Video Summary - 전기기사 실기 단답 귀에 때려박히는 기적의 영상

Main ideas & lessons (structured by topics)

1) Studying strategy for exam short-answer questions (Day 1 intro)

The video compiles all short-answer questions that appeared on the Electrical Engineer practical (실기) exam, roughly from 2001 to 2024.
It’s organized by question type (about 400 questions total).
Suggested study approach:
- Listen to explanations like “radio” while commuting, before sleep, showering, reading, etc.
- Emphasize repetition as the key to memorization.
- Use the textbook PDF linked in the pinned comment.

Electricity & Overhead/Underground Line Fundamentals (core exam content)

2) Overhead line insulation / overvoltage control (Q1-type section)

Main concept: identify causes of overvoltage and how to prevent it.

The text is partly garbled, but the lesson is clearly about overvoltage prevention mechanisms.
A “three-way prevention” is mentioned; the three elements appear related to grounding and system configuration.
Earthing/grounding concepts:
- Overhead ground wire / lightning ground wire role: provides shielding and helps prevent lightning impact from reaching the system.
- Grounding resistance should be small so fault current can drain effectively.
- If resistance is high, add additional buried branch earth wires to reduce overall grounding resistance.

3) Overhead line sag degrees & risks (Q2 section)

Sag degree is used to assess risk.
The video lists multiple sag-related “degrees,” emphasizing that too much or too little sag creates different hazards:
- Sag too large → vibration/contact risk with other overhead wires or during crossings (communication/road/rail).
- Sag too small → increased mechanical tension/energy → wire break risk.

4) Dampers on ACSR conductors (Q3)

Dampers (especially for ACSR) are used to:
- add mass/weight to absorb vibration energy
- reduce oscillation caused by wind or impacts

5) Heavy ice/snow regions and corona design (Q4)

In icy regions, ice forms through melting and refreezing cycles.
Design assumptions mentioned:
- ice thickness about 6 mm
- ice specific gravity around 0.9
Compare ice types: light, low-density snow vs heavy ice.

6) Underground power line installation methods (Q5–Q7)

Three installation methods:

Direct burial
Pipe (duct) method
Culvert / underground tunnel (culvert-type)

Burial depth rule (intent):

Burial depth depends on the method and whether vehicle/pressure risk exists.
The video distinguishes cases where burial depth is 0.6 m vs 1 m, depending on method and pressure condition.
Underground cables are used (contrasted with bare/insulated overhead conductors).

7) Cable types & moisture-blocking (Q8)

Underground cables use key materials/types:
- lead-coated cable type
- aluminum-coated cable type
Both are described as effective at blocking moisture.

8) Underground vs overhead power line advantages/disadvantages (Q9)

Advantages:

Less exposure to weather (typhoons/rain) → reduced maintenance burden
Aesthetic improvements (less “suspended in air”)
Easier multi-line installation

Disadvantages:

Lower transmission capacity due to different heat dissipation (underground cooling is worse than overhead air exposure)
Higher construction cost and longer construction period (tunnels/ducts, excavation)
Fault detection and maintenance can be harder

9) Power conduits & cable fire prevention (Q10)

In conduits/tunnels, implement fire prevention:
- wrap cables with flame-retardant tape
- apply flame-retardant paint (described as “magic power” in the text)

Short-circuit / voltage regulation / busbar systems

10) Reducing system short-circuit capacity (Q11)

Methods list:

Increase impedance → reduces short-circuit current
Use a reactor (H-shaped reactor mentioned)
Split the system into zones → reduces accident scale and short-circuit current

11) Voltage boosting and loss scaling (Q12)

When voltage is boosted from V to 2V, the video explains how:
- voltage drop and losses scale inversely with voltage (statements resembling 1/V and 1/V² relationships)
Takeaway: increasing voltage reduces voltage drop/loss rates.

