Voltage transformer ferroresonance

Key Features
1) For the ferromagnetic resonance circuit, in the same loop power supply potential role may be more than a stable working condition. circuit breakers in the end what kind of work in a stable condition caused by external shocks depends on the situation of the transition process.
2) PT is to produce the non-linear ferromagnetic properties of the root causes of ferromagnetic resonance, the saturation effect ferromagnetic element itself limits the over voltage amplitude. Moreover return loss also damped resonance over-voltage and limitations. When the loop resistance is greater than a certain value, do not

Will be a strong ferromagnetic resonance over-voltage.
3) series resonant circuits, generate magnetic resonance voltage is a necessary condition ω0 = 1/L0C <; ω. Therefore, ferromagnetic resonance can occur within a large range.
4) maintain and satisfaction resonant oscillation circuit resistance energy loss by frequency power transformers supply. Frequency of the energy is converted into energy of another resonant frequency, the conversion process must be periodic and a rhythm that ... 1/2 (1,2,3 ...) times the frequency of resonance.
5) damage to the PT ferromagnetic resonance. Magnetic resonance (divide) should generally have the following three conditions.
① ferromagnetic voltage transformer (PT) nonlinear effect is to produce the main ferromagnetic resonance.
② PT capacitive reactance is 100 times less than that match the parameters in the resonant range.
③ must excitation conditions, such as PT sudden closing, single-phase ground suddenly disappeared, outside interference on the system or systems operating over voltage generated.
According to tests the resonant frequency of the current is more than 240 times the nominal current, the frequency of the resonant current is the normal current of about 40 to 60 times, high-frequency resonance current is smaller. In these resonance, the resonant frequency of the destruction of the largest, if PT is well insulated, frequency and high frequency are generally not

Compromise the safety of the device, and 6kV system has the above conditions.

Common abnormal voltage transformer

⑴ unbalanced three-phase voltage indication: a phase reduction (to zero), and the other two-phase normal line voltage is not normal, or accompanied by sound, light signals, it may be high or low voltage transformer fuse blown;
⑵ neutral non-effectively grounded system, three-phase voltage unbalance indication: a phase reduction (to zero), and the other two-phase increased (up to line voltage) or pointer swings, may be single-phase ground fault or baseband resonance such as three-phase voltage also increased, and more than line voltage (refer to

Needle can be placed on the head), it may be divided or high frequency resonant;
⑶ high voltage fuse repeatedly blows, serious damage may be internal insulation, such as the interlayer or inter-turn winding short-circuit breakers fault;
⑷ effectively earthed neutral system, the bus switching operation occurs when the phase voltage increases and low swing, usually a series resonant phenomenon; without any operation, the sudden appearance of the phase voltage is abnormal increase or decrease, it may be transformer internal insulation damage, such as insulating support

Stand around, sometimes winding layers TURN SHORT CIRCUIT;
⑸ neutral effectively grounded system, put into operation when voltage transformer electri cenergy meter indicates instability, may be high voltage winding N (X) is grounded poor contact.
(6) floating potential discharge, may be connected to the core through the core bolts and loose, causing the bolt in the floating potential; metallic foreign body in the floating potential discharge; insulated bracket nut potential suspension;
(7) arc discharge, and can be discharged cascade winding on the core, the insulating supporting frame and the discharge poor; insulated water wet; ungrounded end of the primary winding;
(8) Heat Fault

Precautions voltage transformer

1. Voltage transformer is put into operation in accordance with the rules of order before the test and inspect the items. For example, measuring the polarity, connect groups, shaking insulation, nuclear phase sequence.
2. Voltage transformer wiring should ensure its accuracy, the primary winding and the circuit under test in parallel, and the secondary winding should be connected to the measuring instrument, following the
Electrical protection devices or automatic device voltage coils in parallel, keeping in mind the polarity.
3. Connected to the voltage transformer secondary side load capacity should be appropriate, then the voltage transformer secondary side of the load should not exceed its rated capacity, otherwise, make transformer error increases, the accuracy of measurement is difficult to achieve.
4. Voltage transformer secondary circuit breakers is not allowed. Since the voltage transformer internal impedance is small, if the secondary circuit is shorted, there will be a large current will damage the secondary equipment and even endanger personal safety. Voltage transformer fuses can be installed on the secondary side in order to protect their self-

