A selection of 50 examples of practical electrical knowledge is enough for you to learn for a while!

Browr specializes in medium voltage electrical equipment, such as C-GIS switch cabinets, solid insulated ring network cabinets, vacuum circuit breakers, load switches and other core units related to ring network cabinets.

Browr covers an area of 1,1565 square meters and a construction area of 11,000 square meters. It is a high-tech medium voltage switchgear enterprise focusing on R&D and manufacturing in China. The new 33,335 square meter plant will be put into use by the end of 2022. We have installed over 270,000 C-GIS switching devices around the world (currently the main market in China). Today we have compiled 50 common sense in the electrical industry for you. I hope it will be useful to you!


  1. What are the hazards of single-phase grounding of Shizuko windings?

Since the neutral point of the generator is an ungrounded system, when single-phase grounding occurs, the current flowing through the fault point is only a small capacitive current in the generator system. This current does not cause much harm to the generator, so the generator can be operated for a short period of time, but if not treated in time, it may burn the Shizuko iron core, or even develop into a short circuit between turns or phases.


  1. What is the phenomenon of mutual understanding?

The phenomenon of inducing electric potential in an adjacent circuit due to a change in the current in one circuit is called mutual sensing.


  1. Inspection of transformers during operation

① Oil color oil level, clean body, no oil leakage

② The casing is clean and free of cracks, damage, discharge and other abnormalities

③ Sound, fan, and upper oil temperature are normal

④ WSJ has no gas, and the respirator silicone has not changed color

⑤ Airway and protective film are intact

⑥ No heat or discoloration of the lead wires on each side

⑦ The housing is well grounded


  1. Resistance, a factor affecting resistance

When current flows through a conductor, the resistance received is called resistance, which is expressed by R. The conductor resistance is directly proportional to the length of the conductor, inversely proportional to the cross-sectional area of the dissimilar body, and is also related to the material of the conductor. The relationship between them can be expressed by the following formula: R = L/s.


  1. Electric energy

Electric energy is used to indicate the function of an electric field force over a period of time W indicates W=PT

W: electric energy (kw.h)

p: electric power (w)

t: time (h)


  1. What is meritorious, what is unsuccessful?

In the process of transmission and use of AC energy, the part of the energy used to be converted into non-electric or magnetic forms (such as light, heat, mechanical energy, etc.) is called effective. The part of energy used to exchange electrical and magnetic fields within a circuit is called futile.


  1. What is power factor, what is the difference between the advance phase of power factor and the delay phase?

The power factor of an AC motor, also known as power factor, is the ratio of active power to apparent power, that is, COS=p/s. Under a certain rated voltage and rated current, the higher the power factor of the motor, the greater the proportion of active power. Synchronous generators usually have both success and failure. We call the operating state where the power factor is both active and active, or lagging, and the operating state where the power rate is active and absorbs no action, called the power factor advance phase, or advance.


  1. What is the significance of increasing the power factor of the power grid?

Most of the electrical equipment used in production and daily life is inductive load, and their power factor is low, which causes the power generation equipment to easily not be fully utilized and the loss on the transmission line is increased. After the power factor is increased, the power generation equipment can send less reactive load and more active load. At the same time, it can also reduce the loss on power generation and supply equipment and save electricity.


  1. What is current? How is the direction of the current specified?

Current: The regular operation of free electrons or ions under the action of an electric field force is called current. The direction of positive charge movement is specified as the direction of current, and the direction of free electron movement is opposite to the direction of current.


  1. The transformer has and only one grounding reason

① A point of grounding is to prevent the transformer from generating a suspension potential during operation and testing, causing ground discharge.

② Only one point of grounding is allowed because a closed circuit is formed after two points are grounded. Circulating current is generated when the main magnetic flux passes through the circuit, causing partial overheating.


  1. Handling incidents involving reduced voltage

① When the bus voltage at all levels falls below 95% of the rated value, the electrician should immediately adjust the excitation of the generator to increase the reactive load so that the voltage remains within the normal range.

② When the bus voltage of all levels falls below 90% of the rated value, the generator accident overload capacity should be used to increase the reactive maintenance voltage. (Pay attention to checking the generator temperature and recording the overload factor and time) At the same time, the active load can also be appropriately reduced, and the value is reported to be adjusted and limited.

③ If the upper processing voltage continues to drop below 5.4KV, the electrician asks the value length to dissolve the system. When the system voltage returns above 5.7KV, it will be juxtaposed with the system as soon as possible.


  1. Handling frequency reduction accidents

① When the system frequency drops below 49.5 HZ, the electrician should immediately report the long value, contact the machine and furnace to increase the unit load to the maximum possible output, and contact the area adjustment at the same time.

② When the system frequency drops below 49HZ, in addition to increasing the output, it also requires zonal adjustment to eliminate frequency operation, so that the frequency returns to 49HZ or more within 30 minutes, and above 49.5 HZ within a total of one hour.

