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Unformatted text preview: r111 EE740 Name _____________ __ pledge "N0 aid given,
received, or observed" Department of Electrical
Engineering The Ohio State University I 4W” Problem 1. A {3% phase distribution feeder has two loads : Load#1
is rated 133.4 kva with power factor of 0.0 leading. Load #2 is rated
100 kW with power factor of 0.6 lagging. Both loads are connected to
the same load bus. 1f the bad voltage is to be maintained at 4.4 kV( line value), compute the power factor at the load bus and the direction of active and reactive power )ﬂow I .
{15$ “ﬂiLa—faz'iaow mewwin P=9(o;e. ualaat’w " 3km”! Kw“
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giaiszlhbuwVa ‘33.!!! _‘?3?:‘ = ‘00 VW tit3‘ ") Problem '2. A balanced wye connected generator rated 460 volts (line Value) is supplying a balanced wye connected resistive load of
10 ohms through a balanced transmission line with 25 = 8 +j10, zab=zbc=zca=zm= )4 (ohms). If the generator is grounded and load is not grounded , draw the positive, negative and zero sequence F I 6 I .
networks. i; L 1 o “EL—ﬂ
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f 21:25.. 2...: east. \7) Problem 3 Same as problem 2, but both the generator and loads are
grounded. Compute the Symmetrical components of currents. £1; 5 "265811.? .._£é_5:.§if:‘i = I ~ “lo I
3 1. ‘gﬂb — "L154, HAIL J‘W 5"vv'uu'l' M I I .
.‘ Problem‘l. A three phase transformer rated 63 kV (wye connected
and grounded)/ 20 kV(de1ta connected) .100 WA and 10% short
circuit reactance supplied from a grounded power system with short
circuit capacity of 1000 MVA. Assume a balanced three phase fault
on 20 kV side while the 63 kV side is supplied from the power system at the rated voltage. Compute the short circuit capacity of 20
kV bus. \ooomﬁ‘r 63/20,”
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g‘c‘c Mr» = 9Xoo '1: 9m, x" /. / Problem 1. Consider the power system given below. Assume the
following cases: Case 1): two phases are short circuited at bus 2 and
then connected to ground. Case 2): one phase connected to ground at the mid secn'on of 20 ohm transmission line between bus 6 and bus
7. Case 3): three phases are short circuited at bus 5 and then
connected to ground. Determine whether the ground current will
now by indicating "yes" or "no" in the Table given below. Location Case] Case 2 Case 3
Ground reactance
of trans. T3 0 LV side Y¢$ Y“ N0 ________ —————In“.CInuuuniCHI.Chin—OQUCCCIQutttue Ground reactance of
of generator 61
Ground reactance
of motor M  —_...._—__—_*_"w~n¢—oco—a—oun—n“up—nu. Ground reactance
of generator 62  .— _._...  .. —      ——  _     . _ Ground reactance of
trans.T4 on HV side Problem (3. A three phase transformer rated 63 kV ( grounded wye)
f20 kV(de1ta ) ,100 WA and 10% short circuit reactance supplied
from a grounded power system with short circuit capacity of 1000
MVA. Assume a balanced three phase fault on 20 kV side while the
63 kV side is supplied from the power system at the rated voltage.
Compute the short circuit capacity of 20 kV bus. WONIan 5191 % 90098? 595th» gin... “M: I) CamvpszCus 17loch
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P, :. Io f u EE740 Name ............. __ pledge "No aid given, received, or observed" Department of Electrical Engineering
The Ohio State University Fall 2000 Problem}. A three phase transformer rated 138 kV ( grounded wye} £118 kV(grounded wye),100 MVA and 10% short circuit reactance supplied from a
grounded power system with short circuit capacity of 1000 MVA. The power system bus
voltage is 138 IN. The 13.8 kV side of transformer is fully loaded with a power factor of
0.0 lagging at rated voltage. Compute the fault current for a single line to ground fault at
13.8 kV bus for the following conditions: a) if the load is connected as a grounded wye . b) if the load is connected as an ungrounded wye . Assume that the impedance of
positive, negative and zero sequence networks are equal. CAUGFE bajg “cliff/185 qj .n___— LLH
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. L I =I a“: '7 'J'IWP” Compute the fault current for a single Ime to ground fault st 13.8 kV
following conditions: a) if the load is  J E.
