1: What is an electrical wire chart at once? Secondary wiring diagram? A: A circuit diagram used to represent the generation, aggregation, and distribution of electrical energy, called an electrical wire-once-wire diagram. An electrical diagram that represents the connection between secondary devices is called an electrical secondary wiring diagram.

2: What is electrical secondary equipment? What is the electrical secondary equipment included?

A: Electrical secondary equipment is the equipment used in the protection, signal measurement, control, and operation loop diagrams related to a single device.

Mainly includes instrumentation, control, and signal components, relay protection devices, operation, signal power supply circuit, control cables, and connecting wires, sound signal originals, terminals, and fuses.

3: What is an electrical device at once? What is included in the electrical once-in-a-time equipment?

A: An electrical once-in-a-time device is a one-time electrical connection that is represented in an electrical once-wire diagram. Mainly includes generators, transformers, busses, circuit breakers, lightning shockers, knife gates, resistors, voltage transformers, current transformers, fuses, cables, electric motors.

4: The role of voltage transformers and current transformers

A: Voltage Transformer: Transforming voltage: The high voltage will be converted to a low voltage suitable for secondary device applications in a certain proportion, which is generally 100 volts, making it easy to standardize secondary equipment. Isolation: Electrical isolation of high voltages from low voltage systems to ensure the safety of workers and secondary equipment.

Current Transformer: Turn high currents into small currents for relay protection and current coils for meters, while ensuring the safety of equipment and staff, typically 6 amps.

5: What is a gap arc? What harm does it do?

A: A gap arc is an arc that forms periodic extinguishing and re-ignition. This arc can cause relatively resonant overvoltages, which can be up to 2.5to3 times more than the phase voltage. This overvoltage is transmitted to the entire power grid with a direct electrical connection to the grounding point, which may cause another relative breakdown in a less insulated area, causing a two-phase short circuit. The higher the voltage of the power grid, the smaller the margin of the insulation of electrical equipment, and the greater the risk of overvoltage caused by the gap arc.

6: What is the role of circuit breakers and knife gates?

A: Circuit breaker: First, control, according to the needs of power grid operation, will be part of the power equipment or line into or out of operation, and second, the protection effect, that is, in the power equipment or equipment failure through the relay protection device acting on the circuit breaker, the fault part from the grid quickly cut, to ensure the normal operation of the trouble-free equipment part.

Knife gate:A: Isolating electrical equipment from the live power grid, B; Change the way you operate, C: Turn the small current circuit on and off.

10:What is Ming Spare? What do you mean dark standby?

A: Set up a set of equipment as the main equipment backup equipment, normal operation, the main equipment running, the backup equipment is not put into operation, when the main equipment failure, the backup equipment automatically put into the load with fault equipment, this equipment is called Ming backup.

Do not set up a set of equipment as backup equipment for the main equipment, normal operation, both sets of equipment are running, when a set of equipment failure, another set of equipment can carry the load of faulty equipment, normal operation, both sets of equipment are half-load operation, this way called dark standby.

11:What is the purpose of relay protection? A:(1)To quickly disengage the protected equipment from the grid in the event of a failure sufficient to damage the equipment or endanger the safe operation of the grid;(2)To send a timely warning signal to the abnormal operation of the power grid and the abnormal state of certain equipment to deal with it quickly and return it to normal;(3)Automation and remoteness of power systems and automatic control of industrial production.

12:What is the basic principle of relay protection? A: When the power system fails, the basic feature is the sudden increase of current, voltage drop, and the phase angle between current and voltage change, all kinds of relay protection devices are to seize these characteristics, in the reaction of these physical changes, the use of normal and fault, protection within the range and external failure and other physical differences to achieve protection, there is a reaction current rise and action of the overcurrent protection, low voltage protection of the reaction voltage reduction, There is the overcurrent direction protection of the reaction current and the reaction phase angle change, and the distance protection of the reaction voltage to the current ratio, and so on.

13:What is the insulation absorption ratio of transformers? A: When selecting and maintaining a transformer, you need to determine the insulation absorption ratio of the transformer, which is equal to the ratio of the insulation resistance value measured in 60 seconds to the insulation resistance value measured in 15 seconds, i.e. R 60/B 15 With the absorption ratio can be used one step to determine whether the insulation is wet, dirty or local defects, the procedure stipulates that at 10 to 30 degrees C, 35 to 60kV windings are not less than 1.2, 110 to 330kV windings are not less than 1.3。

14:What is the selectivity of the relay protection device? A: The selectivity of the protection device is determined by the protection scheme and the adjustment calculation, when the system fails, the relay protection device can quickly and accurately remove the fault equipment, so that the damage caused by the failure and the scope of power failure are minimized, to ensure that the non-fault equipment continues to operate normally, the protection device can meet the above requirements, it is called selective.

