, a current transformer and voltage transformer principle and structure design
Transformer is also known as instrument transformer, current transformer and voltage transformer.
High voltage will become low current, low voltage, high current is used to measure or protection system.
Its function is mainly to high voltage or high current in proportion to transform into standard low voltage (
Small current (or standard
5 a or 1 a, all the rating)
In order to realize the measuring instrument, protect equipment and automatic control equipment standardization, miniaturization.
Transformer can also be used to separate the high voltage system at the same time, to ensure the safety of person and equipment.
Voltage transformer voltage transformer can be in high pressure and ultra-high voltage power system used in measurement of voltage and power, etc.
With current transformer and relay device coordination, mainly occurred in line short circuit overload failure, such as to provide signal to relay device to cut off the fault circuit, to protect the security of the power supply system.
Protection with micro current transformer entirely different working conditions and the measurement of transformer, transformer protection is just in several times more than normal current current when to begin to work effectively.
Basic structure: special transformer is to increase the voltage range, basic structure is the same as the ordinary transformer.
So the voltage transformer primary side and pay electric voltage U1, U2 = W1 / W2.
Main cooperate with measuring instrument, measuring current transformer in line under normal working state, which is used to measure current, voltage, power, etc.
Measuring the micro current transformer main requirements: (1) insulation and reliable;
(2) the measuring accuracy of high enough;
(3) when the circuit under test failure of large current transformer should be in the proper range of saturated (
If 500% of the rated current)
In order to protect the measuring instrument.
Ct (current transformer) current transformers can be used in the exchange of current measurement, exchange of electrical measurement and protection of electric drive circuit.
Using the transformer, vice edge is proportional to the current characteristics.
Its working principle, the equivalent circuit is the same as the general transformer, just the original winding in series in the circuit under test, and the number of turns less;
Vice edge windings current meter, relay coil current, such as low impedance loads, similar to a short circuit.
The original boundary current (
The current to be measured)
And deputy side current depends on the load circuit under test, and has nothing to do with vice side of the current transformer load.
As vice edge closer to the short circuit, so original, deputy side voltage U1 and are small and excitation current I0 is very small.
Operation of the current transformer, vice edge is not allowed to open.
Because once open, have become primary side current excitation current, the magnetic flux and vice side voltage more than normal and endangers one's personal and equipment safety.
Therefore, vice edge is not allowed to answer the fuse in the circuit, current transformer are not allowed in the runtime removed without bypass current meter, relay and other equipment.
The connection mode of current transformer load according to the receive operation requirement.
The connection mode of the most commonly used for single-phase, three-phase star and incomplete star.
Basic structure: when the current transformer is a used to expand the range of the converter.
Use, the original edge with the circuit under test load series, pay the concatenated 5 a current meter and protection relay coil because of its primary side with thick wire, the number of turns is only a turn or a few turns, the solid and the cathode is small, low voltage, and therefore does not change after the circuit being measured series offset current, pay a wire is very thin, number of turns a lot, but its induction electric potential is not high,
Only a few volts)
Pay the current meter and relay coil resistance is very small, work, pay edge can be regarded as short circuit state, according to the principle of transformer running: the ratio of current transformer primary side current should be is inversely proportional to the number of turns: L1 / L2 = W1 / W2 or L1 = W2 / W1L2.
W1 / W2 = K2 strain ratio.