|DESS 7||Overview||Why Use DESS|
This area of the site contains support information and files for current DESS users. If you don’t find what you’re looking for here, please contact us directly and we’ll be happy to help you.
Essex Energy Corporation
2199 Blackacre Dr.
DESS 6 Latest Maintenance Release
September 22, 2014 – Download DESS 18.104.22.168
DESS 7 Latest Release
September 9, 2020 – Download DESS 22.214.171.124.77
These are the latest maintenance releases of DESS for existing customers with valid DESS maintenance. If you are not a customer with a valid maintenance agreement, please contact Essex Energy to find out how to obtain or upgrade your copy of DESS.
If you wish to download the DESS User Manual (without downloading the rest of the software), use the following link:
Frequently Asked Questions
What general features does DESS have?
If you are looking for something specific, please don’t hesitate to contact us. The feature you’re looking for may already be part of DESS.
What types of analysis can DESS do?
DESS tools are focused on distribution system network analysis. As such we don’t offer many individual tools such as cable pulling, grounding grid, line sag and tension, etc. These can be purchased separately from 3rd parties who specialize in these areas if needed.
Can I import data into DESS from my GIS system?
Modules exist to import data into DESS from a number of popular GIS systems, including GIS systems from ESRI, Intergraph, Enghouse and Canmap. Some of these import modules are available from Essex Energy, and some are available from the GIS company. Please contact us for details.
Can I import data into DESS from my CAD system?
CAD systems generally do not contain the connectivity information necessary to build a model of the network in DESS. However, you can use maps from a CAD system as background layers in DESS (export from the CAD system as DXF or SHP files), and if necessary, these layers can be used as a guide so you can ‘trace over’ a system in DESS by entering the data manually.
Can I use DESS to model distributed generation on my distribution system?
Yes. DESS allows you to represent both induction and synchronous generation on your system. For synchronous generation DESS allows you to model generator voltage regulation and VAR output limits. The effects of generation is automatically included in any studies, including load flow and short circuit, so you can determine the effect on system voltages and flows, fault levels and losses.
When should I use a distribution transformer element and when should I use a power transformer element?
You use a distribution transformer when you have no interest in what happens below the LV terminal of the transformer. You use a power transformer element if you are interested in modeling loads or lines on the LV side of the transformer. If you have a node with a distribution transformer, any loads on that node are assumed to be applied at the LV side of the transformer. Modeling the distribution transformer gives you the benefit of computed values for secondary voltages, and transformer losses due to series (or copper) losses and due to no load (or core energization) losses.
Should I use DESS to model the customer-owned transformers on my system?
Probably not. If you meter a customer above the transformer then the loading values you have represent a combination of the customers load and any transformer losses. Therefore, the most accurate way to model this is as a single load element on a node, with no transformer. This way, the load values on the element will match the load values you use to measure and bill the customer. If for some reason you need to know the transformer losses, or the secondary voltages for a customer-owned transformer then you should go ahead and model it as a node with both a distribution transformer and load elements.
Can I copy reference data from one set of system data to another?
Yes. You can use the Tools | Import Reference Data command to copy reference data items (such as conductors, transformers, load modeling definitions or protection items) from another system.
How can I connect two different voltages together (i.e. at a substation)?
You would use a Power Transformer element to connect a node on one layer (HV terminal) with a node on a different voltage layer (LV terminal of transformer). You can do this by selecting the nodes (hold down the CTRL key to select more than one node), and then clicking the power transformer button on the toolbar.
What causes the difference between maximum and minimum fault values for the short circuit analysis?
The difference between maximum and minimum fault values are caused by a number of factors. The source impedance elements which are used at the supply point to your system let you specify maximum and minimum source impedances. The maximum source impedance applies to the minimum fault currents, and vice versa. Maximum fault current levels are reported for the case where motors and generators are assumed attached to the system. Minimum fault current levels assume that generation and large motors are not currently attached.