15: What are the characteristics of current speed break protection? A: No time-limited current speed break can not protect the entire length of the line, it can only protect a part of the line, the change of the system operation mode, will affect the protection range of the current speed break, to ensure the selectivity of the action, its starting current must be the maximum operating mode (i.e., through the line current for the maximum operating mode) to adjust, but this protection range for other modes of operation is shortened, the minimum protection range required by the procedure should not be less than 15 full line length ％。 In addition, the length of the protected line also affects the characteristics of speed protection, when the line is longer, the protection range is larger, and the system mode of operation is less affected, on the contrary, when the line is short, the impact is larger, the protection range will even be shortened to zero.

16:What are the general reasons for excessive motor vibration?

A: When the motor is running, it is often due to a weak foundation, loose ground screws, and inconsistent center of the implement, the foundation should be re-reinforced. In addition, the motor also vibrates when the coil is shorted or the rotor is disconnected. At this time, the motor should be removed and sent to the repair unit for repair.

17:Why do two transformers running segmented insulation side by side in a large ground system, zero-order current voltage protection to jump the neutral point without grounding the transformer, and then jump the ground transformer?

A: When power plants or substations have more than two transformers running side by side, only some transformer neutral points are normally grounded to maintain a certain number of grounding points, while the other part of the transformer neutral points are not grounded when the bus or line is in operation In the event of a ground fault, if the protection of the barrier element is denied, the zero-order current protection action of the neutral point ground transformer cuts the transformer, so the local system may become a neutral point ungrounded system and operate with a ground fault point. This causes the transformer neutral point phase to rise to the phase voltage, which will damage the insulation of the graded insulated transformer. Therefore, the main variable ground protection does not jump the ground transformer when moving and then jumps the ground transformer.

18:Why does the end voltage rise on an empty line?

A: For transmission lines, in addition to line-sensing impedance, there are line-to-ground capacitance, the capacity of the general line resistance is much greater than the line’s sensitivity, in the case of load-free current, the circuit will flow through the capacitive current, because of the line sense resistance on the pressure drop and line capacity resistance on the pressure drop reverse, so the line will not end there will be a larger voltage rise

19:What harm is there to the transformer when the low-voltage side of the three winding transformers is open? What protective measures should be taken?

A: When the low-voltage side of the three-phase transformer is open because the electrostatic induction voltage will cause harm to the insulation of the low-voltage side winding, a valve-shaped lightning avoider should be installed on the lead line of the low-voltage side winding, when the low-voltage side is connected When a cable with a metal outer skin of 20M or more is used, the capacitor of the cable acts as a protective weapon, at which point the valve-type lightning protector can be installed

20:What is the generator demagnetometer indication and what should be done about it?

A: When the generator loses magnetism, the meter indicates as follows:(1) the rotor current indication is equal to zero or near zero;(2) the sator ammeter indicates elevation and oscillation;(3) the active power meter indicates a decrease and oscillation;(4) the generator bus voltage decreases and oscillates; (5)The reactive power meter indicates a negative value, and the power factor table indicates a phase;

Treatment:(1) After the generator is de-magnetized, the water turbine generator should generally be unlisted for the operation to find out the cause of the diamagnetic loss. (2) After the generator is diamagnetic, the generator output power is not too much, the generator unit can keep in sync with the system, can not be listed, but should as soon as possible to find out the cause, restore excitation, and should closely monitor the operating status of the unit (someone on duty). (3) For power plants that are unattended and undersized, the unit’s degaussing must be automatically de-listed for a shutdown.

21:Why is an inductor equivalent to a short circuit in a DC circuit and a capacitor equivalent to an open circuit in a DC circuit?

A: The voltage at both ends of the inductive circuit is proportional to the amount of change through inductive current, in the DC circuit, the current size and direction are constant, so the voltage at both ends is zero, equivalent to a short circuit, capacitor circuit, the current and capacitor voltage change rate are proportional, in dc circuit, the voltage is constant, so the current is zero, equivalent to open circuit.

22:How to improve the natural power factor of electrical equipment?

