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1.
What is the zero sequence impedance for Yyn 4-leg two-winding transformer?
Z
=
¥
0
zero sequence – składowa zerowa
two-winding – dwu uzwojeniowy
2.
Does the zero sequence current flow in ZYy transformer when s-c occurs on the
primary side?
YES
s-c short circuit – zwarcie
3.
Draw the equivalent circuit diagram of YNd transformer for zero sequence.
Assuming that earthing impedance is equal 0.
4.
Draw the vector diagram of voltages and currents at fault location for single-phase
fault at phase S in isolated network.
5.
In which case the transformer impedance for zero sequence is higher?
4-leg core (rdzeŃ 4-kolumnowy)
(3-leg core)
6.
How does a return wire influence sequence of cable lines?
Influence - wpływ
Z
1
– no influence
Z
2
– no influence
Z
0
- decrease
7.
Assuming single-phase s-c at busbar B in the system presented below, mark in
tab, zero sequence current flows through indicated points of the network. UE1
and UE2 have their neutrals effectively grounded.
Indicated - wskazany
8.
Classy for phase-connection occurs at the same moment.
Occurs – występuje
Simultaneous - jednoczesny
Simultaneous
9.
Frequency of s-c current occurrence depends on:
Occurrence - wystepowanie
Type of line
10.
PodpisaĆ na ryzunku i
nok
i i
ok
.
2
1,5
I
ONK
1
0,5
0
-0,5
I
OK
-1
-1,5
11.
In what conditions aperiodic components appear In voltage time course?
Aperiodic –nieokresowy
R
a
/L
a
=1
R
a
/L
a
=R
b
/L
b
R
a
/ L
a
=L
b
/ R
b
12.
How does the generator G in fig. view a single-phase s-c behind the transformer
T1 Ynd connected?
Single-phase s-c
line –to-line s-c 3-phase s-c
13.
From the given below effects of s-c currents in effectively grounded networks the
most important is:
Dynamic effect
overvoltage’s electric shock threat
(przepięcia)
(zagrożenie porażeniem)
14.
From the given below causes of s-c in overhead lines the most typical is:
Lighting strokes
current overloading contamination of line insulation
(udeżenia piorunów)
(przeciążenie prądem)
(zanieczyszczenie izolacji)
15.
Frequency of s-c current occurrence in a given network depends on:
Nominal voltage of the network
neutral grounding network configuration
16.
A 2-phases with ground s-c, in which phase connection occure at the same
moment, is classified as:
durable
simultaneous
(trwały)
(jednoczesny)
17.
Does a fault location influence the value of fault current in isolated network?
Fault current – prąd zwarcia
18.
Select most characteristic advantages of isolated network operation during earth
fault:
a)
low value of fault current
b)
high value of fault current
c)
low constant value I
0
d)
high values of overvoltage’s
19.
During single-phase+earth fault in isolated network phase currents in non-
faulted phases:
a)
have constant value I0
b)
increase along the line from 0 at the end to I
0
at the beginning
c)
increase along the line from 0 at the end to 3I
0
at the beginning
20.
Assuming an earth-fault at the middle of line, what is the value of POSITIVE
SEQUENCE current at the end point of the line:
a) I
0
b) 3I
0
c) 0
21.
Assuming an earth-fault at the middle of the line, what is the value of EARTH-
FAULT current at the end point of the line:
a) I
0
b) 3I
0
c) 0
22.
The voltage displacement between neutral and earth during single-phase+earth
fault in isolated network is equal to:
Displacement – przemieszczenie
a) E
1
b)
2
E
1
c)
3
E
1
23.
What is the reason for resonance earthing:
a)
reduce fault current at s-c location
b)
reduce overvoltages in non-faulted phases
c)
reduce fault duration
24.
Will residual current appear when adjusting the Petersen Coil to resonance with
phase-to-earth capacitance of the network?
Residual – pozostały, szczątkowy
Capacitance - pojemność
a) yes
b) no
25.
The state of resonance occurs in compensated network if the following condition
is fulfilled:
Fulfilled – spełniony, zrealizowany
1
1
1
a)
W
L
U
−
=
0
b)
3
W
L
U
−
=
0
c)
W
L
U
−
=
0
W
C
W
C
3
W
C
( )
( )
( )
0
0
0
26.
What will be the result of line disconnection in overcompensated network:
Overcompensated – przekompensowana
a) higher overcompensation state
b) transition to undercompensation state
27.
What are phase voltages in LV network when single-phase to earth fault occurs
in the supplying network of 15kV operating with isolated neutral:
a) increase to
3
b) increase to
2
c) remain unchanged
28.
Earthing with current limitation is applied to:
Limitation – ograniczenie
a) decrease fault current
b) decrease overvoltage’s
c) decrease fault duration
(czas trwania zwarcia)
29.
What type of neutral handling is applied in LV networks?
Handling - obsługa
a) low-impedance earthing neaural b) earthing with current limitation
c) direct earthed
30.
Criterion for the selection of earthing impedance value in HV network is:
a) proper operation of protection against electric shock
b) phase voltage values during s-c
c) reducing 3-phase s-c current
31.
Resistance earthing (AWSC) is applied in compensated network in order to:
a) decrease fault current b) decrease overvoltage’s
c) decrease fault duration
(czas trwania zwarcia)
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