LADWP Electric Station Operator
Study Guide Comprehensive Exam
Questions with Correct Answers and
Rationales Latest Update 2026 |
LADWP Electric Station Operator Study Guide Comprehensive |
Comprehensive Examination
LADWP Electric Station Operator Study Guide
Comprehensive Exam Questions with Correct Answers and
Rationales Latest Update 2026 actual exam preparation
INTRODUCTION
This document is an important and very helpful preparation
resource for LADWP Electric Station Operator Study Guide
Comprehensive Exam Questions with Correct Answers and
Rationales Latest Update 2026. Every item uses a focused exam
stem, four response options, a keyed response, and a clear
rationale, making it easier to understand the subject, spot
distractors, and build real exam confidence.
Page 1
, Question 1
A 230 kV bus differential relay (87B) operates for a fault on the bus. Which of
the following best explains why the relay must be high-impedance or
percent-differential with harmonic restraint?
A. To prevent maloperation due to CT saturation during through-faults
and to avoid tripping on magnetizing inrush current.
B. To ensure fast operation for internal faults while remaining stable for
external faults and inrush.
C. To provide backup protection for the bus and adjacent lines.
D. To coordinate with the transformer differential relay and avoid
nuisance tripping.
Correct Answer: B - To ensure fast operation for internal faults
while remaining stable for external faults and inrush.
RATIONALE
Bus differential protection must be both dependable for internal faults
and secure against external faults and inrush. Harmonic restraint
blocks during transformer energization, while percent-differential or
high-impedance settings prevent misoperation from CT saturation.
Option A is partially correct but incomplete; B captures the dual
requirement. C and D describe backup and coordination, not the
primary reason for the specific relay design.
Question 2
During a switching sequence to isolate a 115 kV circuit breaker for
maintenance, the operator must apply grounds. Which of the following
correctly describes the sequence according to LADWP safe switching
procedures?
A. Open breaker, open both disconnects, test for absence of voltage,
apply grounds on the line side of the breaker.
B. Open breaker, open both disconnects, test for absence of voltage, apply
grounds on the bus side of the breaker.
Page 2
, C. Open breaker, open both disconnects, apply grounds on both sides of
the breaker without voltage test.
D. Open breaker, open both disconnects, test for absence of voltage,
apply grounds on the breaker terminals.
Correct Answer: A - Open breaker, open both disconnects, test
for absence of voltage, apply grounds on the line side of the
breaker.
RATIONALE
Proper grounding requires testing for absence of voltage after opening
disconnects, then applying grounds on the side where work will be
performed. For breaker maintenance, grounds are typically applied on
the line side to protect against backfeed. Option B places grounds on
the bus side, which may not protect the work area; C omits the voltage
test; D may not provide adequate protection if the breaker is the
isolation point.
Question 3
A transformer is rated 100 MVA, 230/115 kV, with 10% impedance. A
three-phase fault occurs on the 115 kV bus. Assuming infinite bus on the 230
kV side, what is the approximate fault current on the 115 kV side?
A. 2,510 A
B. 5,020 A
C. 10,040 A
D. 1,255 A
Correct Answer: B - 5,020 A
RATIONALE
Base current on 115 kV side = 100 MVA / (3 × 115 kV) 502 A. Fault
current = base current / per-unit impedance = .10 5,020 A.
Options A, C, and D are off by factors of 2, 2, and 0.25 respectively,
likely from misapplication of 3 or MVA base.
Page 3
, Question 4
In a SCADA system, an operator receives a 'Transformer Sudden Pressure'
alarm. Which of the following actions is most appropriate?
A. Immediately trip the transformer manually and investigate.
B. Verify the alarm, check for concurrent alarms (e.g., differential,
overcurrent), and dispatch field personnel to inspect.
C. Acknowledge the alarm and continue monitoring; sudden pressure
alarms are often nuisance.
D. Reduce transformer load to 50% and wait for further indications.
Correct Answer: B - Verify the alarm, check for concurrent
alarms (e.g., differential, overcurrent), and dispatch field
personnel to inspect.
RATIONALE
A sudden pressure alarm may indicate an internal fault. The operator
should verify the alarm, look for corroborating indications (e.g.,
differential relay, oil level, temperature), and dispatch personnel.
Immediate manual trip (A) may be unnecessary if it's a false alarm,
but ignoring (C) is dangerous. Reducing load (D) without
investigation is not standard.
Question 5
Which of the following best describes the purpose of a lockout relay (86
device) in a substation protection scheme?
A. To provide time delay for overcurrent coordination.
B. To automatically reclose the breaker after a transient fault.
C. To trip and lock out the breaker, requiring manual reset after a
protective relay operation.
D. To monitor and display fault current magnitude.
Correct Answer: C - To trip and lock out the breaker, requiring
manual reset after a protective relay operation.
