Settings are illustrative starting points — confirm with a protection coordination study per IEC 60255 / IEEE 242.
📚 Calculation book
CALCULATION BOOK
1000 kVA · 10kV/0.4kV · single · illustrative
1. Load calculation
Standard: IEC 60076 · IEC 60364-5-52
Parameter
Formula
Value
Connected load
P = sum(kW)
900 kW
Demand factor
Kd
1
Demand power
Pd = P x Kd
900 kW
Power factor
cos(phi) before -> after
0.90 -> 0.95
Design apparent power
Sd = Pd / cos(phi)
947 kVA
Transformer loading
Sd / Srated
95%
2. Short-circuit calculation
Standard: IEC 60909
Parameter
Formula
Value
System impedance (pu)
Zs = S / Ssc
0.20% (on 1000 kVA base)
Transformer impedance
Zt = Z%
4%
Total impedance
Z = Zt + Zs
4.20%
LV prospective Isc
Isc = In / Z
34.4 kA
HV prospective Isc
Isc = Ssc / (sqrt(3) x V)
28.9 kA
Breaking check
Icu >= Isc
LV 36 kA (1.0x 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)
1.2% at full load
4. Reactive power / harmonics
Standard: IEC 61921 (PFC) · IEEE 519 (harmonics)
Parameter
Formula
Value
Required compensation
Qc = Pd x (tan1 - tan2)
140 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
Reliability data
Illustrative industry-typical failure and downtime values — no specific standard
O&M mode:omMode (smart) indicates your current baseline; the calculator always compares manual vs smart O&M so you can see the achievable saving regardless of your starting point.
Illustrative assumptions:O&M cost rates (1.5% / 0.9% of asset value), the 30% failure-reduction benefit and 3% monitoring investment are industry-typical planning values, not guarantees. Actual savings depend on your failure profile and site conditions.
Not a performance warranty:Predictive maintenance reduces, but cannot eliminate, unplanned outages. ROI figures are planning estimates.
Not economical at low failure rates:If your failure rate is already low, the monitoring investment may not pay back — the calculator shows a negative saving in that case.
Scope:This is a commercial O&M comparison tool — it does not design the monitoring system. Contact us for a SCADA / condition-monitoring scope tailored to your assets.
What is predictive maintenance for power equipment?
Predictive maintenance uses condition monitoring — Dissolved Gas Analysis (DGA), partial discharge, temperature, vibration — to detect faults before failure. It cuts unplanned downtime 30-50% and maintenance cost 10-25% versus reactive maintenance. The calculator compares manual vs condition-monitoring O&M costs.
What is the ROI of smart O&M monitoring?
Smart O&M typically pays back in 1-3 years, driven by avoided downtime (a Transformer failure can cost $50,000-500,000 in outage and replacement) and lower labor. The calculator estimates downtime savings, ROI and payback conservatively for a power-equipment fleet.
What condition monitoring parameters matter most for transformers?
For oil-immersed transformers, dissolved gas analysis (DGA) per IEC 60599 detects incipient faults; oil temperature, moisture and partial discharge round out the picture. For dry-type, temperature and partial discharge dominate. The calculator models a monitoring program covering these parameters.
How much does unplanned downtime actually cost?
Unplanned downtime cost = lost production plus repair and possible penalties. For a process plant a single day can cost $10,000-500,000 depending on the facility. Predictive maintenance targets a 30-50% reduction in such events. The calculator uses your downtime cost and frequency to estimate savings.
What is the difference between preventive and predictive maintenance?
Preventive maintenance services equipment on a fixed schedule regardless of condition, often wasting effort. Predictive maintenance acts only when condition data shows degradation, targeting interventions and cutting cost. Predictive is the higher-ROI strategy for fleets. The calculator models the cost shift from scheduled to condition-based.