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Power Distribution System Design & Pricing Calculator

Size the transformer, HV/LV switchgear, cables and grounding for any distribution project — with standard-based design (IEC / NEC / GB) and an instant bill of materials with FOB pricing.

Start Calculating

Standard

Transformer type *

Total connected load (kW) *

HV voltage (kV) *

LV voltage (kV) *

Average power factor *

Circuits (feeders)

Target power factor

Demand factor

Upstream short-circuit Ssc (MVA)

Soil resistivity ρ (Ω·m)

Feeder run length (m)

Redundancy

Winding

Efficiency / series

HV switchgear type

Cable branch boxes

Advanced parameters

Defaults match the standard design baseline — adjust for site-specific conditions.

Grounding rod length (m)

Grounding rod diameter (mm)

Grounding target (Ω)

Cable conductor

Cable phase

Max voltage drop (%)

Detuned reactor rate (%)

Smart Monitoring & Control

Add SCADA / protection IED / DC panel / metering to the BOM. None keeps the design unchanged.

Automation tier

Protocol

How it works

Enter the connected load, voltage level and a few site parameters. The calculator applies the demand factor, sizes the transformer to the standard kVA rating, selects the HV/LV switchgear, and checks short-circuit and voltage-drop limits — then prices the equipment.

Worked Examples

Example 1 — 500 kW Industrial Distribution System · FOB $50,364

Distribution system · iec standard

500 kVA transformer

S13-M-500/10

Est. total (FOB)

$50,364

📦 Bill of Materials (example)

Equipment	Model	Spec	Qty
HV incoming panel	KYN28A-12-630-315	630 A / 31.5 kA · vacuum	1
Main transformer	S13-M-500/10	500 kVA · Oil-Immersed · Copper · S13	1
LV incoming panel	GGD-1000	1000 A busbar · In 722 A	1
LV feeder panel	GGD-1000	distributes 4 circuits	1
PFC capacitor bank	150 kVAR	automatic · GCK LV cabinet	1
Series reactor (detuned)	CKSG-9.0/0.4	9.0 kVAR · 6% · 0.4 kV	1
Main feeder cable (TX→LV)	YJV 0.6/1kV 240 mm² ×2	2× 240 mm² Cu · ΔU 0.88% @ 60 m · $123.0/m	2
Feeder cable — LV feeder circuit 1 (×4)	YJV 95 mm²	95 mm² Cu · 212 A · ΔU 1.3% · $47.2/m	4
Main busbar (Cu)	Cu 63×6.3	63×6.3 · 900 A rating · ref $47/m	included
Grounding electrode	Φ20mm × 2.5m rod	R₁ 39.6 Ω → 13 rod(s) ≤ 4 Ω	13

📐 Single-line diagram

⚙️ Electrical schematic (protection & metering)

⛳ Grounding grid layout

🔌 Cable schedule & routing

🗄 Switchgear arrangement

🛡 Protection configuration

📋 Protection settings

Circuit	Protection	Setting	Time	Standard
HV incoming 10 kV	50 instantaneous	231 A	inst	IEC 60255-151 / IEEE 242
HV incoming 10 kV	51 overcurrent	35 A	0.5 s	IEC 60255-151 / IEEE 242
HV incoming 10 kV	51N earth-fault	6 A	0.5 s	IEC 60364-4-41
Transformer 500 kVA	49 thermal overload	84% of rated	alarm 90%	IEC 60076-7 / IEEE C57.91
LV incoming 0.4 kV	50 instantaneous	5774 A	inst	IEC 60947-2
LV incoming 0.4 kV	51 overcurrent	866 A	0.3 s	IEC 60947-2 / IEC 60255
LV incoming 0.4 kV	51N earth-fault	144 A	0.3 s	IEC 60364-4-41
LV feeder circuit 1	50/51/51N (MCCB)	Ir 233 A · Im 1698 A · Ig 42 A	0.1 s (grading)	IEC 60947-2 / IEC 60255
LV feeder circuit 2	50/51/51N (MCCB)	Ir 233 A · Im 1698 A · Ig 42 A	0.1 s (grading)	IEC 60947-2 / IEC 60255
LV feeder circuit 3	50/51/51N (MCCB)	Ir 233 A · Im 1698 A · Ig 42 A	0.1 s (grading)	IEC 60947-2 / IEC 60255
LV feeder circuit 4	50/51/51N (MCCB)	Ir 233 A · Im 1698 A · Ig 42 A	0.1 s (grading)	IEC 60947-2 / IEC 60255

Settings are illustrative starting points — confirm with a protection coordination study per IEC 60255 / IEEE 242.

