1. If the cable sheath enters the junction box wall less than 8mm or more than 15mm, it is considered as misfiring. ( × )
2. When there are two or more voltages in the underground low-voltage distribution system at the same time, the voltage grade of low-voltage electrical equipment may not be marked. ( × )
3, low-voltage motor control equipment, should have short circuit, overload, single-phase disconnection, leakage locking protection device and remote control device. ( )
4, it is forbidden to underground distribution transformer neutral point grounding directly. It is forbidden to directly supply power to the underground by the transformer or generator directly grounded by the ground neutral point. ( )
5. Flameproof electrical equipment refers to electrical equipment that puts all components that can generate sparks, arcs and dangerous temperatures into a shell with sufficient strength to prevent external explosive mixture from exploding inside the shell. The symbol is horse. ( × )
6. If the pressure plate lead-in device lacks the compression bolt or the compression bolt is not tightened, the hand will shake, which belongs to the electric explosion loss. ( )
7. The rubber cable sheath is damaged, with the scar depth exceeding 1/3 at the thinnest part, the length exceeding 200mm or being lost along the circumference 1/4. ( × )
8. The explosion-proof electrical equipment repairman (part-time explosion-proof inspector) shall check the explosion-proof electrical equipment under his jurisdiction at least once a day. ( × )
9, when the electrical equipment may accumulate pulverized coal, the highest surface temperature should not exceed 65438 050℃. ( × )
10, the common over-current faults in coal mines are leakage, overload and phase failure. ( × )
Second, single or multiple choice questions. (2 points for each question, ***20 points)
1, intrinsically safe electrical equipment refers to the electrical equipment in the circuit system. Under normal and fault conditions, its spark and temperature cannot cause the explosion of explosive mixture. The symbol is a.
A, B, C, D, D, D.
2. Which of the following situations belongs to electrical explosion C?
A the nut type lead-in device is not tight enough to loosen the compression nut by hand.
B the clearance between the inner diameter of the sealing ring and the outer diameter of the cable is 0.5mm..
C after the cable is flattened by the crimping nozzle, the flattening amount exceeds 10% of the cable outer diameter.
D screw in 7 buttons for the spiral nozzle.
3. The local grounding electrode ABCD shall be installed in the following positions.
A, equipped with electrical equipment cavern and separate installation of high voltage electrical equipment.
B. Low-voltage distribution points or places equipped with more than three electrical equipment.
C. metal connection device for connecting high-voltage power cables.
D, there is no low-voltage distribution point of coal winning machine working face transportation lane, return air lane, centralized transportation lane (belt transportation lane) and tunneling faces are separately powered by substation.
4. The grounding bus connected to the main grounding electrode shall adopt ABC.
Copper wire with a cross section of not less than 50mm2.
B galvanized iron wire with a cross section not less than 100mm2.
C flat steel with a thickness of not less than 4mm and a cross section of not less than 100mm2.
D, aluminum conductor with a cross section of not less than 80mm2.
5.BCD is the main cause of motor overload.
A, the power supply voltage is too high. B, frequent startup. C, the startup time is long. D, mechanical jam.
6. The relay protection device of distribution system should be checked and set 1 time every d months, and the setting should be timely when the load changes.
a、 12 B、 1 C、3 D、6
7. For 660V low-voltage power grid, the resistance setting value of leakage protection device is kiloohms.
a、 1 1 B、22 C、20 D、2.5
8. The metal shell of electrical equipment with a voltage above C V and the metal shell of electrical equipment that may generate dangerous voltage due to insulation damage must have protective grounding.
a、 127 B、220 C、36 D、 12
9. Ordinary portable electric measuring instruments must be used in places with gas concentration below B. ..
a、0.5% B、 1.0% C、 1.5% D、2.0%
10, "Coal Mine Safety Regulations" stipulates that motors of B kW and above shall be controlled by vacuum electromagnetic starter.
a、55 B、40 C、25 D、 1 1
Fill in the blanks. (2 points for each space, ***20 points)
1. Underground protective grounding system: it consists of main grounding electrode, local grounding electrode, grounding bus, auxiliary grounding bus, grounding conductor and connecting conductor.
2, low-voltage motor control equipment, should have short circuit, overload, single-phase disconnection, leakage locking protection device and remote control device.
3. On the flame-proof surface fastened by bolts, the specifications of bolts and nuts at the same position are inconsistent, and the depth of steel fastening bolts screwing into nuts is less than the diameter of bolts.
4. The sealing ring of underground electrical switch is not completely installed on the lead skin of armored cable, or there are other objects between it and the lead skin, or the gap between it and the lead skin is greater than 1 mm ... If there is no metal gasket between the inlet nozzle and the sealing ring, the flattening of the laminated nozzle after pressing the cable exceeds 10% of the cable diameter, which belongs to explosion damage.
5. The grounding resistance of any protective grounding point on the grounding network shall not exceed 2 ohms. The resistance value of cable core and grounding connection wire for protective grounding between each mobile and handheld electrical equipment and local grounding electrode shall not exceed 65438 0 ohms.
Second, short answer questions. (***4 questions, 30 points)
1. What are the four common AC voltages in our mine? (4 points)
A: 127V, 660V, 1 140V, 6000V.
2. What are the main requirements of coal mine power supply system? (6 points)
Answer: The power supply is reliable, safe and economical.
3. What procedures must be performed before electrical equipment maintenance or relocation? (10)
Answer: 1, cut off the power supply;
2, check the gas, the gas concentration in the roadway airflow is lower than 65438 plus or minus 0%;
3, with the power supply voltage to adapt to the test pen inspection;
4. After checking that there is no electricity, conduct conductor-to-ground discharge;
5, lock, hang someone work are not allowed to send someone warning signs.