The role of the neutral gap current transformer of the transformer

The transformer protection should be configured with the system protection, the transformer neutral point is equipped with gap protection (that is, zero sequence overvoltage protection) and zero sequence overcurrent protection, and the neutral point is equipped with a current transformer, which is used for zero sequence current protection device. When the neutral grounding knife is closed, the zero-sequence overcurrent protection is put into use. When the neutral grounding switch is in the open state, the gap protection (zero sequence overvoltage) is put into operation.

If the fault point still exists, the neutral point potential of the transformer will rise, the discharge gap will break down and start, and the transformer that is not grounded will be cut off by instantaneous action.

Hello:— 1. Current transformer.

The voltage between "L1" and "L2" on the primary side is extremely low and very low. Otherwise, the load voltage will be greatly reduced, and the electrical appliances will be affected. Therefore, the theory of "secondary high pressure" is misleading.

2. The secondary side of the current transformer is in a short-circuit state, and the magnetic field generated by the current on the secondary side cancels out the primary magnetic field, so the current transformer can work normally.

3. When the current transformer is open, the secondary current disappears, canceling the magnetic flux of the primary magnetic field.

It will also disappear, and the primary coil and core will become an inductance of the nature of a "choke".When the primary side is high-current, the magnetic field of the core is highly saturated, which causes the temperature of the core to rise rapidly, and then burns out the transformer. This is the fundamental reason why current transformers cannot be opened.

4. In the recommended answer, "If the voltage of the secondary side of the open secondary side is the AC voltage of the primary side multiplied by the variable ratio, so the voltage will be very high when the open circuit is opened" is wrong: the AC voltage of the primary side is very low, will the open circuit induced voltage be high?..From the design of the transformer, can one or several coils be connected to 220V?

Q: The difference in the magnetic characteristics of the current transformer at both ends : The difference in the magnetic characteristics of the current transformer at both ends is mainly reflected in the following aspects:

1.The coil structure is different: the coil structure of the current transformer at both ends is different, in which the coil at one end is the main coil and the coil at the other end is the secondary coil.

The main coil is generally a multi-turn coil, and the secondary coil is generally a single-turn coil. 2.The core material is different:

The core material of the current transformer at both ends is also different, the core material of the main coil is generally a soft magnetic material, and the core material of the secondary coil is generally a hard magnetic material. 3.The number of turns of the coil is different:

The number of turns of the coil of the current transformer at both ends is also different, and the number of turns of the main coil is generally more than that of the secondary coil. 4.The coil position is different:

The coil position of the current transformer at both ends is also different, with the main coil generally located in the center of the core and the secondary coil located at one end of the core. These differences result in the pat-blank magnetic characteristics of the current transformers at both ends.

The output characteristics of a variable gap inductive sensor are related to the active position of the armature, the power supply, the number of coil turns, and the core clearance.

It has the outstanding advantages of simple structure, fast dynamic response and easy non-contact measurement, and is especially suitable for acid, alkali, chloride, organic solvent, liquid CO2, ammonia, PVC powder, ash, oil-water interface and other liquid level measurement, and is widely used in metallurgy, petroleum, chemical, coal, cement, grain and other industries.

The inductance value is inversely proportional to the gap.

If the gap is too small, saturation may occur if the operating DC conditions are used.

Variegated inductive sensing reeds are commonly used to measure linear displacement, and their output characteristics are related to the following factors:

Gap between detector head and target: Gap can affect the length of the magnetic circuit and the strength of the magnetic field, which can affect the magnitude of the output voltage.

Core material and size: The permeability and size of the core material affect the size and sensitivity of the inductor, which in turn affects the voltage of the output.

Frequency and magnitude of drive current: The frequency and magnitude of the drive current affect the frequency response and sensitivity of the sensor, which in turn affects the voltage magnitude and stability of the output.

The number of coil turns: The number of coil turns will affect the sensitivity of the sensor, which will affect the voltage of the Tongtong.

Magnetism and shape of the target object: The magnetism and shape of the target object affect the magnetic field distribution and strength of the sensor, and thus the magnitude of the output voltage.

In summary, the output characteristics of variable gap inductive sensors are affected by a variety of factors, and it is necessary to consider the need to achieve more accurate measurement results.

