Setyr worked example — TX-04 Collector Transformer — Cable Termination Isolation Not approved for use. Version 1 · 2026-09-25
Worked example only — your site must author, review and approve its own
procedure under 29 CFR 1910.147(c)(4). setyr.com/procedures
TX-04 Collector Transformer — Cable Termination Isolation
Wind energy
Medium-voltage cable termination at a wind farm collector transformer. Covers backfeed from adjacent turbines on the same collector circuit, capacitive charge on the array cable, and earthing before contact.
This is a worked example, not a procedure you can adopt. It describes equipment that does not exist, with illustrative tag numbers.
29 CFR 1910.147(c)(4) requires the employer to develop, document and
utilise energy control procedures specific to their own machines, and (c)(6)
requires the employer to inspect those procedures periodically. Neither duty
can be delegated to a vendor or discharged by this document.
Isolation points
| # | Tag (illustrative) | Type | Disposition | What it does and why | Dwell |
|---|---|---|---|---|---|
| 10 | TX-04-NAC-BRK | Block | Apply & verify | Turbine rotor brake and rotor lock, engaged before any electrical work at the base. Caution: A freewheeling rotor drives the generator and backfeeds the converter even with the grid isolated. Set the rotor brake and insert the rotor lock pin. Must be ENGAGED. | — |
| 20 | TX-04-HV-ISO | Breaker | Isolate & lock | 34.5 kV collector circuit breaker at the substation feeding this string. Caution: Racking out is the isolation. An open breaker still racked in is not isolated. Open the breaker, rack out, and lock in the disconnected position. Prove dead at the cable termination. | — |
| 30 | TX-04-LV-ISO | Disconnect | Isolate & lock | 690V low-voltage side isolator between the transformer and the turbine converter. Caution: A transformer isolated only on the HV side can be backfed from the turbine converter on the LV side. Open and lock. Prove dead on the LV side. | — |
| 40 | TX-04-ARRAY-A | Disconnect | Isolate & lock | Array cable disconnect toward the next turbine upstream on the collector circuit. Caution: Turbines on the same collector circuit backfeed each other. Isolating at the substation alone leaves the array cable live from the neighbouring machine. Open and lock. Prove dead at the termination. | — |
| 50 | TX-04-ARRAY-B | Disconnect | Isolate & lock | Array cable disconnect toward the next turbine downstream on the collector circuit. Caution: The second array leg is the one crews forget when the turbine either side is stopped and appears harmless. Open and lock. Prove dead at the termination. | — |
| 60 | TX-04-CAP-DIS | Bleed | Isolate & lock | Array cable capacitive discharge point at the termination cabinet. Caution: A kilometre of screened MV cable holds a capacitive charge after the source is removed. Proving dead immediately after isolation can read dead and then recover. Apply the discharge stick to each core in turn and hold for the full discharge time before applying earths. | 300s |
| 70 | TX-04-EARTH | Chain | Apply & verify | Portable earths applied to all three cores at the termination. Caution: Earths applied before discharge can weld. Discharge first, then earth. Apply earths after proving dead and after capacitive discharge. Must remain APPLIED throughout. | — |
| 80 | TX-04-AUX-PWR | Breaker | Isolate & lock | Transformer auxiliary supply feeding cooling fans, tap changer and protection relays. Caution: The auxiliary supply is fed from a different board than the main. It stays live when the transformer is isolated. Open and lock. | — |
| 90 | TX-04-TAP-BLK | Block | Apply & verify | On-load tap changer mechanism block. Caution: A tap changer with a charged spring mechanism operates on loss of control power. Engage the mechanical block on the tap changer drive. Must be ENGAGED. | — |
| 100 | TX-04-UPS | Breaker | Isolate & lock | Turbine UPS and battery bank supplying the controller and safety chain. Caution: A UPS keeps the controller alive with every external supply isolated. Locking the incomer proves nothing about the battery. Open and lock the UPS output only after confirming the safety chain is not required for the work. | — |
| 110 | TX-04-OBST-LT | Breaker | KEEP ENERGISED | Aviation obstruction lighting on the nacelle, fed from the essential supply. Caution: Isolating obstruction lighting on a turbine grounds the site under aviation rules and is not within the crew authority to do. Do NOT isolate. Obstruction lighting is a regulatory requirement and must remain in service. | — |
What your site must supply
- Your own asset and isolation-point tag numbers. The tags shown are illustrative and refer to equipment that does not exist.
- The actual location of every disconnect, valve and vent on your equipment.
- Measured stored-energy magnitudes and the dwell time required to dissipate them.
- Your verification method for each point, and who is authorised to perform it.
- Any additional energy sources present on your equipment and absent here.
Authorship and validation
This example was authored by Setyr for domain validation. It is not derived from any customer's controlled documents. It illustrates the elements 29 CFR 1910.147(c)(4)(ii) requires a procedure to contain — it does not certify compliance, which is a property of an employer's programme rather than of any document.