12) Transformer substation busbar types & meaning of “ideal infinite bus” (Q13–Q16)

Busbar types (3 methods):

Single busbar
Double busbar (ring “Hwan” concept mentioned)
“Fantasy mothership / mother bus” naming used as a diagram memory aid

“Infinite bus” concept:

Treated as:
- voltage magnitude and phase remain constant regardless of load change
- “inertia constant” is described as the stability-maintaining property
- implies infinite capacity

Double busbar advantages (Q15):

One busbar can be inspected/maintained while the other supplies power (service continuity)

Busbar switching circuit breaker purpose (Q16):

Allows inspection/operation without interrupting power by switching between busbars

Conductor configuration, corona, and flicker

13) Multi-conductor method vs single-conductor (Q17)

Four advantages (listed):

Increased transmission capacity (skin/“epidermal” effect reasoning)
Reduced losses (effective radius change)
Reduced inductance → improved stability
Other electromagnetic benefits mentioned (including reactance behavior)

Three disadvantages (mentioned):

Higher installation cost
Multiple wires interact/twist
Spacing/interactions introduce additional mechanical/electromagnetic constraints

14) Corona phenomenon & partial air breakdown (Q18)

Corona occurs when voltage exceeds air breakdown level near conductors/insulators.
Air near the conductor acts as an insulator until high voltage causes partial breakdown:
- produces crackling arcs/sparks
- generates ozone and electrical noise

15) Corona effects (Q19) and prevention (Q20)

Four corona impact points (essence):

current leakage into air → power loss
ozone accelerates wire corrosion
induction/disorder on communication lines
audible noise from discharge

Two prevention measures (Q20):

increase conductor radius (use thicker conductor)
use multi-conductor systems

16) Corona critical voltage formula factors (Q21–Q22)

Critical corona voltage depends on:

wire radius/diameter (thickness)
equivalent electrical distance
air density (relative air density)
temperature and weather coefficients

Key relationships described:

larger diameter → higher critical voltage
larger equivalent distance → higher critical voltage
higher altitude → lower atmospheric pressure → lower critical voltage
higher temperature → lower air density → lower critical voltage

17) Distribution line voltage adjustment methods (Q23)

Three methods:

Automatic voltage regulator (SVR)
Voltage boosting transformer
Power capacitor (reactive power compensation effect)

18) Network power supply method (Q24)

Four advantages:

parallel operation of multiple transformers keeps supply uninterrupted
improved reliability
low voltage fluctuation rate
good adaptability to load increases

19) Flicker/blinking and countermeasures (Q25–Q26)

Flicker basics:

occurs when supply voltage fluctuates significantly (often due to voltage drops and sudden load changes)

Supply-side countermeasures (3):

raise voltage automatically when it dips (SVR/boosting case)
use systems with large short-circuit capacity (more stable voltage)
use dedicated transformer for sensitive loads

Receiver-side/compensation concepts (3):

compensate the reactor component using capacitors
compensate transformer-related voltage boost components (offset boosting issues)
absorb load power fluctuations via appropriate reactive power compensation

Power factor correction (capacitors) & harmonics

20) Power factor improvement principle (Q27)

Loads often draw inductive reactive current.
Install capacitors in parallel to generate leading reactive current that cancels inductive reactive current.
Result:
- reduced line current
- improved power factor
- reduced losses

21) Impact of worse power factor (Q28)

Three effects/penalties:

increased current → higher I²R loss → higher electricity cost
increased voltage drop/loss (due to current and reactive components)
overall inefficiency increases

22) Capacitor installation purposes (Q29)

Four purposes:

power factor improvement → reduce line current
reduce power loss (I²R)
reduce voltage drop
reduce apparent power demand → free capacity / reduce required supply power

23) Capacitor sizing & overcompensation (Q30–Q31)

Choose capacitor reactive power to match the load’s inductive reactive power (or slightly less).
If too large → overcompensation:
- phase C can cause voltage rise
- power factor can worsen again
- harmonic issues may appear (generator/malfunction effects mentioned)

