HV Protection Relay Testing SWMS

High voltage protection relay testing is high risk construction work in New South Wales because the work is carried out on or near energised electrical installations and, where cable basements, trenches and pits are entered to reach the CTs, in or near confined spaces. Section 291 of the Work Health and Safety Regulation 2025 (NSW) captures both categories, and a safe work method statement is required under section 299. SafeWork NSW is the regulator. AS 2067 governs the substation installation and AS 2467 the maintenance of electrical switchgear.

Protection testing occupies a position no other electrical work does: **the protection is off while it is being tested.** That is not a side effect — it is the definition of the task. For the duration of the test the plant is running with its protection out, which means the test window is also the exposure window for everything the scheme was installed to prevent. This is why a relay test is planned around its restoration as much as its execution, why the plant it protects is often taken out of service for the duration, and why a scheme is never, under any circumstances, left offline over a break, a shift change or a weekend.

The mechanism that kills on this work is the **open-circuited CT secondary**. A current transformer with load current flowing in its primary and its secondary open develops several thousand volts across the break — a saturated core forcing the voltage up until something arcs. The rule is absolute and it is the wrong way round from every other circuit an electrician touches: **short the CT secondary before you open it, never after.** Alongside it sit injection that is switching by another name, VT circuits that back-energise through their own secondaries, and spring-charged mechanisms that operate whether or not a hand is in the way. This SWMS is authored around those mechanisms and around the discipline of returning the scheme exactly as it was found.

Hazards identified

14 hazards covered, sorted by priority.

Control measures

Hierarchy-of-controls order: elimination → substitution → isolation → engineering → administrative → PPE.

1. 1**Short every CT secondary before it is opened, never after** — an open CT secondary with primary current flowing develops several thousand volts across the break. Use the shorting links or test blocks provided, prove the short, and treat any CT circuit as live whenever primary current can flow.
2. 2Establish and maintain the approach distances to energised HV plant under AS 2067, work only within the access permit issued by the asset owner, and treat all HV plant in the room as live regardless of what is being tested.
3. 3Obtain an arc flash risk assessment establishing incident energy and approach boundaries at the actual switchgear, relay panel and marshalling cubicle, verify upstream protection, and close covers for any test that can be done closed.
4. 4**Withdraw the trip links before injection** — injection is switching by another name, and a relay that operates during a test will trip or close real plant with real people at it. Confirm the trip and close paths are physically interrupted, and confirm with the control room before every injection.
5. 5Identify every source into the plant before any isolation is accepted — alternative supplies, embedded generation, UPS and inter-tie — isolate at each, and prove dead at the point of work with an instrument proved on a known source before and after.
6. 6Treat cable basements, trenches and pits as confined spaces under Part 4.3 Division 2 — permit, atmospheric testing, forced ventilation, a standby person who does not enter, and rescue in place before entry.
7. 7**Isolate VT secondaries before work and treat every VT secondary as a back-energisation path to the primary** — a voltage applied to a VT secondary appears on the HV side, and the conductor you proved dead is energised from a direction nobody isolated.
8. 8Discharge or block every spring-charged mechanism before any hand enters it, prove the charge released, and never rely on the mechanism's position indicator as evidence of a discharged spring.
9. 9Take the protected plant out of service for the duration of the test where the network permits, cover any unavoidable unprotected period with an agreed alternative arrangement, and **never leave a scheme offline over a break, a shift change or a weekend**.
10. 10Supply the test set from an RCD-protected source, inspect leads before every use, and keep test leads out of the traffic and switching path in the substation environment.
11. 11Work to a link and setting register that records every link out, every setting change and every inhibit at the moment it is applied, and **sign each line back and functionally prove the scheme before the plant returns to service** — a scheme left defeated is silent until the demand event.
12. 12Treat any SF6 switchgear that has interrupted a fault as containing toxic and corrosive arc by-products which are heavier than air — do not open without the asset owner's procedure, RPE and low-level ventilation.
13. 13Confirm egress is clear and known before opening any panel, work with a second person present, and never work alone in a substation or switchroom.
14. 14Use mechanical aids and two-person handling for test sets, cable drums and panel components, and stage equipment at the point of use in restricted substation space.

Applicable Codes of Practice

High-Risk Construction Work triggered

Worked example

A protection technician is secondary-injecting an overcurrent relay on a feeder that is carrying load. He needs to lift the CT wiring at the test block to isolate the relay from the live CT circuit. He opens the link. The CT's core saturates instantly and drives the secondary voltage up until it finds a path. The technician is holding it. He does not survive. The investigation is short, because the mechanism is not obscure: a current transformer is a current source, and a current source with its output open will develop whatever voltage is required to keep current flowing — in a protection CT with load current in the primary, that is thousands of volts across the break. The shorting link on the test block existed precisely to prevent this and was three centimetres from his hand. The rule is that the secondary is shorted **before** the circuit is opened, so that the CT always has a path. It is the reverse of the instinct every electrician builds on every other circuit, where you open first and short after. The contractor's SWMS listed 'CT circuits — use shorting links'. SafeWork NSW's position was that the document identified the equipment and not the sequence, and that on this hazard the sequence **is** the control: 'use shorting links' is satisfied by a technician who shorts the CT after opening it, which is the exact action that killed the worker. This SWMS states the order explicitly, requires the short to be proved before the circuit is opened, and requires every CT circuit to be treated as live whenever primary current can flow.

Related legislation

• Work Health and Safety Act 2011 (NSW) — primary duty of care (s19), consultation (s47), notifiable incidents (ss35–38), industrial manslaughter (s26A)
• Work Health and Safety Regulation 2025 (NSW) — HRCW (s291), SWMS content and requirement (s299), SWMS review (s302)
• Work Health and Safety Regulation 2025 (NSW) — Part 4.7 Division 4, sections 154 and 157 — prohibition on energised electrical work
• Work Health and Safety Regulation 2025 (NSW) — Part 4.3 Division 2 — confined spaces (cable basements, trenches and pits)
• Electricity Supply Act 1995 (NSW) and the licensing framework administered by NSW Fair Trading — electrical work licensing

Frequently asked questions