This document presents a technical solution for a 500kW/2MWh lithium iron phosphate battery energy storage system, systematically outlining the overall approach and technical roadmap from planning and design to implementation. It covers project overview, design basis, and key technical principles. The document analyzes the current state of commercial electricity consumption and load development trends, proposes a reasonable system integration scheme and construction scale, and verifies the impact of the energy storage system on the safety and reliability of the existing power distribution system through short-circuit current calculations. Based on this, the solution details the selection and system integration design of key equipment such as energy storage batteries, PCS, BMS, and EMS. It also provides a comprehensive assessment of electrical, secondary systems, civil engineering, fire protection, environmental protection, and safety production aspects, ensuring that the project meets relevant standards and operational requirements in terms of safety, reliability, economy, and sustainability, providing a technical basis for the smooth construction and long-term stable operation of the energy storage power station.
1. General Description
1.1 Design Basis
1) GB/T 36547-2018 Technical Specifications for Grid Connection of Electrochemical Energy Storage Systems
2) GB/T 36545-2018 Technical Requirements for Mobile Electrochemical Energy Storage Systems
3) GB/T 36548-2018 Test Specifications for Grid Connection of Electrochemical Energy Storage Systems
4) Q/GDW 11725-2017 Specifications for the Depth of Design Content for Energy Storage Systems Connected to Distribution Networks
5) Q/GDW 36547-2018 Technical Specifications for Grid Connection of Electrochemical Energy Storage Systems
6) Q/GDW 36276-2018 Lithium-ion Batteries for Power Storage
7) Q/GDW 36549-2018 Operational Indicators and Evaluation of Electrochemical Energy Storage Power Stations
8) Q/GDW 36558-2018 9) General Technical Conditions for Electrochemical Energy Storage Systems in Power Systems
10) Q/GDW 10769-2017 Technical Guidelines for Electrochemical Energy Storage Power Stations
11) GB/T 34133-2017 Technical Specifications for Energy Storage Converters
12) GB/T 34131-2017 Technical Specifications for Lithium-ion Battery Management Systems for Electrochemical Energy Storage Power Stations
13) GB/T 34120-2017 Technical Specifications for Energy Storage Converters in Electrochemical Energy Storage Systems
14) Q/GDW 10696-2016 Operation Control Specifications for Electrochemical Energy Storage Systems Connected to Distribution Networks
15) Q/GDW 10676-2016 Testing Specifications for Electrochemical Energy Storage Systems Connected to Distribution Networks
16) NB/T 1816-2018 Coding Guidelines for Identification Systems of Electrochemical Energy Storage Power Stations
17) NB/T 1815-2018 17) NB/T 42090-2016 Technical Specification for Monitoring System of Electrochemical Energy Storage Power Station
18) NB/T 42089-2016 Technical Specification for Power Conversion System of Electrochemical Energy Storage Power Station
1.2 Project Overview
1.2.1 Natural Conditions of the Project
(1) Project Location
The project site is located 50m to the left of the south gate of the energy storage system (the ground below the foundation is solid ground). It is accessible by road (2.5m wide road, 2.7m wide grassland), and surrounded by trees and grassland outside the fence.The project site is located between buildings. It is about 200 meters from the road, with convenient transportation.
1.3 Main Technical Principles
This project is a 500kW/2MWh lithium iron phosphate battery energy storage system, divided into two 250kW/1MWh lines connected to the load side of the power distribution room. The overall layout adopts a container functional unit scheme, and is designed modularly, consisting of 2 battery compartments and 1 PCS compartment.
2. System Overview
2.1 Commercial Power Consumption Overview
Based on on-site survey, the commercial power supply topology is as follows: 10kV high-voltage dual-line incoming line → Medium-voltage switchgear (10kV) → Transformers (10kV/0.4V, 2 x 2000kVA) → Low-voltage switchgear (400V).
Metering Points: High-voltage supply and high-voltage metering are adopted. One three-phase energy meter is installed on each of the two 10kV high-voltage sides to meter the two transformers.
2.2 Load Conditions and Forecast
Current actual power consumption: Transformer #1, installed capacity 2000kVA, actual load 50kW, load factor 2.5%. Transformer #2, installed capacity 2000kVA, actual load 150kW, load factor 7.5%. Both transformers are under low load. Considering the future operation of the commercial main body, the load will increase significantly. Meanwhile, due to the significant difference between peak and off-peak electricity prices in the area, it is considered to add one 250kW/1MWh energy storage system each to the low-voltage side of transformers #1 and #2, totaling 500kW/2MWh.
The energy storage system can implement targeted control strategies based on local time-of-use electricity prices and actual load conditions: charging during the off-peak hours of 23:00-7:00 and discharging during peak hours of 11:00-13:00 and 16:00-17:00, thus smoothing out peak loads.
Schematic Diagram of a 250kW/1MWh System
Transformer Energy Storage Grid Connection Point
Transformer Energy Storage Grid Connection Point
2.4 Construction Scale
The initial construction scale of this project is two 250kW/1MWh systems, totaling 500kW/2MWh.
2.5 Short-Circuit Current Analysis
(1) The short circuit occurs within the energy storage power station area, i.e., outside the low-voltage busbar of the transformer.
In this case, the transfer impedance from the system to the short circuit point is greater than when the energy storage system is not connected, and the short-circuit current on the system side is correspondingly less than the original short-circuit current (when the energy storage system is not connected). This short circuit situation will not affect the existing equipment.
(2) The short circuit occurs within the system, i.e., on the busbar side of transformer #1 or transformer #2.
In this case, the short-circuit current flowing through the low-voltage busbar of the transformer includes the original short-circuit current plus the short-circuit current flowing out of the energy storage power station. Due to the influence of the power devices in the inverter, the maximum output current of the energy storage power station will not exceed 1.5 times the rated current, i.e., 562.5A. Currently, the short-circuit current of transformers #1 and #2 is 36.085kA. After the energy storage system is put into operation, the short-circuit current of the transformer bus will not exceed 36.647kA. The rated breaking capacity of the circuit breaker on the low-voltage outgoing side of the original transformer is 50kA. The short-circuit current analysis results confirm that the new energy storage system will not affect the entire power distribution system and the existing equipment.