24) Harmonics caused by capacitors & series reactor solution (Q32–Q35)

Capacitor banks can generate harmonics (notably 5th harmonic context mentioned).
Solution: install a series reactor with the capacitor to behave like a filter.
Memory points:
- theoretical required reactor relative to harmonic order
- practical selection includes margin:
  - theory ~4%, practical ~6% (as stated)
- similar approach for 3rd harmonic with larger margin:
  - ~11% theoretical, ~13% selected

25) Capacitor installation principles (Q35)

Core constraints (intent):
- capacitor sizing must exceed the inductive part (text unclear about “ground,” but sizing logic is emphasized)
Avoid switching/fusing arrangements that reduce reliability
Use dedicated switching approach; direct connection on the main line is warned against due to switching surge and possible power factor drop if done improperly
When eliminating harmonics: use series reactor
Consider spacing/flamability (“oil sealing” and distance mentioned)

26) Capacitor bank equipment identification (Q36–Q38)

Exam-style components:

Circuit breaker
Discharge coil (to discharge residual voltage)
Series reactor
Power capacitor

Additional requirement:

discharge coil should reduce residual voltage to ≤ 50 V within ~5 seconds

27) Capacitor equipment accident causes (Q39)

Three accident categories:

busbar/connection-side short circuit
capacitor device body short/insulation breakdown
wiring short inside capacitor equipment

28) Protection devices for capacitor banks (Q40–Q41)

Converter/protection types (3 mentioned):

overcurrent/circuit-breaker style protection
overvoltage correction/operating device (trigger based on overcompensation activation voltage)
undervoltage account unit (during outage: opens/disconnects)

Inspection items (3):

terminal looseness + overheating
thermal imaging/overheating check
external insulation condition (ceramic/porcelain cracks)

Capacitor control, SVC, harmonics suppression, and THD

29) Capacitor switching control methods (Q42)

Control elements (4 categories):

control based on reactive power / proxy similar to Young’s modulus (power factor relationship)
current-based control
voltage-based control
reactive compensation logic (leading reactive compensation)

30) Neutral point detection methods for capacitor bank protection (Q43)

NCS: current sensor (detects neutral current during faults)
NVS: neutral voltage sensor (detects unbalanced voltage between neutral points)

31) Motor load + capacitor overcompensation risk (Q44)

If capacitors cause excessively leading current:
- motor magnetic flux increases abnormally
- terminal voltage rises above rated value
- can damage the motor

32) SVC (static VAR compensation) concept (Q45)

Uses thyristor switching for fast reactive power control:
- parallel capacitors + shunt reactors controlled by high-speed switching
Purpose:
- stabilize voltage fluctuations
- suppress flicker

33) Harmonic current generation causes (Q46)

Three main causes:

transformer/motor excitation (magnetizing nonlinear behavior)
power electronic converters (inverters, converters, choppers)
arc furnace processes (industrial arcs)

34) Harmonics effects (Q47)

Four disadvantages:

equipment overheating / increased iron loss / mechanical/electrical stress
protective relay misoperation due to waveform distortion
communication line induction noise/data errors
neutral conductor overheating in 3-phase 4-wire systems (harmonic components add)

35) Harmonic suppression measures (Q48)

Five measures:

increase “pulse chopping” / reduce pulse width to smooth waveform
harmonic filters
series reactors (for capacitor harmonic suppression)
multi-conductor/bundling for corona suppression
delta transformer connection to trap/limit 3rd harmonic circulation

36) THD definition & calculation (Q49)

THD uses RMS values:
- denominator: RMS of the fundamental component
- numerator: RMS of harmonic components (sum of squares)
Video mentions an “external ratio” style memory approach.