A:(1)Choose the capacity of the motor reasonably so that it is running close to full capacity. (2) For induction motors with an average load of less than 40%, switch to a small capacity motor or change the stator winding triangle wiring to a star wiring. (3)Improve the operation of electrical equipment and limit the operation of empty loads. (4)Correctly select the capacity of the transformer and increase the load rate of the transformer. (5)Improve the service quality of the induction motor.

23:What causes the high-voltage fuse of the voltage transformer to fuse?

A: There may be four reasons:(1) a single-phase intermittent arc grounding occurs in the system;(2) a ferromagnetic resonance in the system;(3) a single-phase ground or inter-layer, inter-phase short circuit failure occurred inside the voltage transformer;(4) When the voltage converter secondary circuit is shorted and the secondary fuse selection is too thick to fuse, A fuse on the high-pressure side may be caused.

24:What is sine AC? Why is sine AC now widely used? A: Sine AC refers to the current, voltage, and potential of the circuit in the size and direction of the sine function over time according to the law of sine function, this overtime to do periodic changes in the current is called alternating current, referred to as AC. AC can convert voltage through a transformer, and when transmitting from a distance, increase the voltage to reduce line losses for optimal economic results. And when used, you can also use the buck transformer to turn high pressure into low pressure, which is conducive to safety, but also reduce your insulation requirements for equipment. In addition, AC motor and DC motor comparison have the advantages of low cost, easy maintenance, and so on, so AC has been widely used.

25:Why should electrical measuring instruments, meters, and relay protection devices use CT with different secondary coils as much as possible? A: The measurement and protection levels of domestic high-voltage CT are separate to meet the different requirements of electrical measurement and relay protection. Electrical measurement of ct accuracy level requirements are high, and should make the instrument by short-circuit current impact is small, so when the short-circuit current increases to a certain value so that the measurement grade iron core saturation to limit the growth multiple of the secondary current, the protection grade iron core should not be saturated in the short circuit, the secondary current, and the first current proportional growth, to meet the protection sensitivity requirements.

26:What is the difference between an AC welding transformer and a normal transformer?

A: ( 1 ) Normal transformers operate in a normal state, while welded transformers operate in a short circuit. ( 2 ) When a load of ordinary transformers changes, the voltage of their secondary voltage changes are very small, while welding transformers require a certain arc voltage (60 to 75 volts) when welding, when the welding current increases, the output voltage drops rapidly, when the voltage drops to zero, the secondary current is not too large. ( 3 ) The original and sub-coils of ordinary transformers are concentrically encased on an iron core post, while the original welding transformer and the secondary coil are mounted on two iron core columns respectively.

27:What is an internal overvoltage?

A: The internal overvoltage is caused by the operation (close, pull gate) accident (ground, disconnect, etc.), or other reasons, causing a sudden change in the state of the power system, there will be a transition process from one steady-state to another steady-state, in the process may produce dangerous overvoltages to the system, these overvoltages are caused by the oscillation and accumulation of electromagnetic energy inside the system, so-called internal overvoltage. This can be divided into operating overvoltages and harmonious vibration overvoltages, the former is caused by system operation or failure, the latter is the power grid capacitor components and inductive components in the grid (especially ferromagnetic inductive elements with iron core), the adverse combination of parameters resonance produced

28:Why should the signal action be self-sustaining?

A: Because the impact relay action is started by the shock current, so that the signal (to inform or accident signal) loop action, to enable the impact relay XMJ to repeat the action, that is, the requirements of the first pulse signal action immediately after the return, ready to act again. At this point, if the self-hold loop is not installed, the sound (buzzer or alarm) will end immediately when the pulse signal disappears. To ensure reliable transmission of the audio signal, rather than stopping due to the return of the shock relay XMJ, self-hold is added to the circuit of the intermediate relay that starts the sound.

29: Resistance of the universal meter Why “zero” when measuring resistance, how to adjust?

A: Before measuring the resistance, after selecting the appropriate magnate, first touch the two pens so that the pointer is at zero, if the pointer is not at zero, you should first adjust the “zero adjustments” twist, the pointer still does not mean in “zero”, the battery voltage is too low, Replace the battery before using it.

30, the use of coincidence gate device what is the significance?

A: Because the factors for the failure of the protected line of equipment are varied, especially in the event of a failure of the protected overhead line, it is sometimes a temporary failure, and after the fault disappears, the circuit breaker can be restored to normal operation, thus reducing the damage caused by the power failure.