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.

9 Energy Saving Principles

  1. Event venues open to the public
    Large public multi-purpose venues such as conference halls and gymnasiums have staff use control switches that are restricted to the public. The staff often needs to roam large areas just to control them which is inconvenient and time wasting. Thus these places are ideal candidates for being remotely monitored and controlled.
  2. Schedule remote control
    The schedule should be easily changed without the need for a specialist. The schedule should have different control methods for peak and off peak periods. During peak periods, local controls are disabled and central control takes over completely. While during off-peak periods, central relinquishes control to the local, and the local control could be achieved using either sensors or wall switches.
  3. Daylight Harvesting
    The purpose of which is to reduce the amount of artificial lighting needed by maximizing the use of natural daylight. This can be achieved by using either a preset time schedule or by using lux sensors during daytime.
  4. Restrict the Use of the A/C
    There should be conditions before the air conditioning can be turned on to avoid having turning them on arbitrarily. These conditions can be in the form of having a temperature limit, time restriction or card insertion before allowing the a/c could be operated.
  5. More Granular Circuit Wiring
    The lights and the air conditioning should be on separate circuits, while each area should divided into smaller areas, this way the lights need not all be turned on and off all at the same time, and only specific areas need to be lit.
    Taking into consideration whether or not the area is exposed to daylight or adjacent to a window is also very important in how the circuit wiring is to be divided.
  6. Single Rooms
    The most power consuming portion of any building are the many individual rooms when added together. Thus they are the focal point of any energy saving measure.
    For rooms that can charge the user for its use, then a prepaid card system or a remote tariff system should be used as much as possible, as these would be the most effective and fair methods to implement energy saving.
    For rooms that are suited to charging the user, then one can make use of a remotely controlled system in conjunction with interactive energy saving smart switches. The purpose of the remote system is to control the room either through a preset time schedule or by the facility manager. The facility manager can decide whether or not to turn on the lights and a/c depending on whether or not there are people present.
  7. Local Conditions
    Rooms with different functions would also make use of different types of energy saving smart switches.
    For discrete rooms or small rooms, one could make use of sensor based energy saving smart switches such as the K24 or the K15. These can be operated in either occupancy or vacancy modes of energy saving control.
    Occupancy mode is used for rooms wherein people go in and out frequently and stay only for a short time such as the restroom or the kitchen.
    Vacancy mode is used for rooms wherein people stay for a long periods of time such as the reception area, lounges and offices.
  8. Air Conditioner Energy Saving Smart Switches (K62)
    In order to avoid having the a/c used unnecessarily, one can utilize the K62. The a/c can only be turned on manually when the temperature conditions are met; when the occupant leaves, the a/c is turned off automatically after a certain delay.
  9. Power Socket Control
    It is not only the lights and the a/c that can be placed under managed control to save energy, but the power sockets can be as well. As a matter of fact, power sockets can be as much a source of saved energy as well and cannot be ignored.

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.