EET-115 Lab 11 - GFCI & Arc Fault Protection

Q2 Figure Q2 shows a single line diagram of a power system and the associated data of this system are given in Table Q2. The pre-fault load current and A-Y transformer phase shift are neglected. (a) (b) If a Single Line-to-Ground (S-L-G) fault occurs at Bus 5 and the pre-fault voltage is 1.0 pu, calculate the subtransient fault current in Ampere. (c) (d) (e) Using base of 100 MVA and 11 kV at generator G₁, construct the positive sequence, negative sequence and zero sequence networks with their corresponding component values indicated. G₁ Recalculate (b) if the neutral on HV side of T3 is solidly grounded. Repeat part (b) with Line-to-line (L-L) fault. What will happen to L-L fault current in (d) if the neutral on the HV side of T3 is solidly grounded? Bus 1 T₁ Bus 4 Line 1 Line 2 Figure Q2 Bus 5 T2 T3 Bus 2 Bus 3 G₂ G3

Q2: A generator supplies motor through a star-delta transformer. The generator is connected to the star side of transformer. A fault occurs between the motor terminals and the transformer. The symmetrical components of the rubtransient current in motor and transformer toward the fault as table below laz(per unit) j2.0 lao(per unit) j3.0 las (per unit) Motof toward the fault Transformer toward the -0.8-j2.6 0.8-j0.4 j1.0 fault Assume X-X,- X2 for both the motor and gencrator. Describe the type of fault. Find (a) the prefault current, in line a, (b) the subtransient fault current in per unit and (c) the subtransient current in each phase of the gencrator in per unit. Gén. Motor

Describe the process of fault current analysis in power systems and its significance in protecting electrical equipment from damage.

Q2. The single-line diagram of a simple three-bus power system is shown in Figure-2. Each generator is represented by an emf behind the sub-transient reactance. All impedances are expressed in per unit on a common MVA base. All resistances and shunt capacitances are neglected. The generators are operating on no load at their rated voltage with their emfs in phase. A three-phase fault occurs at bus 3 through a fault impedance of Zf = j0.19 per unit. (i) Using Th'evenin's theorem, obtain the impedance to the point of fault and the fault current in (ii) Determine the bus voltages per unit. ) j0.05 j0.075 j0.75 2 j0.30 j0.45 Figure-2: Single line diagram of the power system network for Q2 3

Describe the concept of fault current analysis in power systems and its role in protecting electrical equipment.

Q3. i) Identify the type of the fault can happen for the situation below. "when a mechanical excavator cuts quickly through a whole 3 phase overhead line". Justify your answer. ii) Examine the assumptions and calculation steps for the identified fault analysis in Q3(i). iii) Illustrate applications of the fault analysis in the Q3(ii).

b) A fault occurs at bus 2 of the network shown in Figure Q3. Pre-fault nodal voltages throughout the network are of 1 p.u. and the impedance of the electric arc is neglected. Sequence impedance parameters of the generator, transmission lines, and transformer are given in Figure Q3, where X and Y are the last two digits of your student number. JX20 /0.1X p.u. jXa2) 0.1X p.u. JX20 j0.2Y p.u. V,= 120° p.u. V, 120° p.u. V, 120° p.u. jX4-70.2X p.u. jX2 j0.2X p.u. jX o 0.2Y p.u. jXncay J0.25 p.u. jXna J0.25 p.u. 3 jXno0.3 p.u. jXTu) /0.2Y p.u. jXra j0.2Y p.u. - j0.2Y p.u. Xp-10.1X p.u. jXa j0.1X p.u. jXp0)- j0.05 p.u. 0 Figure Q3. Circuit for problem 3b). For example, if your student number is c1700123, then: jXac1) = j0.22 p.u., jXac2) = j0.22 p.u., and jXaco) = j0.23 p. u. X-2 Y=8 (iv) Determine the short-circuit fault current for the case when a phase-to- phase fault occurs at bus 2.

ignore X and Y values

Metal-Clad switchgear fuses, what they are and types, and IEEE and IEC standards.

Problem #2: A transformer is fed from a 100 MVA, 18 kV generator via a 5-cycle breaker. Generator reactance are: X"F18%, X'=25%, Xe=120%. A three-phase fault occurs at the load side of the breaker when the transformer was unloaded. Find: A)The sustained short circuit current in the breaker. B) Initial symmetrical rms current in the breaker. C) Maximum de short circuit component in the breaker.