Category Archives: Electricity & Water Meters

Energy Meters Do Not Save Energy

Many media reports that one can save energy simply by installing smart meters. This is a myth.

Smart meters can only provide real time data to the operator to let them know how the power is being utilized, or it can identify how energy is being shared to the different areas or departments.

Thus smart energy meters are only half of the energy saving equation, the other half is the  auto meter reading software or the prepaid card system that makes use of this data. It is only by combining the two can an effective energy saving solution be achieved.

Having a meter installed is not the end in itself, but rather its integration into an actionable interface that is the final objective.

DAE is a company that provides such an integrated solution.

Regular versus Dedicated CTs

Most traditional regular CTs have a 5 ampere as its output, thus most energy meter manufacturers make 5 ampere input meters to match these CT types. Most meter manufacturer themselves do not make the CTs. However this has several disadvantages.

  1. Most traditional CTs are big and cannot fit into existing panels
    When an existing panel needs to be retrofitted with CTs, regular CTs cannot be used because they are too large to fit within the tight spaces between the wiring; thus, to accommodate regular CTs, the load wire needs to be extended and drawn out of the panel to a new panel just for installing the meters and the CTs.
    This method is possible, but it is labor intensive and expensive, not to mention that job is complicated and the power needs to be interrupted during installation and would take a long time. Which would most definitely disrupt the work of the electricity user. Then there is the problem of finding space for the new panel, which may not even be possible. Even the aesthetics of the space is made more unappealing.
    Thus the need for the dedicated CT.
    As a result of the dedicated CT being small, they can be easily installed within an existing panel without the need to change any of the existing wiring or having new panels installed for them, the job becomes much simpler and the installation costs are greatly reduced.
  2. Regular CTs are only suited for large amperage currents.
    Regular CTs are more suited for amperages of 200 or greater. But the large majority of branch circuits will often have amperages that is less than 100 and greater than 20, which are much less than the typical 200 amps found in feeder circuits. Thus, when regular CTs are used to measure such small currents, the load wire needs to be looped through them several times. Otherwise the meter will give grossly inaccurate results.
    For example:

    1. A load circuit only has 50 amperes, but a 200 ampere CT is used, 4 loops are needed.
    2. The same CT as above with a 20 ampere load, 10 loops are needed.
      In contrast, with a dedicated CT, not only are they physically small, they are sensitive enough to be able to measure minute current differences. Thus they don’t need looping and the load wire can be passed through directly through the CT once.
  3. Regular CTs have poor accuracy.
    There are of course highly accurate regular CTs, such as those with class 0.5 or even class 0.2, but their price are prohibitively high and are often cost several times that of an ordinary CT. Whereas dedicated CTs are ordinarily found with a class 0.3 accuracy, and are only a fraction of the price.

Evaluating a Current Transformer

  1. Big inner diameter; small outer diameter
    A small outer diameter occupies less space and can fit better in cramped places, while a large inner diameter makes it easier to fit onto the load wire.
    Note that the load capacity is not necessarily the determining factor for the size of the CT, as the actual wire size will determine whether it can fit within the inner window of the CT.
  2. Accuracy
    The true test of accuracy is the accuracy when measuring very small currents, the lower the starting current the better; at the same time the lower phase deviation the better, but this technically harder to achieve.
    When the CT is produced, each would have minor deviations from the other which will make them not entirely compatible with one another (especially when it comes to the shift in the phase angle), this is the result of deviations in their material and construction. If their consistency is poor, then it would be necessary to have the meter be calibrated to each CT.
  3. Interchangeability
    Whenever either the meter or the CT needs to be replaced, then both need to be replaced at the same time. In
  4. Current output better than voltage output
    Small current transformers are available with current and voltage outputs types. The voltage output type is susceptible to noise, while the wiring cannot be extended for long distances because of the voltage drop and capacitive effect. In contrast, the current output type is more stable, reliable and is not easily affected by noise. Thus, most industries choose to use 4~20mA signal transmitters.
  5. Multiple primary windings
    When a regular 5A output CT has a small primary such as 30A, 50A or 100A, it is often necessary to loop the load wire twice or more around the CT primary to compensate for the small signal, otherwise the signal is strong enough to make it usable. But small sized dedicated CTs have such sensitivity and accuracy that they need no looping to compensate.
  6. Comprehensive selection to match all types of meters
    In addition to a selection of current ratings, the CTs should also be available in split core. The meter manufacturer should have the right CT to meet every need, the inventory should be stock, all of these will have an effect on the seamlessness of the project implementation.

Special Considerations

  1. Different CT brands are not interchangeable
    Unlike regular CTs, dedicated CTs for meters from different manufacturers cannot be changed with a CT from another manufacturer. Even more so, regular 5A output CTs most definitely cannot be used, otherwise, the meter could be damaged.
  2. Are the same dedicated CT type from the same manufacturer interchangeable?
    This will depend on the consistency and quality of the CT used by the manufacturer. Most won’t, but DAE’s dedicated CTs are of very high quality and can be interchanged among the same type. When the CT are not of consistent quality then the meter will need to be recalibrated together with the CT, if this is not possible then the alternative would be to replace the meter together with the CT.
  3. What about for regular 5A out
    If a regular 5A output CT is already being used then a dedicated 5A CT need to be used, the CT can either be of the solid or split core type. Be sure to use it with the model of meter that accepts the dedicated 5A CT.