What about the turn ratio of the meter transformer?
★ for three-phase four wire watt hour meters, it is equipped with three current transformers, while single-phase watt hour meters are rarely equipped with current transformers, because the maximum current of single-phase watt hour meters is 80A. The current transformer configured in the measuring instrument has high accuracy, as shown in the figure below.
Current transformer is a kind of current conversion device, which has the dual functions of current conversion and isolation. It converts the large current of high-voltage circuit or low-voltage circuit into low-voltage small current (generally 5a), and supplies instruments and relay protection devices to realize the functions of measurement, metering, protection, etc.
During actual measurement, in order to better match the instrument range, there are also transformers that convert small current below 5A into large current (5a).
★ the wiring method of three-phase four wire watt hour meter with transformer is shown in the figure below.
1, 4 and 7 of the electric energy meter are connected to the s ₁ terminal at the secondary side of the current transformer, that is, the current incoming line terminal.
The 3, 6 and 9 of the electric energy meter are connected to the s‹terminal at the secondary side of the current transformer, that is, the current outlet.
2, 5 and 8 of the electric energy meter are respectively connected to the three-phase power supply, and 10 and 11 are connected to the zero terminal. For the sake of safety, the s‹terminal of current transformer shall be connected and grounded.
★ the current transformer can be penetrated for one turn, two turns, three turns, etc.
Calculation of inner circle turns
1. One turn of threading, meter degree × Transformer magnification = power consumption;
2. Two turns of threading, meter degree × Transformer magnification /2= power consumption;
3. Three turns of threading, meter degree × Transformer magnification /3= power consumption.
For example, the meter reading degree is 1000, the transformation ratio is 500/5, and the number of through center turns is 2, 1000 × 100/2=50000 degrees. The power load is small, the transformation ratio of current transformer is large, and the number of turns can change the transformation ratio of current transformer to make the measurement more accurate.
Responsible editor: LQ