On the morning of the 23rd.
1 1. If the active calculation load of our factory 10KV system is 4000Kw and the reactive calculation load is 3000KVar, the annual average active load system is 0.75 and the annual average reactive load is 0.8. If the power factor is compensated to 0.95 by the parallel capacitor, the capacity of the parallel capacitor should be increased.
A 14 19 kva B 1660 kva C 22 13 kva D 1809 kva.
Reference answer: C.
12. If the rated current of shunt capacitor is 88A and the coefficient is 10KVA, the calculated loop current of capacitor and the long-term allowable truncation of conductor should not be less than the following.
a 88A B 1 18.8 a C 132 a D 100 a
Reference answer: C.
13. Explain which of the following grounding methods should be used for parallel capacitor banks:
Triangular grounding
B neutral ungrounded form or double star connection
The neutral point is connected to the ground through the arc suppression coil star.
Neutral point direct grounding star grounding
Reference answer: b
14. There is no series part in the parallel capacitor bank. Which of the following protections should be configured when using a single star connection?
Voltage differential protection can be installed.
B can be equipped with open delta voltage protection.
C neutral point unbalanced current protection can be installed.
D can be equipped with voltage differential protection and differential current protection.
Reference answer: b
15. A county plans to replace the overhead conductor of sewage treatment station 12KM 10KV with XLPE insulated cable and lay it together with other currents in the tunnel. The normal load of this line is 2MKV, and the XLPE aluminum core cable with power factor of 0.9 will be laid overhead.
50 mm 70 mm 95 mm 120 mm
Flow145a190a215a240a
? (ω/KM)0.64 0.46 0.34 0.253
x(ω/KM)0.082 0.079 0.076 0.076
It is known that the short-circuit current on the power supply side of the line is 15KA, the protection action time is 0. 15S, and the thermal stability coefficient of the protection current is 77. The current comprehensive correction coefficient of 0.8 requires that the voltage drop at the end of the current is not more than 7%, and the calculated current cross section is 10KV.
A 50 B 70 C 95 D 120
Reference answer: D.
16. It is known that the neutral point of sewage treatment 10KV power supply is grounded via arc suppression coil. What is the most economical and reasonable cable insulation level and why?
a 6/ 10KV B 10/ 10KV C 8.7/ 10KV D 6.3/ 10KV
Reference answer: C.
17. 10KV medium-sized arc suppression coil is grounded. What is the required peak value of lightning impulse withstand voltage to the ground? Explain why.
A 60KV B 75KV C 80KV D 95KV
Reference answer: b
18. The gold wire voltage of an enterprise substation is 35KV. After passing through the step-down transformer, power will be supplied to the high-voltage electrical equipment and users in the factory with 10KV, and then to the nearby low-voltage users with 10/0.4KV distribution transformer.
It is known that all 10 systems are fed by cables, in which the longitudinal length of current with a cross section of 95mm2 is 15KM, and the length of current with a cross section of 120 mm2 is 10KM. Try to calculate the single-phase capacitance current of 10KV system, and the results are the closest to the following values:
A 2 1A B 27A C 30A D 35A
Reference answer: C.
19. Assuming that the calculated value of the single-phase grounding capacitance current of the above system is 32A, if it is necessary to operate under ground fault, try to analyze which of the following neutral grounding methods is most suitable for 10KV system, and please explain the reasons.
A ungrounded B directly grounded C high resistance grounded D arc suppression coil grounded
Reference answer: D.