Body is not damaged due to short circuit the secondary side. Where possible, the primary side of the fuse should be installed to protect the high-voltage grid is not due to the high voltage winding power transformers or leads a systematic failure endangering safety.
5. To ensure that people in contact measurement instruments and the safety relay, voltage transformer secondary winding must have a little ground. Because the ground, when the primary and secondary windings insulation damage can be prevented with high voltage meter and relay endanger personal safety.
6, the voltage transformer secondary side will not allow short circuit.

Voltage transformer works

It works the same transformer, the basic structure is the core and the primary and secondary windings. Characterized by a constant and relatively small capacity, when normal operation is close to empty state.
Impedance voltage transformer itself is small, once the secondary side short circuit, the current will increase dramatically and burned coils. To this end, the voltage transformer primary side is connected with fuses, the secondary grounded, so the primary and secondary side insulation is damaged, the secondary appeared on the ground caused by the high potential

Personal and equipment accidents.
Measuring voltage electric transformer are generally made of a single-phase double-coil structure, and its primary side voltage is measured voltage (such as the power system line voltage), you can use single-phase can also be used as a two-phase connected into VV-shaped be used. Laboratory voltage transformer primary side is often more pumping

Head to suit the needs of different voltages measured. For protective grounding voltage transformer also comes with a third coil, said three coil voltage transformers. The third phase coils connected in open delta, the opening of the triangle two terminals and the ground voltage protection relay

Coil connection.
Normal operation, the symmetrical three-phase voltage power system, the third coil of the three-phase induced electromotive force is zero. In the event of single-phase, the neutral point displacement occurs, open triangle will appear between the terminals so that the zero-sequence voltage relay to the power system

Statistics play a protective role.
The zero-sequence voltage coil corresponding iron hearts will be zero-sequence flux. To this end, this three-phase voltage transformer yoke iron core using the next (10KV and below) or using three single-phase voltage transformer. For this transformer, the accuracy requirements of the third coil is not

High, but requires a certain degree of over-excitation characteristics (ie, when the primary voltage is increased, the iron core is also a corresponding increase in the magnetic flux density in multiples without damage).
Voltage power transformers are power plants, substations and other transmission and distribution system is indispensable to a electrical appliances.
Precision voltage transformer is used to electrically test laboratories to expand the range, the measured voltage, power and energy of an instrument.
Voltage transformer and the transformer is very similar, are used to transform the voltage on the line.
Why do we need convert line voltage it? This is because under the generation, transmission and consumption of different circumstances, the voltage on the line sizes, and disparities, some low-voltage 220V and 380V, some tens of thousands of volts or even hundreds of thousands of high-voltage volts . To directly measure this

These low and high voltages, it is necessary according to the size of the line voltage, low-voltage and high-voltage production of the corresponding voltage tables and other instruments.

The main types of voltage transformers

⑴ at the installation site can be divided into indoor type and outdoor type. 35kV and below, made more indoor type; 35kV or more is made of outdoor type.
⑵ Press phases can be divided into single-phase and three-phase, 35kV and above can not be made of three-phase.
⑶ can be divided by the number of winding double and three-winding voltage electric transformer ,  three winding voltage transformer in addition to primary and basic secondary side, there is a set of auxiliary secondary side for ground protection.
⑷ Press insulation can be divided into dry type, cast type, oil-immersed and inflatable. Dry-type voltage transformer simple structure, no fire and explosion hazard, but a lower dielectric strength, applies only to the following indoor 6kV devices; cast voltage transformer compact, maintenance side

It is suitable for 3kV ~ 35kV indoor power distribution unit; immersed voltage transformer insulation performance is good, can be used for more than 10kV outdoor power distribution unit; inflatable voltage transformer for SF6 fully enclosed appliances.
⑸ divided according to the principle, can be divided into electromagnetic voltage transformer, capacitor voltage power transformers and electronic voltage transformer.