③ When the system frequency drops to 48.5HZ, the low cycle protection of the switch juxtaposed with the system in our factory should be activated. Otherwise, it should be executed manually. When the system frequency returns to 48.5HZ or above, it should be juxtaposed with the system as soon as possible.


  1. Precautions for inspection of high-voltage equipment

① When inspecting high-voltage equipment, no other work shall be carried out, and the fence shall not be removed or crossed.

② In case of thunderstorms, wear insulated boots and stay away from lightning arresters and lightning rods.

③ When high-voltage equipment is grounded, the room must not be close to the fault point within 4m, the outside must not be close to 8m, the entry range must be insulated boots, touch the equipment shell, and wear insulating gloves when framing.

④ The door must be locked when entering and leaving the high-pressure chamber.


  1. How does a synchronous generator generate three-phase alternating current?

The steam turbine drives the rotor to rotate. The excitation windings (rotor windings) on the rotor come into contact with the slip ring through the brush, and the DC generated by the excitation system is introduced into the rotor winding to generate a stable magnetic field. Under the steam turbine rotation at a certain speed, the three-phase stator coil continuously cuts the rotor magnetic flux, generates inductive electric potential, and generates load current after loading, that is, three-phase alternating current. (alternating: alternating current with equal frequency and potential but different phases)


  1. What does “synchronization” mean in a synchronous generator, and the relationship between the frequency, speed, and magnetic pole logarithm of a synchronous generator

① Synchronization means that the speed n=60f t and direction of the rotating magnetic field of the generator rotor is the same as the rotational speed and direction of the stator magnetic field.

② Frequency, magnetic pole logarithm, rotor speed relationship: f = p n /60 (n: rotor speed p: magnetic pole logarithm f: frequency)


  1. What is the impact of COSreduction during generator operation?

When COSis below the rated value, the generator output should decrease, because the lower the COS, the greater the reactive component of the stator current. Since inductive reactive powerlessness demagnetizes, the effect of offsetting magnetic flux is greater. In order to keep the stator voltage unchanged, the rotor current must be increased. If the generator output remains unchanged at this time, it will inevitably cause the rotor current to exceed the rated value, causing the temperature of the stator winding to rise overheating.


  1. Why should I check the three-phase static current meter to check the no-load rotor voltage and current when the generator is empty and boosting?

Before the generator is closed and connected to the grid, the three-phase static current should be 0. If a current is found, it means that there is a short circuit in the Shizuko circuit, and the demagnetization switch should be opened immediately for inspection. The purpose of calibrating the no-load rotor voltage and current is to check whether the generator rotor winding has an interlayer short circuit. If the static voltage reaches the rated value and the rotor current is greater than the value at the no-load rated voltage, then the rotor winding has an interlayer short circuit.


  1. Characteristics of series resistors

① The current flowing through each resistor is the same.

② The point voltage on the series resistor is equal to the sum of the voltage drops on each resistor.

③ The point resistance of a series resistor is the sum of each resistor.


  1. Why should a groove be made on the surface of the slip ring?

During operation, when the slip ring is in contact with the carbon brush, a high thermal reaction occurs. There is a spiral groove on the surface of the slip ring. This is to increase the heat dissipation area and enhance cooling. On the other hand, it is to improve contact with the brush, and it is also easy for the powder of the electric brush to drain out along the spiral groove.


  1. What are the requirements of the generator for the excitation system?

① The excitation system should not be affected by the external power grid. Otherwise, a vicious cycle will occur in the event of an accident, so that the telephone grid affects the excitation, and the excitation affects the power grid, and the situation will get worse and worse.

② The adjustment of the excitation system itself should be stable. If it is unstable, that is, the excitation voltage changes a lot, it will cause the generator voltage to fluctuate greatly.

③ Power system failure The voltage at the generator end drops, and the excitation system should be able to quickly raise the excitation to the peak value.


  1. What is the excitation multiplier? What should I pay attention to after a strong movement?

Strong excitation multiplier, that is, the ratio between the forced excitation voltage and the rated voltage of the excitator Ue. For steam turbine generators with air-cooled excitation windings, the strong excitation voltage is 2 times the rated excitation voltage, and the allowable time for strong excitation is 50 years. After the strong excitation action, the carbon brush of the excitator should be checked once. Also, pay attention to whether the relay contacts of the short-circuit magnetic field resistor are open and whether the contact contacts are intact after the voltage is restored.


  1. What is the role of the demagnetization resistor of the excitation circuit?

① Prevent overvoltage between rotor windings so that it does not exceed the allowable value.

② Turn magnetic field energy into heat energy to speed up the demagnetization process.


