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The main learning objectives associated with these slides are to: Introduce and explain the simplified formulas in IEC 61508, part 6 for calculating the average probability of failure on demand (PFDavg) Introduce and discuss some of the related concepts and assumptions.
10 Αυγ 2020 · The most common cause of unbalance for three-phase motors is the loss of phase resulting from an open fuse, circuit breaker, connector, or damaged conductor. Unbalances in other connected loads can also affect the motor. A voltage unbalance of 3.5% can produce a 25% or greater increase in motor temperature. This results primarily from negative ...
18 Νοε 2019 · Solidly Grounded Systems. Ground fault currents in solidly grounded systems can approach phase fault levels. Ground fault protection for these systems is usually provided by residual protection, either calculated by relay or by external CT residual connection to IN input.
This white paper will go inside the motor and provide a more detailed look into what happens when one phase of the power supply is lost and how Sprecher + Schuh overload relays handle the phase failure. Most of the motors that we encounter are delta-connected squirrel cage induction motors.
This let-ter addresses three definitions of voltage unbalance from three different communities and provides a numerical example and analysis to com-pare them. These definitions have important implications when study-ing for example, the effects of voltage unbalance on the performance of three-phase induction machines.
Magnitude of the asymmetry (transient component) depends on the phase of the generator voltage at the time of the fault. In this class, we will use the steady-state current component, , as our primary fault current metric. The reactance of the generator was assumed constant in the previous example.
Cross polarization: (protective relaying) The polarization of a relay for directionality using some proportion of the voltage from a healthy (unfaulted) phase(s). One example of this is quadrature polarization. In this case, the polarizing voltage is in quadrature to the faulted phase voltage.