📚 Calculation book

CALCULATION BOOK

500 kVA · 10kV/0.4kV · single · illustrative

1. Load calculation

Standard: IEC 60076 · IEC 60364-5-52

Parameter	Formula	Value
Connected load	P = sum(kW)	500 kW
Demand factor	Kd	0.8
Demand power	Pd = P x Kd	400 kW
Power factor	cos(phi) before -> after	0.85 -> 0.95
Design apparent power	Sd = Pd / cos(phi)	421 kVA
Transformer loading	Sd / Srated	84%

2. Short-circuit calculation

Standard: IEC 60909

Parameter	Formula	Value
System impedance (pu)	Zs = S / Ssc	0.10% (on 500 kVA base)
Transformer impedance	Zt = Z%	4%
Total impedance	Z = Zt + Zs	4.10%
LV prospective Isc	Isc = In / Z	17.6 kA
HV prospective Isc	Isc = Ssc / (sqrt(3) x V)	28.9 kA
Breaking check	Icu >= Isc	LV 25 kA (1.4x 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	240 mm² · dU 0.88% @ 60 m
Limit	max 3%	within 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)	116 kvar
PFC bank	standard step	150 kvar
Detuned reactor	p = 6%	9.0 kvar @ 6% (anti-resonance)

5. Grounding

Standard: IEC 60364-5-54 earthing arrangements and protective conductors LV earthing target 10 Ω (TN systems); 4 Ω 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.

🔧 Secondary schematic (control & signal)

🔩 Terminal strip (typical)

📏 Standard basis (依据标准)

Topic	Standard
Standard basis	IEC · IEC 60364-5-52
Conductor ampacity	IEC 60364-5-52 Table B.52.2–B.52.5 (copper, 3 loaded conductors, 30°C ambient, PVC) — typical/rounded values, conservative (±3%)
Voltage-drop limit	IEC 60364-5-52 Annex G · max drop 3%
Winding temp rise	IEC 60076-2 — winding temp rise 65 K (Class A insulation, ONAN)
kVA ratings	IEC 60076-1 R10 preferred numbers
Breaker frames	IEC 60947-2 frame sizes (In)
Grounding target	IEC 60364-5-54 earthing arrangements and protective conductors — LV earthing target ≤ 10 Ω (TN systems); 4 Ω used as a conservative design target · target 4 Ω

🧮 How it was calculated

1. Loads: P=500 kW, PF 0.85, 4 circuits

2. Demand: 500 × 0.8 = 400 kW

3. PFC: Qc = 400 × (0.620 − 0.329) = 116 kVAR → 150 kVAR bank

4. Transformer: S = 400 ÷ 0.95 = 421.1 kVA → 500 kVA standard

4b. Loading: 421 ÷ 500 = 84% (good range)

4c. Voltage regulation: 84% × 4% × sinφ ≈ 1.1% at full load

5. HV: In 28.9 A, Isc 28.9 kA → KYN28A-12-630-315

6. LV: In 722 A, Isc 17.6 kA (Xfmr Z 4% + system 0.1%) → GGD-1000, 1 feeder panel(s)

7. Grounding: R₁ 39.6 Ω → 13 rod(s)

8. Main feeder: 2× 240 mm² · ΔU 0.88% — OK

Example 2 — 800 kW Dry-Type (N+1) Distribution System · FOB $130,066

Distribution system · iec standard

800 kVA transformer

SCB13-800/10

Est. total (FOB)

$130,066

📦 Bill of Materials (example)

Equipment	Model	Spec	Qty
HV incoming panel	KYN28A-12-630-25	630 A / 25 kA · vacuum	2
HV bus-tie panel	KYN28A-12-630-25	630 A / 25 kA · vacuum	1
Main transformer (each)	SCB13-800/10	800 kVA · Dry-Type · Aluminum · SCB13	2
LV incoming panel	GGD-1600	1600 A busbar · In 1155 A	2
LV bus-tie panel	GGD-1600	1600 A busbar	1
LV feeder panel (×2)	GGD-1600	distributes 8 circuits	2
PFC capacitor bank	150 kVAR	automatic · GCK LV cabinet	2
Cable branch box (LV)	DFW-0.4	1-in / 4-out · 0.4 kV · 630 A	1
Series reactor (detuned)	CKSG-9.0/0.4	9.0 kVAR · 6% · 0.4 kV	1
Main feeder cable (TX→LV)	YJV 0.6/1kV 240 mm² ×3	3× 240 mm² Cu · ΔU 1.25% @ 80 m · $123.0/m	3
Feeder cable — LV feeder circuit 1 (×8)	YJV 70 mm²	70 mm² Cu · 160 A · ΔU 1.8% · $37.0/m	8
Branch trunk cable (LV → branch box 1)	YJV 185 mm² ×2	2× 185 mm² Cu · 642 A · ΔU 1.4% · $103.0/m	2
Main busbar (Cu)	Cu 80×8	80×8 · 1400 A rating · ref $75.6/m	included
Grounding electrode	Φ20mm × 2.5m rod	R₁ 59.3 Ω → 19 rod(s) ≤ 4 Ω	19

