Failure phenomenon: current transformer is in operation due to iron core overheating.

Analysis: running inductance transformer overload, secondary open circuit, and insulation damage cases, such as discharge can cause abnormal voice, caused by semiconductor paint besmear brushs uneven local corona, as well as the core for clamping screw loose, can also cause larger noise.

The overheating of the current transformer core may be caused by prolonged overloading or secondary circuit opening caused by ferromagnetic saturation.

If discover the abnormal phenomenon, first of all, should be carefully observed and through the instrument and so on to determine the cause of abnormal sound or core overheating, if it is should be taken to reduce the load caused by overload, below rating and observe its operation.

If the secondary circuit is caused, the operation should be stopped immediately (or the load minimized to a minimum), and necessary security measures are taken to prevent the shock.

If discharge is caused by the insulation damage, it should be replaced.  

(1) malfunction: the magnetic insulation is damaged.

Analysis and treatment: the reason of the magnetic insulation damage should be analyzed and replaced.

(2) failure phenomenon: explosion occurred in operation.

Analysis and treatment: generally, the seal of the arrester changes its characteristics. Since the zinc oxide arrester has a good voltammeter, it is widely used, and the relative failure is low, and the annual inspection and pretest should be strengthened.

Fault phenomenon: single-phase grounding short circuit, two-phase and three-phase grounded shorting.

Analysis: due to the power cable is belong to another professional, and the fault is interphase short circuit of power cable, even single phase short circuit but due to reasons such as discharge time is long, will soon develop into more than two phase short circuit.

Therefore, it is necessary to find out the cause of the cable line and after treatment, otherwise it could cause a greater accident. The treatment method is to check the point of failure, then process, then do the experiment after treatment, and then the electricity can be sent.

1. Voltage transformer

Fault phenomenon: the running voltage transformer is fused at one time.

(1) it is possible to fuse the fuse due to the interturn, interphase or interphase of the voltage sensor, and the failure of a phase to the ground.

(2) secondary circuit failure, which is the second side failure of the transformer, the secondary side fuse is too large to cause a side fuse to fuse.

(3) 10 kv unified phase.

One to 10 kv system, the other two phase of voltage rise of square root of three times, for voltage transformer Y0 / Y0 wiring, will become the two relatively normal voltage line voltage, caused by the voltage current is added, may fuse fuse.

(4) the power system has a ferromagnetic resonance.

In recent years due to the large increase in power distribution lines, cable and user, make the 10 kv power distribution system of electric parameters changed a lot, gradually formed the resonance condition, together with some excitation characteristic of voltage transformer is not good, therefore, ferroresonance overvoltage often occur, when the power system harmonic eddy currents on voltage transformer, besides causing a side fuse break, also often lead to voltage transformer fire accident.

Analysis: when a voltage transformer primary side blown fuse, should pull open isolating switch voltage transformer, and take the second insurance, check whether the fuse, the exclusion of voltage transformer fault or secondary fault itself, to replace the fuse will be qualified voltage transformer in operation.

1. Type of explosion-proof electrical equipment

Explosion-proof electrical equipment with flameproof sign (d), increased safety sign (e), oil filled (mark o), sand mold filling sign (q), intrinsically safe (mark I), positive pressure type sign (p), no spark type (n) and special type sign (s) of the equipment.

For example d Ⅱ BT4 is flameproof, Ⅱ class B, T4 group of explosion-proof electrical equipment.

2. Selection of electrical equipment for hazardous environment

Explosion-proof electrical equipment should be selected according to the type and grade of the installation environment and the type of electrical equipment. The level and group of explosion-proof electrical equipment selected should not be lower than the level and group of the explosive mixture in the environment.

1. according to the electrical equipment of manufacture date, calculate electrical equipment have been used.

2. Test the insulation capability of electrical equipment.

When the electrical insulating capacity is reduced to the extent that it cannot be allowed, it can be determined that it is ageing and can no longer be used. This is usually done with a megohm test to get accurate data.

