You should always understand how a relay element works before you test it. Relay instruction manual sizes are out of control and design engineers often don’t notice that the relay manufacturer has changed definitions or functionality between models or firmware revisions. You are the last line of defense, and you are the only person in a position to find these mistakes. But you won’t find them by reprogramming the relay. Let’s look at what we can do to truly understand how a relay applies it’s protective elements.
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I have tested relays and changed settings in the relay in order to get a relay to pass. The techs that taught me did so as well.
I really like the idea of not changing anything in the relay. The problem I normally have is asking myself “what do I need for this element to operate?”
Thanks for the comment.
The answer to “what do I need for this element to operate?” is almost always:
1. Apply Prefault Voltage for a few seconds
2. Create a realistic fault by:
a. lowering the fault voltage
b. raise the fault current
c. put the angle int he forward or reverse direction
Chris can you explain torque control more in depth?
The Torque control equation in SEL relays means “Can the element operate?” If the equation resolves to ON, TRUE, or 1; then the element can operate. If the logic resolves to OFF, FALSE, or 0; then the element can not operate. It allows the engineer to enable or disable an element based on pre-defined logic conditions.
The term torque control comes from electro-mechanical (E-M) relays like CO or IAC. The disc on these relays turn when torque is applied to them via a shading coil. No torque = no operation. Some E-M relays added torque control by putting a directional element’s output contact in series with the shading coil. If the directional contact closed, the shading coil could apply torque to the disc. If the contact was open, no torque could be applied to the shaft and it would never turn.
You can replace the phrase “torque control” with “element enabled”. If the logic is ON, then the element is enabled.