Voltage unbalance limits (distribution systems)

37) Unbalance limits in single/three-phase systems (Q50–Q52)

Key limits stated:

Single-phase 3-wire system imbalance rate: ≤ 40%
Three-phase regulation: imbalance limit mentioned as ≤ 30%

Exceptions/special cases:

dedicated transformer cases (low voltage)
specific high-voltage/special conditions
using multiple dedicated transformers

Memory mnemonic (“dates” 2 vs 3):

relates to the equilibrium concept: distributing loads across phases/transformers to maintain balance

Low-voltage wiring and installation rules (Indoor cabling section)

38) Cable material selection (Q53)

Distinguish vinyl-clad vs chloroprene-rubber (“captive cable”) types
Use triangles/cross marks based on:
- exposed vs concealed installation
- voltage range (e.g., rules for 400 V and below mentioned)

39) Indoor low-voltage wiring methods (Q54–Q55)

Wiring permitted depending on environment, including:

cable construction
metal pipe
vinyl-clad conduit
cable tray construction

Conditions vary by whether installation is exposed/concealed and whether inspection is feasible.

40) When to omit switching devices (Q56)

Switch/disconnection device may be omitted in two cases:

switching is already included as part of the equipment structure
a dedicated branch circuit breaker exists for maintenance, so only that circuit is isolated

41) Distribution panel placement and design considerations (Q57–Q59)

Design considerations (5):

wiring method (2-wire vs 3-wire, etc.) affects voltage drop and circuit protection choices
load usage rate (simultaneous operation assumptions)
expansion allowance and spare capacity
route/path length affects voltage drop/power loss
inspection needs: add inspection ports during design

Panel installation rules (Q58):

one per floor
branch circuit length: ≤ 30 m
total circuit breaker count:
- ≤ 42; if exceeded, split into two panels
mounting heights:
- top ≈ 1.8 m
- mid ≈ 1.4 m
- bottom ≈ 1.0 m
separate commercial vs emergency power supplies (no crossover)

Outlet placement rules (Q59–Q60, partial):

avoid outlets in certain branching sections
minimum outlet rule by room area:
- based on 5 m² steps with increasing counts
- example direction: ≥ 15 m² → 3 outlets (text garbled, but the intent is area → minimum outlets)

42) Voltage drop limits and starting current exception (Q62)

Voltage drop limits differ by system (example):
- lighting circuits: about 3% (and higher allowances in other situations)
Exception:
- motor starting inrush allows exceeding limits (referenced “minimum table exceptions”)

43) Wiring accessories: boxes and conduits (Q63–Q64)

Regular/junction box: for conduit interconnection
Pull box (full box): used to allow long conduit pulling
Components mentioned:
- locknut, bushing, coupling, saddle/band, ring, switch box, outlet box

44) Time-of-use night power system (Q65)

Uses a time switch and a nighttime tariff meter
Night-only devices operate after a set time (e.g., after 10 PM) and are off by morning
Wiring/installation considerations follow similar branching and conduit rules

Lighting fundamentals (color temperature, color rendering, efficiency, types)

45) Blackbody & color temperature (Q66)

Kelvin is absolute temperature:
- 0°C = 273.15 K
Approximate color temperatures:
- ~2700 K: reddish
- ~6500 K: daylight / bluish-white
Light color corresponds to blackbody temperature conceptually.

46) Color rendering (Q67)

Depends on how the lighting spectrum matches a standard (solar spectrum).
Color rendering index (CRI) concept:
- higher CRI → closer to true object colors
- lower CRI → more color distortion

47) Luminous efficiency / lighting efficiency (Q68)

Two related metrics:
- lighting efficiency: emitted light energy / input power
- luminous efficacy: luminous flux (lumens) vs input

48) Principles of light emission (Q69)

Three principles:

thermal radiation
electric luminescence (gas discharge)
deployment/luminescence (LED/semiconductor emission)

49) Photodegradation compensation rate (Q70)

As lamps age, brightness decreases.
Design uses a maintenance margin (e.g., design higher like 115 lux to achieve 80 lux later).

50) Fixture light distribution categories (Q71)

Direct lighting
Semi-direct lighting
(The provided text ends mid-list; remaining items are not present.)