Designing for energy efficiency in power plants has many challenges from technical to non-technical obstacles. Those that pertain to electrical engineering include:
- In power plant design, electrical engineering is often the last department to engage after mechanical and control systems.
This leaves little for electrical engineers to engage is proper integrated energy efficiency design. This often has damaging effect on the energy efficiency of power plants. This means that all of the internally consumed energy through the electrical system which is inefficiently used.
- The power system is the first item that is designated.
This causes further restrictions on the allotted time that electrical engineers can spend on conceptual studies important for internal power plant operations. Conceptual studies usually present the best opportunity to understand the impact of basic energy efficiency improving design changes which are developed around greater efficiency improvements based on analysis. The power quality studies for energy efficiency include:
- Load Analysis
- Power Flow and Voltage Drop Analysis
- Motor Starting Analysis
- Short-Circuit Analysis
Load analysis is one of the most important engineering steps for increasing energy efficiency. Gathering information and data about all the loads that the power system will encounter is the first step towards design. This means understanding critical loads, duty cycle, seasonal variations, and startup requirements. These sources usually come from the mechanical and controls design team. Due to fragmentation of suppliers, compiling a detailed load list is never an easy task. For those without actual data on current designs can consult similar past projects as a guide.
Load analysis should begin with quantifying the maximum operating load based on actual loads and loading factors. Inflated values given from the manufacturer can lead to oversizing of the supply. The load analysis should also take into account for the number of loads on the system.
Power Flow and Voltage Drop Analysis
Power plant system voltages have a definite impact on energy efficiency. Choosing a higher bus voltage where possible will reduce the ohmic losses due to lower current levels relative to low voltage buses. Selecting medium voltage rather than low voltage drives and motors will reduce ohmic losses in drive-power equipment. Motors and transformers rated at higher voltage levels ultimately have higher efficiencies. Thus, higher bus voltages will allow the designer to specify fewer, larger transformers and will increase overall system energy efficiency.
Motors with soft starters draw much more than their full load operating current during startup. High torque demands during startup will increase the load on the power system leading to oversized components, which leads to extra expense of lower continuous running efficiency. Understanding the requirements of motor startup will help in designing for interconnecting components without over estimating parameters, essentially designing for exact operating conditions for proper components.
The primary purpose of short-circuit analysis is the ensure that breakers will not be over-dutied under short circuit conditions. Breakers must be capable of carrying normal load current and should be able to interrupt fault currents. If breakers are suppose to interrupt current higher than their interrupted rating then damaging consequences can follow. Making sure that the rated current and interrupting rating are within reasonable ranges will improve chances of preventative damage to system components.
The Importance of Equipment Sizing and Bus Design
Correctly balancing loads across buses will improve power quality and energy efficiency. In power plants there are multiple power sources and acquiring a correct balance will lead to optimizing sizes of power system components and reduce startup requirements for each bus.
A proper analysis will yield the optimum breaker and cabling sizes. Poor sizing of components can have consequences on both energy efficiency and protective functions. Understanding that undersized cables have higher losses is important for cable size determination.
Some guidelines for copper busbar sizing include increasing the cross section to reduce energy losses, doubling the conductor cross section area to cut the resistance in half and reducing losses by essentially half. The first few incremental size increases above the minimum allowable will make a sizeable difference in loss, but with each incremental increase the return decreases. Selecting multiple bars of a single bus is another issue a design engineer has to consider for achieving a lower system loss.
Busbars are long-lived plant components, which gives their running energy cost more weight in lifecycle calculation. In order to select a proper busbar requires an understanding of voltage drop, short circuit current, and skin effect that the system encounters during normal operations.
Designing for Proper Power Plant System Cabling Layout
The physical layout for power system components and the length and diameter of cables should be selected for minimal losses. Power loss is wasted in cables in electrical systems. Losses also include those for switchgears and other current carrying devices such as controls and protection circuits. Design guidelines for reducing losses include:
- Centrally located the load center for transformers, switchgears to:
- Reduce length of cable runs
- Reduce losses and voltage drops
- Keep buses and taps as short as possible to:
- Reduce the distance between auxiliary unit transformer and generator
- Increase cable diameter of smaller cables to one or maximum two gauge higher to gain benefits including:
- Lower ohmic losses
- More cable of fewer different cable sizes reduces wastage during installation, and get better terms such as minimum order quantities.
The main equipment is laid out before the connections are determined between them. Determining design choice of smallest allowable diameter cables to reduce initial material costs, at the expense of much larger lifetime operating costs.
Cable Design Determination
Determining cross-section of cables between interconnecting loads must be calculated in relation to operating conditions and cable length. Factors that influence cable cross-section include:
- Permitted loading under normal conditions, taking account of ambient temperature and layout methods.
- Thermal short-circuit strength
- Permitted voltage drop along the cable run under normal conditions and starting phase.
- Protective device response in the event of overloads and the smallest possible short-circuit current to interrupt dangerous voltages.
Cable Route Planning
Cable routing in complicated facility installations, power plants, and switching stations requires an immense amount of work on the engineer and planners part. It involves arranging cables to give the shortest path between their starting point and final destination, while ensuring that certain combinations do not adversely influence each other.
Computer aided design (CAD) has been widely used as a means for developing and engineering proper implementation of component and cabling layout. Power plant facilities require tremendous care when developing a fully functional and energy efficient flow.
E3.3D Routing Bridge
E3.3D Routing Bridge allows for easy path routing with full integration with mechanical CAD softwares. Determining wire length, diameter, and standards for cable selection between interconnecting components has never been easier.
To help strive for the best in show design, Zuken has developed links between E3.series and all major MCAD (mechanical CAD) vendors, allowing the creation of fully integrated design model. Using the E3.3D Routing Bridge, schematic and connection information from E3.series can be interfaced to all major MCAD systems. Features including:
- Transfer Component Information to MCAD (connectors, pins, splices)
- Transfer to-from Data to MCAD
- Check for Collision, or clash, detection in MCAD
- Check for Wire Bend Radius
- Automatically Calculate Length of Wires and Segments in MCAD
- Automatic Creation of Manufacturing Documentation in E3.Formboard
Designing and documenting electrical controls systems including schematic diagrams, terminal plans and PLCs. It helps prevent errors as you design so you can develop systems for the best energy efficient design. Easy drag and drop interface to save time designing connections and components for development so more time can be dedicated toward the plant efficiency and less on product development. Easily integrates work through multiple platforms for integration between mechanical and electrical design. This gives strides for design development for electrical engineers when mechanical and control systems are designed ahead of electrical consideration. E3.Schematic offers the following features for easing the design phase:
- Creates and documents your electrical schematics efficiently
- Prevents errors with built-in design rules
- The ability of engineers to design with a huge library of pre-designed, pre-approved and tested components
- Design with drag and drop
- Easily connect electrical components
- Do your wiring number automatically
- Pre-define your own sub-circuits
- Manage terminals across multiple sheets with intelligent software design
- Generate project documentation in simple single steps
Are there ways that your facility could become energy efficient? Comment on what you would like to improve.