Substation commissioning: tests, sequence and energisation
Deskely Completions team Singapore
Substation commissioning proves that every piece of primary and secondary equipment in a substation is installed correctly, tested, and works together as a protected system, before the substation is energised and connected to the network. One missed CT polarity or relay setting can trip a feeder on the first fault, or fail to trip it.
This guide covers the commissioning sequence, the tests on transformers, switchgear, instrument transformers and protection, the SCADA and earthing checks, energisation, and the records the owner expects at handover.
- Commissioning runs from equipment tests, through protection and scheme tests, to energisation and on-load checks.
- Protection is proven by secondary injection of relays and primary injection through the CTs.
- The single line diagram is the master drawing for testing, isolation and energisation.
- Every breaker, relay, CT and transformer is a tag; energisation waits until all of them are signed off.
The commissioning sequence
- 01Installation checks
Equipment installed and terminated to the drawings; nameplates checked against the design; earthing connected.
- 02Equipment tests
Transformers, switchgear, CTs, VTs, cables and batteries tested individually (see below).
- 03Protection and control
Relay settings applied and tested by secondary injection; CT circuits proven by primary injection; trip and close circuits tested.
- 04Scheme and interlock tests
Interlocks, intertrips, bus protection and automatic schemes tested end to end.
- 05SCADA and communications
Every signal checked point to point from the bay to the control centre.
- 06Pre-energisation checks
All test records reviewed, punch items closed, earths removed, switching programme approved.
- 07Energisation
Energised in steps under a switching programme, with checks at each step.
- 08On-load checks
Phasing, CT polarity and protection stability checked with real load; meters and SCADA values confirmed.
Equipment tests
| Equipment | Typical commissioning tests |
|---|---|
| Power transformer | Insulation resistance, winding resistance, turns ratio, vector group, magnetising current, power factor (tan delta), sweep frequency response (SFRA), oil tests, protective device checks (Buchholz, temperature, pressure relief) |
| Circuit breakers | Contact resistance, timing and travel, insulation resistance, operation of trip and close coils, SF6 gas or vacuum checks, interlocks |
| Disconnectors and earthing switches | Contact resistance, operation, interlocks, alignment |
| Current transformers | Ratio, polarity, magnetisation (excitation) curve, winding resistance, insulation resistance, burden |
| Voltage transformers | Ratio, polarity, insulation resistance, secondary circuit checks |
| Cables | Insulation resistance and, for HV cables, a withstand test such as VLF; sheath tests |
| Batteries and DC system | Capacity test, charger operation, earth fault monitoring |
| Earthing system | Earth grid resistance, continuity of earth connections, step and touch potential where required |
Test methods and acceptance values come from the manufacturers, the project specification and standards such as the IEC 60076 series for power transformers, IEC 62271 for switchgear, IEC 61869 for instrument transformers, IEEE C57.152 for field testing of transformers and, in North America, the ANSI/NETA Acceptance Testing Specifications. Insulation resistance tests follow the method in the megger test guide.
Protection testing
Secondary injection tests each relay by injecting currents and voltages into its inputs from a test set, checking that every protection function operates at its setting and in the right time, and that it trips the right breakers. Primary injection pushes current through the primary of the CTs to prove the whole chain: CT ratio and polarity, wiring and the relay's measurement.
Protection functions are named by their ANSI device numbers: 50/51 overcurrent, 87 differential, 21 distance, 27 and 59 under- and overvoltage, 86 lockout. Differential schemes need particular care: a reversed CT can cause a trip on load or on a through-fault.
Energisation
Energisation follows a written switching programme: each step, the equipment it energises, who operates, and the checks before the next step. Before the first step, the commissioning lead confirms that every test record is signed, that A punch items are closed, that all temporary earths are removed and that the protection is in service. The single line diagram is used to plan and track it.
After energisation, on-load checks confirm phasing between incoming supplies, CT polarity and protection stability with real load, directional elements, and metering and SCADA values.
Records and handover
The owner or network operator expects a complete record for every item: test results against acceptance values, relay settings as applied, primary and secondary injection reports, SCADA point-to-point sheets, punch lists and the as-built drawings. On a large substation or a renewables collector substation that is thousands of records.
In Deskely each breaker, relay, CT, VT and transformer is a tag on the one-line, with its test records, punch items and certificates attached, so the team can see what still stands between each bay and energisation.
The Deskely products for this
Frequently asked questions
What tests are done when commissioning a substation?
Equipment tests on transformers, breakers, disconnectors, CTs, VTs, cables, batteries and the earthing system; protection relay tests by secondary and primary injection; scheme, interlock and SCADA tests; then energisation and on-load checks.
What is the difference between primary and secondary injection?
Secondary injection tests a relay by injecting signals directly into its inputs. Primary injection drives current through the CT primaries to test the whole chain from CT to relay.
What transformer tests are done at commissioning?
Typically insulation resistance, winding resistance, turns ratio, vector group, magnetising current, power factor or tan delta, SFRA and oil tests, plus checks of the protective devices.
What is a switching programme?
A written, approved sequence of switching operations for energising or isolating equipment, with the checks at each step and who performs them.
Which standards apply to substation commissioning tests?
Manufacturer and project specifications first, with standards such as IEC 60076, IEC 62271, IEC 61869, IEEE C57.152 and, in North America, the ANSI/NETA Acceptance Testing Specifications.
- In production since 2014
- Thousands of daily users
- On MODEC FPSO projects since 2016