Introduction to Power System Design
The design or planning or design of an industrial electric power system is a design stage that includes various aspects starting from the selection of main components (panels, transformers, cables and protection), to the arrangement of distribution and load control. —Omazaki Engineering is a power consultant who serves power system design consulting services. If you are looking for electric power system consultant company to study and design your project or power systems facilities in Indonesia and South East Asia contact Omazaki Engineering by sending an email to cs@omazaki.co.id or filling in the form in contact.
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Purpose of Electrical System Planning and Design
The main objective of this industrial electrical power system design is to provide a reliable, efficient and safe power supply, so that critical machines and production systems can run smoothly. In addition, good design also aims to:
- Ensure continuity of operations, thus minimizing downtime due to supply disruptions
- Ensure safety, both for personnel and equipment, through protection against overcurrent, short circuits, and voltage disturbances
- Increase energy efficiency, thus reducing long-term operational costs
- Meet regulations and standards, both from authorities and customers.
With this understanding, designing an industrial power system is not just about connecting cables, but designing a mature and sustainable electrical structure. Good design will also facilitate the installation phase of the power system later.
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Types of Electrical Power System Design
Conceptual Design
Conceptual design is the initial stage of project design that focuses on the initial idea and big picture of the project. The main purpose of conceptual design is to determine the project vision, main concepts, and technical and economic feasibility.
One of the key components in the conceptual design stage is the feasibility study (FS). This study includes:
- Technical feasibility: can the load requirements be met by available technology?
- Economic feasibility: what are the initial costs, operating costs, and ROI of the project?
- Regulatory feasibility: does the system meet government, PLN, and industry standard requirements?
- Operational feasibility: to what extent can the system be operated and maintained with available resources?
The results of this feasibility study are the basis for decision making whether the project is feasible to proceed to the next stage or needs to be changed. The results of the feasibility study are also usually used as a basis for proceeding to the Front-End Engineering Design (FEED) or Preliminary Design stage, where system planning becomes more technical and detailed.
Preliminary Design/Basic Design
Preliminary Design or Basic Design is an engineering design stage developed based on the results of Conceptual Design. This stage is often referred to as Front End Engineering Design (FEED), especially in the oil and gas industry. At this stage, the design of the electric power system begins to be formulated in a more structured and technical manner, but is not yet fully detailed.
All outputs from the Preliminary Design will be the main foundation of the DED (Detailed Engineering Design) stage, especially for the tender process. In other words, the FEED or Basic Design document acts as a “rough blueprint” that will be refined and detailed in the form of engineering drawings, detailed calculations, and a complete list of materials at the DED stage.
Detailed Engineering Design (DED)
Detailed Engineering Design (DED) is a further stage in the industrial electric power system design process that aims to produce complete and ready-to-use technical documents in the construction tender stage. After going through the Conceptual Design and Preliminary Design stages, the DED stage perfects all planning into a form that can be directly implemented in the field.
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Stages of Industrial Power System Design
Defining Estimated Load
Load definition includes load survey, demand and diversity analysis, and load characteristic definition. At this stage, data is collected on all equipment to be used, such as electric motors, lighting, HVAC, control panels, and other supporting equipment. This estimate must also include power factor, starting current, peak load, and future load growth. The goal is simple but crucial, namely to prevent the system from being under-capacity or even wasteful due to excess power.
Determining Design Philosophy
Design philosophy is a “mind map” of the entire system. The design philosophy or planning of an electric power system includes a set of principles and approaches that underlie the design and operation of an electric power system to ensure reliability, efficiency, safety, and sustainability. This is where several key aspects of the electric power system design philosophy are determined, such as:
- Reliability, where the system must be able to provide continuous and stable power without significant disruption.
- Safety, where the safety of personnel operating and maintaining the system, as well as the general public is the main priority.
- Efficiency, where the system must be able to optimize the use of energy and resources, and minimize power losses during distribution.
This philosophy is the basis of all subsequent design stages. If this stage is wrong, then the entire design can deviate from the original goal.
Preparing a Preliminary Single Line Diagram (SLD)
A preliminary single line diagram (SLD) is a rough but comprehensive picture of the power system to be built. It depicts the relationship between resources (transformers/generators), distribution systems (MSB, panels), and loads. Although preliminary, this SLD is very important as a communication tool between engineers, project teams, and facility owners.
Calculating, Analyzing, and Sizing
This section is the main stage of the design or planning process of the electric power system. At this stage, a power system study is carried out, namely a series of analyses and investigations of the electric power system to ensure its reliability, safety, and operational efficiency. Common power system studies include:
- Load Flow Study, to analyze the system’s ability to supply the connected loads, including power loss calculations.
- Short Circuit Study, to analyze the impact of short circuit currents on the system and equipment.
- Protection Coordination Study, to ensure the protection system is working effectively to isolate faults.
- Transient Stability Study, to analyze the behavior of the system during a transient fault.
- Harmonic Study, to analyze and control harmonic distortion in the system.
- Arc Flash Study, to analyze potential arc flash hazards and implement preventive measures.
- Power Quality Study, to evaluate the quality of power supplied by the system.
- Grid Impact Study, to analyze the impact of the power system on the wider electrical grid.
All the results of this analysis and calculation will be used to select and size the right equipment, both from a technical and economic perspective.
Fixed Single Line Diagram (SLD)
After the analysis is completed, the final single-line diagram is prepared as the main blueprint. At this stage, all design elements have been verified: equipment ratings, connection types, protection, grounding, and load distribution. This diagram will be used in the procurement, installation, and commissioning process.
