Load Flow Analysis Module
Overview
The load flow analysis is probably the most important tool for system planning and design. Given system configuration, supply voltages and loading, a load flow analysis will calculate voltages, current flows and losses throughout the entire system. This module contains a normal load flow analysis along with a number of other analyses based on the load flow including motor starting, an ‘energy’ load flow and a load flow that incorporates real measurement data for improved accuracy.
Load Flow
The Load Flow Analysis in DESS allows you to determine conditions including voltage, current flow and losses for all points on the system. The modeling for this analysis (as for all analyses in DESS) fully represents single-phase and unbalanced components. Detailed modeling for voltage regulation, distributed generation and capacitor bank control is also included. Powerful load modeling with load curve definitions allows you run the analysis for a full range of load conditions for different times of day and different seasons and not just peak load.
The Load Flow Analysis is the key tool for system planning and for identifying problem areas on a system. The load flow analysis lets you evaluate the voltage profile of a feeder under different conditions. You can also find overloaded lines and evaluate the effect of different conductoring. You can compare the losses of different supply options to new loads, test the effects of distributed generation, simulate voltage conversion on older parts of the system or evaluate a proposed new substation. As you perform these types of evaluation the load flow results will provide you with the accurate data you need to confidently plan improvements to your distribution system and justify the decisions you make.
DESS uses a sweep type algorithm for solving the load flow. For distribution networks this gives a number of advantages over traditional generic algorithms such as Newton-Raphson and Gauss-Seidel. Naturally, it also solves networked and looped systems. Stability is excellent even on systems that are traditionally hard to solve, and performance is very good even on large systems (50,000+ busses).
Motor Starting
Motors, especially induction machines, can draw substantially higher loads under starting conditions. The Motor Starting Analysis helps you to determine the voltage conditions on the system during starting and to compare voltages before and during starting in order to identify the magnitude and location of sags on nearby parts of the system. You can control the starting parameters of the motor and you can also include generators or multiple machines in the starting simulation.
Annual Load Flow
The Annual Load Flow analysis works by running a series of load flows covering every loading condition throughout a year. Instead of looking at a single condition like the basic load flow, you can now look at the range of voltages you will see at a specific point, the range of currents on a line, and the total energy lost to line or transformer losses. This allows you to calculate energy consumption and losses in a way which can be useful for life cycle economic costing.
Load Loss
The losses on a system caused by an individual load vary depending on where that load is located and on the location of other loads and the existing feeder structure. The Load Loss Analysis calculates the percentage real and reactive system losses caused by an incremental load at a specified location. This can help with an economic evaluation of the lifecycle cost of losses associated with a load. This is especially important in a jurisdiction where these costs are passed on to the customer or need to be justified to a regulator.
SCADA Load Flow
The SCADA Load Flow Analysis lets you supplement the default load model in DESS with a set of real measurements (e.g. from SCADA data). This additional data is used to dynamically scale supplied loads in order to match the measured values. For example, a default load flow might predict a current flow of 120A on one phase of a feeder. If the real measurement data recorded a flow of 100A, then all the loads downstream of that point would be dynamically scaled so that the resulting feeder current matched the measured value.
Simulating real system loads is one of the biggest challenges in system modeling. Even though DESS provides detailed load modeling for representing typical load changes over a day or a season it cannot capture inherent day to day variation. By combining real measurement data with a model built on historical data you can create a very accurate snapshop of the system at any given point in time. The algorithm used by DESS can match current flow, real and reactive power flows and multiple measurements along a feeder can be used simultaneously where data is available.
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