Acrel Application of AM6-PW Protection and Control Device for Box-type Substations in Overseas Integrated Energy Storage Step-up Units

Abstract: 

The industry for integrated energy storage and step-up units is undergoing rapid expansion, with high-power, liquid-cooled, and highly integrated models becoming the mainstream. Market concentration among leading manufacturers continues to rise, and integrated solutions are gradually replacing traditional split-system equipment due to their advantages in cost, installation, and operation and maintenance. These integrated units typically utilize ring main units (RMUs) for both high- and low-voltage sides; given the compact space and high transformer capacity, it is necessary to consolidate multiple protection functions—such as overcurrent and differential protection—into a single device, known as a protection and control unit for box-type substations.
Keywords: Integrated energy storage and step-up unit; ring main unit (RMU); protection and control unit for box-type substations

1. Project Overview

Driven by top-level policies regarding "dual-carbon" goals and the construction of new power systems, the installed capacity of wind, solar, and new energy storage in China continues to grow rapidly. Large-scale projects—including wind/solar paired with storage, independent energy storage, and integrated source-grid-load-storage systems—are being implemented across the country. Traditional "split" solutions—characterized by the decentralized layout of inverters, Power Conversion Systems (PCS), box-type transformers, switchgear cabinets, and other components—suffer from numerous pain points, such as long construction periods, large footprints, high cable losses, complex multi-device coordinated commissioning, and difficult operation and maintenance (O&M). Meanwhile, as the upstream and downstream supply chains (including IGBTs, transformers, and thermal management systems) mature and relevant industry standards are refined, integrated new energy step-up units have emerged and gained rapid popularity. These units offer full-lifecycle advantages, including lower costs, high integration, shorter construction periods, convenient O&M, and reduced power generation losses. In overseas markets, energy transitions are advancing across Europe, the Americas, Australia, Southeast Asia, and the Middle East; however, projects often face challenges such as high local construction labor costs and insufficient on-site integration capabilities, leading to steady growth in demand for exported prefabricated integrated energy storage units.
An integrated energy storage step-up unit houses the PCS, step-up transformer, high/low-voltage ring main units (RMUs), EMS/BMS, and thermal management systems within a standard container. DC power from the battery is converted by the PCS and stepped up directly within the unit to 10kV or 35kV for grid connection. Replacing traditional decentralized PCS-plus-transformer solutions, this has become the mainstream standardized equipment for large-scale independent energy storage. This project outlines the protection configuration requirements for integrated energy storage step-up units (ranging from 8MW to 48MW) destined for overseas markets.

2. Project Requirements

Since integrated energy storage step-up units are equipped with ring main units (RMUs) on both the high- and low-voltage sides—incorporating primary equipment such as circuit breakers—protection devices are required. These devices must trip the circuit breakers promptly in the event of faults like short circuits or overcurrents to prevent the fault from escalating. Currently, most integrated energy storage step-up units feature large-capacity transformers (exceeding 2000 kVA). Consequently, differential protection is necessary to calculate the vector sum of currents across the high- and low-voltage sides (or three sides, in the case of split-winding transformers) and to trip the circuit breakers immediately upon detecting a differential current. Unlike the conventional approach in user-side substation projects—where transformer differential protection and backup protection are configured separately—the integrated step-up unit utilizes a ring main unit (RMU) with limited switchgear space. Consequently, these protection functions must be integrated into a single device to provide protection for the high- and low-voltage sides of the box-type transformer (or for all three sides, in the case of a dual-split transformer).

3. Product Solution

The AM6-PW protection and control device for box-type transformers, configured to meet user requirements for this project, is primarily installed in the high-voltage RMUs of integrated energy storage step-up units (with capacities such as 8MW, 10MW, 36.8MW, and 48MW). Using the dual-split transformer shown in the figure below as an example, the primary protection functions configured for the AM6-PW are described below.

Figure 1 shows a split-winding transformer configured for an overseas project; the transformer is rated at 20 kV/0.8 kV–0.8 kV with a capacity of 7,000 kVA. The equipped AM6-PW protection and control device for the box-type substation acquires current, voltage, and circuit breaker status data from all three sides (the high-voltage side and both low-voltage sides), enabling protection functions such as transformer differential protection and overcurrent protection. Details regarding specific protection functions are provided in the table below.

4. On-site Installation Example

For this project, the protection and control device for the box-type substation is installed locally on the high-voltage ring main unit of the integrated step-up unit; on-site installation photos are shown below.

5. Protection Function Configuration