Design of electrical power system for a 1000MW nuclear power generating station

Transcription

1 Design of electrical power system for a 1000MW nuclear power generating station K Raja, K Yesunadam Dept. of Electrical & Electronics Engineering, Lingaya s Institute of Management & Technology, Vijayawada, India. {raja.k233, kondayesunadam1}@gmail.com Abstract The successful operation of any nuclear power generating stations depends on the electrical power supply systems. The electrical power supply systems have normal, emergency power systems and uninterruptable power supply systems. These systems play a vital role to operate and safely shutdown the reactor during both normal and anticipated conditions. The objective of this paper is design the electrical power system for a 1000MW nuclear power generating station. For nuclear power generating stations the emphasis is based on the design of systems is based upon nuclear safety, personal safety reliability and economic considerations. This typical electrical system is designed for generalized nuclear power generating station irrespective of type of nuclear plant. The reference for this design was based on IEEE papers & standards. This work covers the designing of the electrical power system for a nuclear power generating station. Keywords- Normal power supply systems (NPS), Emergency power supply Systems (EPS), UPS systems. I. INTRODUCTION The typical system has a net output of 1000 MW. In achieving this station relies on auxiliary plant and services whose electrical power is supplied from the AC power systems. The total connected load is in excess of 100 MW. The electrical system is the main source of power to the reactor cooling auxiliaries during normal operation, for the protection system and the safety systems during normal and fault conditions. This paper will consider the designs of both the Emergency power supply systems [1] and the Normal power supply systems [2]. Both offsite (grid) and on-site (Diesel generators) electrical power supply systems are provided and the reliability of both these systems has direct effect on the safety of the plant. The electrical power supply systems design is as follow: Off-site power system(grid connection) Turbo-Generator and its auxiliaries. Class IV-Normal AC power supply systems Class1E-Emergency power supply systems. (Class III AC Emergency power supply system. Class II-AC supply from battery & Inverter Class -1 DC supply from batteries.) Variable speed drives, Preheating systems, Lighting, cabling and protection systems II. NORMAL POWER SUPPLY SYSTEM The Normal Power supply System connects the power station to the National Transmission System (Grid) and distributes power throughout the power station at system voltages postulated by engineering considerations. This power is used both for auxiliaries required to operate the power station and to supply the Emergency power supply Systems with its preferred source of power. This power is also called as Off-site power The designed system has bus voltage of 11kV. Safety Design Bases The MPS provides power to process plant not forming a part of the essential systems but which may make a significant contribution to nuclear safety,their availability is desirable for nuclear operation and safety To supply power to auxiliary loads with a high reliability and integrity so as to limit the number of challenges to the EPS All supplies are designed to be continuously available during routine operation s including those associated with a reactor trip with the grid[3] 11 kv System The connection of the NPS to the grid is in the power station's 400kV substation. The substation is designed to operate with both bus-coupler breakers and both bus-section breakers closed. Individual circuits supplying the NPS will be selected to either the main busbar or the reserve busbar. The system has two unit buses and two station buses. This system has generator transformer, unit auxiliary transformers, station transformer as shown in figure