  1. What effect will the three-phase current asymmetry of the generator have?

When the three-phase current is asymmetrical, a negative rotating magnetic field is generated, which sweeps through the rotor surface at twice the speed of rotation. The main consequences are:

① Heat the surface of the rotor.

② Make the rotor vibrate


  1. What is the problem caused by the change in air temperature difference in and out of the generator?

Under the same load, the temperature difference between the inlet and outlet air should remain the same. If the wind temperature difference is found to increase, it means that the internal loss of the generator has increased, or the air volume has decreased.


  1. When inspecting a generator, look at the end of the motor from the peephole. What should be the focus of inspection?

① Check whether the end of the stator wire rod a is loose b whether the insulation is intact c for corona.

② Inspection of end structural components: The main thing is to check whether the fastening condition of the pressure ring bracket, nut, end hoop, etc. is good.


  1. Under what circumstances may the positive and negative polarities of the excitator change?

① When testing after maintenance, such as measuring resistance or performing voltage adjustment tests, the excitation circuit is not disconnected, and when reverse current is added, the excitation is offset or the opposite.

② The excitator is suddenly short-circuited. Due to the strong armature reaction, the demagnetization effect exceeds the main magnetic field, which may cause the polarity to change.

③ When a sudden short circuit occurs in the power system, due to the sudden increase in current in the stator of the generator, the constant flow is sensed in the rotor, which may cause the rotor to have opposite polarity.

④ Since the magnetic field circuit of the excitator is heavily disconnected and connected, the polarity may be reversed.


  1. No-load characteristics of the generator

The generator rotor rotates at the rated speed, the stator winding is open (without load), and the relationship curve between its potential Eo and the excitation current Il during operation.


  1. Armature reaction

When the synchronous generator is under load, the rotating magnetic field (armature magnetic field) generated by the three-phase current in the stator winding has an effect on the rotor rotating magnetic field with a flux of I generated by the excitation current in the rotor winding, thus changing the air gap magnetic field. This effect is called an armature reaction.


  1. Shizuko or one of the rotor meters suddenly has no instructions, what to do

① When the instructions are lost, continue to operate according to the rest of the meter, and see if it may not change the operation mode of the generator. Contact the relevant personnel to check the circuit and clear the fault.

② If normal operation is affected, reduce the load until shutdown as appropriate.


  1. What is the difference between the operation of a generator and the operation of a motor

The change to camera adjustment means that the generator loses the main power (the main valve is closed), the active power drops below 0, and the generator is actively absorbed from the system to maintain energy loss. Changing to an electric motor means that the generator loses both driving force and loss of magnetism at the same time. At this time, the system absorbs both active and inactive, and becomes a load in the power grid. Both are extremely harmful to generators.


  1. The oil temperature of the upper layer of the transformer is regulated. When will the main factory turn on the fan?

The upper oil temperature should not exceed 85℃ frequently when the ambient air temperature is 40℃, the maximum should not exceed 95℃, the temperature rise should not exceed 55℃. When the upper oil temperature reaches 55℃, the exhaust fan should be turned on to enhance ventilation and cooling.


  1. Properties of charge

There is an interactive force between charges. Same-sex charges repel each other, and charges of the opposite sex attract each other.


  1. Operating principles for putting in and disabling transformers

① A circuit breaker must be used when the transformer is put in and out of use.

② The main transformer should be boosted from zero to the rated value as much as possible, and then juxtaposed with the system, the opposite when stopped.

③ The factory transformer should be charged with the high voltage side switch first, then the low voltage side switch, the opposite when stopped.


  1. Precautions for measuring transformer insulation

① Clean the insulator sleeve, remove all ground wires, and detach the neutral wire before shaking the test.

② Select the appropriate rocking meter, and record the oil temperature of the transformer at that time during the shaking test.

③ It is not allowed to touch the charged conductor with your hands during the shaking test. The windings should be discharged after shaking the test.

④ In the shaking test project, the double winding transformer measures the primary side to the secondary side and the ground, the secondary side to the ground, and the secondary side to the ground.


  1. The role of oil pillow

Reduce the contact surface between oil and air, reduce the possibility of oil and moisture oxidation, and install gas cut-off appliances and oil thermometers.


  1. The role of respirators and oil purifiers

Respirator: Prevents moisture from the air from entering the oil in the oil pillow.

Oil purifier; improves the performance of transformer oil in operation, prevents oil aging, absorbs water, dregs, acids and oxides in the oil, keeps the oil clean, and prolongs the service life of the oil.


  1. Electric field

In the space surrounding a charged body, there is a special substance that acts as a force on any charge placed in it. This special substance is called an electric field.