📐 Single-line diagram

⚙️ Electrical schematic (protection & metering)

⛳ Grounding grid layout

🔌 Cable schedule & routing

🗄 Switchgear arrangement

🛡 Protection configuration

📋 Protection settings

Circuit	Protection	Setting	Time	Standard
HV incoming 10 kV	50 instantaneous	370 A	inst	IEC 60255-151 / IEEE 242
HV incoming 10 kV	51 overcurrent	55 A	0.5 s	IEC 60255-151 / IEEE 242
HV incoming 10 kV	51N earth-fault	9 A	0.5 s	IEC 60364-4-41
Transformer 800 kVA	87 differential	9 A	inst	IEEE C37.91 / GB/T 14285
Transformer 800 kVA	49 thermal overload	89% of rated	alarm 90%	IEC 60076-7 / IEEE C57.91
LV incoming 0.4 kV	50 instantaneous	9238 A	inst	IEC 60947-2
LV incoming 0.4 kV	51 overcurrent	1386 A	0.3 s	IEC 60947-2 / IEC 60255
LV incoming 0.4 kV	51N earth-fault	231 A	0.3 s	IEC 60364-4-41
LV bus-tie	50/51 overcurrent	1386 A	0.3 s	IEC 60947-2
LV feeder circuit 1	50/51/51N (MCCB)	Ir 176 A · Im 1283 A · Ig 32 A	0.1 s (grading)	IEC 60947-2 / IEC 60255
LV feeder circuit 2	50/51/51N (MCCB)	Ir 176 A · Im 1283 A · Ig 32 A	0.1 s (grading)	IEC 60947-2 / IEC 60255
LV feeder circuit 3	50/51/51N (MCCB)	Ir 176 A · Im 1283 A · Ig 32 A	0.1 s (grading)	IEC 60947-2 / IEC 60255
LV feeder circuit 4	50/51/51N (MCCB)	Ir 176 A · Im 1283 A · Ig 32 A	0.1 s (grading)	IEC 60947-2 / IEC 60255
LV feeder circuit 5	50/51/51N (MCCB)	Ir 176 A · Im 1283 A · Ig 32 A	0.1 s (grading)	IEC 60947-2 / IEC 60255
LV feeder circuit 6	50/51/51N (MCCB)	Ir 176 A · Im 1283 A · Ig 32 A	0.1 s (grading)	IEC 60947-2 / IEC 60255
+2 more feeders	50/51/51N (MCCB)	per feeder load	0.1 s (grading)	IEC 60947-2

Settings are illustrative starting points — confirm with a protection coordination study per IEC 60255 / IEEE 242.

📚 Calculation book

CALCULATION BOOK

800 kVA · 10kV/0.4kV · N+1 · illustrative

1. Load calculation

Standard: IEC 60076 · IEC 60364-5-52

Parameter	Formula	Value
Connected load	P = sum(kW)	800 kW
Demand factor	Kd	0.85
Demand power	Pd = P x Kd	680 kW
Power factor	cos(phi) before -> after	0.90 -> 0.95
Design apparent power	Sd = Pd / cos(phi)	716 kVA
Transformer loading	Sd / Srated	89%

2. Short-circuit calculation

Standard: IEC 60909

Parameter	Formula	Value
System impedance (pu)	Zs = S / Ssc	0.23% (on 800 kVA base)
Transformer impedance	Zt = Z%	6%
Total impedance	Z = Zt + Zs	6.23%
LV prospective Isc	Isc = In / Z	18.5 kA
HV prospective Isc	Isc = Ssc / (sqrt(3) x V)	20.2 kA
Breaking check	Icu >= Isc	LV 25 kA (1.3x 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	240 mm² · dU 1.25% @ 80 m
Limit	max 3%	within limit
Transformer volt. reg.	dU ~ loading x Z% x sin(phi)	1.7% at full load

4. Reactive power / harmonics

Standard: IEC 61921 (PFC) · IEEE 519 (harmonics)

Parameter	Formula	Value
Required compensation	Qc = Pd x (tan1 - tan2)	106 kvar
PFC bank	standard step	150 kvar
Detuned reactor	p = 6%	9.0 kvar @ 6% (anti-resonance)

5. Grounding

Standard: IEC 60364-5-54 earthing arrangements and protective conductors LV earthing target 10 Ω (TN systems); 4 Ω 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)	59.3 ohm
Rods required	n = R1 / (target x 0.8)	19 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.