Classification of current transformers

Classification by dielectric
Dry-type current transformer. By the common insulating materials by dipping treatment as insulation.
Casting current transformer. Mixed with epoxy resin casting materials or other forming a current transformer.
Oil-immersed Current Transformer. The insulating paper and the insulating oil as insulation, usually for the outdoor type.
Gas-insulated current power transformers . Main insulation composed of gas.
Classified according to installation
Through the current transformer. To pass through the wall panels or a current transformer.
Pillar-type current transformer. Installed in the plane or pillars, cater pillar with a primary circuit breakers conductor current transformer.
Bushing current transformers. No one conductor and one insulation package directly on the insulating sleeve a current transformer.
Busbar current transformer. Not once but once the conductor insulation on the bus directly packages, the use of a current transformer.
According to principles of classification
Electromagnetic current transformer. According to the principle of electromagnetic induction current transformer for current transformation.
Electronic current transformers.

Transformer Works

electric transformer in the supply of electricity lines in the current and voltage differences between large and small, from a few to tens of thousands Ann Ann has. In order to facilitate the secondary instrument measurement needs to be converted to more uniform current, while higher than the voltage on the line, such as direct measurements are very dangerous. Current transformer on Play a role in the current transformer and electrical isolation. Analog display instrument most current and voltage table, so most of the current transformer secondary current is ampere level (eg, 5, etc.). With the development of the times,mcb circuit breaker the power measurement has been achieved mostly digitized, and the computer sampling The signal is generally mA level (0-5V ,4-20mA, etc.). Micro current transformer secondary current of milliamps, mainly from the large transformer and a bridge between samples. Micro current transformer called "Instrument current transformers." ("Instrument current transformers" There is a layer of meaning is more current than laboratory use precision current transformer, generally used to expand the range of the instrument. ) Current transformer schematic circuit diagram miniature current transformers and transformer similar work is based on the principle of electromagnetic induction, the transformer transforms the voltage micro current transformer transforms the current Bale. Winding N1 then measured current, called the primary winding (or primary winding , The primary winding); winding N2 connected measuring instrument, called a secondary winding (or secondary winding, secondary winding). Micro current transformer primary winding and the secondary winding current I1 I2 current ratio, called the actual current ratio K. Micro current transformer at rated operating current work of the current ratio is called the current transformer rated current ratio, expressed by Kn. Kn = I1n/I2n

Zero sequence transformer

Zero sequence current protection of the basic principle is based on Kirchhoff's current law: inflow of any node in the circuit current of complex algebra and zero. In line with the electrical equipment under normal circumstances,Electric transformer the vector sum of the phase currents is zero, so the two zero-sequence current transformer

Secondary winding is no signal output actuator does not operate. When a ground fault occurs in each phase current vector is not zero, the fault current to zero sequence current transformer toroidal flux is generated, zero-sequence current transformer secondary induced voltage actuators move

Work, drive tripping device, switch power supply network, reaching ground fault protection purposes. Role: When the circuit electric shock or leakage fault occurs, the protective action, cut off the power. Use: in the three-phase line of the tube with a current transformer, or let the three phase conductors

Together through a zero-sequence current transformer can also be installed on the neutral line N a zero-sequence current transformer,Circuit breaker  use it to detect three-phase current vector. Zero sequence current transformer is made of ABS plastic shell, resin cast into sealed, effectively avoiding the transformer in

Long-term use in the process of corrosion. Good insulation, beautiful appearance. High sensitivity, good linearity, reliable operation, convenient installation. Its performance is superior to the general zero-sequence current transformer, using a wide range, not only for electromagnetic relay, also

Can be applied to electronic and computer protection device.

