Electrical Power Systems Interview Knowledge Questions
power cable inspection which inspection items?
A: Power cable inspection inspection items are:
(1) Check the cable and terminal box for leakage of oil, insulating plastic is softened overflow.
(2) Insulator is clean and complete, whether there are cracks and flashover traces, wire connectors are intact and not heat.
(3) exposed cable sheath is complete, whether the solid support.
(4) the skin is good ground.
main control room, relay protection indoor and 10 (6) kV power distribution indoor equipment normal patrol what projects?
A: Indoor equipment, the normal inspection items are:
(1) no sound and Jiao smell.
(2) All instruments, signals, indicator windows should be consistent with the operating conditions, the instructions are correct.
(3) to protect the connection piece position is correct (should be consistent with the actual).
(4) system three-phase voltage balance (approximate), and in the specified range.
(5) power line, the main switch three-phase ammeter approximate balance.
transformer oil shortages on the operation of what harm?
A: The transformer oil level is too low will make light gas action; serious lack of oil, the core and winding exposed to the air easily damp, and may cause insulation breakdown.
forced oil circulation transformer stopped the oil pump why not allowed to continue to run?
A: The reason is that the transformer housing is flat, the cooling area is very small, and even can not transform the transformer no-load loss of heat generated by scattered out. Therefore, forcing the oil circulation transformer to completely stop the cooling system operation is dangerous.
take the operation of the gas in the transformer one should pay attention to what safety matters?
A: The security issues that should be noted are:
(1) to take gas gas must be carried out by two people, one person operation, one guardianship.
(2) climbing transformer should take a safe distance from the gas to prevent high-throw.
(3) to prevent accidental collision probe.
What causes the transformer to issue unusual sound?
A: The following causes the transformer to make an unusual sound:
(1) Overload. (2) internal contact is bad, discharge spark.
(3) individual parts loose. (4) The system is grounded or shorted. (5) large motor starting to make a big change in load.
voltage transformer in operation, why not allow a short circuit twice?
A: The voltage transformer in normal operation, the secondary load impedance is very large, voltage transformer is a constant voltage source, the internal impedance is very small, small capacity, a winding wire is very small, when the transformer secondary short circuit, Current is great, if the second choice of improper fuse, the fuse can not be fused, the voltage transformer can easily be burned.
What happens when the capacitor should immediately exit the operation?
A. The capacitor should be removed from operation immediately upon any of the following conditions:
(1) casing flashover or serious discharge.
(2) joint overheating or melting.
(3) expansion of shell deformation.
(2) joint overheating or melting.
(3) expansion of shell deformation.
(4) the internal discharge sound and discharge equipment abnormal sound.
arc suppression coil switching tap the operation of what provision?
A: Operational requirements are:
(1) The tap-changer tap should be switched according to the position of the tap assigned by the dispatcher.
single busbar 10kV system single-phase grounding, the line-by-line power failure to find, grounding phenomenon is still not disappear What is the reason?
A: There are two reasons:
(1) Both lines are earthed at the same time.
(2) the bus station equipment grounding.
fixed-time over-current protection is the setting principle?
A: The definite time overcurrent protection action current setting principle is: the action current must be greater than the load current, the maximum load current protection device does not act, when the next level line external short circuit, if the current relay has been in action, Subsequent protection After the fault current has been removed, the protection of this stage should be reliably returned.
distribution lines why only installed over-current does not install quick-break protection?
A: 10kV distribution line power supply distance is short, the line short-circuit current and the end of the first little difference between the value, quick-break protection by bypassing the line short-circuit current setting, protection is too small; In both cases, it is not necessary to install a current quick-break protection.
export intermediate relay contacts Why should series current coil?
A: The purpose of contact series current coil is to prevent the protection action after the contact jitter, vibration or a very short time can not switch on and off tripping. So to protect the middle of the outlet is usually used in contact with a series of current coil self-sustaining wiring. In the event of a fault, the contact is closed and the current coil in series is energized to produce a self-holding to ensure a reliable trip of the switch.
transformer differential protection is based on what the principle of installation?
A: The transformer differential protection is installed according to the principle of circulating current. Two current transformers with the same model are installed on both sides of the transformer. In the normal and external fault, there is no current in the differential relay, and in the transformer internal phase short circuit occurs, the differential relay will have a great current flow.
transformer zero sequence protection under what circumstances put into operation?
A: Transformer zero sequence protection should be installed in the transformer neutral point directly to the ground side, to protect the side of the winding internal and lead-wire short-circuit, can also be used as the corresponding bus and line ground short-circuit protection, so when the Transformer neutral grounding knife into the joint, the zero sequence protection can be put into operation.
What line of differential protection device installed cross-linked? What is the fault of the transverse differential protection response?
A: In the same impedance of the two parallel lines can be installed cross differential protection. Transverse differential protection protects against internal faults in parallel lines and does not respond to external faults in parallel lines.
synchronous reclosing under what circumstances do not move?
A: No action in the following cases:
(1) If the line has a permanent failure, with no reclosing the circuit breaker reclosing immediately after the break, the same reclosing will not move.
(2) no pressure reclosing refuses to move, the same period reclosing will not move.
(3) synchronous reclosing refuses to move.
Under what circumstances will the reclosing of the circuit breaker exit operation?
A: The reclosing operation is exited in the following cases:
(1) the circuit breaker interrupter capacity is less than the bus short-circuit capacity, the reclosing out of operation.
(2) the number of circuit breaker failure trip exceeds the requirements, or though not more than the provisions, but the circuit breaker serious fuel injection, smoke, etc., should be agreed after the operation of the reclosing out.
(3) line with live operation, when the duty dispatcher command reclosing will be out of operation.
