of your comment.

Regards,

Marco

Thanks Marcot--

I looked up ISLANDING PHENOM. and only found global warming pablum.

What happens when you are slightly out of phase--will the line pull it in? and is it the same for the voltage and current to be in phase?

Does the voltage have match the line exactly?

Sorry I have a ton of questions.

ISLANDING is caused by the network protections tripping and disconnecting a section of line where a generator is operating. This section is kept alive by the generator while the rest of the network is down. Your street then becomes an island of light in a dark city. This is dangerous for the utility work crew as they expect the power to be off. It can also prevent some protections to re-connect to the network as the voltage and phase relationship is not likely to be maintained between the utility and your generator.

A generator (windmill or diezel...) needs some sort of protections to disconnect from the line when the network fails.

The voltage and phase relationship to the line are important if you use a synchronous generator or an inverter. Induction generators are not sensitive to these parameters but have very little control over the power transfered. Induction generators also need to have an active network to generate power. They are less prone to islanding than synchronous generators but can still present some dangers. You have to choose between a simple technology with little control on the performances or the optimum technology that almost requires a PHD in controls to operate.

Another parameter to considers is what happens when you loose the network. If it represents a large part of your load, the windmill can over-speed and be damaged.

One has to do a cost benefit analysis to evaluate the technology that suits the application.

Hello marcot

from me for noticing my error.

We had a teacher who used to say, when we caught him out:"Just checking to see if you're awake, lads", and I could have used that excuse, except it was my genuine inadvertent error.

Thanks for pointing it out.

Kind Regards....

This might help.

Anytime amps exceed 400, CT metering (using a reduced current at a transformed ratio with a multiplier applied to the measurement - does not carry the actual system current in the meter) is used for a myriad of practical reasons, and the bussing and cables are sized for the actual load. The metering is essentially the same either way and is usually provided by the utility you connect to. The panel will be yours to provide. Also the utility will dictate the panel details for you.

The double metering mentioned above would be a customer owned meter panel on the customer side of the utility metering. The two readings will never be exactly perfectly matched over years of time, but in the short term should be within the stated accuracy parameters of the meters. Perfection is not an option.

Inverters are used for DC generation, yes it is usually fairly 'dirty' in sinusoidal terms.

AC generation is usually started like any other motor, and when the power source (Wind etc) adds power to the system the phase angles reverse and generation out to the grid begins, same as for any motor. The output of an inverter has some electronic phase/voltage matching circuitry usually, but once connected it acts much like the AC generation, reversing the phase angles to generate, but with a bit of a 'dirty' sine wave.

System outage sensing relays act to protect the generation facility and the grid repairmen as previously discussed in 'islanding'.

Hopefully you are planning to have a qualified contractor set this installation up for you, working with the connecting utility. This is for the sake of all that expensive equipment at stake there.