Hello, you can look at the following familiar topics. Basically, it is not difficult to pass the exam with the teacher. The greater the transmission energy, the greater the capacity and the longer the transmission distance, the lower the safe transmission voltage. about
The metal core of the voltage transformer and the shell at one end of the secondary side should be firmly grounded or connected to zero.
The meter exchange of current transformer should be carried out during operation to prevent secondary short circuit.
High and low voltage disconnectors cannot be used to switch on and off the load current, but they can switch off the short-circuit current.
However, the high and low voltage disconnectors must be corresponding high and low voltage circuit breakers and power supplies. When the power supplies work in the same sequence, you should first turn off the disconnector and then turn off the circuit breaker.
Under normal circumstances, the substation is powered off, the first switch of each load switch is closed, and the capacitor bank switch is switched off.
The oil temperature on the transformer oil tank should not exceed 55°C and must be used.
Discharge circuit breaker and fuse protection of capacitor bank. Manual method compensation
Increasing the power factor is usually enough to connect the inductive load in series with the capacitor.
According to the regulations of Shanghai, the grounding point at home should be no small, 2.7M
Requirements in Shanghai: The minimum cross-sectional area of the entrance line is 4M square meters.
Shanghai stipulates that households should use hard copper or aluminum wires with good insulation.
The power distribution room should be well ventilated to ensure the safety and reliability of the lighting system, and the indoor lighting power switch should be located in the inner power distribution room.
The secondary circuit of current transformer should be equipped with fuse short circuit protection.
In Shanghai, it is stipulated that the center of the billing watt-hour meter is 1.4- 1.8M from the ground.
The ratio of rated current of fuse upper limit and lower limit shall be less than 2 times.
Plug-in fuses should be installed vertically, and the rated current of fuses should not be less than that of fuses with rated current.
The ambient temperature of the capacitor room shall not exceed 35 C. 。
The line equipment should have sufficient insulation strength, and the insulation strength of indoor wires and cables should not be lower than AC 450/750.
The maximum allowable current of wires and cables depends on the cross-sectional area of wires and cables and the working mode of their material structure.
The selection of conductor cross-sectional area, the distribution branch line that the distributor must meet, and the number of lights illuminating each single-phase parallel connection should not exceed 15.
The number of single-phase parallel lamps for building outline lighting shall not exceed that of 50 yuan.
On the distribution branch line, the maximum load current of each branch is less than 25A. Main loop/>; For gas discharge lamps, the cross section of the N line should not be larger than that of the phase line.
What is the minimum cross-sectional area for laying plastic sheathed cables? Copper, indoor 1.5 m 2, the head part is connected or in the junction box.
The grounding conductor of sheathed cable is not heated on the cross, and the place protected by steel is vulnerable to mechanical damage, so insulation protection should be adopted.
The rated voltage of the pipe-penetrating conductor should not be lower than AC 400V conduit, and there should be no joint.
The minimum cross-section of pipe-penetrating conductor should not be 654.38+00,000 square meters, and the insulated copper cable of aluminum core insulated conductor should not be 654.38+0.5 m ㎡. /& gt； Steel pipe, connected with the beam, crossed with round steel or flat steel at both ends of the ground to form a good electrical path, and any two resistance values should be less than 4 ohms/>; The bending angle and surface line radius of the pipeline shall not be less than 6 times of the pipe diameter. /& gt； The bending diameter of the pipe should not exceed the angle between 90 degrees.
Cable laying depth shall not exceed 0.7m
The total cross section of metal trunking, control, signal or similar wires, wires or cables shall not exceed 40 ‰ of the cross section of the conduit, and the number of wires and cables is not limited.
Use both ends of yellow/green jumper, and the internal connection of metal trunking should be firmly grounded or grounded, and can also be used as the grounding conductor of equipment. /& gt； Temporary lines should be connected from one end of electrical equipment to one end of power supply, and then in reverse order, when the lines are deleted.
Temporary power switches, sockets, fuses and outdoor electrical equipment for leakage protection shall be installed in the switch box.
In crowded places, separate local lighting must be used.
The chandelier with weight exceeding 1 kg, metal chain or other means support the online chandelier force.
Lighthouse fluorescent lamps should not be closed on flammable building surfaces, and ballasts of flat-top fluorescent lamps should be sealed and preserved.
Halogen lamps should be installed horizontally, and the inclination should not exceed 10, otherwise the life of the bulb will be shortened.
When moving household appliances, you must turn off the electrical switch.
Common business areas should be as many as possible, and I like it very much, using class II tools. Equipment needs leakage protector or isolation transformer.
Class II tools should be used in narrow spaces such as boilers, metal containers and pipelines.
The protective conductor is connected to the grounding or neutral system and is made of insulated copper wire. The cross section should not be 1, 5 mm.
Lightning protection device consists of lightning receptor, down conductor and grounding wire.
The protection radius of lightning rod is 0, and the height of lightning rod is 5 times of the ground.
Buildings or structures equipped with lightning rods allow electrical equipment to be grounded at the same point, but the grounding resistance of the grounding device at the same point is less than 4 ohms.
In order to prevent the invasion of lightning wave, the lightning arrester of the equipment is installed as close as possible to the protected place, and the resistance of the independent grounding device is small, which should be 4 ohms.
All portable electronic equipment and hand-held power tools must be equipped with residual current protection devices. /& gt； In order to avoid fault and leakage protection, the invalid current is less than 1/2 of the working current.
The current in the wire and cable will generate heat, but the heating temperature through the normal maximum load current is lower than the maximum allowable temperature. /& gt； For three-phase four-wire or two-phase three-wire distribution lines, when most single-phase electrical equipment is under power load, the cross section of N-wire or PEN-wire is not easy to be larger than that of phase wire.
Pipeline wiring, moisture-proof, fire prevention, corrosion protection and moth prevention, etc. , can be used in places where metal rot termites are serious.
Conductors in AC circuits should pass through steel pipes, and plastic pipes are not allowed to pass through monofilaments, but DC circuits and protective grounding wires. /& gt； Semi-rigid plastic pipes can only be used in ordinary houses less than six years old, and the minimum pipe diameter should not be less than 10mm/> AC single-core cables cannot pass through steel, but in the same period, a single cable passes through the same steel pipe.
The connection of metal trunking shall be uninterrupted, and the connecting bolts for fixing the locking device shall be fixed from the outside to the inside. /& gt； Low-voltage circuit breakers are widely used as protection for low-voltage distribution lines, and can also be used as control switches for frequently starting motors. /& gt； Install an open load switch, which should be installed vertically, so that all directions can be closed from top to bottom, and switch from bottom to prevent accidental closure.
In the same power supply system, the power supply equipment should be grounded, and the lighting and socket can share the grounding.
The ammeter should be connected to the voltmeter of the measured load circuit, and the load circuit should be connected in series. read
When measuring the insulation resistance of electrical equipment, the insulation resistance meter should stop shaking. /& gt； The multimeter measures the AC voltage, DC voltage, current and resistance of electrical equipment under charging state.
As long as it takes more than 4 to 6 minutes, brain hypoxia will cause irreversible damage, so once it is found to be "clinical death", mouth-to-mouth resuscitation must be carried out immediately.
"Clinical death" occurs when the tissues and cells in the body are seriously deprived of oxygen, which is very urgent. Time is life and must be sent to the hospital at once.
During external heart massage, your hands and heels should be placed on the right side of the clamp, which is the outcrop of the left chest.
Electricians without special operation certificates can only do maintenance work on all power equipment or lines.