Substation

Substation Switchgear Selection (IEC 62271)

Circuit breaker rating verification, enclosure type selection, and bay configuration per IEC 62271-100/200 and IEC 60909.

IEC 62271-100 IEC 62271-200 IEC 60909 IEC 60529
Presets
System Parameters
Short-Circuit Parameters (IEC 60909)
Circuit Breaker Ratings
Disconnector / Earthing Switch
Enclosure Type (IEC 62271-200)
Bay Configuration
Circuit Breaker Rating Checks (IEC 62271-100)
CB Overall: PASS κ = —
Disconnector / Earthing Switch Checks
Rated Current ≥ Load Current PASS
Short-Time Withstand ≥ Ik" PASS
Enclosure Type (IEC 62271-200)
Enclosure Type —
IP Rating (IEC 60529) —
Bay Configuration
Bay Type —
Switchgear Rating Envelope vs Fault Level
Export
1. Rated Voltage (Ur ≥ V_sys) ▸
Ur ≥ V_sys

IEC 62271-100 §4.2: The rated voltage of a circuit breaker shall not be less than the maximum system voltage. Standard values: 7.2, 12, 17.5, 24, 36, 52, 72.5, 123, 145, 170, 245, 300 kV.

2. Rated Short-Circuit Breaking Current (Isc_rated ≥ Ik") ▸
Isc_rated ≥ Ik"

IEC 62271-100 §4.4: The rated short-circuit breaking current Isc_rated is the rms value of the symmetrical component of the prospective test current at instant of contact separation. Isc_rated ≥ Ik" (initial symmetrical short-circuit current from IEC 60909).

3. Peak Withstand (Ip_rated ≥ κ·√2·Ik") ▸
Ip_rated ≥ κ·√2·Ik" (κ = 1.02 + 0.98·e-3R/X)

IEC 62271-100 §4.3: The rated peak withstand current Ip_rated shall be not less than the peak value of the short-circuit current calculated per IEC 60909. κ = 1.02 + 0.98·e^(-3R/X), typically 1.6–1.8 for power systems.

4. Short-Time Thermal (Ith_rated ≥ Ith·√(t_f/t_r)) ▸
Ith_required = Ith · √(t_fault / t_rated)

IEC 62271-100 §4.5: The rated short-time withstand current Ith_rated is expressed for a rated time t_r (1 s or 3 s). Thermal equivalence: Ith_required = Ith·√(t_fault/t_rated). For 1 s rated: Ith_rated ≥ Ik"·√(t_f/1s).

5. Enclosure Type (IEC 62271-200) ▸

IEC 62271-200 classifies switchgear as: GIS (SF₆, sealed, ≤ 72.5 kV indoor preferred), AIS (air-insulated, outdoor, cost-effective), Hybrid (combined, 72.5–145 kV). IP rating per IEC 60529: indoor minimum IP2X, GIS typically IP5X.

≤ 36 kV: GIS (indoor) / AIS (outdoor)
36–72.5 kV: AIS (outdoor) / GIS (indoor)
72.5–145 kV: Hybrid
≥ 145 kV: AIS
6. Bay Configuration ▸

IEC 62271-200 Annex A: Incomer bays feed power in from upstream transformer/line; coupler bays connect bus sections; feeder bays connect outgoing lines/cables; transformer bays interface power transformers with dedicated protection (87T, 95, 49, 26).

Frequently Asked Questions
What is IEC 62271-100 vs IEC 62271-200? +
IEC 62271-100 covers circuit breakers — their rated voltage, breaking current, peak withstand, and mechanical endurance. IEC 62271-200 covers the assembly of switchgear and control gear — the complete switchgear cubicle including disconnector, earthing switch, CT/VT, and protection relays. Both are required for switchgear specification.
Why is the κ factor used for Ip calculation? +
The peak fault current Ip = κ·√2·Ik" (IEC 60909-0 §4.3). The κ factor accounts for the DC offset in the first cycle of a short-circuit, which depends on the R/X ratio of the system. For a purely reactive system (R=0), κ=1.8; for systems with significant resistance, κ approaches 1.02. Default κ=1.6 for typical power systems (R/X ≈ 0.2).
When should GIS vs AIS be selected? +
GIS (SF₆ gas-insulated) is preferred for indoor installations ≤ 36 kV where space is limited, for coastal/harsh environments, and when very high reliability is required. AIS (air-insulated) is preferred for outdoor substations where space is available and first cost must be minimized. Hybrid is standard for 72.5–145 kV transition voltages. Life cycle cost often favors AIS despite larger footprint.
What is the difference between 1 s and 3 s rated short-time withstand? +
IEC 62271-100 allows manufacturers to declare Ith_rated at either 1 s or 3 s rated time. A 3 s rating gives more thermal headroom for the same current (Ith²·t is constant). If CB is rated 31.5 kA for 3 s, its thermal capacity is 31.5²×3 = 2974 kA²s, equivalent to only 25 kA for 1 s. Always check the rated time and convert when comparing against fault duration.
What bay type should I specify? +
Incomer bay: connects transformer or incoming line to busbar — requires distance protection and overcurrent backup. Coupler bay: connects two bus sections — requires directional overcurrent and synchro-check. Feeder bay: connects outgoing cable/line — requires three-stage IDMT overcurrent plus distance protection, and auto-reclose if required. Transformer bay: connects power transformer — requires differential protection (87T), Buchholz, and temperature monitoring.
How does altitude affect switchgear selection? +
IEC 62271-1 §6.2 specifies altitude correction for dielectric withstand. Above 1000 m ASL, the air density correction factor k = 1/√(1 - 0.00001·(H-1000))² reduces dielectric strength. At 2000 m, k ≈ 1.12 meaning the equipment must be rated ~12% higher. For 145 kV switchgear at 2000 m, a 170 kV rated CB may be required. Enclosure IP rating also requires consideration for altitude — higher altitude increases risk of internal condensation in sealed enclosures.