Clamp transformer

Clamp current transformer is a precision current transformer (current sensor), is designed for field measurement of electrical characteristics are measured using the design. The series transformer selection of high permeability material, high accuracy. Linear optimization. Anti-interference ability. Can be directly used

Then caught the bus or busbars without serif blackout its easy to use. Q8O series clamp current transformer railway departments have repeatedly been detected on the train at the beginning of the current D-word frequency current signal. AC current transformer, it can be used with a variety of measuring instruments,electri cenergy meter power meter

Field calibrator, multifunction power meter, oscilloscope, digital multimeter, double clamp earth resistance tester, double clamp phase voltammetry table, etc., can continue to power transformers in the state in power, for a variety of electrical parameters were measured and compared .

Current transformer

Current transformer field tester according to national standards for measuring current transformer ratio error and the angular difference, but also measuring current 1% to 200% of any percentage ratio between the difference and the angle difference; directly measuring current transformer ratio and polarity; may actual field measurements of the current transformer

Secondary load and so on. Instrument uses a high-precision, automatic linear regulated DC and AC power; high speed, high reliability digital processing module; high measurement accuracy, high stability of pre-measuring instruments to measure the circuit to ensure the accuracy and high stability. In addition, the instrument

Uses the latest development out of the 320x240 large LCD full Chinese interface platform technology, with user-friendly interface, prompts wiring and operation, and has saved any measurement parameters and measurement results printing function.
Current transformer principle is based on the principle of electromagnetic induction. Current transformers are closed by the core and windings. It is a small number of turns, the current string in the line to be measured, so it is often the entire current flows through the circuit, the secondary winding turns

More, connected in series in the measuring instrument and the protection circuit, a current transformer in operation, it is always the secondary circuit is closed, the measurement instrument and the series impedance of the coil protection circuit is small, close to the operating state of the current transformer short circuit.
Principle
In power transformers generation, transformation, transmission, distribution and electricity lines in the current size of the gap, from a few to tens of thousands Ann Ann has. For ease of measurement, protection and control needs to be converted to more uniform current, the Voltage stabilizer on the other line higher than the general risk, such as direct measurement is

Insurance. Current transformer to play the role of current transformation and electrical isolation.

Current transformer

Current transformer field tester according to national standards for measuring current transformer ratio error and the angular difference, but also measuring current

1% to 200% of any percentage ratio between the difference and the angle difference; directly measuring current transformer ratio and polarity; may actual field

measurements of the current transformer

Secondary load and so on. Instrument uses a high-precision, automatic linear regulated DC and AC power; high speed, high reliability digital processing module; high

measurement accuracy, high stability of pre-measuring instruments to measure the circuit to ensure the accuracy and high stability. In addition, the instrument

Uses the latest development out of the 320x240 large LCD full Chinese interface platform technology, with user-friendly interface, prompts wiring and operation, and

has saved any measurement parameters and measurement results printing function.
Current transformer principle is based on the principle of electromagnetic induction. Current transformers are closed by the core and windings. It is a small number of

turns, the current string in the line to be measured, so it is often the entire current flows through the circuit, the secondary winding turns

More, connected in series in the measuring instrument and the protection circuit, a current transformer in operation, it is always the secondary circuit is closed, the

measurement instrument and the series impedance of the coil protection circuit is small, close to the operating state of the current transformer short circuit.
Principle
In power generation, transformation, transmission, distribution and electricity lines in the current size of the gap, from a few to tens of thousands Ann Ann has. For

ease of measurement, protection and control needs to be converted to more uniform current, the voltage on the other line higher than the general risk, such as direct

measurement is

Insurance. Current transformer to play the role of current transformation and electrical isolation.