3. Energy Storage System
3.1 Battery Selection
3.1.1 Lithium-ion Battery Storage
Lithium-ion batteries use lithium metal oxide as the positive electrode material and graphite or lithium titanate as the negative electrode material, as shown in the figure. Lithium-ion batteries are characterized by high energy density and have advantages such as stable discharge voltage, wide operating temperature range, low self-discharge rate, and the ability to charge and discharge at high currents. Lithium iron phosphate has a theoretical capacity of 170Wh/kg, good cycle performance (after 2000 cycles at 100% depth of discharge (DOD), retaining over 80% of its capacity), high safety, and can be continuously charged and discharged at 1-3 times the charge/discharge rate (1C-3C), with a stable discharge platform and an instantaneous discharge rate reaching 30C. However, lithium iron phosphate batteries have poor low-temperature performance; at 0℃, the discharge capacity is only 70-80%, and the cycle life can reach 5000-6000 cycles. A schematic diagram of its structure is shown in the figure.
Lithium-ion Battery Structure
This design utilizes lithium iron phosphate batteries. These batteries offer high production capacity and large output, are produced using fully automated equipment, ensure good product consistency, have a long cycle life, and generate no environmental pollution during production. The modular design facilitates production and installation. They also boast high energy density and a small footprint.
The rated voltage/capacity of a single battery cell is 3.2V/205Ah. The 80% DOD cycle life can reach 6000 cycles.
3.2 Battery Storage Installation Method Selection
3.2.1 Installation Method
This project adopts the container installation method.
Generally, the basic design and external dimensions of a standard container are referenced. After modification and decoration, the battery, bidirectional power conversion system (PCS), distribution cabinet, etc., are installed in a prefabricated container.
3.3 PCS Selection
PCS (Power Conversion System) is a device in an electrochemical energy storage system that connects the battery system to the power grid (and/or load) to achieve bidirectional power conversion. It can control the charging and discharging process of the battery, perform AC/DC conversion, and directly supply power to AC loads in the absence of a power grid. It is the core equipment of the energy storage system.
High-quality, high-performance, and mature products are used. Based on the project requirements, a 250kW PCS is adopted. The PCS consists of a DC/AC bidirectional PCS, a control unit, etc. The PCS controller receives control commands from the background through communication and controls the PCS to charge or discharge the battery according to the sign and magnitude of the power command, thereby regulating the active and reactive power of the power grid. Meanwhile, the PCS can communicate with the EMS via the CAN interface to obtain battery status information, enabling protective charging and discharging of the battery and ensuring safe battery operation.
3.3.1 Basic Requirements for PCS
(1) The PCS body must have an emergency stop operation switch and protection against accidental contact.
(2) The PCS must be able to display various real-time operation, real-time fault, and historical fault data.
(3) The PCS body should have a local/remote switching switch. When switched to Local mode, it should be able to perform Local power-on, power-off, and parameter setting operations; all Local operations require authentication.
(4) The PCS should automatically detect the communication connection with the monitoring system. When communication is interrupted, the bidirectional energy storage PCS should issue an audible and visual alarm and, after an adjustable delay, switch to standby mode.
(5) The PCS should have measures to address the circulating current and uneven output of each DC branch caused by direct parallel operation on the AC side.
(6) The PCS requires a live-operated circuit breaker on the DC side and a contactor and circuit breaker on the AC output side to form a safety isolation point from the grid connection point.
(7) The quality of electrical energy delivered by the PCS device to the local AC load should meet relevant national standards in terms of harmonics, voltage deviation, voltage imbalance, DC component, voltage fluctuation, and flicker.
3.3.3 Operation Control
(1) Start-up and Shutdown
The PCS has complete hardware and software self-checking functions during startup. It should alarm and record relevant information in detail when the device malfunctions or is abnormal. It also needs to confirm normal communication with the monitoring system during startup.
The PCS is equipped with a self-reset circuit. If it still cannot work normally after reset, it should be able to issue an abnormal signal or information.
Start-up time: The time from initial power-on to rated power operation should not exceed 15s.
Shutdown time: Under any operating condition, the time from receiving the shutdown command to the AC side switch being disconnected should not exceed 100ms.
The change in active power output during device startup should not exceed the set maximum power change rate.
Except in the event of an electrical fault or receiving instructions from the power grid dispatching agency, the power simultaneously disconnected by multiple PCS devices should be within the maximum power change rate allowed by the power grid.
(2) Device Control Mode
The PCS should be equipped with three control modes: Local and Remote.
Local: In this mode, the PCS Local control unit does not accept remote control from the monitoring system's host computer. Operators can perform and confirm operations step-by-step according to the operating procedure in the Local mode, ultimately achieving steady-state operation.
Remote control: Automatic start or stop of the operating condition is achieved via EMS commands.
Local control is completed on the control panel of the cabinet, while Remote control is completed by issuing control commands through the monitoring system according to the communication protocol. The priority of Remote and Local control modes increases sequentially.
The control parameters for both Local and Remote modes of the energy storage PCS can be set.
3.4 Battery Management System (BMS)
3.4.1 Battery Management System Framework
The protection and monitoring functions of the battery system are implemented by the BMS. The BMS system has a three-level network architecture: Battery Management Detection Module (CCM), Battery Management Slave Unit (BMU), and Battery Management Master Unit (BCU). The main functions of each module are as follows:
CCM: Monitors the voltage and temperature of individual cells and transmits this information to the BMU in real time, enabling control of the voltage balance of individual cells. BMU: Collects and manages voltage and temperature data from multiple CCMs, and transmits this information to BCU in real time via the CAN protocol. It can also control the CCMs to perform balancing based on balancing commands issued by the BCU.
BCU: Monitors the total voltage and current of the entire battery pack, collects information from lower-level BMUs, and can estimate the remaining battery capacity and health status in real time. It also transmits this information to EMS in real time via the CAN protocol. It controls the opening and closing of relays and provides alarms and protection for the battery pack.
