EPRI Chapter Test Questions with Verified Solutions

EPRI Chapter Test Questions with Verified Solutions If a generator is producing 500MW and 200Mvar, the generator is: Lagging 87 Is the IEEE device number for a differential relay. Can a Synchronous machine have a negative torque angle? What doies this mean? Yes, the machine is absorbing active power. A customer load is fed at 12o Volts. The customer's voltage is doubled while the load magnitude stays the same. What effect does this have on the power losses? Decreases the losses by a factor of 4. In a DC circuit, a 100V battery is connected to both sides of a 2 ohm resistor. What is the current through the resister and the power usage of the resister? 50A/5000W Which of the following is not a synchronizong variable? MW flow differential. In a typical multi-stage steam turbine, the governor control valves control steam entry into the: High pressure turbine The high side of a delta-wye connected transformer is connected to a power system with 199KV L-G high side voltage. What is the voltage across the winding of the delta transformer? 345KV Thermal limits are the direct result of? The thermal capability of system equipment. Reactive power flow is influenced more by system power and torque angles than reactive power. True or False False At what line power angle does the MW transfer across a transmission path equal 1/2 of the path's Pmax? 30 degrees A transmission line is rated at 1000MVA. The power flow on the line is 0MW and 1001Mvar. Is the transmission line overloaded? Yes The TTC limit has been determined to be 1000MW from east to west for a particular transmission path. The transmission path operator sells 500MW of its TTC. What is the path's ATC? 500MW A distribution line is rated for 50MVA. The line's power flow is currently 50MW and -50Mvar. The line is overloaded. True or Flase True Angle instability is the result of: High torque and power angles. If the resistance is ignored, the maximum theoretical MW flow across a transmission line will occur at a power angle of: 90 degrees. If the resistance is ignored, the maximum theoretical Mvar flow across a line will occur at a power angle of: 180 degrees 200MW is schediuled to flow from bus X to bus Y. Transmission line A-B has a distribution factor of 10% for this schedule. How many MW will flow on transmission line A-B? 20MW According to the load/frequency relationship, a 1% change in frequency will lead to what approximate magnitude of load change in a typical 10000MW system? 200MW A governor with a 0% droop is called: An isochronous governor Steam turbine generators typically have better governor response than hydroelectric generating units. True or False False A balancing authority's frequency bias is equal to: The balancing authority's frequency response characteristic (FRC), the natural response of the BA, The AGC system's bias value. All of the following are modes of AGC except: flat tie-line control, isochronous control, flat-frequency control, tie-line bias control Isochronous control In which stage of a generators response to a system disturbance is the power flow supported primarily by the generators excitation field Electromagnetic energy state. If system frequency were to run at 60.02Hz for two consecutive hours, how much positive time error would occur? 2.4s A Balance authority has a bias of -150MW. Frequency falls 0.05Hz due to an external disturbance. How many MW would you expect this BA to provide to the disturbance? +75MW An isochronous governor has a droop setting of: 0% What element of the power system is typically most susceptible to damage frolm prolonged operation at frequencies above or below 60Hz? Low pressure turbine stage blades. Hydro electric generators typically exhibit better governor response than thermal generators because: Hydro-electric generators typically have more stored energy. A generator with a 6% droop governor is connected to a 60HZ power system. Initially, the generator is 100% load. Frequency then falls 0.9HZ. What is the generator's new % output? 100% What magnitude of frequency change would cause a 10% droop governor to move its generator from zero to full output in a 60Hz system? 6HZ Which component of the CPS is intended to limit the magnitude of unscheduled power flows? CPS2 What is the upper limit to the CPS1 Magnitude? No limit What is the Mvar production of a 50Mvar shunt capacitor that is energized at 90% of it'snominal voltage? 40.5Mvar A 5% change in voltage will typically lead to what change in the total load magnitude? 3% A tranformer can be over-excited it exposed to which of the following? High voltage, Low frequency, high voltage and low frequency, or all of the above All of the Above What is the approximate Mvar/mile production for a 345KV overhead line? 3/4 A 345KV transmission line operates at various voltage levels throughout the day. At which voltage level does the transmission line produce more Mvar? 345KV, 340KV, 350KV, 360KV 360KV. Mvar production is a function of voltage. A transmission line has 50 ohms of inductive reactance. 25 ohms of series capacitors are inserted in the line. What is the line's % compensation? 50% The MW loading at which the Mvar from the line's natural capacitance is equal to the Mvar that the line needs to support its voltage. Surge Impoedance Loading (SIL) What is the approximate Mvar/mile production for a 500KV overhead line? 2.0 Given a purely inductive load, what can be said about the MVA this load draws from the power system? The load draws only Mvars A generator with spare Mvar is Always a source of dynamic reactive reserve. True or False False The nominal load is: Equal to the rated load A period of voltage instability always results in a voltage collapse. True or False False The critical voltage and critical MW transfer are located at the: knee of the P-V curve During voltage instability prone conditions, tap changing to support secondary voltage should generally NOT be used if the secondary load is formed by Non-motor load PV curves indicate the ____ margin from voltage instability MW VQ curves indicate the ____margin from voltage instability Mvar UVLS differs from UFLS in that: UVLS is based on voltage whereas UFLS is based on frequency In which type of voltage instability does a key element trigger the voltage instability? Classical Voltage Instability A P-V curve relates: The MW transferred across a system to the voltage at the receivning end of the system. In a radial power system, the addition of shunt capacitors at the receiving end of the system tends to: Flatten the P-V curve and increase the critical voltage. In which type of voltage instability does a simultaneous stalling of large amounts of induction motor load trigger the voltage instability? Transient voltage instability. If a 2 pole generators rotor is spinning at 3601 RPM while the generator is connected to a 60HZ system, how fast is the generator's torque angle changing? 6 degrees/second Neglecting losses, the difference between a generator's mechanical power input and electrical power output is called: Accelerating power According to the equal area criterion for transient stability: The decelerating area must at least match the accelerating area A generator is angle unstable whenever its torque angle exceeds 90 degrees. True or False False High speed transmission protection is a benefit to angle stability because of which of the following: fault duration is reduced, accelerating time is reduced, angle spread is reduced or all of the above. All of the Above The primary difference between an out of step event and a fault is: The speed at which the apparent impedance changes.