Power System Protection

What you'll learn

• Explain the purpose of power system protection, the qualities of dependability, security, selectivity and speed, and how overlapping zones, primary protection and backup protection are arranged.
• Calculate three-phase, line-to-line, line-to-ground and double-line-to-ground fault currents with symmetrical components, including fault resistance and the effect of delta-wye transformers, under maximum and minimum conditions.
• Specify and check current and voltage transformers for protection, including accuracy classes, burden, saturation from DC offset, CVT transients and loss of potential.
• Apply instantaneous and inverse-time overcurrent elements using the IEEE and IEC curve equations, and choose pickups, curves and time dials for phase and ground elements.
• Coordinate feeder relays, reclosers, sectionalizers and fuses on a distribution feeder, including fuse saving and fuse blowing, and evaluate the limits of each.
• Explain directional elements and their polarizing quantities, set a zero-sequence directional element, and assess ground fault sensitivity in the presence of fault resistance.
• Set stepped distance zones for a transmission line in primary and secondary ohms, including zero-sequence compensation, infeed effects and relay loadability checks.
• Compare POTT, DCB and line current differential schemes, their channels and their behavior when the channel fails, and calculate their clearing times.
• Set transformer differential protection with ratio compensation, percentage restraint and harmonic restraint, and specify sudden pressure, overexcitation and backup protection.
• Select and set generator protection functions, including loss of field, reverse power and negative-sequence protection, and protect induction motors against stalling and overload.
• Design high-impedance bus differential protection and breaker failure schemes, and apply automatic reclosing with appropriate dead times, synchronism checks and blocking.
• Assess the protection impacts of distributed energy resources under IEEE 1547-2018, calculate arc flash incident energy for NFPA 70E compliance, apply cybersecurity principles to protection systems, and assemble a substation protection study.