BMS Architecture Diagram
3.4.2 Battery Management System Functions
The Battery Management Module (CCM) and Battery Management Unit (BMU) manage battery module-level units (single or multiple battery modules), monitor battery status (voltage, temperature, etc.), and provide communication interfaces for the batteries. The Battery Management System (BMS) monitors battery status (temperature, voltage, current, state of charge, etc.), provides communication interfaces, and has a protection system. Specific requirements are as follows:
1) High-precision, high-reliability acquisition of individual battery cell voltage and temperature, with a temperature acquisition range of -40℃ to 85℃.
Real-time measurement of electrical and thermal data related to the battery, including individual cell voltage, battery module temperature, battery module voltage, series circuit current, insulation resistance, and other parameters.
2) The measurement accuracy of each status parameter should comply with the specific provisions of "5.2 Measurement Requirements" in GB/T 34131-2017 "Technical Specification for Lithium-ion Battery Management System for Electrochemical Energy Storage Power Stations". 3) Estimate the battery's state of charge (SOC), charging and discharging energy (Wh), maximum charging current, maximum discharging current, and other state parameters, with power-off retention capabilities and the ability to upload data to the monitoring system. The measurement accuracy of each state parameter should comply with the specific requirements of "5.3 Calculation Requirements" in GB/T 34131-2017 "Technical Specification for Lithium-ion Battery Management System for Electrochemical Energy Storage Power Stations".
4) Achieve inter-cell charge balancing, which is performed through a balancing control circuit.
5) The BMS's voltage and temperature detection, balancing control, and state estimation circuits are completely electrically isolated from the control power supply and CAN bus. The isolation level of the control power supply and CAN bus communication is guaranteed to be 2500V, thus ensuring the requirement for high-voltage battery cells to be connected in series.
6) The BMS implements high-voltage insulation resistance detection, requiring electrical isolation of related circuits and full consideration of noise effects. Multiple sampling and averaging of the collected data are performed to obtain more accurate sample values. 7) The BMS should be able to accurately estimate the State of Charge (SOC) of the battery energy storage device. The accuracy requirement is ≤5% when SOC ≤ 30%; ≤5% when 30% < SOC < 80%; and ≤5% when SOC ≥ 80%. It should also be able to dynamically calibrate the SOC value and provide a corresponding SOC accuracy estimation table.
8) The BMS should effectively manage charging and discharging to ensure that overcharging and over-discharging do not occur during the process, preventing charging current and temperature from exceeding allowable values. During charging, the battery's allowable charging voltage should be controlled within the maximum allowable charging voltage; during discharging, the current and voltage should be controlled within the minimum allowable discharging voltage. It should be able to provide battery temperature and other control signals to the thermal management system and assist the thermal management system in controlling and achieving an average temperature difference of 5°C between batteries.
9) The BMS should implement charging and discharging strategies, requiring real-time monitoring throughout the entire charging and discharging process. Upon detecting abnormalities, it should immediately take alarm and protection actions to ensure battery safety. 10) The BMS employs a three-level alarm protection function for battery energy storage equipment, with refined alarm protection level settings. Depending on the severity level, measures such as power reduction, prohibition of charging and discharging, and disconnection of battery circuits are taken to ensure the safe, stable, and reliable operation of the battery pack.
3.5 Overall Design of Energy Storage System
Based on the reserved site area for the project, this scheme adopts three prefabricated energy storage modules, including two battery modules and one PCS module. The total installed capacity is 2MWh, divided into two energy storage branches. Each energy storage branch consists of one 250kW energy storage converter, one 1MWh energy storage battery, and one energy management system. The two energy storage branches are respectively connected to the 400V low-voltage busbars of transformers #1 and #2 in the distribution room.
Energy Storage Unit Schematic Diagram
The energy storage system consists of battery storage, power conversation system(PCS), a battery management system (BMS), and an energy management system (EMS). The battery storage are connected to the AC bus after DC/AC conversion via the PCS, enabling energy storage and release. The PCS controls the charging and discharging of battery storage: during charging, the PCS acts as a rectifier, converting AC to DC for storage in the batteries; during discharging, the PCS acts as an inverter, converting the stored DC to AC to support the operation of relevant loads within the community. The BMS monitors the voltage, current, and temperature of battery storage in real time. By transmitting this key information to the EMS, the EMS coordinates and manages the charging and discharging process of the energy storage system, preventing overvoltage, undervoltage, and overcurrent problems, and also provides charge/discharge balancing management.
The energy storage system is charged and discharged through a software system. The system can achieve both single-point control and total quantity control. The energy storage system is controlled according to dispatch commands, and the output power can be adjusted as needed within the rated operating range of the PCS. The system adopts one-button control, and each energy storage unit further controls its subsystem according to the overall command requirements. The battery charging and discharging rate complies with national standards and is adjustable within the range of 0-0.5C.
3.6 Energy Storage System Efficiency Analysis
The energy exchange between the battery storage and the grid connection interface point involves two main links: the PCS and the main line. During charging and discharging, each link incurs a certain amount of energy loss. Considering the energy loss inherent in the battery system itself during charging and discharging, the overall system efficiency is affected by three factors.
Based on existing industry standards and equipment manufacturing levels, the overall charging and discharging efficiency is determined by the PCS efficiency (97%), battery charging efficiency (90%), and line loss (3%). The majority of losses (10%) in battery charge-discharge cycles occur during charging. Therefore, for every 1Wh of energy storage capacity, in a single charge-discharge cycle (considering a DOD of 90%), approximately 0.87Wh (1*0.9*(0.97*0.997)) of energy is released during the discharge process, while 1.034Wh (0.9/(0.9*0.97*0.997)) is consumed during the charging process.
3.7 Energy Storage System Safety
3.7.1 Battery Safety
This is a lithium iron phosphate battery. During charging, the BMS regulates the battery and charging environment to prevent hydrogen generation. A series of ventilation measures are installed in the battery compartment to ensure that any explosive gases are monitored and discharged in a timely manner. Each BESS is equipped with automatic fire suppression equipment.
3.7.2 Operational Safety Assurance
The BMS provides comprehensive monitoring and management of the battery and energy storage system's operating parameters. It monitors the collected information on battery status, equipment operating status, and grid status throughout the entire process. It also diagnoses battery health and can automatically repair batteries with minor problems, and alarms and promptly notify users of erroneous or abnormal operating conditions.