3. Observe the surface of electrical equipment.

All the electrical connection contact undesirable, thread tripping, insulating cover breakage, insulation protection, electrical equipment in use there is abnormal phenomenon such as smell, explain equipment has been aging, should immediately stop using for maintenance.

4. Electrical equipment within the building may also be determined according to the time of use of the building.

For example, when the home buys the decoration and has not carried out the new decoration, its residential electric wire is still the power line that builds a room, can calculate the time that the wire already USES and its ageing degree.

5. According to the environment of the use of electrical equipment?

Including temperature, humidity, chemical corrosion degree and load degree? Make judgments.

For example, electrical equipment used in environments with constant humidity, constant temperature, and chemical corrosion can be used for years or even decades. On the contrary, if the environment is too high or humid, chemical corrosion is too heavy, electrical equipment can be easily damaged.

Isolation switch - action isolation switch is used to reliably isolate the parts of the power distribution device that need power supply and the live parts to ensure the safety of the maintenance work. Isolating switch contact all exposed in the air, has obvious disconnect point, isolating switch no arcing devices, therefore cannot be used to cut off the load current or short circuit current, otherwise under the effect of high pressure, the disconnect will produce strong arc, and difficult to put out by oneself, even may cause arcing (relative or interphase short circuit), burning equipment, endanger personal safety, this is known as "load pull isolating switch" serious accidents. The isolation switch can also be used to switch operations on certain circuits to change the way the system works. For example, in a two-bus circuit, a separate switch can be used to switch the running circuit from one bus to another. It can also be used to manipulate small current circuits.

1. After the breaking of the brake, establish reliable insulation clearance, and the equipment or circuit that will need to be overhauled shall be separated from the power supply by an obvious cut-off point to ensure the safety of maintenance personnel and equipment.

2. Replace the wiring according to the operation needs.

3, can be used to points, small current in a circuit, such as casing, busbar cables, connectors, short charging current, pressure switch capacitance of capacitive current, double bus exchange when the circulation of the excitation current and voltage transformer, etc.

4. According to the specific situation of different structure types, the no-load excitation current of transformer can be divided and combined. The simple point is that the switch of the lamp used in the home is similar, which is an obvious cut-off point, only applied to the line of high voltage grade, without an arc suppressing function.

arrester of fault handling content: found lightning arrester in any of the following signs, lightning arrester and the power supply should be disconnected.

(1) the arrester porcelain bottle, casing burst or explosion.

(2) after the lightning discharge, connecting severe burns or burn out, cut off the fault before the lightning arrester, should be examined for earthing phenomenon, if there is grounding phenomenon is not isolated, the switch is off, lightning arrester and should report to the superior disposal. The above contents are arranged according to the problems encountered in the actual work of the students. Please contact and correct any questions.

The overvoltage refers to any voltage that is higher than the corresponding peak of the maximum steady-state voltage under normal operation. In engineering, it means any dangerous voltage that may cause damage to the equipment. Therefore, in the project, some of the overvoltage of the normal operating voltage of the equipment is not sufficient to endanger the normal working of the equipment. The overvoltage includes:

(1) transient overvoltage, duration of millisecond or shorter, is the main protection object of the arrester.

(2) transient overvoltage or transient overvoltage, which lasts a relatively long time, usually between 0.1 s and 1s.

The main sources of transient overvoltage are: lightning strike, switch operation, electrostatic discharge and nuclear explosion. At the communication station, it is mainly lightning overvoltage or lightning overvoltage.

The transient overvoltage is mainly: the overvoltage of transfer overvoltage, zero overvoltage, fracture resonant overvoltage and neutral line drift. In addition, the capacitance effect of the no-load line, the asymmetric grounding fault and the sudden load can also generate dangerous overvoltage.

There are two basic principles of overvoltage protection of communication power system: first, system protection principle and probability protection principle.

(1) system protection principle

The principle of system protection is because:

1) the coupling mechanism of the dangerous overvoltage, especially the lightning overvoltage, is varied and all-pervasive;

2) there is a wide range of electrical connections between communications equipment because of the power supply, data and information transmission and other business needs.

The principle of system protection includes the following:

1) both the protection of transient overvoltage and the tolerance and protection of transient overvoltage shall be considered.

