Customised toroidal split CT

The current transformer is a special transformer. Its function is to convert large current into a small standard current, and it works in conjunction with equipment such as measuring instruments, calibration instruments, and relays. This can have the effect of expanding the detection range of the instrument and improving the reliability and safety of the power circuit. The schematic diagram of the wiring circuit of the current transformer is as shown in the figure. The primary electromagnetic coil of the current transformer is connected in series in the primary main power circuit, and the electromagnetic coils of its secondary connected instruments and automobile relays are also connected in series.   Usually when people use current transformers, they mainly consider the two performance parameters of transformation ratio and accuracy.   1. Transformation ratio   The rated voltage value of the secondary side of the current transformer is 5A or 1A. Under normal circumstances, 5A is selected. Common transformation ratios for accurate measurement of current transformers are 5/5, 10/5, 15/5, 20/5, 25/5, 30/5, 40/5, 50/5, 75/5, 100/5, 150/5, 200/5, 250/5, 300/5, 400/5, 500/5, 600/5, 750/5, 800/5, etc. So how to appropriately choose the transformation ratio of the current transformer?   The "Design Specifications for Electrical Measuring Instruments in Electrical Power Installations" requires that "the selection of the detection range of pointer measuring instruments should ensure that the rated current of the power project is marked at 2/3 of the instrument scale." According to this standard, people can use the following The formula is used to calculate the transformation ratio N of the selected current transformer.   In this formula calculation, I is the maximum load current of the control loop, 0.7 means that the maximum load current is indicated at 70% of the instrument panel, and 5 is the secondary rating of the current transformer.   current. Then select the transformation ratio of the relative current transformer based on the measured transformation ratio value. For example, if I is 50A, N=14.29 can be obtained according to the calculation method, so a current transformer with a 75/5 ratio is selected.   2. Accuracy   The accuracy of the current transformer is also called precision, because the ratio deviation and angular deviation of the current transformer are unavoidable. The accuracy of a current transformer is calibrated as a percentage of the deviation limit of this ratio. For example, the maximum ratio deviation of a class 0.5 current transformer is ±0.5%. There are 0.1, 0.2, 0.5, 1, 3, and 5 levels of current transformers for accurate measurement, and 5P and 10P level two current transformers for maintenance. Under normal circumstances, choose level 0.2 for metrological verification, choose level 0.5 for precision measurement, and choose level 1 for general monitoring instruments.   In addition, people must pay attention when using current transformers: the secondary side of the current transformer must be grounded to prevent high voltage from the primary side from flowing into the secondary side, which may endanger the safety of equipment and life; pay attention to the first and second sides of the current transformer Optical rotation, optical rotation will ablate the instrument in serious cases; the secondary side of the current transformer cannot be leaded, and it is forbidden to install a circuit breaker on the secondary side to prevent the secondary side lead from magnetic induction of high voltage, endangering life and road safety.

A current transformer is a current conversion device. It transforms high voltage and low voltage currents into lower voltage currents to supply appearance and maintenance equipment and to isolate appearance and maintenance equipment from high voltage circuits. The current transformer's secondary current is 5A, which makes it safe and convenient to measure the appearance and relay maintenance equipment, and also enables it to be standardised in production.   The structure of the current transformer is composed of iron core, primary winding, secondary winding, terminal and insulation support. The primary winding of the current transformer turns less, connected in series in the demand for measuring current in the line, the flow of large measured current, the secondary winding turns more, connected in series in the measurement of the appearance or relay maintenance circuit.   　　The secondary circuit of the current transformer is not allowed to open circuit. Current transformer in operation, its secondary circuit has always been closed, but because of the measurement of the appearance and maintenance equipment series winding impedance is very small, the current transformer operation is close to the short-circuit situation, the primary current magnetising force is greatly offset by the secondary current, the total flux density is not large, the secondary winding potential is not large. When the current transformer open circuit, the secondary circuit impedance is infinite, the current is equal to zero, the primary current has completely become the excitation current, in the secondary winding seizure of a very high potential, hostage to personal safety, constitute the appearance of the maintenance equipment, transformer secondary insulation damage.   　　The secondary circuit of the current transformer must be grounded to avoid a breakdown of insulation, the secondary string of high pressure, hostage to personal safety, damage to equipment.