3.7.3 Power Equipment Safety Assurance
The energy storage system has DC and AC side voltage and current overload protection, short circuit protection, over-temperature protection, and grid safety protection. When the grid voltage, phase, or frequency is unstable and exceeds the thresholds set within the equipment, an alarm will be immediately triggered or further shutdown protection will be implemented. 3.7.4 BESS Fire Protection System Design
Automatic fire alarm and extinguishing systems are a crucial element ensuring the safe operation of energy storage systems. They must react rapidly upon the detection of a fire or smoke alarm, thereby protecting the energy storage power station and minimizing equipment and property damage.
The fire protection design of BESS is carried out from the following aspects:
(1) Real-time monitoring of the operating temperature of the battery system, PCS system, and power distribution system. If a serious temperature abnormality occurs, an alarm will be triggered or even the system will stop operating.
(2) Flame-retardant materials are selected for the equipment, battery boxes, cabinets, and cables.
(3) Flame-retardant metal polyurethane sandwich panels are selected, with a thickness of 50mm and a fire resistance rating of not less than 1 hour.
(4) A manual/automatic integrated gas extinguishing system is installed inside the container. The extinguishing medium is heptafluoropropane (HFC-227ea) and dry powder extinguishing devices. The cabinet-type heptafluoropropane is installed in the battery compartment, and the dry powder extinguisher is installed in the PCS compartment.
(5) The entire system adopts a fire-fighting linkage design. When the fire controller issues an alarm signal, the energy storage system, ventilation and heat dissipation systems will stop operating to ensure that the fire extinguishing system can extinguish fires normally.
3.8 Container
This project is supplied in the form of containers and requires system integration. A total of 2 BESS energy storage batteries are supplied in this phase. The container must possess excellent maintainability and replaceability to facilitate equipment maintenance, repair, and replacement.
3.8.1 General Requirements
(1) The container's protection rating must be no lower than IP54 and it must possess unlimited full-load lifting strength within its service life (within 25 years).
(2) The container must be uniformly painted. The logo on the container's exterior can be painted according to the owner's requirements.
(3) Self-consumption: The equipment's self-consumption rate during system operation must be low, ensuring that the maximum self-consumption power does not exceed 15kW under extreme temperature conditions.
(4) Waterproofing: The top of the container must not accumulate water, leak, or seep water; the sides of the container must not allow rain to enter; and the bottom of the container must not leak water.
(5) Thermal Insulation: Prefabricated bulkheads and doors must be treated with thermal insulation measures. Under an environmental condition where the temperature difference between the inside and outside of the container is 55℃, the heat transfer coefficient must be less than or equal to 1.5W/(m²·℃). (6) Corrosion Resistance: The appearance, mechanical strength, and corrosion resistance of the prefabricated cabin ensure it meets the requirements for 25 years of practical use.
(7) Fire Resistance: The outer shell structure, thermal insulation materials, and internal and external decorative materials of the prefabricated cabin are all made of flame-retardant materials.
(8) Sand Resistance: The prefabricated cabin has sand-blocking capabilities; under natural ventilation conditions, the fresh air intake volume is ≥20%, and the sand-blocking rate is ≥99%.
(9) Earthquake Resistance: Under transportation and earthquake conditions, the mechanical strength of the prefabricated cabin and its internal equipment meets the requirements, and no deformation, functional abnormalities, or malfunctions after vibration occur.
(10) UV Protection: The properties of the materials inside and outside the prefabricated cabin will not deteriorate due to ultraviolet radiation, and it will not absorb the heat from ultraviolet rays. rting the stored DC to AC to support the operation of relevant loads within the community. The BMS monitors the voltage, current, and temperature of battery storage in real time. By transmitting this key information to the EMS, the EMS coordinates and manages the charging and discharging process of the energy storage system, preventing overvoltage, undervoltage, and overcurrent problems, and also provides charge/discharge balancing management.
3.8.2 BESS Equipment Configuration
(1) Battery (PACK) Installation Interface
The container is equipped with pre-embedded battery rack mounting components to ensure reliable connection between the battery rack and the pre-embedded components in the container base plate.
(2) Distribution Box
The distribution box provides AC power to indoor AC electrical equipment, and is responsible for AC power distribution for the battery room air conditioning, lighting, fire protection, emergency lights, and internal and external sockets of the cabinet;
(3) Temperature Control System
The container needs to take effective measures to regulate and control the ambient temperature inside the compartment. The measures taken should minimize power consumption to ensure the maximum power supply capacity of the container. The air conditioner should be capable of continuous operation 24 hours a day, 7 days a week, with a service life of no less than 5 years.
(4) Monitoring System
The container is equipped with video surveillance and door magnetic alarm functions. The video equipment ensures comprehensive monitoring inside the container, allowing real-time observation of the equipment inside the container. When someone attempts to forcibly open the compartment door, the door magnetic sensor generates a threatening alarm signal, which is transmitted to the monitoring backend via Ethernet remote communication. This alarm function should be able to be disabled by the user.
(5) Smoke and Temperature Sensors
The compartment is equipped with safety devices such as smoke sensors and temperature and humidity sensors. The smoke sensors and temperature and humidity sensors must be electrically interlocked with the system's control switch. Once a fault is detected, the user must be notified through audible and visual alarms and remote communication, and at the same time, the running lithium battery system must be shut down.
Depending on the container layout, some containers are equipped with a dynamic environment monitoring host, which collects fire protection information and temperature and humidity sensor information from this compartment and adjacent compartments. The dynamic environment monitoring host is connected to the intelligent auxiliary control system screen in the main control compartment via shielded Category 5 twisted-pair cable.
(6) Compartment Lighting
The compartment is equipped with lighting and emergency lighting. The lamps have explosion-proof functions. An emergency lighting system is installed in the container. Once the system loses power, the emergency lights in the container will immediately activate. 3.8.3 Energy Storage Container Electrical System
(1) Control Switches and Sockets
A lighting control switch is installed next to the container door, and a five-hole power socket is installed inside the container. Power supply is not allowed until the ground wire of the three-phase socket is connected (i.e., the plugs of the L and N lines cannot be inserted into the socket without connecting the ground wire). The power sockets are connected to the distribution box with independent circuit breakers for short-circuit, overload, and selective protection.
