EECE 370 Midterm, Summer 2017

(()) DEPARTME ae RTA RY : Prof. R. Chedid gs July 7, 2017 Exam duration: 90 minutes — Closed Book _ Part A: Comment on the following st i/ The reluctance of a m | material ( ) atements by indicating: True (T) or False (F) agnetic circuit is proportional to the permeability of the magnetic 4 lis normally equal to 1 ( ae 1€ magnetic losses in the system ( y minimized by reducing the ac voltage Wy The relative permeability of hon-magnetic materia ul, The hysteresis loop provides information about tl iy. The intensity of eddy currents is practical] to the magnetic circuit ce ) vy. A magnetic field produces a force on the ) applied lally shows only excitation losses and not 2 R losses (_ ) a o—_—=—__—_sereeew~S>=S_L X1. 60-Hz transfi | Part B: Solve in details the following problems. OT > 1. A balanced 3-phas¢ 866-\V) line-to-line), 60- Hz-¥-connected source feeds a balanced A- connected load via 3+06-km long 3-wire transmission line. The impedance of each wire of the transmission line is 1+ j2 Q. The per-phase impedance of the A-load is 177-j246Q. Determine: aa se currents I,p and Ica at the load Ls AL | active power (real power) absorbed by the load e+ Sd 1 power dissipated in the line ; sarmer Vielded the following v\ : | tvwrn 9 De 7X a eon ne ~ —— aan Ue yr Pen circuit test 240 ) Hz single-phase tran when tested j * . oe | Voltage (V} i Current (A) || Be ) oOo we | amas (@¥ Calculate the parameters of the ang draw the circuit. 'Y) Calculate the voltage regulation at rated load —....... g)Kalculate the efficiency of the tr equivalent circuit referred to the ~\ low voltage Side— and unity power factor. ansformer at rated load and unity power factor. P oe Consider an ideal core (the permeability of the core is infinity). The dimensions are given in millimeters and the non-magnetic sleeve has CPseneebiiey Vie The core thickness is 20 mm. ; — el Calculate the flux density in the air gap shown below. (Ignore fringing) Dimensions inmm 7% Non-magnetic sleeve § | Ac 230 kVA, 2300/230 V, 60 Hz, step-down two winding transformer has an efficiency of When it operates at half load with unity power factor. If the transformer is now tO Operate as 230/2530 V autotransformer. Determine the efficiency at half load factor lagging. Mik 54 { 1 Od nv tthe result Dp Ower rating a ypmer has the followin The parameters of the equivalent circuit referred to the primary side (in Ohms) —— a —e aioe ie parameters ser unit Values of the transformer Th +tF ae The currents flowing in Rc and Xm in Amperes Good Luck