Rancang distribusi tenaga untuk infrastruktur perkotaan — penerangan jalan dan terowongan, jembatan/terowongan, pemompaan, dan beban pengisian EV, dengan gardu beton prefabrikasi, ring main unit SF6, dan distribusi tegangan rendah.
Jaringan perkotaan bersifat kompak, rendah kebisingan, dan sangat andal. Kalkulator ini mengagregasi beban kota, menerapkan faktor simultanitas, dan mengukur gardu prefabrikasi (box) dengan ring main unit SF6 terintegrasi plus jaringan ring sesuai GB 50052, CJJ 45, dan GB 50054.
Worked Examples
Example 1 — Urban Ring Network (Lighting + Pumping + EV Charging) · FOB $897,825
Urban infrastructure power system · 12kV/0.4kV · dispersed
Settings are illustrative starting points — confirm with a protection coordination study per IEC 60255 / IEEE 242.
📚 Calculation book
CALCULATION BOOK
1250 kVA - 12kV/0.4kV - single - illustrative
1. Load calculation
Standard: IEC 60076 - IEC 60364-5-52
Parameter
Formula
Value
Connected load
P = sum(kW)
1,550 kW
Demand factor
Kd
0.7
Demand power
Pd = P x Kd
1,085 kW
Power factor
cos(phi) before -> after
0.90 -> 0.95
Design apparent power
Sd = Pd / cos(phi)
1,142 kVA
Transformer loading
Sd / Srated
91%
2. Short-circuit calculation
Standard: IEC 60909
Parameter
Formula
Value
System impedance (pu)
Zs = S / Ssc
0.42% (on 1250 kVA base)
Transformer impedance
Zt = Z%
4%
Total impedance
Z = Zt + Zs
4.42%
LV prospective Isc
Isc = In / Z
40.9 kA
HV prospective Isc
Isc = Ssc / (sqrt(3) x V)
14.4 kA
Breaking check
Icu >= Isc
LV 50 kA (1.2x margin) PASS
3. Voltage drop
Standard: IEC 60364-5-52 Annex G
Parameter
Formula
Value
Main feeder
dU = sqrt(3) x I x L x R / V
300 mm2 - dU 5.86% @ 400 m
Limit
max 3%
EXCEEDS limit
Transformer volt. reg.
dU ~ loading x Z% x sin(phi)
1.1% at full load
4. Reactive power / harmonics
Standard: IEC 61921 (PFC) - IEEE 519 (harmonics)
Parameter
Formula
Value
Required compensation
Qc = Pd x (tan1 - tan2)
169 kvar
PFC bank
standard step
200 kvar
Detuned reactor
p = 6%
12.0 kvar @ 6% (anti-resonance)
5. Grounding
Standard: IEC 60364-5-54 earthing arrangements and protective conductors LV earthing target 10 ohm (TN systems); 4 ohm used as a conservative design target - target 4 ohm
Parameter
Formula
Value
Single rod resistance
R1 = rho/(2 x pi x L) x ln(4L/d)
39.6 ohm
Rods required
n = R1 / (target x 0.8)
13 rod(s) <= 4 ohm
Rod spec
dia x length
20 mm x 2.5 m
This calculation book is illustrative it consolidates the computed values with the referenced standards. A licensed engineer must verify and seal final design documents for construction.
Estimated total (FOB Qingdao, EXW) — priced equipment
$897,825
📋 Design notes
Pricing basis:FOB Qingdao (EXW) equipment price. Freight, duty and installation are not included — add for landed economics.
Transformer loading:91% at design demand — high, consider the next size up.
Short-circuit check:HV 14.4 kA vs 25 kA (1.7× margin) · LV 40.9 kA vs 50 kA (1.2× margin).
Voltage regulation:≈ 1.1% at full load (typical limit 5%).
Power factor correction:200 kVAR automatic bank corrects PF to 0.95.
Voltage-drop check — FAIL:ΔU exceeds the 3% limit on: main feeder 5.9%, Zone feeder 1 3.2%, Zone feeder 2 3.2%, Zone feeder 3 3.2%, Zone feeder 4 3.2% … +6 more — increase cross-section or add a parallel run.
