Isolation transformer - a device that provides galvanic isolation of the primary and secondary chain decoupling AC, and having an improved insulation among structural features between windings. Sometimes referred to as separating transformers common design to emphasize the purpose of the device.
In Russian literature, little attention is paid to an isolation transformer, the drafters of Wikipedia copied excerpts from PUE and GOST R 50571.11. Let's start with the basic terms:
- Under the double insulation refers to security measures, when, along with the protection of housing conductors or compartment made of insulating material, which eliminates the risk of electric shock, for example, in case of unintended splashing. Electric hand tools are manufactured in a similar performance.
- Heavily insulated equipment equipped with a metal housing or conductive parts are working under the shock. For example, an electric drill.
- The grounded shield is called winding (network, spiral, etc.), Included between the primary and secondary circuit. Sometimes it is called a Faraday shield, the purpose of the measures - to eliminate between circuits capacitive AC coupling.
It would seem that the problem in the transformer includes AC transmission. And useful. The windings are designed to pass a frequency of 50 Hz. Capacitive bond capable violate a rule, the secondary circuit will go interference. If the level is high, what is happening is able to close the current to ground and pose a threat to human life or equipment integrity. For example, mooring the ship and board from the ground are mainly through the screen transformers Faraday housing to prevent corrosion by electrolytic current, reaching through the water to the bottom.
Currents flow due to the difference in potential between the neutral land and the lower layers of the Gulf. To eliminate the effect, apply NGR resistors. This small resistance, calculated on the current 5 A (at a voltage of up to 5 kV) and relieving potential with the hull, for closing the circuit through an extremely low resistance. The resulting resistive divider eliminates potential skid here formed by the neutral currents. What causes non-uniform load of phases.
Among other things, this malicious phenomenon easily cause a spark. If an ordinary freighter is connected via an isolating transformer without a screen, tankers and gas storage facilities likewise prohibited feed. Otherwise it is impossible to predict where the shape of the body and create a higher voltage spark, resulting in a high degree of probability to sad consequences.
It is seen from the diagram that the grounded neutral transformer tanker is moored to the housing to equalize potentials. This action blocks the flow of current through the water, and an isolation transformer excludes other dangers. In this case, the "care" of the hull and the contents of the tanks, it is assumed that the operating personnel know how to behave at the hazardous facility.
NGR system compares favorably with isolated neutral or gluhozazemlonnoy absence of large magnitude currents on the neutral conductor in the circuit area and relative safety. It becomes possible by simple means to control the excess leakage currents above an acceptable level, and even switch (to break and recombine) with a relay link neutral ground, if there is necessity.
In the case of the vessel with mooring resistor to ground circuit allows simple methods to avoid difficulties with the destruction of the housing as described above.
The man and the water
On a similar principle, constructed and protection of the person in contact with water. If the zones near the bath and allowed to use only equipment with safe extra low voltage unable to cause harm because of the small values of the outlet (for example, on the washing machine) are put through a separation transformer. Faraday shield does not become a mandatory measure, weak current bite will not hurt a person and does not cause corrosion of the bath. Only prohibited anywhere in the ground the secondary winding.
The idea drawn from the techniques of three-phase circuits with a neutral point earthed. It is believed that the vanishing of the housing - reliable protection. In the area of land specified wire kontachit all phases. A potential on one of them at any time below ground. Consequently, the current will go there, and not to man, carelessly holding Exposed metal, which is not expected to find a high voltage. Grounding is considered as a complementary measure.
Likewise, whether one point of the secondary winding is grounded, the current would be closed up through man, water and soil to the specified point. Outcome of an event depends on the ratio of the plurality of circuit components of the resistance, but the current light bite is not called. Possible deaths.
After isolating transformer is placed fuse or circuit breaker, except for the differential. Dangerous option circuit may occur between the two windings without the earthing points.
With increasing height above the ground potential of the atmosphere increases. Already at the top of the human level it is a decent value. People does not beat shock because the surface of the skin, clothes holds an electrical charge. As a result, standing on the ground component is aligned with the ground, and lifted the envelope field. In fact, we represent mound.
