DS Quick Advantage Methods

The following methods are immediately available to a user who has the EasyPower DS tool, without any or with minimal addition of DS specific data (motor, generator, exciter, governor data, etc.). Thus, having the DS tool will supply a host of features for improving your system model, and gaining insight into your system model’s behavior without spending significant time on data addition.

3.9.1 Steady State Run Checks All Device Pickups, Proper CT Selection

In one actual instance, an EasyPower user decided to enter the DS Focus simply to see how a large case performed. That case was really meant only for an Arc Flash study. After entering and running a simple 5 second steady run (which is supposed to do nothing but plot a flat line), a host of protective devices tripped off, filling the message log. Further investigation showed that each device that tripped had an improperly specified CT. Thus, DS can be one additional validation check on your system model, without any DS specific data entered.

3.9.2 Symmetrical Fault Simulation Check on Protective Device Selectivity

You can use DS to do a quick check on simulated device selectivity. First, enter DS with your case. Next, go to DS Options and set the Double Click action for bus faults to keep the fault on

past the time of the simulation. If the simulation end time is 6 seconds, set the fault time to 7 seconds. Finally, fault the applicable bus. DS will simulate the fault and all protective device action to clear the fault. The Message Log will contain a detailed list of devices that operated and the times at which they operated.

3.9.3 Balanced Switching Fault Voltage Depression Check

You can use DS to do a quick voltage depression check on your system. First, enter DS with your case. Next, go to DS Options and set the Double Click action for bus faults to keep the fault on past the time of the simulation. If the simulation end time is 6 seconds, set the fault time to 7 seconds. Finally, fault the applicable bus. After the simulation is complete, pan about on the oneline to see the voltage conditions in your system. Note that the voltages shown are those that would exist on your system immediately after the fault was applied before any machines (motors or generators) respond to the fault.

3.9.4 Balanced Switching Fault Contactor Action Check

With a minimal amount of data additions, you can get a quick check on motor contactor action.

First, go to one contactor in your system, the stability tab, and enable the contactor with some default settings. You can use the ones already there, or set the dropout voltage and time as you think best represents your plant devices. Click on OK and exit the dialog. Now copy this contactor to all of the contactors you want to check, making all of them use the same default setting (use copy, and select all other contactors, and then paste). You may want to avoid saving this case if you had other specific information in each of the contactors. Next, enter DS, and go to DS Options. Set the Double Click action for bus faults to keep the fault on past the time of the simulation. If the simulation end time is 6 seconds, set the fault time to 7 seconds. Finally, fault the applicable bus. Your protective devices should clear that fault, and, if the clearing is delayed or too long, you should see contactors trip on motors that satisfied both the voltage and time setting of the contactor.

3.9.5 Fuse I

T Percentage to Blow to Predict Fuse Fatiguing

A feature unique to EasyPower’s DS tool is I²T percentage of blow in a fuse. To use this feature, have a system with a fuse or fuses properly specified in part of your system where other down-stream devices should clear the fault first. Next, go to DS Options and set the Double Click action for bus faults to keep the fault on past the time of the simulation. If the simulation end time is 6 seconds, set the fault time to 7 seconds. Finally, fault a bus on the load side of all the protective devices that will be seeing the fault current. After the simulation is complete, review the Message Log and find the message for the fuse in question. You will see a percentage of I²T that the fuse was exposed to during the fault. If the value is above 90%, you may have a condition where the fuse may fatigue from exposure to the fault current. This may cause false operation of the fuse later when exposed to later short circuit currents.

3.9.6 Check Relay Travel to Predict Device Racing

A feature unique to EasyPower’s DS tool is percentage of travel in a relay. To use this feature, have a system with a relay or relays properly specified in part of your system where other down-stream device should clear the fault first. Next, go to DS Options and set the Double Click action

for bus faults to keep the fault on past the time of the simulation. If the simulation end time is 6 seconds, set the fault time to 7 seconds. Finally, fault a bus on the load side of all the protective devices that will be seeing the fault current. After the simulation is complete, review the Message Log and find the message for the relay in question. You will see a percentage of disk travel that the relay was exposed to during the fault. If the value is above 90%, you may have a condition where devices are racing and competing to clear the fault. A system designed with conditions like this may make root cause determination more difficult, as the system may not have been truly selective.

3.9.7 Real-Time Simulated Arc Flash to Symmetrical Currents

A feature unique to EasyPower’s DS tool is simulation of real-time arc flash behavior. This has most of its real application after dynamics data has been supplied for motors and generators, but still supplies you with useful insight with no dynamics data at all. To use this feature, have a system with protective devices already specified, just as you would do for an Arc Flash study.

Next, go to DS Options and set the Double Click action for bus faults to keep the fault on past the time of the simulation. If the simulation end time is 6 seconds, set the fault time to 7 seconds.

Also, go to the Arc Flash tab, and check the box that says “Use Arc Flash Simulation for Faults”.

Finally, fault a bus at the location you desire to check. After the simulation is complete, review the Message Log and find the list of messages at the end of the simulation that supply detail on the arc flash results. These results will include arc flash energies and PPE for a simulation that included real-time tripping behavior of any number of devices in your system. The Message Log also shows you which devices tripped, and the times they tripped.

3.9.8 Balanced Switching Analysis for Switching of Any Device

If you desire to see the voltage and flow conditions in your system that occur immediately after a switching even, you can by following this method. First, enter DS. Next, double click on the breaker or switch that will create the change in the system. After the simulation is complete, review the oneline to see how voltage and flows have changed in the system. These conditions are also called To+ conditions, as they represent the system network condition immediately (+) after the switching event at time To (time T-zero) before any dynamic behavior of machines have manifested.

3.9.9 Run Power Flow with Motors Showing Correct PQ Loading

When a motor is partially loaded in real life, the kw loading drops while the var loading can remain fairly constant. Thus, there is a reduction in power factor as mechanical loading decreases. The Power Flow focus however does not do this, and simply scales watts and vars down by the Power Flow scaling factor. To see how the actual motor responds to reduced mechanical load, first add some generic data to your motor in the DS tab in the motor data dialog. As best as you are able, try to match the data in the library with your actual motor HP etc.

Next, scale down the motor in the Power Flow tab. This is done using the Power Flow Tab Scaling Factor. This will in essence only scale the mechanical loading of the motor down as the pre-event power flow is solved upon entering DS Focus. Next, enter DS and simply look at the results on the one line.