(2) Cables and Wiring
The wiring terminals of different power supply circuits in the distribution box shall use different identification colors (i.e., colored wiring terminals are used to identify different power supply circuits); all wires and cables in the power supply system shall use cross-linked polyethylene insulated flame-retardant cables with different color markings. The cables have independent insulation and sheath layers, and their long-term allowable operating temperature is not less than 90℃. The rated insulation withstand voltage of the wires and cables is one level higher than the actual voltage value. The cross-sectional area of the neutral wire and ground wire of the cable shall not be less than the cross-sectional area of the phase wire, and the minimum cross-sectional area of the cable phase wire shall not be less than 4mm²; the technical performance, identification, safety, and wiring methods of the distribution box must meet the requirements of the strictest clauses in national standards.
3.8.4 Grounding and Lightning Protection
The bolt fixing points of the container are reliably connected to the non-functional conductive conductors of the entire container. At the same time, the container provides 4 grounding points that meet the strictest power standards. The grounding points form a reliable equipotential connection with the non-functional conductive conductors of the entire container.
A reliable high-quality lightning protection system is installed on the top of the container. The lightning protection system is connected to the grounding grid at 4 different points through grounding flat steel or grounding round steel.
3.8.5 Energy Storage Container Installation
The container provides bolt mounting and fixing interfaces. There should be no gap between the bottom of the container and the pier columns after placement. 3.8.6 Cables
(1) Cable Selection: Low-voltage power cables shall be flame-retardant copper-core cables; high-voltage power cables shall be flame-retardant armored cables; control cables entering the communication and monitoring system shall be shielded cables; communication cables shall be shielded twisted-pair cables or fiber optic cables.
(2) Cable Laying: Cable design and laying shall meet the requirements of GB50217-2007 "Code for Design of Power Engineering Cables". When different types of cables are arranged horizontally and crossed, the spacing shall meet the requirements of the standard.
(3) Cable Fire Protection: Measures shall be taken to prevent cable fire and flame spread; all cable shafts, wall openings, and cable holes at the bottom of switchgear and control and protection panels shall be sealed. Fire-resistant partitions shall be installed at the cable trench connections between different voltage levels of power distribution devices and between different sections of power distribution devices. Fire-retardant coating shall be applied within 1.5 meters on both sides of the fire-resistant partitions in the cable trench. After the cables are laid through pipes and walls, both ends of the pipes shall be sealed with fireproof and waterproof materials.
4. Electrical Section
4.1 Main Electrical Wiring Diagram
The power conversion system (PCS) is a key component for AC/DC conversion in the energy storage system. Based on the specific requirements of this project, a 250kW string inverter was selected. Each 250kW/1MWh energy storage system consists of four 62.5kW modules connected in parallel. The AC output is then combined and connected to the low-voltage busbar side of the transformer. The primary schematic diagram is shown in the figure below.
Schematic Diagram
4.2 Electrical Equipment Layout
Considering factors such as safety, construction, operation, maintenance, and land use, and in conjunction with the battery pack layout scheme, the energy storage system is designed with 2 energy storage units and 1 power conversion unit.
4.3 Lightning Protection and Grounding
4.3.1 Lightning Protection
Surge protectors are installed on both the PCS input and DC side to protect against surges caused by indirect and direct lightning strikes or other transient overvoltages.
The energy storage station consists of 3 container units with no outdoor electrical equipment. Referring to GB50057-2010 "Code for Design of Lightning Protection for Buildings" Section 5.3.7, the design requirements for Class II lightning protection buildings are followed.
Protective grounding mainly involves the safety grounding of the enclosure of the container unit. This creates a good conductive connection between the metal parts of the system that are normally not energized and the ground, protecting equipment and personnel safety. The energy storage cabinet has one external grounding point, and a grounding busbar is installed inside the container. Lightning protection grounding, as part of the lightning protection measures, serves to divert surges through the lightning arrester into the earth. Lightning protection for electrical equipment mainly involves connecting one end of the lightning arrester to the protected equipment and the other end to the grounding device. When a direct lightning strike occurs, the lightning arrester diverts the resulting surge to itself, and the surge current enters the earth through its down conductor and grounding device, thus preventing damage to electrical equipment or endangering personal safety. In this scheme, both AC and DC lightning arresters are installed inside the energy storage container, and their fault status is monitored by the energy management system.
4.3.2 Grounding
According to (DL/T621-1997) "Grounding of AC Electrical Installations," all electrical equipment enclosures and other metal components that may become energized in case of an accident are required to be reliably grounded. The specific requirements are as follows:
(1) All battery pack brackets are directly connected to the grounding grid to prevent static electricity accumulation and provide protective grounding for all conductive parts of the equipment; all equipment enclosures are connected to the main grounding grid through grounding wires.
(2) Protective grounding, working grounding, and overvoltage protection grounding use the same grounding grid. The grounding grid adopts an artificial composite grounding grid method. The energy storage station's main grounding grid primarily consists of horizontal grounding electrodes, supplemented by an appropriate number of vertical grounding electrodes, forming a composite grounding grid. Galvanized flat steel is recommended for the main grounding grid.
4.4 Cable Laying
Cables are laid using conduits or cable trays. Cable fire protection and flame retardancy requirements are implemented according to national standard GB50217.
4.5 Station Power and Lighting
4.5.1 Connection of Station Power Supply and Wiring
The energy storage station's power and lighting (AC220V) will be supplied by the municipal power grid.
4.5.2 Layout and Equipment Selection of Station Power Distribution Devices
The station power supply is AC220V, and all power switches are located in the energy storage inverter compartment. The circuit breakers in the distribution box are all high-quality brands. The power supply principle is as follows:
Power Supply Schematic Diagram
4.5.3 Station Area Lighting
According to the "Technical Regulations for Lighting Design of Thermal Power Plants and Substations" DLGJ56-95, floodlights are installed in the energy storage station area, and the power supply is connected from the energy storage station's lighting distribution box.