20. The grounding network of the above-mentioned substation is shown in Figure 5- 1. If the earth resistivity ρ = 3000 Ω. Com, which of the following values is closest to the power frequency grounding resistance of grounding grid?
a R = 265ωB R = 3ωC R = 9ωD R = 300ω
Reference answer: b
2 1. The low-voltage distribution system of the substation is TN-S grounding system. The rated voltage of a motor is 380V, and the power supply is supplied by 3*50+ 1*25 mm2 cable. It is known that the phase protection resistance per unit length of cable RL =1.59 Ω/km. When a short circuit occurs in the collision shell, calculate the grounding potential on the motor shell (ignore
a UC = 1 10V B UC = 147v C UC = 253v D UC = 220v
Reference answer: b
6. An enterprise has a 2MW asynchronous motor connected to the 3kV socket of the workshop distribution panel. If the total single-phase grounding capacitance current of 3kV power grid is 10.5A, try to answer the following questions:
22. In order to protect the phase-to-phase short circuit of the motor winding, which of the following protection devices should be installed? And explain why.
(a) current quick break protection
(b) longitudinal differential protection
(c) First, consider current quick-break protection, and set differential protection when the sensitivity does not meet the requirements.
(d) out-of-step protection
Reference answer: b
23. The motor circuit single-phase grounding current 6A, which of the following ways is correct for the configuration of motor grounding protection? And explain why.
(a) Grounding protection is not required.
(b) Grounding detection devices can be installed.
(c) Grounding protection shall be installed, and the protection device shall act when tripping or signaling.
(d) Grounding protection should be installed, and the protection device can only act on signals.
Reference answer: C.
24. If the motor circuit is grounded in single phase, the capacitive current flowing through the circuit is 7A. If single-phase grounding protection is installed, which of the following values is the primary current range of the protection device (the protection sensitivity coefficient is 1.25)? (eight books)
(A) ≥8.75A (B) ≤8.4A
(C)>5.6A (D) ≤5.6A
Reference answer: D.
On the afternoon of the 23rd
1. Which of the following signals is a typical analog signal of PLC input and output module?
a 、- 10～+ 10V
b 、- 15～+ 15V
c、4~20mA
d、0~+ 10V
2. During normal operation, allowable values of terminal voltage deviation of electrical equipment:
A, the motor is plus or minus 5%; General workplace lighting is 5%; Unless otherwise specified, it is 5%.
B, the motor is plus or minus 5%; General workplace lighting is +5%,-10%; Unless otherwise specified, it is 5%.
C, the motor is plus or minus 5%; General workplace lighting is +5%,-10%; +5% and-10% unless otherwise specified.
D, the motor is plus or minus 5%; General workplace lighting is 5%; +5% and-10% unless otherwise specified.
3. Low-voltage power distribution shall adopt the following radial power distribution:
First, the capacity of electrical equipment is large;
B, the nature of the power load is very important;
C. Factories and buildings with special requirements;
D, electrical equipment close to each other.
4. When the oil content of the transformer in the indoor substation is more or more, a separate distribution room should be set up:
A: 60
B, 80
c、 100
d、 120
5. In the residential areas of small and medium-sized cities and towns where the environment permits, when the transformer capacity is large, it is appropriate to set up pole-type or high-table substation:
630 pounds
500 pounds
200 pounds
d、3 15
6. On-off current operating appliances can use load switches and circuit breakers, and also can use:
A. relay
B. Current contactor
C, semiconductor appliances
D. fuse
7. In the parallel capacitor bank, the connection between the discharger and the capacitor bank is as follows:
The discharger is connected in series with the current limiting resistor and then in parallel with the capacitor.
The discharger, current limiting resistor and capacitor are connected in series.
C. the discharger is directly connected in parallel with the capacitor.
The discharger is connected in series with the capacitor bank.
8. If the active calculated load of the plant 10kV system is 4000kW, the reactive calculated load is 3000kvar, the annual average active load coefficient is 0.75, and the annual average reactive load coefficient is 0.8, if the power factor is compensated to 0.95 with parallel capacitors, which of the following values should be increased? (I don't remember which ones to choose. A and B are both right. )
a . 1260 kvar； B.960kvarC.2280kvard . 1809 kvar；
9. If the rated current of the shunt capacitor bank selected for 10kV system is 88A, the long-term allowable ampacity of cables and conductors supplying power to it should not be less than which of the following values?
A.88Ab . 1 18.8 a； c . 132 a； D. 100A。