Page 4
Study Guide Comprehensive Exam
Questions with Correct Answers and
Rationales Latest Update 2026 |
LADWP Electric Station Operator Study Guide Comprehensive |
Comprehensive Examination
LADWP Electric Station Operator Study Guide
Comprehensive Exam Questions with Correct Answers and
Rationales Latest Update 2026 actual exam preparation
INTRODUCTION
This document is an important and very helpful preparation
resource for LADWP Electric Station Operator Study Guide
Comprehensive Exam Questions with Correct Answers and
Rationales Latest Update 2026. Every item uses a focused exam
stem, four response options, a keyed response, and a clear
rationale, making it easier to understand the subject, spot
distractors, and build real exam confidence.
Page 1
, Question 1
A 230 kV bus differential relay (87B) operates for a fault on the bus. Which of
the following best explains why the relay must be high-impedance or
percent-differential with harmonic restraint?
A. To prevent maloperation due to CT saturation during through-faults
and to avoid tripping on magnetizing inrush current.
B. To ensure fast operation for internal faults while remaining stable for
external faults and inrush.
C. To provide backup protection for the bus and adjacent lines.
D. To coordinate with the transformer differential relay and avoid
nuisance tripping.
Correct Answer: B - To ensure fast operation for internal faults
while remaining stable for external faults and inrush.
RATIONALE
Bus differential protection must be both dependable for internal faults
and secure against external faults and inrush. Harmonic restraint
blocks during transformer energization, while percent-differential or
high-impedance settings prevent misoperation from CT saturation.
Option A is partially correct but incomplete; B captures the dual
requirement. C and D describe backup and coordination, not the
primary reason for the specific relay design.
Question 2
During a switching sequence to isolate a 115 kV circuit breaker for
maintenance, the operator must apply grounds. Which of the following
correctly describes the sequence according to LADWP safe switching
procedures?
A. Open breaker, open both disconnects, test for absence of voltage,
apply grounds on the line side of the breaker.
B. Open breaker, open both disconnects, test for absence of voltage, apply
grounds on the bus side of the breaker.
Page 2
, C. Open breaker, open both disconnects, apply grounds on both sides of
the breaker without voltage test.
D. Open breaker, open both disconnects, test for absence of voltage,
apply grounds on the breaker terminals.
Correct Answer: A - Open breaker, open both disconnects, test
for absence of voltage, apply grounds on the line side of the
breaker.
RATIONALE
Proper grounding requires testing for absence of voltage after opening
disconnects, then applying grounds on the side where work will be
performed. For breaker maintenance, grounds are typically applied on
the line side to protect against backfeed. Option B places grounds on
the bus side, which may not protect the work area; C omits the voltage
test; D may not provide adequate protection if the breaker is the
isolation point.
Question 3
A transformer is rated 100 MVA, 230/115 kV, with 10% impedance. A
three-phase fault occurs on the 115 kV bus. Assuming infinite bus on the 230
kV side, what is the approximate fault current on the 115 kV side?
A. 2,510 A
B. 5,020 A
C. 10,040 A
D. 1,255 A
Correct Answer: B - 5,020 A
RATIONALE
Base current on 115 kV side = 100 MVA / (3 × 115 kV) 502 A. Fault
current = base current / per-unit impedance = .10 5,020 A.
Options A, C, and D are off by factors of 2, 2, and 0.25 respectively,
likely from misapplication of 3 or MVA base.
Page 3
, Question 4
In a SCADA system, an operator receives a 'Transformer Sudden Pressure'
alarm. Which of the following actions is most appropriate?
A. Immediately trip the transformer manually and investigate.
B. Verify the alarm, check for concurrent alarms (e.g., differential,
overcurrent), and dispatch field personnel to inspect.
C. Acknowledge the alarm and continue monitoring; sudden pressure
alarms are often nuisance.
D. Reduce transformer load to 50% and wait for further indications.
Correct Answer: B - Verify the alarm, check for concurrent
alarms (e.g., differential, overcurrent), and dispatch field
personnel to inspect.
RATIONALE
A sudden pressure alarm may indicate an internal fault. The operator
should verify the alarm, look for corroborating indications (e.g.,
differential relay, oil level, temperature), and dispatch personnel.
Immediate manual trip (A) may be unnecessary if it's a false alarm,
but ignoring (C) is dangerous. Reducing load (D) without
investigation is not standard.
Question 5
Which of the following best describes the purpose of a lockout relay (86
device) in a substation protection scheme?
A. To provide time delay for overcurrent coordination.
B. To automatically reclose the breaker after a transient fault.
C. To trip and lock out the breaker, requiring manual reset after a
protective relay operation.
D. To monitor and display fault current magnitude.
Correct Answer: C - To trip and lock out the breaker, requiring
manual reset after a protective relay operation.
Page 4