Look at the maximum current in the circuit, and the current that needs to be measured. For example, if the maximum current in the circuit is 400A, and the current to be measured is 5A (for example, the meter current is 5A), then a 500-to-5 transformer should be selected. Choosing 400 to 5 is not appropriate, think about the margin a little.

There are only so many specifications of the transformer, not just choose from you, just choose the most recent one.

For the selection of relay protection current transformer ratio, at least the following conditions should be selected:

1. Calculate the proportion of current to the rated current on the primary side of the current transformer for the primary side;

Second, according to the requirements of relay protection;

3. The calculated primary current multiple MJS for the current transformer is less than the saturation multiple MB1 of the current transformer;

Fourth, it is stable according to heat;

Fifth, for the press stability.

As for the selection of 10kV current transformers for measurement, there is no such thing as this because it is used for measurement under normal operating conditions.

2. Article 3 requirements.

It should be when the secondary side of the voltage transformer is connected to the voltmeter (because the internal resistance of the secondary side is very large), when the secondary side of the voltage transformer is connected to the voltmeter (the internal resistance of the voltmeter is very small), so the secondary side of the transformer is equivalent to a current source for the voltmeter, and when the secondary side of the current transformer is connected to the ammeter (because the internal resistance of the secondary side is very small), When the secondary side of the current transformer is connected to the ammeter (the internal resistance of the ammeter is very large), the secondary side of the current transformer is equivalent to a voltmeter for the ammeter.

This ** introduces in detail how to configure the neutral point zero sequence current transformer of the transformer through the specification, which is simple and clear! Just take a look at it! I am an electrical design note, sharing electrical design knowledge every day, speaking with specifications, paying attention to me, taking your design to take you fly!

The role of voltage transformers.

A voltage transformer is essentially a step-down transformer that converts a high voltage into a low voltage of a certain value for measurement, etc.

Provide voltage signals for metering, measuring, and protection equipment.

The function of the voltage transformer is to convert the high voltage into a standard secondary voltage of 100V or lower in proportion to the ratio for protection, metering and instrumentation devices. At the same time, the use of voltage transformers can isolate high voltages from electrical workers.

Although the voltage transformer is also a device that works according to the principle of electromagnetic induction, its electromagnetic structure relationship is just the opposite compared with that of the current transformer. The secondary circuit of the voltage transformer is a high-impedance circuit, and the magnitude of the secondary current is determined by the impedance of the circuit. When the impedance of the secondary load decreases, the secondary current increases, so that the primary current automatically increases by one component to satisfy.

The electromagnetic equilibrium relationship between the primary and secondary sides. It can be said that the voltage transformer is a special transformer with a limited structure and use form. Simply put, it is a "detection element".

Principle of voltage transformer.

A voltage transformer is a transformer with an iron core. It is mainly composed of:

1. It is composed of secondary coils, iron finger chain car cores and insulation. When a voltage U1 is applied to the primary winding, a magnetic flux is generated in the core, and according to the law of electromagnetic induction, a secondary voltage U2 is generated in the secondary winding. Changing the number of turns of the primary or secondary winding can produce different ratios of primary voltage and secondary voltage, which can form voltage transformers with different ratios.

The voltage transformer converts the high voltage into the low voltage proportionally, that is, 100V, the voltage transformer is connected to the primary system on the primary side at the primary side, and the measuring instrument and relay protection are connected to the secondary side; It is mainly electromagnetic (capacitive voltage transformer is widely used), and there are non-electromagnetic types, such as electronic and photoelectric types.

Classification of voltage transformers.

1) It can be divided according to the installation location.

It is available for indoor and outdoor use. 35kv and below are mostly made of indoor type; Above 35kV is made into an outdoor type.

2) According to the number of phases, it can be divided into single-phase and three-phase type, and 35kV and above cannot be made into three-phase type.

3) According to the number of windings, it can be divided into double winding and triple winding voltage transformer, and in addition to the primary side and the basic secondary side, the three-winding voltage transformer also has a group of auxiliary secondary side for grounding protection.

Voltage transformer key rewrite judgment.

For measuring. Phase voltage.

Usually the secondary.

Y-shaped wiring. The point of hunger is directly grounded.