  1. Factors affecting oil temperature changes


② Changes in ambient temperature

③ Internal transformer fault

④ Whether the heat dissipation tube is unobstructed

⑤ Condition of the cooling system


  1. Too high voltage is harmful to transformers

The normal voltage does not exceed 5% Ue. Too high will cause the magnetic flux of the iron core to be severely saturated. In severe cases, the iron core and components will generate high heat due to magnetic leakage. In severe cases, the transformer insulation will be damaged, and the components will be partially deformed, shortening the life of the transformer.


  1. In what situations should the transformer be stopped immediately during operation?

① The interior is loud, uneven, and has a bursting sound

② Under normal load and cooling conditions, the temperature is abnormal and does not rise continuously

③ Oil pillow, explosion-proof tube fuel injection

④ Severe oil leakage, causing the oil level to fall below the indicated limit of the oil level gauge, and the oil cannot be seen

⑤ The color of the oil has changed too much, and carbon appears in the oil

⑥ The casing is seriously damaged, let the oil go


  1. In what situations should the transformer be stopped immediately during operation?

① The interior is loud, uneven, and has a bursting sound

② Under normal load and cooling conditions, the temperature is abnormal and does not rise continuously

③ Oil pillow, explosion-proof tube fuel injection

④ Severe oil leakage, causing the oil level to fall below the indicated limit of the oil level gauge, and the oil cannot be seen

⑤ The color of the oil has changed too much, and carbon appears in the oil

⑥ The casing is seriously damaged, let the oil go


  1. Possible reasons for the light gas operation of the transformer

① Air entry

② Lower oil level

③ Secondary circuit failure

④ Minor internal failure


  1. How to send electricity after the motor has been overhauled?

① The work ticket has been terminated and the conditions to start are in place

② No one works on the motor and nearby, on-site cleaning

③ Complete wiring

④ Dismantling related safety measures

⑤ The insulation resistance of the measuring motor is qualified


  1. The reason why the starting motor only doesn’t sound?

① Shizuko’s one-phase disconnection (fuse is broken in phase, cable head, switch knife gate is in poor contact)

② The rotor circuit is broken or the wire is not in good contact

③ The machine is stuck

④ Wrong coil wiring

⑤ Scan


  1. What is the reason for the violent vibration of the motor?

① The center of the motor and mechanical parts is incorrect

② Unit imbalance, mechanical damage

③ Scan

④ Bearing damage

⑤ Shaft bending

⑥ The bottom foot is loose


  1. When will the motor immediately cut off the power

① Personal accident

② Mechanical damage or obvious short circuit

③ Strong vibration

④ Abnormal sound

⑤ Bearing temperature exceeds regulations

⑥ The motor smokes, catches fire, and has a burning smell

⑦ The motor current has suddenly risen, exceeding the regulations.


  1. What are the disadvantages of starting the motor directly, and what are the methods for step-down starting the motor?

① When starting directly, the starting current is large, which has a great impact on the grid voltage.

② Step-down starting method: a in the stator circuit, the reactor b star triangle step-down, c autocoupled step-down.


  1. Why should an alcohol thermometer be used to measure the temperature of a transformer?

① Mercury is a good conductor. If placed in an area with a strong alternating magnetic field, an eddy current will be generated, causing the temperature to rise, and the temperature cannot be measured accurately.

② During measurement, in case the thermometer is damaged, alcohol is non-toxic, easy to evaporate, and easy to clean, while mercury may become a toxic gas, making cleaning difficult.


  1. What is the copper loss and iron loss of a transformer?

Copper loss refers to the sum of the energy consumed by the transformer’s primary and secondary currents flowing through the coil resistors. Since coils are mostly made of copper conductors, it is called copper loss, which is proportional to the square of the current. Iron loss refers to the power consumed by a transformer in the iron core at rated voltage, including excitation loss and eddy current loss.


  1. What effect does too large or too small air gap of an asynchronous motor have on the operation of the motor?

Excessive air gap increases magnetic resistance, so excitation current increases, power factor decreases, and motor performance deteriorates. The air gap is too small, the iron core loss increases, and the stator and rotor are prone to collision during operation, causing the load to be scanned.


  1. Inspection items during oil switch operation

① The lead and connecting parts are in good contact, and there is no loosening, heating, or discoloration.

② The oil level is normal, the oil color is clear and transparent, and light yellow.

③ The porcelain casing should be clean and complete without damage or discharge marks.

④ The split closing indicator indicates the correct one.

⑤ The operating mechanism is intact, the grounding is firm, the pins are not falling off, and the rod has no signs of breaking.

⑥ The secondary terminal row is firmly installed, and the wire should not be rotten.

⑦ The switch shield is intact and locked.


The above is the 50 basic common sense compiled by Brwor for everyone. If you are about to buy Sogear Solid Insulated Ring Network Switchgear,Nxring Series SF6 Compact Gas-insulated Switchgear,XGN Gas Insulated Metal-enclosed Switchgear,V Cabinet Circuit Breaker Operating Mechanism and other equipment, you can contact us.

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