TX-04 Collector Transformer — Cable Termination Isolation
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.
How Setyr addresses Wind Energy →
It refers to equipment that does not exist and illustrates the elements 29 CFR 1910.147(c)(4)(ii) requires a procedure to contain. It is not a document to adopt. Under (c)(4)(i) the employer must develop and document energy control procedures specific to their own machines, and under (c)(6) must inspect them at least annually.
11 points, in sequence
Turbine rotor brake and rotor lock, engaged before any electrical work at the base.
Method: Set the rotor brake and insert the rotor lock pin. Must be ENGAGED.
Caution: A freewheeling rotor drives the generator and backfeeds the converter even with the grid isolated.
34.5 kV collector circuit breaker at the substation feeding this string.
Method: Open the breaker, rack out, and lock in the disconnected position. Prove dead at the cable termination.
Caution: Racking out is the isolation. An open breaker still racked in is not isolated.
690V low-voltage side isolator between the transformer and the turbine converter.
Method: Open and lock. Prove dead on the LV side.
Caution: A transformer isolated only on the HV side can be backfed from the turbine converter on the LV side.
Array cable disconnect toward the next turbine upstream on the collector circuit.
Method: Open and lock. Prove dead at the termination.
Caution: Turbines on the same collector circuit backfeed each other. Isolating at the substation alone leaves the array cable live from the neighbouring machine.
Array cable disconnect toward the next turbine downstream on the collector circuit.
Method: Open and lock. Prove dead at the termination.
Caution: The second array leg is the one crews forget when the turbine either side is stopped and appears harmless.
Array cable capacitive discharge point at the termination cabinet.
Method: Apply the discharge stick to each core in turn and hold for the full discharge time before applying earths.
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.
Portable earths applied to all three cores at the termination.
Method: Apply earths after proving dead and after capacitive discharge. Must remain APPLIED throughout.
Caution: Earths applied before discharge can weld. Discharge first, then earth.
Transformer auxiliary supply feeding cooling fans, tap changer and protection relays.
Method: Open and lock.
Caution: The auxiliary supply is fed from a different board than the main. It stays live when the transformer is isolated.
On-load tap changer mechanism block.
Method: Engage the mechanical block on the tap changer drive. Must be ENGAGED.
Caution: A tap changer with a charged spring mechanism operates on loss of control power.
Turbine UPS and battery bank supplying the controller and safety chain.
Method: Open and lock the UPS output only after confirming the safety chain is not required for the work.
Caution: A UPS keeps the controller alive with every external supply isolated. Locking the incomer proves nothing about the battery.
Aviation obstruction lighting on the nacelle, fed from the essential supply.
Method: Do NOT isolate. Obstruction lighting is a regulatory requirement and must remain in service.
Caution: Isolating obstruction lighting on a turbine grounds the site under aviation rules and is not within the crew authority to do.
What your site must supply
This example is structurally complete and factually generic. The things below are the things only you can know — and they are exactly what makes a procedure yours.
- 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.
Author this properly, once
Setyr holds procedures like this as living documents — bound to real isolation points, with lock registries, group lockout, person-in-charge custody and periodic review built in.