4.5.4 Container Interior Lighting
The energy storage unit lighting system consists of normal lighting and emergency lighting. The normal lighting inside the container is powered by the mains electricity, and the emergency lighting part has its own battery for evacuation indication.
LED lighting fixtures are uniformly used for both normal and emergency lighting inside the container. Safety passage indicator lights and evacuation lighting are installed at the maintenance doors on both sides. The illuminance in each area meets the requirements of the "Technical Regulations for Lighting Design of Thermal Power Plants and Substations".
4.6. Energy Storage Unit Electrical Protection
The DC side of the energy storage station may not require separate protection devices; the DC side protection can be implemented by the power conversion system (PCS) and the battery management system (BMS). The DC side protection configuration should meet the following requirements:
4.6.1 Energy Storage Unit Protection Configuration
The protection of the energy storage unit is mainly implemented by the battery management system (BMS). The BMS should comprehensively monitor the operating status of the battery, including the voltage, current, temperature, and state of charge of individual cells/modules and the battery system, and issue alarm information in case of an accident. The BMS should reliably protect the battery pack and have functions such as overvoltage protection, undervoltage protection, overcurrent protection, overtemperature protection, and DC insulation monitoring.
4.6.2 DC Connection Unit Protection Configuration
The DC connection unit refers to the connection between the battery pack and the PCS, mainly including DC cables and DC circuit breakers (disconnectors). A circuit breaker should be installed on the battery outlet side, and a disconnector can be installed on the DC side of the PCS. The protection of this section is not independently configured; it is mainly achieved by the protection of the energy storage unit tripping the circuit breaker on the battery outlet side.
5. Secondary System Section
5.1 EMS Energy Management System
5.1.1 Design Principles
(1) The energy storage station is designed according to the "unattended operation, manned supervision" mode.
(2) The secondary control of the energy storage station adopts a computer monitoring system.
(3) The integrated automation system adopts an open, hierarchical, and distributed system structure.
5.1.2 System Introduction
The Energy Management System (EMS), based on system requirements and the operating mode of the energy storage power station, performs real-time automatic monitoring and regulation of electrical equipment such as the energy storage power station and control power supply system. It also integrates energy storage PCS and battery monitoring software within the intelligent control and dispatching system, providing monitoring functions for the battery itself and the PCS. The battery energy storage monitoring platform is used for monitoring and control of the battery energy storage system, coordinating the coordinated operation and system access of the energy storage system, and realizing the application of the battery energy storage system. In addition to conventional three-remote functions (telemetry, telecontrol, and teleindication), the energy storage monitoring system has various application modes according to different control needs, such as peak shaving and valley filling functions.
The battery energy storage monitoring system adopts a hierarchical and distributed control scheme, generally including three main parts: the monitoring layer, the control layer, and the local monitoring layer. The monitoring layer is mainly responsible for communication management, data acquisition, data processing, and operation management. The coordinated control layer completes system-level coordinated control functions and sends power control commands to the local controller to achieve power control of each inverter. The local monitoring layer consists of a local monitoring and control system, which monitors the real-time status of the PCS, batteries, and power distribution system, and promptly sends upper-level control commands to each control unit.
5.1.2.1 Functional Description
(1) Real-time Data Acquisition
a) BMS data: Real-time battery data is collected using a CAN bus. The BMS uploads the data of each battery cell to the EMS in packets. The EMS unpacks the data and stores it in the database. The system analyzes the battery cell voltage status in real time, provides early warning of battery lifespan, and takes corresponding measures to reduce battery degradation.
b) PCS data: PCS data is collected according to the PCS communication protocol. The collected data includes voltage, current, and power on the DC side; active power, reactive power, three-phase voltage, three-phase current, frequency, power factor, operating status, conversion efficiency, alarm and fault information, and other common information on the AC side, as well as daily input energy, daily output energy, cumulative input energy, and cumulative output energy.
c) Switch data: The relay switch is connected to the door contact signal. In both the open and closed states of the door, the single-channel relay converts the electrical signal into a digital signal, and then transmits the digital signal to the EMS via RS485 for alarm and warning notifications.
d) Environmental data: Temperature and humidity sensor data or wireless busbar temperature sensor data is collected via RS485.
6. Civil Engineering Works
6.1 Overview
6.1.1 Site Overview
The project is located at xxxx. The site is 50 meters to the left of the entrance of the south gate (4.2m wide, 3.5m high) (the foundation is on solid ground). It is accessible by a road (2.5m wide, with a 2.7m wide grassy area). The surrounding area outside the fence consists of trees and grassland.
6.2 General Layout and Transportation
6.2.1 Overall Planning
This project plan is designed based on the principles of scientific safety, environmental protection, and land conservation, maximizing the reduction of the client's construction period. The energy storage system adopts a standard modular design, integrated into 3 prefabricated cabins, uniformly arranged for easy installation, transportation, maintenance, and system expansion.
6.2.2 General Layout
The prefabricated cabins are arranged on both sides along the length of the site. The PCS cabin is located closer to the power distribution room to facilitate the connection of lines to the power distribution room.
6.2.3 Vertical Layout
The site drainage will utilize concrete drainage ditches built around the energy storage system near the shear walls, connected to a central sump.
6.2.4 Transportation
The site is located 50m to the left of the entrance of the south gate (4.2m wide, 3.5m high) (the foundation is on solid ground), and is accessible by a road (2.5m wide, with a 2.7m wide grassy area). It is planned to use a crane to lift the prefabricated cabins to the designated location (preliminary calculations indicate that a 35-ton crane is required for on-site lifting).
6.2.5 Site Area
The energy storage system is built on a concrete foundation, with solid ground beneath the concrete. The entire area covers approximately 200m2.
6.3 Energy Storage Station Buildings and Structures
6.3.1 Building Section
All equipment in this project is integrated into prefabricated cabins with a service life of 25 years; no new buildings will be constructed.
6.3.2 Structural Section
(1) Prefabricated Cabin Foundation
The foundation will use a reinforced concrete raft foundation according to construction design standards. Concrete strength grade C35, rebar strength grade HRB400.
(2) Retaining Wall Foundation
The retaining wall foundation uses a reinforced concrete strip foundation.