If using the IEC 60909 option, fault currents are not reported for the nominal voltage of the system. Instead they are reported for a prescribed upper and lower voltage (e.g. 110% and 100% for medium voltage). The higher voltage range is applied for the maximum fault level, and the lower voltage range is applied for the minimum fault level. 4) If using the IEC 60909 option, a higher conductor resistance is used to compute the minimum fault currents. This represents the increased resistance due to line heating.
How can I obtain accurate load data to use for load flow analysis?
Accurate modeling of load data is the most difficult part of creating a model of a distribution system. DESS provides extensive tools for modeling load variation over time (using Load Categories). For most large distribution systems (e.g. municipal and rural systems), the best data to use is the monthly kWh billing data, which can usually be exported from the billing system. It is accurate, and by combining this data with the profiling data in a Load Category, it is possible to create a model of the distribution system which accurately represents the variation of load from hour to hour, day to day, and season to season.
I’m not getting the expected results from my short circuit analysis. What should I check?
The most important data required for a short circuit analysis are the source impedances, transformer impedances and line impedances. Generator impedances can also impact a fault study if present. Check the fault levels right at the system source. If this gives the expected results then you know your source impedances are OK. Likewise, expected levels before a transformer and bad results after a transformer can indicate a problem with the transformer impedance. You should also check your system configuration. Do an upstream trace from the fault location to make sure the configuration of the system is correct. Also use the Query menu to check for loops, which increase available fault levels.
Why won’t my load flow converge?
The most common reason why a load flow fails to converge is an error in entering loads or entering lines or conductor information. Basically, if you try to push too much load through too small a conductor, the voltage drops too far (i.e. below 50% of normal) and the load flow cannot converge. A symptom of this is if you can successfully run a load flow with a load scaling factor of .5 or .2 and that when you do so, the voltages at the ends of your feeders are relatively low. If this is the case, check carefully that you used the right type of conductor and that the load values are appropriate. If you entered your own conductor types, check that the impedance values are realistic.
I’m having problems with connectivity/tracing. What could be wrong?
There are lots of possible reasons for connectivity problems, such as disconnected items, wrong phasing, loops, incorrect switching, etc. DESS provides a number of tools to help: Use the Query | Find Disconnected and Query | Find Loops commands to find disconnected nodes and closed loops. Double-click on a node to see the Node Dialog which will list all lines (and phasing) attached to that node. Use the Move Node tool on the toolbar to drag a node or line vertex (This can help to find overlapping nodes, and dragging a node will drag all attached lines). Also, check to make sure the nodes and lines are on the correct electrical layer. You can also use the tracing tools (upstream, downstream, custom and network trace) to help you determine how items are connected.
In the results for the load flow analysis why are the voltages so low/high?
If the voltages are low throughout the system, it is likely that the voltage at the source element (supply point) is too low. Typically the supply voltage to a system is a few percent above the nominal voltage. Also make sure you check taps on substation transformer. Most of the time, substation transformers are tapped to boost the voltage on the secondary so that the voltage at the low voltage bus is above nominal. If the voltage is only low is certain places (e.g. ends of feeders), make sure the feeder loading is reasonable and that you have defined an adequately sized conductor along the feeder. A conductor with too high an impedance, or too much load, will cause larger voltage drops along a feeder.
Do I need to model different types of framing on my overhead lines in order to get accurate results?
It is true that the framing arrangement of a set of conductors (i.e. triangular, vertical, etc) does affect the impedances of a feeder. If you wished, you could use different types of conductor data in DESS for each separate framing of a type of conductor. However, be aware that the change in line impedance is usually only 1-2%, and tracking overhead framing vastly increases the effort required to populate data and enter it into DESS or your GIS. Also be aware that the accuracy of your results will be much more dependent on obtaining accurate load data (e.g. 10-25% variation), so your initial efforts should probably be focused on getting accurate load data and creating accurate load profiles for different types of customers.