Scope
- Transformer substations: building-type, prefabricated (kiosk) and pole-mounted substations; transformer rating and loading analysis.
- MV switchgear and LV boards: layout; selection of busbars, cables and protective devices.
- Earthing: earthing grid design, step and touch voltage calculation (TS EN 50522).
- Studies: short circuit (IEC 60909) and load flow; protection coordination (selectivity) and relay settings (ETAP).
- Commissioning: checks of insulation resistance, earthing, phase sequence and protection settings.
- Equipment: selection and supply of MV and LV switchgear.
Method and instruments
Short-circuit currents are calculated to IEC 60909 and protection coordination in an ETAP model; the results feed equipment selection and relay settings.
The earthing calculation is based on soil resistivity together with the fault current and clearing time obtained from the distribution company; step and touch voltages are compared with the limits of TS EN 50522.
In existing installations, transformer loading is verified with hourly OSOS data or a Kyoritsu KEW 6315 measurement; commissioning measurements are taken with the KEW 6516BT.
Regulations and standards
- Regulation on Heavy Current Electrical InstallationsConstruction and operation rules for MV installations
- Regulation on Earthing in Electrical InstallationsDesign and measurement of earthing systems
- TS EN 61936-1Power installations exceeding 1 kV AC
- TS EN 50522Earthing of power installations exceeding 1 kV AC
- TS EN 62271-200AC metal-enclosed switchgear for medium voltage
- TS EN 61439-1, -2Low-voltage switchgear and controlgear assemblies
- IEC 60909Short-circuit currents in three-phase AC systems
Deliverables
- Single-line diagram and layout drawings
- Calculation reports: short circuit, voltage drop, cable sizing, earthing (step and touch voltages), protection coordination
- Bill of materials and technical specification
- Commissioning check report and measurement results
Frequently asked questions
How do you size the transformer?
The calculation based on installed power and diversity factors is verified with hourly OSOS data or a power analyser measurement in existing facilities. Growth margin, transformer losses and contracted capacity are assessed together.
Is the earthing of our substation adequate?
Measured earth resistance alone does not prove adequacy. Under TS EN 50522 the touch voltage arising at the prospective fault current is assessed; for this, the fault current and clearing time are obtained from the distribution company.
Are our existing protection settings correct?
The single-line diagram, transformer and cable data and the relay and breaker settings are modelled in ETAP; selectivity is checked against the short-circuit currents and, where needed, new setting values are reported.