SUBSTATION
33 kV to 11 kV primary substation single line diagram
This substation single line diagram shows a 33 kV to 11 kV primary distribution substation. The grid incomer passes through a line disconnector, metering and protection CT, and a 1250 A vacuum circuit breaker to the 33 kV bus. A 20 MVA power transformer feeds an 11 kV bus through a second vacuum breaker.
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CASE ANALYSIS
Scenario
This primary substation steps a 33 kV grid supply down to an 11 kV feeder bus for industrial, urban, and rural distribution circuits.
Key decisions
- HV switching: A line disconnector, CT, and 33 kV VCB control the incoming supply.
- Power transformation: A 20 MVA transformer establishes the 33/11 kV interface.
- Differential protection: The 87T relay identifies transformer internal faults.
- Feeder separation: Three 630 A VCBs protect distinct 11 kV distribution circuits.
When to reuse this
Use this for a conceptual primary substation layout. Real substation design needs detailed CT ratios, protection zones, earthing, and utility standards.
FAQ
Frequently asked questions
What does 87T mean?
It is the ANSI function number commonly used for transformer differential protection.
Why are VCBs shown at both transformer sides?
They allow protection and isolation on the HV and MV connections of the transformer.
Is a CT only for metering?
No. Current transformers can supply both metering and protection relays, often through separate cores.
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sld-33kv-11kv-primary-substation