{+1 {0)
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gang: “if 5* a“ M?)& w‘lll‘ PM
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supplying a threephase load consistin of three identical 100 Ohm reactors. Ea single transfcrrner . rated at 100 MVA .138 W“ 3.8 W has a leakage reactance of 12% .The loads
are connected in delta through a transmission line with .1+j.01 Ohm impedance.
Assume transformers are connected in wyeldelta. Perform the following:
Agmmpute the single  phase equivalent circuit . B Compute per unit uivalent circuit for a base of 100MVA and a voltage base of 13.8 V. A} for transformer annealed in Y/Q
V” : Ta Xlééi : zgq rev VL : KU a
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' lam ~ '7 S P” 1.0 w LI$NWﬁ VHV 3364+ Problem "1. A three phase transformer rated 63 kV ( grounded wye) £20 kV(delta ) .100 MVA and 10% short circuit reactance supplied from a grounded power system with short
circuit capacity of 1000 MVA. Assume a balanced three phase fault on 20 kV side while the 63 kV side is supplied from the power system at the rated voltage. Compute the short
circuit capacity of 20 kV bus. Have ‘0
f 5'C‘Cgpdk  Wv i+h=‘,!; 35‘”) Y1.
‘ U...
‘3‘?» smer a”
I95
0‘) 3.. x, Haw/Mm EE74O Name ............. _ pledge "N0 aid given,
received, or observed" Department of Electrical
Engineering The Ohio State University EE 740 —— Midterm Exam Problem 1. Consider a power system given below. The internal impedance of generators is: Zgl = j 0.10
Zg2  j 0.20 All values are in p.u.
1.) Compute YBUS model for power flow studies. 2.) Compute ZEUS model for short circuit studies. Problem 2. For Problun Lassume the following load and
generation schedules: Loads: s1 ' 0.5 + 5.0.5 p.u.132  0.2 — j0.5 p.u. Generators: Generator one is the Swing generator and
generator 2 scheduled power is P=0.5 p.u. Use GaussSeidel and compute Load Voltage at BUS 2. Assume V1  1.10 p.u. (Give your results for one iteration
only.) Problem 3. For Probleml; assume a three phase fault at BUS
2. Compute the fault current seen by circuit breaker A. lgawvr.+ht Loads. Mill EE740 Algorithm for calculations of balanced and unbalanced fault currents. Step 1: Build the positive
sequence Zbua matrix with
reference to ground. Step 2: Build the negative
sequence Z bus matrix. This is normally the same as the positive
sequence. Step 3: Build the
corresponding zero sequence
Z buﬂo) matrix. Step 4: For speciﬁed fault
types, connect the appropriate
network sequences and compute the voltage and current ﬂow at
the faulted bus. 4 Zbusu) 1: positive 2: negative zbus(2) 0: zero zbus(0) l calculate the fault
current based on a
given fault type print the results A. Keyhani A. Keyhani
EE740 Y ﬂ Fault
Phase A to ground D (bus) E (bus) Generator Generator () (0) JIILDlII a; u 1 :5 it I
W. Consider a as shown below: 1100(9) KVA = 133.34 load #3 Pf: 0,0 (leading) VR KVA = 100
100 KW
KVA = 100 load #7 _ . 108d #4 pf = 00
“ad #1 p.f = .6 (leading) 1” ' '6 (1mm) { (lagging) Compute the following: 1) The sauce voltage V3, if V}; is to be maintained at 4.4 V (VR=4.4 kV line
value). 2) The source current and power factor at the source.
3) The total complex power supplied by the source 4) How much reactive power should be connected to the source bus for
obtaining unity power factor at the source bus? ‘ v 
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I5 F" on". ~¢M. 0 Problem 4. For the power system given below: 1.} Assume V1 = 1 p.u. Commute V2 and V3 (Use Gauss
Seidel. First iteration only.) 2.) If after ten iterations of GaussSeidel V2  1.07 p.u.
and V3 : 0.91 p.u, Compute: 2.1) Power mismatch at busl, bus2, and bus3 2.2) Power loss of transmission systems. ...
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 Fall '07
 Keyhani
 Electrical Engineering, Short circuit, Power factor, at bus

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