🔧 Secondary schematic (control & signal)

🔩 Terminal strip (typical)

📏 Standard basis (依据标准)

Topic	Standard
Standard basis	IEC · IEC 60364-5-52
Conductor ampacity	IEC 60364-5-52 Table B.52.2–B.52.5 (copper, 3 loaded conductors, 30°C ambient, PVC) — typical/rounded values, conservative (±3%)
Voltage-drop limit	IEC 60364-5-52 Annex G · max drop 3%
Winding temp rise	IEC 60076-11 — dry-type Class F 100 K rise
kVA ratings	IEC 60076-1 R10 preferred numbers
Breaker frames	IEC 60947-2 frame sizes (In)
Grounding target	IEC 60364-5-54 earthing arrangements and protective conductors — LV earthing target ≤ 10 Ω (TN systems); 4 Ω used as a conservative design target · target 4 Ω

🧮 How it was calculated

1. Loads: P=800 kW, PF 0.90, 8 circuits

2. Demand: 800 × 0.85 = 680 kW

3. PFC: Qc = 680 × (0.484 − 0.329) = 106 kVAR → 150 kVAR bank

4. Transformer: S = 680 ÷ 0.95 = 715.8 kVA → 800 kVA standard

4b. Loading: 716 ÷ 800 = 89% (good range)

4c. Voltage regulation: 89% × 6% × sinφ ≈ 1.7% at full load

5. HV: In 46.2 A, Isc 20.2 kA → KYN28A-12-630-25

6. LV: In 1155 A, Isc 18.5 kA (Xfmr Z 6% + system 0.2%) → GGD-1600, 2 feeder panel(s)

6b. Cable branch boxes: 1 × DFW-0.4 (1-in/4-out) for feeder grouping

7. Grounding: R₁ 59.3 Ω → 19 rod(s)

8. Main feeder: 3× 240 mm² · ΔU 1.25% — OK

How it was calculated

Sizing basis

Transformer kVA = demand kW ÷ target power factor, rounded up to the standard rating; cable section from ampacity and voltage-drop limits; LV short-circuit from transformer impedance plus the upstream system; grounding rod count from the electrode resistance to the target earth resistance.

Applicable standards

Design follows the selected standard for conductor ampacity, voltage-drop limits, winding temperature rise, standard kVA ratings, breaker frames and grounding targets — each output is annotated with its standard reference.

Frequently asked questions

What is an acceptable voltage drop in a low-voltage distribution system?

IEC 60364-5-52 recommends total voltage drop from supply to load stay within 5% (4% in the distribution circuit plus 1% in the final circuit). For lighting circuits the limit is 3%. Exceeding 5% causes motors to draw more current, overheat and trip, so feeders are sized to keep steady-state drop near 2-3% with a margin for motor starting.

How do I calculate the transformer kVA for a distribution system?

Compute demand Sd = total connected kW x demand factor kd divided by target Power Factor. Typical kd is 0.6-0.8 for industrial plants and 0.4-0.6 for commercial buildings. Then select the next standard rating (e.g. 100, 160, 250, 400, 630, 800, 1000, 1250 kVA per IEC 60076) so loading sits at roughly 70-80% for efficiency and future headroom.

Copper or aluminum winding — how much does conductor material change transformer cost and losses?

Aluminum windings typically cut purchase cost 15-25% versus copper but raise load losses about 25-35% for the same rating because aluminium resistivity (2.65 uOhm-cm) is ~1.6x copper (1.68 uOhm-cm). Copper transformers are smaller and cooler; aluminium wins on first cost. The calculator prices S9/S11/S13/S20 series in both materials so you can compare TCO directly.

What short-circuit level should the switchgear be rated for?

Size the Switchgear breaking capacity against the fault level at its Busbar, computed from upstream short-circuit capacity and transformer impedance. A 10 kV/0.4 kV, 1000 kVA transformer with 6% impedance contributes roughly 24 kA at the LV bus, so select 31.5 kA or 36 kA panels rather than 16 kA. IEC 60909 gives the calculation method.

How is the FOB price in the calculator derived?

Prices come from the QDTB pricing matrix (calculator-data.json) with copper-linked factors for transformers. Transformer price follows a capacity curve a*S^b; copper windings track the daily copper price (base ~14,200 USD/t), and switchgear/compensation use range pricing. The total is a reference FOB Qingdao price including standard accessories but excluding freight, duty and installation.

What load diversity or demand factor should I use for my plant?

Demand factor kd = maximum simultaneous demand divided by total connected load. Typical values: continuous process plants 0.8-0.9, general manufacturing 0.6-0.7, commercial/office 0.4-0.6, residential 0.3-0.5. Using the right kd avoids a 30-40% oversized transformer and its extra no-load losses; the calculator applies kd before selecting standard kVA.

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Results are engineering estimates for reference. Final design must be confirmed by a licensed local engineer against site conditions and applicable codes. Prices are FOB Qingdao (EXW) and do not include freight, duty or installation.

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