Measuring current transformers. Production.
measuring current transformers
► Advantages of transformers with amorphous nanocrystalline alloy cores
With the transition in commercial metering of electricity to the use of electronic meters, the requirements for the rated load of the current transformer are reduced: it can be limited to 5 VA (for a current transformer for metering with induction meters, it was 10-20 VA or more), which ultimately proportionally reduces the technical loss of electricity for metering. This is of particular importance due to the fact that the efficiency of the current transformer (the ratio of the active power taken from the secondary winding of the transformer to the active power supplied to the primary winding), in comparison with the efficiency of voltage transformers, is low due to losses in copper and magnetic core : Efficiency is less than 50% at rated currents. It is easy to calculate that if 100 thousand units are installed in the power system. current transformers, then a power saving at each of only 10 W will give a total saving of 1 MW, and the annual electricity saving will be 8760 MWh, or about 440 thousand dollars (at the rate of 0.05 dollars per 1 kWh).
In the event that, according to the operating conditions, it is necessary to place the meters far from the current transformers (for example, at 25 meters or further), it is necessary either to use current transformers with an increased rated load power, or at the same power with a rated current of 1A (while the permissible maximum the external resistance of the secondary circuit increases 25 times). In the latter case, it is necessary to use, accordingly, meters for the rated current not 5A, but 1A.
The high magnetic qualities of the cores of current transformers made of nanocrystalline alloys make transformers based on them sensitive in terms of metrological characteristics to an increase in load (increase in load resistance) in the secondary circuit of current transformers in excess of the nominal at the maximum primary current, which in practice requires strict fulfillment of all the above anti-overload requirements. The overload capacity of such current transformers can be increased by increasing the power of the cores, which is not always economically justified for the manufacturer, since cores made of nanocrystalline alloys are 1.5-2 times more expensive than cores made of electrical steel.
Measuring current transformers based on nanocrystalline alloy cores have the following advantages over current transformers based on electrical steel cores:
1) resistance of metrological characteristics to DC magnetization,
2) high electrical resistance of the material and 4-10 times less eddy current and core reversal losses,
3) increased (double) technological margin in accuracy class,
4) longer service life with preservation of metrological characteristics (and, thereby, a potentially longer calibration interval),
5) lower material costs for the core and windings, smaller dimensions, weight of the core and the weight of the current transformer as a whole.
6) greater resistance to theft of electricity (at consumer loads less than 50% of the nominal) and an increase in commercial losses, while reducing technological losses of electricity and operating costs.
Measuring current transformers.