Cable & grounding pricing:Cable conductors and grounding are priced from the confirmed cables-trays-grounding price reference (per-metre copper YJV; aluminium remains POA). The main copper busbar is POA — its length is project-specific.
Busway (high-current feeders):For LV feeders above ~2500 A, a busway (母线槽) trunking system is recommended instead of parallel cables.
Prefabricated (box) substation:A factory-assembled box substation integrates the SF6 ring main unit, transformer and LV panel — compact, low-noise and quick to energize for urban sites (GB/T 17467).
Ring main network:The MV ring main unit (XGN15-12) keeps supply continuous: a fault on one feeder can be isolated while the ring feeds from the other side.
Load distribution:Dispersed load over a 800 m radius — 2 box substation node(s) keep LV feeders short and reduce cable loss.
EV charging:EV charging is a growing, highly intermittent urban load; size for simultaneous charging diversity and consider dedicated feeders.
Pole-mounted switchgear:For overhead MV sections, a pole-mounted vacuum load-break switch (ZW32/FZW28-12) provides line sectioning and fault isolation — priced at $1,183/unit (FOB reference).
Cara perhitungannya
Cara perhitungan ukurannya
Beban terhubung = penerangan jalan + penerangan terowongan + jembatan/terowongan + pemompaan + pengisian EV. Kebutuhan = terhubung × simultanitas (0,7 tipikal). Beban tersebar pada radius suplai tertentu dilayani oleh beberapa node gardu box, masing-masing mengintegrasikan ring main unit SF6, transformator, dan panel LV (GB/T 17467).
Standar yang berlaku
Perhitungan ukuran mengacu pada GB 50052 (desain pasokan tenaga), CJJ 45 (desain penerangan jalan perkotaan), GB 50054 (desain instalasi tegangan rendah), GB/T 17467, dan IEC 62271 (gardu prefabrikasi).
Pertanyaan yang sering diajukan
What is a prefabricated box substation and when is it used?
A box Substation (compact/Prefabricated Substation) packages Transformer, HV and LV Switchgear in one weatherproof enclosure, following GB/T 17467 and IEC 62271-202. Urban infrastructure uses them for road lighting, tunnels, pumping and EV charging where a brick substation is too costly or too large. Ratings typically run 100-1600 kVA at 12/0.4 kV.
How is road and tunnel lighting power distributed?
Road lighting uses a TT or TN-S system fed from a dedicated transformer or a lighting box substation, with feeder lengths up to 1 km and voltage drop limited to 5% per CJJ 45. Tunnel lighting is a safety load requiring dual supply or emergency power. The calculator models dispersed loads and feeder radius to size the substation.
What is an SF6 ring main unit and why is it used in cities?
An SF6 ring main unit (RMU) is a compact, sealed 12-24 kV switchgear using SF6 gas for insulation and arc quenching, needing little maintenance and fitting in small vaults. Cities use RMUs on 10-12 kV ring networks to feed box substations, giving N-1 supply in dense areas. The calculator includes RMU selection for the urban feed.
What load profile does an EV charging station add to city infrastructure?
EV charging is a sharp, clustered load: a 120 kW DC fast charger can draw 120 kVA and a 10-charger station peaks near 500-1200 kVA. Demand is highly time-correlated, so diversity is low and transformer sizing must account for coincidence. IEC 61851 and GB/T 51313 govern the installation; the calculator includes charging load in the urban mix.
What cable type is used for urban 12 kV distribution?
Urban 12 kV networks use XLPE-insulated cables (YJV/YJV22 in China, IEC 60502) in cross-sections of 120-400 mm2, buried or in ducts. XLPE replaces paper-insulated PILC cables, allowing higher operating temperature (90 deg C) and lower maintenance. The calculator selects feeder cable and checks ampacity and voltage drop.
What emergency power does a city tunnel need?
Tunnels are safety-critical: lighting, ventilation and fire systems need dual supply plus a diesel generator or EPS for evacuation (GB 50052 first-class important load). Emergency lighting must restore within 0.5-15 s per GB 51309. The calculator models the emergency level and sizes the standby path for the urban loads.
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