smart electric meters

[Disha Karnataki]

hello everybody,
if any one has ever installed smart electric meters could u tell me what deffeciency did u find in those meters?
I'm planning for a project based on smart meters & don't want to leave any disadvantages in it .
I'll try to make the best electric meter .
but only thing is u people need to help out with the possible problems that occcured when u were using electric meters .:wink:

 

[hareeshravi]

Hi Disha,
Disadvantages are usually result of design/economic tradeoffs A philosophical thought is gien below. The commercial smart meters are made with economy in mind. Many of them are available, but no single one gives all the features. Usually customer selects the model according to his requirements. Here are the common 'deficiencies' experienced.
1. Complexity of reading/ User Interface.
In field you cannot provide a complete display (size tradeoff) , and hence meters are usually limited to a small 5" displays. So to see a parameter, you have to scroll a lot. SMs do provide computer interfaces, but are not practical in field for normal/routine works. (Big screen => bulkey & space consuming)

2. Complexity of setting up at field.
You have to program these meters during commissioning and replacements. As the meter gives more sophisticated data, more no of parameters need to be set, which can bring errors. (simple: CT ratio, CT TYPE, Star/delta, )

3. Stored data
We require information logs on power quality issues, parameters during various events (blackout, surges, impulses e.t.c) . These require huge memory. This shoots up cost. (Basic Smart energy meters need not have this)


Possible design problems:
1. ISOLATION (Go through Analog Devises Website for more information)
2. Communication interfaces.
3. Memory/Data management

 

[Disha Karnataki]

hey hareeshravi,
i was just thinking how 2 make a digital meter (as my first step towards making a smart meter) & thought how it would be if i keep analog meter as it is (the mechanical construction) & attach another circuitry to convert this analog movement of meter into digital?
is this idea right?

 

[hareeshravi]

Hi Disha,
In my opinion, that approach is not right. It will have deficiency of both Analog & Digital.
1. You can implement using micro controller boards. Make it powerfull by writing code to derive more parameters (eg: pf) and transmit information.
2. You can go further by making your own board, with custom IC's from Texas / Maxim / Analog Devices. They have special IC's for metering and other functions. It will be a very good project if you can implement one (Design PCB, buy the components, get it soldered), though its not that easy .
3. You can also go through evaluation boards or already designed kits to help you out.
Regards.

 

[Disha Karnataki]

hi hareesravi,
can u just tell me how much more precision will the digi meter give than analog?
if both are almost same then why go for differnt coding to find power using microcontroller ? Implement the same technique as in analog meters(i.e take anlog meter itself) & concentrate on adding other circuitry like anti theft system,power management system etc..& turn it into a smart meter ...

 

[hareeshravi]

Hi Disha,
Digital meters can be designed with far better precesion and accuracy compared to analog.
Problems with analog meter is not only with accuracy.
They have very delicate mechanisms and are very prone to errors.
Also if you try to retrofit a mechanism to convert to digital, its double work and will reduce meter accuracy still further.
- Just try to understand the basic mechanism of meter, then find out a way to convert to digital. Then you will understand how easy a full digital system would be.

 

[schmitt trigger]

In addition to what has been mentioned, one must evaluate a full electronic meter during abnormal line conditions;
These may be, but not limited to:

1) Brownouts and blackouts
2) Voltage surges
3) Nearby lighting strikes and/or substation faults
4) Cycle dropouts
5) Overloads and shorts
6) Temperature extremes

Generally, dumb electromechanical meters can survive those events without too much forethought. But in an all-electronic device, it is imperative that protections are designed into, and fully evaluated.
For instance, what happens in an extremely hot day, and the meter is overloaded for a longer time that it takes for the breaker to trip? What happens if it has a severe brownout immediately followed by a voltage surge?
If the memory is being written while a blackout occurs, how do you prevent memory corruption?

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In addition to what has been mentioned, one must evaluate a full electronic meter during abnormal line conditions;
These may be, but not limited to:

1) Brownouts and blackouts
2) Voltage surges
3) Nearby lighting strikes and/or substation faults
4) Cycle dropouts
5) Overloads and shorts
6) Temperature extremes

Generally, dumb electromechanical meters can survive those events without too much forethought. But in an all-electronic device, it is imperative that protections are designed into, and fully evaluated.
For instance, what happens in an extremely hot day, and the meter is overloaded for a longer time that it takes for the breaker to trip? What happens if it has a severe brownout immediately followed by a voltage surge?
If the memory is being written while a blackout occurs, how do you prevent memory corruption?

 

[Disha Karnataki]

thanks hareeshravi

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thanku hareesh

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hi schmitt trigger,
so do u support the idea of keeping the analog meter as it is & just adding the extra features for this electromechanical meter to turn it into a smart meter ?

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hi hareesh,
don't u feel schmitt is right ?it's true that smart meter prices will shoot due to the factors mentioned by schmitt trigger.

 

[hareeshravi]

Hi,
I am not against Analog meters. But IMO if you retrofit an analog meter with digital circuits to make it 'smart', all the problems of both analog & digital will manifest with additional problems due to interface (eg: spring forces may change, affecting the accuracy). Anyway if you want to use a smart meter, as you told, the problems do exist, and has to be taken care by design.