Pandiani said...
"For example: "directional overcurrent relay an overcurrent relay that operates only for overcurrents flowing in the tripping direction." What is tripping direction?"
Envision a motor that uses an electro-mechanical phase-reversing mechanism to change direction of a motor. Each direction is "driven" by a magnetic-relay. Each magnetic-relay has a set of overloads.
At any time, you might experience the Overloads in the "Forward" Magnetic-Relay, or the Overloads in the "Reverse" Magnetic-Relay, "tripping" out. In that case, the "tripping direction" is indicated on the particular Magnetic-Relay.
In some cases, the relays are designed to pass both the Forward current and the Reverse current through the same set of Overloads. In this design, if a "trip" occurs, it will have been because the motor came to an overload condition while running, or trying to run, in one direction, or the other. In this case, the "tripped" indication does not reveal the "tripping direction".
Alternatively...
...although I haven't experienced this in many years... (not since hardwired/tube TV/Radio days... jeez... I remember Howdy-Doody!)
A DC-Circuit where a particular branch might experience DC-Current passing in one direction or the other; each at different times.
In this case, the configuration of that branch is a Diode and a Circuit-Breaker in series, in parallel with another Diode and a Circuit-Breaker, in series, oriented in the opposite polarity.
If the DC-Current in either direction goes over-current, then the associated circuit-breaker trips and prevents current flow in the particular direction.
"Also I found on one circuit braker position label "tripping"."
If you are talking about "tripping current", then that is the nominal current at which the circuit-breaker will trip.
If you are talking about "tripping position", then the indicated position is almost at, but not quite at, the OFF or OPEN position... it is sorta in the mid-position, but slightly towards the OPEN position. When in that position, the circuit-breaker is "tripped".
"Alos term tripping is found when there is talk about torque, so whta does "tripping torque" mean?"
For any given motor, when it runs up against a load, it tries to maintain the nominal, or set, speed. As the load increases, the motor responds by developing more torque... which results from the application of more current as the motor tries to stay at synchronous speed. As the motor falls farther behind in synchronous speed, the current increases.
Eventually, the load overcomes the motor's ability to stay with synchronous speed. At some point, the current exceeds the trip-point of the overloads, or the current-sensor, whatever that might be.
There is really not much difference between a normal overload condition and a "tripping torque" condition. It's simply a matter of "point-of-view".
That is, in a failing motor (internal shorts caused by whatever) current will tend to increase because of the reduction in Counter-EMF. This will eventually lead to an over-current condition.
In a heavily loaded motor situation, eventually the current will increase because the motor is trying to stay at synchronous speed.
In either case... the overloads trip, and the motor shuts down.
"Tripping Torque" refers to the "over"-loading that might occur on a motor. If a motor is trying to draw more current, just for the sake of developing more torque, just for the sake of keeping up with synchronous speed, then, eventually, the current level will exceed the overloads and the overloads will "trip".
I think that covers 'em all.
What say you, Pandiani?