(3) Foundation Treatment
Construction will be carried out in sections according to the construction plan. Compaction density should be tested according to specifications or design requirements. The next step can only proceed after the requirements are met. C30 drilled and grouted piles with a diameter of 600mm are installed under the raft foundation. The piles are sparsely arranged to control settlement. The effective pile length is approximately 10-20m, with a total of about 50 piles.
6.4 Heating and Ventilation
This project is located in a non-heating region, so no central heating system is designed. For compartments requiring temperature and humidity control in both winter and summer, air conditioning and ventilation systems are installed.
Each battery compartment has its own independent air conditioning system.
6.5 Water Supply and Drainage
To prevent water seepage into the pit during rainy and snowy weather, which could lead to equipment corrosion, a concrete wall 300mm wide and 1300mm high is required to be poured along the perimeter of the foundation pit. A 100mm diameter, 2mm thick cable conduit is embedded at the top, with flared ends. After the cable is installed, the conduit should be sealed with oil-soaked cotton or other fire-resistant material. Both the inside and outside surfaces should be coated with a 1:2.5 cement mortar waterproof layer, 20mm thick, ensuring the mortar is full and without voids. A steel ladder is installed on the retaining wall. The ladder's two vertical supports are two Φ22 grade 3 steel bars, and the rungs are Φ14 grade 2 steel bars with a spacing of 200mm. A water collection trough is installed at the bottom and connected to a pre-embedded drainage pipe.
7 Fire Protection
7.1 Fire Protection Design Principles
The fire protection design of this project shall comply with the Fire Protection Law of the People's Republic of China and relevant national policies and regulations. It shall implement the fire protection policy of "prevention first, combining prevention and firefighting," aiming to achieve self-protection and self-rescue, prevent and reduce fire hazards, and ensure personal and property safety. Various effective fire protection measures that meet the requirements of different buildings and facilities will be adopted, using advanced, reasonable, economical, and reliable fire protection technologies. In the layout design, process design, and material selection, relevant fire safety standards, regulations, and specifications must be strictly followed.
7.2 Construction Specifications
The main equipment for this project consists of batteries and a PCS system. The fire hazard classification and fire resistance rating of the building for this project shall strictly comply with GB51048-2014 "Design Code for Electrochemical Energy Storage Power Stations" and GB50016-2014 "Code for Fire Protection Design of Buildings".
Article 11.1.3 of GB51048-2014 "Design Code for Electrochemical Energy Storage Power Stations" stipulates that the fire hazard classification of outdoor lithium-ion battery equipment is Class E (Class E refers to non-combustible materials), which is consistent with Article 6.3 of Q/GDW 11265-2014 "Technical Regulations for the Design of Battery Energy Storage Power Stations".
7.3 Battery Fire Protection
The fire protection measures for the batteries inside the container mainly utilize a heptafluoropropane automatic fire extinguishing system. Fire protection power lines are concealed within non-combustible structures or protected by metal conduits, and all cables are flame-retardant. Fire protection measures for cables include sealing, blocking, and isolation. Fire-resistant sealing materials are used to tightly seal cable entry and exit points in distribution devices and cable trenches.
The heptafluoropropane automatic fire extinguishing system is a modern intelligent automatic fire extinguishing device integrating gas fire extinguishing, automatic control, and fire detection. It complies with the requirements of DBJ15-23-1999 "Design Specification for Heptafluoropropane (HFC-227ea) Clean Agent Fire Extinguishing Systems" and ISO14520-9 "Gas Fire Extinguishing Systems - Physical Properties and System Design" system design and product standards. This system features advanced design, reliable performance, simple operation, and good environmental protection.
The fire protection system consists of a fire alarm controller/gas fire extinguishing control panel, smoke detectors, heat detectors, sound and light alarms, alarm bells, discharge indicator lights, manual emergency start/stop buttons, fire extinguishing devices for the equipment cabinet (including fire extinguishing agent storage cylinders, electromagnetic drive devices, and pressure signal devices), equipment cabinet accessories (nozzles, high-pressure hoses), and fire extinguishing devices for the power supply cabinet (including fire extinguishing agent storage cylinders, electromagnetic drive devices, and pressure signal devices).
This project is based on the efficient utilization of container space, therefore a special design is adopted:
(1) Based on the equipment layout inside the container, the fire extinguishing method uses a total flooding fire extinguishing system. Within the specified time, a designed amount of heptafluoropropane is sprayed into the container, ensuring it evenly fills the entire container;
(2) Due to the limited height inside the container, the heptafluoropropane gas cabinet is directly fixed inside;
(3) The activation method uses an electromagnetic valve device. This device must be removed during transportation and can only be installed after the container is placed in its fixed position, all commissioning is completed, and it is put into normal use.
7.4 Electrical Fire Protection
The PCS compartment is equipped with smoke and heat detectors, and handheld fire extinguishers are placed at the entrance of the compartment.
Emergency lighting: Safety passages are provided inside the container, and evacuation signs with lighting displays are installed at the container entrances and exits.
7.5 Fire Alarm and Control System
The fire alarm and linkage control system is designed according to the relevant requirements of GB500116-2013 "Code for Design of Automatic Fire Alarm Systems".
The automatic fire alarm system equipment installed in the container includes a fire alarm controller, detectors, control modules, signal modules, and manual alarm buttons. It monitors fire alarm signals in all areas of the system and can implement automatic linkage control of each energy storage unit according to fire protection requirements. The fire alarm controller has indicators for the operating status of the controlled equipment and manual operation buttons.
Smoke and heat detectors are selected, and manual alarm buttons and sound and light alarms are installed. When a detector or manual alarm button is activated, the fire alarm controller emits an audible and visual alarm signal, displays the address of the alarm point, and prints the alarm time and address of the alarm point and other relevant information. The normal working power supply of the fire alarm controller is AC 220V.
8 Environmental Protection and Safety Production
8.1 Environmental Protection
8.1.1 Electromagnetic Fields
(1) Electromagnetic field standards followed by the energy storage power station
The limit for high-frequency electromagnetic field (0.1–500 MHz) strength is taken from the safest values in "Environmental Electromagnetic Wave Health Standard" GB9175-88, "Electromagnetic Radiation Protection Standard" GB8702-88, "Methods and Standards for Environmental Impact Assessment of Electromagnetic Radiation" HJ/T10.3-1996, and "Technical Specifications for Environmental Impact Assessment of Electromagnetic Radiation of 500kV Ultra-High Voltage Transmission and Transformation Projects" HJ/T24-1998: <5 V/m.