2 3.3kV System The 3.3kV NPS derives its power supply only from the 11 kv NPS. The system consists of buses termed unit bus and station bus. The unit bus generally supply auxiliaries and loads directly associated with the turbo-generator operation and the station bus supply auxiliaries and loads associated with station services. 415V System The 415V NPS supplies power to non-safety related equipment which is either associated with the turbo-generator or required for station services. Generally all 415V switchboards associated with power generation or station services will be radially fed and their power sources derived from the 3.3kV NPS. The system consists of two tiers of switchgear types ie. Load centres and motor control centres. Load centres incorporate a 3.3kVl433V Class 'C' AN transformer fed by a motor switching device/circuit breaker on a 3.3kV unit or station switchboard of the same separation group. III. EMERGENCY POWER SUPPLY SYSTEMS The Emergency power supply systems (EPS) are divided into four separation groups or trains and provide power to all equipment required to ensure the safety of the Reactor. To ensure that these systems meet their safety functional requirements detailed safety criteria must be satisfied. The following Safety Design Bases include both general and those specific to the EPS. Safetv Design Bases The EPS is designed and qualified to adequately survive external hazards such as lightning, earthquakes, high winds and floods with consideration given to extremes of ambient temperature. The postulated internal hazard such as fire, internal missiles or pipe break coincident with loss of grid sufficient equipment in the EES will remain. Functional to allow a safe shutdown of the Reactor. The separation segregation and isolation criteria for plant and cabling are applied to preserve the independence of redundant essential equipment. The EPS is divided into four similar trains. Each train is capable of supplying its connected loads independently of the other three trains. All auxiliaries and Services required for continued operation of a train are derived from that same train of the EES. The EES will operate when power supplies are available from either on-site or off-site (grid) power sources. Each EES train has its own associated and independent essential diesel generator. Connections from the Main Power Systems are made through qualified devices designed to isolate these connections when necessary [4]. 110V DC Electrical System The function of the llov DC Electrical System is to provide battery backed power, control and switching supplies to the essential switchgear and control equipments. This includes supplies to DC driven Heating, Ventilating and Cooling (HVAC) plant for the essential switchgear, reactor protection equipment and control gear rooms located in the control building. The 11OV DC comprises four trains of equipment, each having a battery, charger, switch board and associated distribution fuse boards for each of the primary and secondary systems within a train. The 110V DC system is normally energised at all times from the 415V system. 11OV AC Essential Uninterruptible Power Supply System The function of the 11OV AC Essential Uninterruptible Power Supply (UPS) System is to provide battery backed single phase instrumentation supplies to control cubicles and other essential equipment. The 11OV AC Essential UPS System comprises four trains of equipment each having a single phase inverter, charger, static switch unit, battery, switchboard and associated distribution fuseboards for each of the primary and secondary systems within a train. Essential UPS System is normally energised at all times from the 415V system. Generally, all electrical plant is located in dedicated rooms with controlled environmental conditions. The Main Electrical Power System..The function of the llov AC Uninterruptible Power Supply (UPS) System is to provide battery backed single phase instrumentation supplies to the control cubicles associated with the data processing system and all other equipment requiring a non-essential UPS.The 11OV AC UPS System comprises two trains of equipment each having a single phase inverter, charger, static switch unit, battery, switchboard and associated distribution fuse boards.. 48V DC Power System The function of the 48V DC Power System is to provide battery backed power for remote control relays for the main station switchgear. The system is significant to safety in that it is used to support restoration of off-site supplies to the system 250V DC System The principal function of the 250V DC Main is to provide battery backed power for the main turbo-generators DC driven plant. These are installed to prevent mechanical damage to the main turbine in the event of loss of normal AC supplies coincident with a turbine trip.. The 250V DC system comprises two trains of equipment each having two batteries, two chargers, two switchboards and associated distribution fuse boards. The system is normally energised at all times from the 415V plant protection boards with the chargers float charging the batteries. IV. DESIGNING PARAMETERS The electrical systems are required to perform reliably and their parameters to remain within defined tolerances during all