Bill of Material (BOM)
Bill of Material (BOM) is a list of all technical components required: cables, panels, MCBs, MCCBs, CTs, relays, connectors, and grounding systems. This BOM is very important in the material procurement process to match the design and specifications.
Bill of Quantity (BOQ)
Unlike BOM which focuses on the type and specifications of equipment, BOQ contains the quantity of items based on drawings and field layouts. BOQ is a technical reference for contractors in preparing price offers and work volume estimates.
Cost Budget Plan
The final stage of the electrical system design process is to prepare a cost budget based on the BOQ and current market prices. This budget may include:
- Material costs
- Installation and labor costs
- Testing and commissioning costs
- Contingency and reserve costs
With a cost budget plan, project owners can see the estimated total costs required and make accurate budget planning.
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What is to be Designed?
Power Supply
It all starts with the energy source. The selection and planning of the power supply greatly determines the reliability and continuity of operations. One important principle in this stage is redundancy. Redundancy means providing a backup source that can immediately take over if the primary source is disrupted. This is very crucial, especially in industries that have critical loads and do not tolerate downtime, such as continuous production systems, healthcare facilities, or data centers.
Redundancy can be implemented in various forms, such as:
- Dual supply, which is two different supply sources that can replace each other
- Using a generator or UPS as a backup source during a blackout
- Power supply configuration with the concept of N + 1, 2N, or 2N + 1, depending on the criticality of the load
Some important questions that need to be answered when designing a power supply system:
- Is dual supply needed to maintain continuity?
- What is the best backup strategy: genset, UPS, or a combination of both?
- Does the system need to be made capable of synchronizing between resources?
By implementing the concept of redundancy from the start, industrial power systems will be much better prepared for emergencies without sacrificing productivity.
Transformers
Transformers are the heart of the voltage distribution system. They function to lower or raise the voltage according to system needs. In its design, the following things need to be considered:
- kVA capacity according to peak load + expansion margin
- Connection type (Delta-Wye, Wye-Wye, etc.)
- Impedance, efficiency, and protection
- Installation location: indoor or outdoor
Circuit Breakers
Circuit breakers function to protect the system from overcurrent and short circuits. The selection should not be arbitrary. Some types of breakers commonly used in industry include:
- MCCB (Molded Case Circuit Breaker)
- ACB (Air Circuit Breaker)
- VCB (Vacuum Circuit Breaker)
Things that must be designed include breaking capacity, protection settings, and coordination between breakers to be selective.
Medium Voltage (MV) Panels
MV panels are medium voltage distribution gateways (usually 20 kV or 6.6 kV) to various transformers or large loads. The design must consider:
- Busbar scheme (single, double, looped)
- Protection and metering relays
- Arc flash rating and ventilation system
- Integration with SCADA systems if required
Low Voltage (LV) Panels
LV panels distribute electricity to loads such as motors, lighting, and other auxiliary equipment. In its design, it is necessary to consider:
- Total current capacity and per circuit
- Panel location to load (reducing voltage loss)
- Protection and segregation between critical and non-critical loads
- Motor panel (MCC) with motor and starter protection
Grounding Systems
Grounding is not just about safety. This system also determines the performance of protection and system stability against disturbances. In grounding design, it is necessary to consider:
- Grounding system: solid, resistance, or isolated
- Placement of grounding rods and grounding mesh
- Grounding for equipment, lightning, and human protection (step & touch voltage)
Power Cables
Cables are the main path for power transmission. One of the most common mistakes is choosing the wrong size or type of cable, which can cause overheating, high power losses, or even fire. In its design, the following are taken into account:
- Load current and ambient temperature
- Installation type (underground, tray, conduit)
- Derating factor and voltage drop
- Insulation and conductor material (CU/AL)
Loads
The last part, but no less important, is the load itself. All previous designs are intended so that the load, be it motors, lighting, HVAC, or process machines, can work optimally. Therefore:
- Loads must be grouped: critical, intermittent, continuous
- Analysis of motor starting characteristics (DOL, star-delta, soft starter, VFD)
- Determination of control and monitoring systems for efficiency
- Estimation of power factor and compensation requirements (PFC)
In practice, electrical loads do not consist of only one type. For proper planning of an electrical power distribution system, it is important for engineers to understand the characteristics of the loads to be handled, including:
- Inductive Load
This is the most common type of load in the industrial world, such as electric motors, transformers, coils, and lamp ballasts. This load tends to absorb reactive power, causing the current to lag behind the voltage (lagging), and reducing the power factor. Therefore, a compensation system such as a capacitor bank is often needed to balance it.
- Capacitive Load
This type of load produces reactive power and causes the current to lead the voltage (leading). Typically arise from compensating devices such as capacitors or harmonic filters. If not controlled, excessive capacitive loads can cause overvoltage or even resonance in the distribution system.
- Resistive Loads
Resistive loads are loads that convert electrical energy directly into heat, without storing energy in the form of magnetic or electric fields. Examples include electric heaters, ovens, and incandescent lamps. The current and voltage are in phase, so there is no reactive power involved. Systems with predominantly resistive loads generally have good power factors and are easier to control.
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References
- IEEE Books on Electrical Power Systems: Design and Analysis
- IEEE Std 493™-2007 IEEE Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems
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Contact Omazaki Engineering if you are looking for an electrical power system design and plan consultant and services for your facilities in Indonesia and South East Asia.
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