The situation is different when there is a high steel antenna on the mast. It's not even in the antenna, and the lights, designed to give the pilot an airliner to understand that in front of the obstacle. Metal parts, lighting fixture act as receiving antenna. And the potential of a high-rise with a radio signal begins to go into the food chain. It is clear that interference is not needed at the bottom, it is a negative effect.
To avoid this, use a transformer with a transmission ratio equal to one. There is no difference where to put the device, it is always isolated from the soil. The most that will happen - draining the static charge on the insulation. The above process is gradual and does not cause harm. Transformer cuts:
- DC component flowing through the copper core power wire. The effect is similar to the effect of the altitude of the antenna due to the altitude difference of potentials. Sometimes people zapped by careless dock connector to your VCR or TV.
- Variables bad components pass through the coil, its parameters are designed for a frequency of 50 Hz (motorized transformer tank is not blocked by Faraday screen, a resonant circuit is formed). The amplitude of this portion is small, but is able to interfere with the equipment included in the overall supply chain.
On the mast with respect to the potential of the soil can be 300 kV. Feed the signal lights is not possible to directly. In order to protect the equipment used specifically isolating transformers Arthur Austin. The future inventor worked as an inspector for communications isolation Pacific Gas & Electric Co and well-studied question. Then even he organized his own company.
Isolating transformers in this case become a household term. In the digital technique used to interchange circuits and normalize signal levels (0 and 1). If the dc component starts to drift, use the transformer is considered a simple way to return the logic level on the spot. With one point of the secondary winding certainly is put into neutral of the secondary circuit. And whether it is connected to the body depends on a particular implementation of the circuit.
Pulse isolating transformer is ideal for inversion signal and shifts the logic level. This is achieved by including a counter coils and change the transmission ratio. In digital technology, the logic level is measured only on the voltage and the current in most cases, does not play a role. Just to have enough for the switching circuits (the minimum threshold stated in the specifications).
Pulse transformers have small dimensions due to the high frequency signals used. This can be gigahertz in which the CPU clock frequency is measured. As a result of this notice, among other chip manages only labeling. For example, quad transformer (muRata) 1600 has a body length of 2 cm.
At the same time provides a stunning separating quality. Insulation resistance voltage 500 VDC GOhm is 10 (as in high-voltage circuits) and include the product is acceptable in forward and backward direction. Secondary and primary windings are identical. This is important in the conversion of levels: an isolation transformer is working on raising or lowering the voltage.
The specifications indicate own capacity products, which directly points to the absence of the Faraday screens. As unnecessary elimination of bulky element helps to save space.
Testing of electrical equipment
Often the new products do not fully thought out in a constructive manner. This causes a high voltage in inappropriate places. If the power supply is grounded at one point, there will be an accident at a touch. Isolating transformer, none of the points whose secondary winding is not connected to ground, becomes reliable protection for the reasons given above.
When testing takes place a comprehensive study of the object, and the defect will be seen, and the danger - removed an amendment to the electrical circuit or process.
Previously, there were schemes where the supporting aluminum or steel chassis could serve as neutral conductor. This applies to electronic tubes. In this case, the module is required to present a high potential, this is a normal mode, a part of the equipment unit can not touch the body of man. So, when testing an isolation transformer is a must. Faraday screen in this case is not considered a mandatory part.
Because of the analog gauges are sensitive to the supply voltage. It concerns evaluation of capacitive and ohmic resistance, a number of other parameters. To improve the accuracy can be decoupled for DC or high-frequency component. In some cases it is necessary to shift the phase of the reference voltage 180 degrees. Simply do this by using an isolating transformer when the primary and secondary windings are to meet.
Individual units are measuring transformers for removal of parameter values for high voltage circuits. Said separation instrument class is usually not called for obvious reasons. For example, a current transformer can detect a short circuit in NGR ground circuit. The product can be adjusted to the resistors for current 5, 10 and 15 A, which corresponds to the 5 chains (6.6), 10 and 15 kV. The switch allows the flexibility parameters of the transformer lead to the desired value.