#pvunl

The 19 September PVUNL disturbance is a sharp reminder of something the power sector often underestimates: protection mis-configurations can trigger outages just as dramatically as real faults. In this case, a zero-millisecond Zone-3 timer — leftover from anti-theft operations at Patratu — became the single point of failure that collapsed 460 MW of export.

A Simple Fault That Should Have Closed Cleanly

The sequence started with a transient Y-phase fault on the 400-kV Tenughat–PVUNL line. Auto-reclose (A/R) logic at both ends kicked in correctly and cleared the fault within a second. Under normal operating conditions, that should have been the end of the incident.

But Patratu’s Main-2 distance relay was still carrying an old construction-stage profile. Its Zone-3 timer was set at 0 ms, originally used to combat theft during line work. That temporary setting had never been rolled back.

So when the transient appeared, the relay responded instantly — tripping the PVUNL–Patratu-1 line in full Zone-3 operation.

One Relay Misfire, One Pathway Left Standing

That single instantaneous trip pushed nearly 460 MW of PVUNL generation onto the only remaining evacuation route. The SPS-linked overcurrent protection then acted decisively, tripping the Tenughat–PVUNL line as well.

What began as a routine auto-reclose sequence turned into a complete evacuation failure. PVUNL’s unit hit overspeed and over-frequency protection, the 400-kV yard went dead, and the station lost more than an hour of generation — not because of equipment weakness or weather, but because a temporary setting was forgotten.

The Bigger Issue: Protection Governance, Not Hardware

This incident exposes a recurring governance gap. Utilities frequently adjust protection schemes during:

• Anti-theft operations • Commissioning and construction • Temporary bypass or maintenance conditions

Yet many of these temporary settings never get normalised afterward. In a system dependent on layered distance-protection logic, even one stray parameter can turn a benign event into an outage of commercial scale.

Why This Matters for India’s Future Grid

As new renewable and thermal assets synchronise into grids still relying on ageing protection systems, the margin for error shrinks. The PVUNL event underscores the need for:

• Independent, periodic relay-setting audits • Mandatory rollback verification for all temporary configurations • End-to-end protection testing under real-fault signatures

The takeaway is simple and uncomfortable: the grid didn’t fail — the configuration did.