Introduce large capacity motor distribution system – motors, power distribution systems – Electric industry
I. Introduction Large capacity motor usually refers to electric power in the hundreds or even thousands of kilowatts of electric motors. The power distribution device with 3kV 10kV voltage level, the power grid capacity, motor and manufacturing processes permit, as far as possible all the way starting voltage directly, but also have appropriate protection equipment to ensure its normal operation. Operation of large motor to the grid and will be Other Drag the safe operation of equipment, have a great impact, it requires careful comparison and analysis and calculation to determine the economical, reliable, technologically advanced distribution program. Ling Ao Nuclear Power Station on the air compressor the following distribution of the engineering example about the distribution characteristics of large-capacity motor, starting conditions and the corresponding verified.
II Projects (A) of the instance description
Ling Ao Nuclear Power Station air compression system consists of three compressor component, the main island to the nuclear plant and the delivery of compressed air. Imported by the British company Air Compressor ATLAS, its motor power were 250kW/50Hz/3phase, voltage rating of 6.6kV. Power supply Quote from the northeast Auxiliary Power Transformer 6.6kV common platform for all plant Distributor Choose the 3×3 (ZR-YJV-10-1×400) in the pressure of about 9×550 m armored cable to the nuclear island Electric 6.6kV power distribution plant after-hours, and then were used ZR-YJV22-3×35 MV armored cable is about 350 meters to the compressor power. The motor and process equipment without special requirements of dynamic thermal stability, but according to regulations, the motor bus voltage should not start when 85% lower than the rated voltage. Based on the above technical conditions in order to determine the voltage when the motor starting current is required to meet the starting requirements to start calculating and then check the motor relay protection requirements. Calculation conditions should be established capacity of power supply system is infinite power, use per unit value, calculated capacity Sj = 100MVA.
(B) in the calculation of the following factors to be considered before:
1, high-capacity motor starters, you need to meet the start-bus voltage fluctuations, motor starting torque motors and process equipment requirements and dynamic thermal stability requirements. Motor and process equipment should be able to withstand the impact when full pressure start, which can meet the electrical and process equipment, dynamic stability requirements. For some motors start at full pressure when needed to meet the manufacturing requirements of thermal stability requirements.
2, large motor starting, its terminal voltage should be guaranteed to be dragging the mechanical requirements of starting torque, and in the distribution system voltage drop caused by other electrical equipment should not hinder the work. According to national standards, "Power Quality. Slide and flicker voltage to allow "(GB12326-93) requirements, under normal circumstances
, Motor starting when the voltage on power distribution bus should not be less than 85% of rated voltage for starting the motor frequently, not less than 90% of rated voltage.
3, start calculating (1) Impedance Calculation: based power system is infinite-capacity power supply, use of per unit value, with the system impedance (X * xt) calculated starting voltage when the voltage drop should cause the largest event that the system capacity of the smallest, short-circuit capacity of the largest cases.
B. Line impedance (X * l1): X * l1 = X × Sj/Uj2 the formula: X?? Line reactance per phase ( ); Uj?? Line reference voltage (kV); c. on the bus Other load reactance (X * fh); X * fh = Sj / Sfh the formula: Sj?? baseline capacity, taking 100MVA; Sfh?? bus on the other capacity calculated value (MVA); d. line impedance (X * l2)
X * l2 = X × Sj/Uj2 the formula: X?? Line reactance per phase ( ); Uj?? Line reference voltage (kV); e. motor starting impedance (X * d)
X * d = 1/Kq × Sj / Sed the formula: Kq?? Motor full voltage starting current multiples; Sed? Motor rated capacity.
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