4 x 200MW Thermal Power Plant Electrical Design and Protection

This paper includes the main wiring design of 4 × 200MW thermal power plant, the calculation of short-circuit current, the selection of some electrical equipment, and the transformer longitudinal differential protection. Finally, the lightning protection is set up.  The power system is a whole consisting of power generation, power supply and electricity. Since most power plants and load centers are located in different areas and cannot store large amounts of electricity, the production of electricity must always be balanced with consumption. The design includes: main wiring design, short circuit calculation, part of the electrical equipment selection and transformer differential protection. Power plant site overview: The plant is a pit-mouth power plant, and all fuel is directly supplied by the coal mine. In addition to the electrical energy produced by the power plant, all 220kV lines are sent to the peripheral system. There is a large river near the site, which is rich in water. The maximum wind speed is 20m/s. The annual average temperature is +12 °C, the highest temperature is +41 °C, the lowest temperature is -2 °C, and the soil resistivity is >500. Units with single capacity of 100-125 MW should be directly boosted into 220 kV power network when system stability is required. Units with single capacity of 500 MW and above should be directly boosted into 500 kV power network. 220 kV Voltage Level Connection Mode Electrical main wiring is the main part of the electrical part of power plant and substation[1], which reflects the function of each equipment, the connection mode and the relationship between the circuit. It is directly related to the selection of electrical equipment, distribution arrangement, relay protection, automatic device, control mode and so on. There are two possible main wiring schemes.  The double bus section connection method is adopted, and the double loops are connected to different bus sections respectively, so as to reduce the influence range of bus faults.  1 for the main connection form. Design Scheme 2. The double bus connection is adopted, and the circuit breaker adopts high-reliability circuit breaker.  2 for the main wiring form. Scheme 2 can be operated by switching two groups of bus dis-connectors, and one group of buses can be overhauled in turn without interrupting power supply[2]. When overhauling any circuit breaker, the circuit shall be cut off for a short time. The circuit breaker adopts a circuit breaker, so that the maintenance period is long, frequent maintenance is not required, and the probability of power failure during maintenance of the circuit breaker is reduced. Through comparison, it can be seen that the feasibility of scheme 1 is slightly higher than scheme 2 in terms of reliability. Although the reliability of scheme 2 is slightly lower than that of scheme 1, the SF6 circuit breaker is used in the circuit breaker, which has a long overhaul cycle and does not need regular overhaul. In this way, the probability of power failure in circuit breaker maintenance can be reduced. In terms of economy, scheme 2 is obviously higher than scheme 1, so the choice of scheme 2 is considered comprehensively.

Field of study: Engineering