Power system design is the process of fully designing, on paper, the electric system before beginning to place contracts for equipment order and construction. The design process can range from a simple Single Line Diagram with supporting notes up to complex packages that specify everything down to cable gland sizes.
In our experience, we have found that companies who skip this step, or provide only a very simple outline designs to contractors often end up in contractual arguments and have problems on site when the interface between two key items of equipment has not been properly considered. At Aurora we would always suggest that a thorough design is undertaken for any power system, this helps eliminate costly mistakes and schedule delays, but frequently the design cost is trivial when compared to the cost of the equipment purchase and installation contractor, and when done properly can often save money.
The design process for a power system can vary enormously depending on the complexity of the power system and the existing site configuration. At one end of the spectrum, we can provide guidance for a simple low voltage DNO connection, while at the other extreme we can design a tie-in to a complex brownfield site that has limited space and outage windows.
As part of the design approach Aurora will typically begin by estimating the total power demand, selecting appropriate voltage levels, transformer rating, earthing approach, circuit breaker ratings and fault levels. On more complex sites, we can also then help to establish the required reliability and maintenance requirements of the system, and consider whether to use single radial feeders, ring feeders, or dual radial feeders and different busbar configurations and the need for emergency power supplies.
Cable Sizing calculations, is an often misunderstood design process, and it is common to find cables that are not correctly sized, for one reason or another, typically with designers forgetting to consider a cables fault rating, de-rating factors or sheath sizing. At Aurora we regularly undertake sizing calculations for cables using the different approaches given in BS 7671, IEC 60364, 60502-2 and 60287 and sometimes even the old ERA 69-30 method. At Aurora are capable of sizing everything form LV cables up to complex 400kV transmission cables and their associated Sheath Voltage Limiters (SVLs). Our design process ensure that we consider all key aspects of the cable installation and any identify and correctly account for any factors that may affect the cables rating, as well as formally sizing it for the required short circuit carrying capacity.
Aurora have the capability to undertake a wide range of detailed substation designs, from small pad-mounted LV feeder pillars, up to much larger 400kV outdoor substations and complex GIS substation, or hybrid substations. As part of our design we will typically prepare plan and layout drawings, and associated civil foundation and trench details and during the design we will consider any arc flash containment ductwork, overhead cranes, battery room configuration and ventilation, shielding between power and control systems, transformer pen layouts, cable routing and bending radii, F&G detection, working and operational areas, safety isolation and safety clearances, access for maintainability and also operator access and egress. When considering GIS substation design, we will liaise directly with GIS manufacturers to ensure that the layouts and design reflect the manufacturers requirements.
Protection and Control design is a particularly complex area of electrical engineering, and one that carries a high risk if mistakes are made. At Aurora we pride ourselves on our detailed knowledge of protection schemes from simple LV power distribution systems, up to complex transmission systems and large MV motors and generators.
Our approach to protection design is to consider what will be the most appropriate protection scheme for any given item of plant or system, and select the most cost effective scheme based on the amount of capital invested in key equipment and the criticality of the system. As part of the protection design we would typically consider CT sizing calculations, take decisions on whether the use of differential protection at 33kV and 11kV is justified, and the appropriate selection of some of the more sophisticated types of protection devices required for generators and large motors. Part of this design process also considers the type of control system required, the need for any power management system and the type of communication protocols such as IEC 61850, DNP, MODBUS/TCP, Profibus etc. as well as the system architecture for the control network.
An often overlook aspect of power system design is the correct sizing of equipment, and use of appropriate de-rating factors; as incorrect sizing can lead to overheating of equipment and loss of useful service life. At Aurora we regularly undertake sizing calculations for transformers, switchgear and generators and battery sizing calculations for UPS’s. Our design process ensure that we consider all key aspects of the design requirements and any identify and correctly account for any factors that may affect the equipment rating, such as ambient air temperature, altitude and design life.
Aurora can prepare a wide range of detail design drawings to define the power system design. These documents are necessary to fully define an electrical system and allow a turnkey solution to be provided. Typical drawings that we prepare for clients are: Single line diagrams, protection diagrams, cable routing diagrams, lighting and small power layouts, earthing layouts, hazardous area drawings, wiring diagrams, schematic diagrams, architecture diagrams, block diagrams and many more types!
Aurora has a wide range of established equipment specifications and data sheet templates that can be easily adapted for most Clients’ needs. Preparation of equipment specifications, data sheets and operating philosophies can often seem like an arduous task, but it is vitally important; as allowing manufacturers to provide their standard design, can often lead to contract disputes, and expensive rework.