3 steady state operating conditions. The frequency excursions which have been addressed within the design are as follows [3]: The Voltage limits will be permitted to exceed the nominal +_ 6% limit under transient conditions. The tolerances, both during steady state and transient conditions, are a significant factor in the design and specification of the mechanical systems and plant. The voltage profile for the voltage levels at the load terminals are given in Table 2 [3] The electrical systems design is to be verified by a series of calculations/studies to demonstrate that their performance is satisfactory under all credible conditions of operation. The studies will include the following: 50 Hz Nominal frequency Hz Full station output to be maintained Hz Output may be reduced with frequency, although Frequencies in the range Hz will not exceed 15 minutes duration Hz System load flow Steady state voltage profile Fault levels Frequencies in this range will not exceed 15 minutes duration Hz These frequencies will not persist for more than 1 minute. Table 2. Voltage Profile for the AC Power System Voltage Levels Nomi nal ge V Volta Up per (%) Stea dy Stat e (%) Motor starting studies Fault recovery studies Transi ent EES (%) 11KV +6-5 N/A K V Transient MPS (%) The System Fault Levels are given in table 3 below.[3] Fault level (MVA) e) k) Table 3. System Fault Levels 11kV 3.3kV 415VLC 415V 900(Mak 750(Brea MCC The Equipment Parameters are given in table 4 below.[3] The Main Power Systems Plant Parameters are given in table 5 [4] Main Power Systems Plant Parameters(Per Train) System Battery Charger/UPS 110V DC 1200 A hr 200A 48V DC (Control Building) 48V House) Table 4 11kV 3.3kV 415 V Interrupt ing Device Continuous Short Circuit Largest Connected Motor Vacu um Circuit er DC(Turbine 800 A hr 2 250A 400 A hr A 250V DC A hr A 110V UPS(Turbine House) Break Vacuu m Circuit Breake r/motor switch Device 3150A 2500A/450 A 121kA/3 9.4kA 7300 kw 40kA/11k A W 1130k LC con tactor 324A 43kA 166 kw 800 A hr 150 KVA 110V UPS(TSC) 400 A hr 50 KVA 415V MCC conta ctor 47A 43kA 22k W

4 Figure 1: Normal Power System & Emergency Power system of a Nuclear Generating Station

5 The Emergency power Systems Plant Parameters are given in table 6 [4] Emergency Electrical Systems Plant Parameters(Per Train) System Battery Charger/U PS 110V DC (Primary) 600 A hr 160A 110V (Secondary) DC 600 A hr 160A 48V DC(Primary) 1200 A hr A 48V DC(Secondary) A hr 2 40 A 110V UPS(Primary) 900 A hr 50 KVA 110V UPS(Secondary) 800 A hr 50 KVA V. CONCLUSION This paper covers the designing of the electrical power system of a nuclear power plant. The efforts made to design the system are only indicative. In actual practice lot of considerations to be taken to design the electrical systems. The type of nuclear plant also very essential, But this design is generalized for all types of nuclear plants. The most important factor in designing is economic considerations naturally plays a significant role in the nuclear power generating station. REFERENCES [1] K Raja,N Theivarajan Emergency Power Supply System of a Nuclear Power Plant-Modelling and Simulation Studies of Diesel Generators and Load Pickup on Emergency Transfer International Conference on Electrical Energy Systems (ICEES 2011), 3-5 Jan [2] M Prasad, N Theivarajan Normal Power Supply System of a Nuclear Power Plant-Modeling and Simulation Studies for Fast Bus Transfer International Conference on Electrical Energy Systems (ICEES 2011), 3-5 Jan [3] N Stenstrom, The design of the AC electrical power systems IEEE Electrical and Control Aspects of the Sizewell B PWR,International Conference on Date:14-15 Sep [4] B Wheeler, Design of the DC and UPS electrical power systems IEEE Electrical and Control Aspects of the Sizewell B PWR,International Conference on Date:14-15 Sep [5] K.E.Yeager,J.R.Willis, Modelling of Emergency Diesel- Generators in an 800 MW Nuclear Power Plant, IEEETrans on Energy Conversion,Vol.8, No.3,September1993. [6] Modern Power Station Practice, Third edition, is incorporating Modern Power System Practice, British Electricity International London, Volume D, Electrical systems & Equipment, [7] IEEE Std , Criteria for Class 1E Power Systems for Nuclear Power Generating Stations. [8] IEEE Std , Qualification of Class 1E Lead Storage Batteries for Nuclear Power Generating Stations. [9] IEEE Std , Recommended Practice for the Design of DC Auxiliary Power Systems for Generating Stations. [10] IEEE Design Guide for Electric Power Service Systems for Generating Stations, IEEE Std [11] IEEE Std , Qualification of Class 1E Static Battery Chargers and Inverters for Nuclear Power Generating Stations. [12] IEEE std 387. Criteria for diesel generator units applied as stand by power supplies for Nuclear Power Generating station