This video shows you what resistive, inductive, and capacitive phasors look like so that you can start applying realistic faults into relays to guarantee they operate without changing settings.
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Introduction to Relay Testing
16 Topics
Isolate the Relay from the System
2 Topics
Connect the Test-Set to the Relay
3 Topics
Upload the Relay Settings
2 Topics
Perform an Acceptance Test
5 Topics
How to Test Protective Elements
17 Topics
Perform a Commissioning Test
9 Topics
Perform Maintenance Tests
5 Topics
Post Testing Tasks
4 Topics
Chris,
What happened to video S1-7-05 or at least your discussion on setting prefault conditions?
Hi Shaun,
This was the video on prefault. You can simulate prefault by applying a realistic three-phase balanced condition with a lagging current on all three phases between 10-30 degrees. However, that would mean that you will have to do some phasor and maybe some sequence component math when you’re calculating your trip values. This can cause problems when you solve for fault impedance in a test, for example, and the relay is actually using positive sequence impedance.
Most relay testers apply balanced three phase voltage to prime the relay and remove logic functions like LOP; but they leave the currents at zero so that don’t have to do any math, or know what formula to use because most equations balance out. For example;
A phase to ground fault with no prefault, I residual = A Phase current.
A phase to ground with some prefault current, I residual = Ia, Ib, Ic added vectorally
Hi,
what is the behavior of capacitive and inductive of a cable when a fault(3 ph, 1 ph-neutral & ph-ph, 2 ph-netral/grough) occurs on the line?
Thanks
Joshua
Capacitance is considered negligible (0) for conductors less than 50 miles long. For non-zero capacitance, any capacitance beyond the fault would be shorted out, so the apparent capacitance at the relay would appear to drop.
Inductance rises significantly because the magnetic fields of self-inductance and mutual inductance go up when the current rises during a fault. The resistance doesn’t change, so the X/R ratio gets larger, which means the current lags more during a fault.
We cover in this in much more detail in the upcoming Overcurrent Relay Testing Seminar.