For power frequency electromagnetic fields (50 Hz), according to "Technical Specifications for Environmental Impact Assessment of Electromagnetic Radiation of 500kV Ultra-High Voltage Transmission and Transformation Projects" HJ/T24-1998, the power frequency field strength is <4 kV/m, and the magnetic field induction intensity is <0.1 mT. The radio interference standard, according to "Technical Specifications for Environmental Impact Assessment of Electromagnetic Radiation of 500kV Ultra-High Voltage Transmission and Transformation Projects" HJ/T24-1998, is no greater than 55 dB(μV/m) under clear weather conditions at a test frequency of 0.5 MHz.
8.1.2 Noise
This project strictly controls noise levels during equipment selection. All ventilation and cooling equipment uses low-noise fans to ensure that the noise level within 1 meter outside the enclosure during normal operation is below 70 decibels.
8.1.3 Pollutant Emissions
Pollutant emissions include wastewater discharge and solid waste discharge.
During the construction period, wastewater mainly consists of construction wastewater and domestic sewage generated by construction personnel. Construction wastewater should be discharged in an orderly manner according to the relevant construction organization design; since this project is adjacent to the substation, domestic sewage will be discharged using the facilities within the substation.
Solid waste during the construction period mainly consists of construction waste and domestic waste. It is required that the waste be removed and disposed of as it is generated to prevent solid waste from being blown around by the wind and polluting the surrounding environment. 8.2 Occupational Safety
8.2.1 Analysis of Main Hazardous Factors
(1) Analysis of Hazardous Factors During Construction
During the construction of this energy storage project, the most likely types of work to cause safety accidents are: working at heights, transportation and lifting operations, and electrical work. The hazardous factors associated with these three types of work are identified below.
① Potential hazardous factors in working at heights include:
Inadequate protective measures, working in strong winds, and falling equipment.
② Potential hazardous factors in transportation and lifting operations include:
Unauthorized operation, broken lifting ropes, overloading, unbalanced outriggers, excessive lifting angle, cross-operation, broken hooks, improperly secured hooks, operational errors, malfunctioning limit switches, improper command, and lifting in strong winds.
③ Potential hazardous factors in electrical work include:
Lack of leakage protection, unauthorized operation, equipment leakage, electric arc flash, welding without protective equipment,
multiple machines connected to one switch, damaged wiring, lack of protective measures, damaged wire insulation, incompatible equipment power supply, and lightning discharge during thunderstorms.
8.2.2 Main Preventive Measures
(1) Fire Prevention Design Measures
After the energy storage power station is completed and put into operation, the fire hazard mainly comes from the possibility of fire and potential explosion risks from batteries and other flammable materials. To reduce the risk of hazards, the following measures should be taken in the design:
① The minimum spacing between prefabricated modules in this project shall not be less than the provisions of the current "Fire Protection Design Code for Thermal Power Plants and Substations" (GB 50229-2006) and "Code for Fire Protection Design of Buildings" (GB 50016-2014), maintaining a safe fire distance.
② Hazardous materials and flammable and explosive materials should be stored in limited quantities, not exceeding the limits, and should not be mixed with other items. They should be stored in dedicated warehouses.
(2) Preventive Measures During Construction
During the construction of the energy storage power station, the main hazards include electric shock, mechanical injury, burns, noise, falling objects, foundation pit collapse, high temperature, and cold. To ensure the health and safety of personnel and safe production, the person responsible for accidents should be clearly identified during construction, various construction safety measures should be implemented, and construction safety technical requirements should be strictly followed.
8.2.3 Occupational Safety Factors
(1) Personal Safety Measures
The layout of the energy storage power station's power distribution equipment shall comply with relevant safety work procedures.
(2) Anti-Electric Shock Safety Measures
To meet the safety requirements for personnel and equipment during operation, the design of the energy storage power station should meet the safety clearances of various electrical equipment. The enclosures of switchgear shall be reliably grounded. To ensure safe operation, high-voltage electrical equipment should be equipped with complete anti-misoperation interlocking devices, and the anti-misoperation interlocking devices shall not be arbitrarily taken out of service.
(3) Electromagnetic Field Strength Values and Protection Measures for Personnel
The energy storage power station shall comply with relevant environmental electromagnetic wave health standards, and the electromagnetic field strength values shall be less than the limits of national standards for occupational exposure and public exposure.
9 Construction Conditions and Large Equipment Transportation Plan
9.1 Main Construction Plan
9.1.1 Foundation Construction
The foundation of this project has a shallow burial depth and no deep foundation pits. Rebar fabrication should be carried out according to the drawings, paying attention to ensuring the thickness of the protective layer of the bottom layer of rebar, and using spacers to ensure the spacing between the upper and lower layers of rebar. Rebar intersections should be securely tied point by point, and any loosening caused by subsequent construction should be re-tied.
The above-ground part adopts a fair-faced concrete process. Commercial concrete is used, and the construction is carried out according to the large-volume concrete construction process, with thorough vibration to avoid surface quality defects.
9.1.2 Equipment Lifting
(1) Crane Selection
The crane should be selected based on a lifting capacity not exceeding 90% of the maximum rated lifting capacity of a truck crane or 70% of the maximum rated lifting capacity of a crawler crane, with a lifting radius of not less than 15m. Preliminary calculations indicate that a 35-ton crane is needed for lifting.
(2) Lifting Plan
Lifting and transportation will utilize the road on the east side of the station area. The lifting sequence will be from north to south. If a crawler crane is used, the equipment transport vehicle can be parked on the access road, and the equipment can be positioned and installed by the crane carrying the load. Wooden planks will be laid on the road surface for protection. If a mobile crane is used, lifting positions can be set up in the north, central, and south areas, depending on the crane's lifting capacity. Equipment transport vehicles will then transport the equipment to the most convenient lifting positions.
