Share 20 electrical professional questions and answers with you (I)

1. Briefly describe what tasks should be done by the central signaling device?

A: The central signal device should be able to perform the following tasks:

(1) The central signalling device should ensure that the position indication of the circuit breaker is correct.

(2) An audible signal (buzzer) is issued when the circuit breaker trips.

(3) Another type of sound (alarm) that can signal a different accident when a fault occurs.

(4) When the acoustic signal occurs, it should be able to be manually reset or automatically reset, and the fault property display is retained.

(5) It is possible to check whether the signal device and the photon card are intact.

2. What are the precautions for measuring insulation resistance near live equipment?

Answer: When measuring the insulation resistance near the live equipment, the position of the surveyor and the shaker should be properly selected to maintain a safe distance so as not to touch the live part of the watch lead or lead support. When moving the lead, care must be taken to prevent the worker from getting an electric shock. When the wind is above 5th grade, the measurement is forbidden; when the wind is below the 5th grade, pay attention to the wind deviation of the wire and maintain the specified safety distance.

3. What is the hazard of the DC bus voltage being too high or too low? How to adjust when the bus voltage is too high or too low?

A: The hazards and adjustment methods are:

(1) When the DC bus voltage is too high, the relays and indicators that are energized for a long time are easily overheated and damaged. When the voltage is too low, the action of the switch protection may be unreliable.

(2) In the case of DC system operation, if the bus voltage is low, check whether the float current is too small, check whether the DC load suddenly increases, etc., and adjust the float charging device to increase the output current appropriately; In the event of an accident, when the DC load suddenly increases, the contacts of the discharge regulator should be quickly adjusted to keep the bus voltage within the allowable range.

(3) When the bus voltage is too high, the float current should be reduced to restore the bus voltage to normal.

4. What should I do if there is a misalignment or a wrong pull-off switch during operation?

Answer: When the switch is misaligned: Even if the fault is made even if the arc occurs during the closing, the knife gate will not be pulled open again, because the load pull-isolation switch will cause a three-phase arc short circuit. When the isolation switch is wrongly pulled, an arc will occur when the blade just leaves the fixed contact. At this time, it should be closed immediately to eliminate the arc and avoid accidents. However, if the isolation switch has been fully opened, the isolation may not be isolated. The switch is closed again.

5. What is the danger of starting and running the three-phase power supply relative to the asynchronous motor?

Answer: When the three-phase asynchronous motor lacks phase power, the motor will not start and there is a strong “click” sound. If the motor in operation is missing a phase power supply, although the motor can continue to rotate, the speed decreases if the load Without reducing, the stator current of the motor will increase, causing overheating and even burning the motor.

6. What are the organizational and technical measures to ensure safety on electrical equipment?

A: Organizational measures for working on electrical equipment to ensure safety: work ticket system, work permit system, work monitoring system, work interruption and termination system. Technical measures: power outage, power inspection, installation of grounding wire, hanging signage and installation of barriers.

7. What is the standard for power quality? What are the adverse consequences if the power quality is unqualified?

Answer: The standard of power quality is: the voltage is normal, the deviation is ±5% of the rated voltage value; the frequency is normal, and the deviation from the rated frequency does not exceed ±0.2-0.5 Hz. If the power quality is unqualified, it will cause: waste, defective products; reduce the output of the motor; in severe cases, it will damage the equipment and personal accidents.

8. In the DC circuit, what is the frequency of the current, the inductance of the inductor, and the capacitive reactance of the capacitor?

Answer: In a DC circuit, the frequency of the current is equal to zero, so the inductive reactance of the inductor is equal to zero; the capacitive reactance of the capacitor is equal to infinity, which is equivalent to an open circuit.

9. What is the difference between resistance and resistivity?

Answer: Resistance refers to the resistance of current flowing in the conductor, while resistivity refers to the resistance value of a certain conductor material when the cross-sectional area is 1 millimeter long and the temperature is 20 °C. Its unit is O.M.

10. What is a phasor diagram?

A: Several sinusoids of the same frequency are represented by phasors and drawn in the same coordinate system. The resulting graph is called a phasor diagram.