Electrical concepts

This guide covers essential electrical engineering concepts for working with ekx's single-line diagram editor.

Power systems overview

Electrical power systems generate, transmit, distribute, and utilize electrical energy:

Generation:

Utility power plants
On-site generators
Renewable sources

Transmission:

High voltage (115kV to 765kV)
Long distance
Minimal losses

Distribution:

Medium voltage (4kV to 35kV)
Local delivery
Substations step down voltage

Utilization:

Low voltage (120V to 600V)
End-use equipment
Lighting, motors, electronics

ekx models distribution and utilization systems - the portions inside facilities.

Single-line diagram purpose

Single-line diagrams (SLDs) show electrical systems in simplified form:

What SLDs show:

Major equipment (transformers, switchgear, motors)
Protection devices (breakers, fuses)
Power flow paths
Voltage levels
Ratings and nameplate data

What SLDs omit:

Three separate phase conductors (shown as single line)
Control wiring
Grounding details (mostly)
Physical layout

SLDs communicate system architecture to engineers, electricians, and operators.

Per-unit vs engineering units

Engineering units (actual values):

Volts (V), kilovolts (kV)
Amperes (A), kiloamperes (kA)
Watts (W), kilowatts (kW), megawatts (MW)

Per-unit (normalized):

Voltage as fraction of nominal: V_pu = V_actual / V_nominal
Example: 460V on 480V base = 0.958 pu
Simplifies analysis across voltage levels
Typical range: 0.95 to 1.05 pu

Use per-unit for power flow analysis (easier to spot issues). Use engineering units for equipment verification (matches nameplates).

Voltage levels

Low voltage (utilization):

120V, 208V, 240V, 277V, 480V, 600V
Building distribution
Direct connection to loads
NEMA standards

Medium voltage (distribution):

2.4kV, 4.16kV, 4.8kV, 13.8kV, 23kV, 34.5kV
Campus or facility distribution
Requires transformers to utilization voltage
IEEE standards

High voltage (transmission):

69kV, 115kV, 138kV, 230kV, 345kV, 500kV, 765kV
Utility transmission
Not typically modeled in ekx

Choose voltage levels based on load size and distance. Higher voltage reduces current and losses but costs more in equipment.

Three-phase power basics

Most industrial/commercial systems use three-phase power:

Advantages:

More power from same conductors
Constant power delivery (no pulsation)
Smaller motors and generators
More efficient

Common configurations:

Wye (Y): Four-wire (three phases + neutral), 480Y/277V, 208Y/120V
Delta (Δ): Three-wire (three phases only), 480V delta

Phase voltage vs line voltage:

Wye: V_line = √3 × V_phase
Example: 480Y/277V means 480V line-to-line, 277V line-to-neutral

Three-phase power formula:

P = √3 × V_L × I_L × PF

Fault current concepts

Normal current:

Load current during proper operation
Conductors sized for normal current
Typically <1000A for most circuits

Fault current (short-circuit current):

Current during electrical fault
Can be 10× to 100× normal current
Thousands to tens of thousands of amperes
Must be interrupted quickly to prevent damage

Fault types:

Three-phase (all three phases short together)
Phase-to-phase (two phases short)
Phase-to-ground (one phase shorts to ground)

Protection devices must interrupt fault current within cycles to prevent fires and equipment damage.

Protection coordination overview

Protection coordination ensures only the faulted section loses power:

Selectivity:

Downstream device operates first
Upstream device remains closed
Minimizes outage area

Coordination methods:

Time delay (upstream slower than downstream)
Current magnitude (upstream higher setting)
Device characteristics (time-current curves)

Properly coordinated systems isolate faults to smallest possible section.

Grid connection points

Service entrance:

Where utility power enters facility
Metering location
Main disconnect required
Utility feed in ekx represents this point

Point of common coupling (PCC):

Interface between utility and customer
Fault contribution from both sides
Coordination boundary

Power quality basics

Voltage sag:

Temporary voltage drop
Causes: motor starting, faults on parallel circuits
Can cause equipment malfunction

Voltage swell:

Temporary voltage rise
Less common than sag
Can damage equipment

Harmonics:

Non-sinusoidal waveforms
Caused by electronic loads
Increases heating in conductors and transformers

Power factor:

Ratio of real power to apparent power
Poor power factor = wasted capacity
Corrected with capacitors

ekx's power flow analysis assumes fundamental frequency (60Hz) and sinusoidal waveforms.

Electrical safety

Arc flash:

Explosive release of energy during fault
Can cause severe injury or death
PPE required based on incident energy
Reduced by lowering fault current or clearing time

Shock hazard:

Direct contact with energized conductors
Prevented by insulation, barriers, grounding
GFCI protection for personnel safety

Equipment protection:

Overcurrent protection (breakers, fuses)
Ground fault protection
Differential protection for critical equipment

Safety is the primary purpose of electrical protection systems.

Understanding components - Component categories and functions
Connection rules - Valid electrical connections
Power flow analysis - Electrical calculations