2) the protection of all kinds of overvoltage shall be considered as well as the protection of electromagnetic pulse.

3) consider the protection of each port;

4) to treat the surge protector and protected circuit as a whole, with good coordination and coordination;

5) the overvoltage protection measures must meet the requirements of relevant standards and specifications;

6) the addition of overvoltage protection measures shall not affect the normal operation and interconnection between other communication devices;

7) to put forward reasonable environmental requirements;

The principle of system protection includes the following:

1) both the protection of transient overvoltage and the tolerance and protection of transient overvoltage shall be considered.

2) the protection of all kinds of overvoltage shall be considered as well as the protection of electromagnetic pulse.

3) consider the protection of each port;

4) to treat the surge protector and protected circuit as a whole, wconsidered as well as the protection of electromagnetic pulse.

3) consider the protection of each port;

4) to treat the surge protector and protected circuit aith good coordination and coordination;

5) the overvoltage protection measures must meet the requirements of relevant standards and specifications;

6) the addition of overvoltage protection measures shall not affect the normal operation and interconnection between other communication devices;

7) to put forward reasonable environmental requirements;

8) provide reasonable installation and maintenance requirements.

(2) probabilistic protection principle The principle of probability protection is because: 1) there are certain randomness and uncertainty in the formation and occurrence of lightning, and the value of lightning parameters also has certain statistical properties. 2) the lightning protec 8) provide reasonable installation and maintenance requirements. (2) probabilistic protection principle

The principle of probability protection is because:

1) there are certain randomness and uncertainty in the formation and occurrence of lightning, and the value of lightning parameters also has certain statistical properties.

2) the lightning protection device cannot prevent the formation of lightning.

3) due to technical limitations, the lightning protection device cannot completely eliminate or prevent all overvoltage, and the over-voltage tolerance of the equipment is limited.

According to the principle of probability protection, it should be done:

1) simulate impact test of various waveforms and amplitude of equipment;

2) put forward voltage resistance index to the protected equipment;

3) the index of impact flow capacity of equipment should be significantly higher than that of domestic and foreign standards.

2. Methods of overvoltage protection

(1) the basic method of overvoltage protection

In order to prevent the overvoltage from threatening the normal operation and safety of the equipment, first of all, it can reduce or prevent the overvoltage energy from reaching the equipment. Such methods include:

1) attenuation or transfer of energy, such as the use of shielding, filtering, charging of the surge protector (SPD), etc.

2) disconnect the dangerous line, such as the use of fuse, short circuit, etc. This method can only be implemented when conditions permit.

3) electrical isolation, such as isolation transformer, optical coupling, etc.

Parameter name unit model

20 ZN27 ZN28-12/1250-12/1250-12/1250-31.5 ZN27A - - 40

Voltage parameter

Rated voltage kV 10

Maximum voltage 11.5

Insulation level

The working frequency withstand pressure electrode, extremely pair of ground 42

Fracture between 48

Impact resistance electrode, extreme pair of 75

Fracture between 84

Current parameter rated current A 1250 1250 3150

Rated short circuit break kA 2031.5 40

Rated peak withstand current kA 50 80 100

The short time resistance of 4S is 2031.5 40

Rated temporary closing current (peak) kA 5080100

Rated single capacitor group open circuit A 630 800

Rated back-to-back capacitor sets A 400 400

Lifetime rated short circuit breaking current times 50, 50, 30

Machine life 10000

Other rated operational sequence points - 0.5s - - - 180s - 180s - 180s - 180 - - - score

The total open number is not greater than 60

Use the operating mechanism CD or CT

The rated current reaches 5000A, the breaking current reaches a good level of 50kA, and has been developed to a voltage of 35kV.

Before the 1980s, vacuum circuit breakers were in the initial stage of development and were constantly groping, unable to set technical standards, and did not develop the relevant product standards until 1985.

Insulators are used to support and fix bus lines and live conductors, and to make the electrically charged conductors or conductors between the earth and the earth in sufficient distance

Insulation. Insulators should have sufficient electrical insulation strength and moisture resistance.