Case study · Industrial safety
PLN — High-voltage Cubicle Wi-Fi Control
Wireless on/off control for high-voltage cubicles in PLN electrical substations — built so operators never have to stand next to energized equipment to switch it.
The problem
In Indonesian electrical substations — gardu induk — high-voltage cubicles are still often switched manually. An operator walks up to the cubicle and physically opens or closes it. The cubicles carry tens of kilovolts. A faulty line, a closed switch on a backfed circuit, an arc-flash event — any one of those can kill the person standing in front of it.
Conventional HMI solutions exist, but most run a wired control cable from a remote panel right back to the cubicle itself. The cable carries low-voltage signals, but routing it through high-voltage gear creates its own failure surface: insulation degrades, faults backfeed, the cable becomes one more thing that can go wrong near energized equipment.
PLN — the Indonesian state-owned electricity utility — needed a way to take the operator out of the danger zone entirely.
What we built
A custom embedded device that controls cubicle switching wirelessly over Wi-Fi.
The hardware is a 4-channel OPEN/CLOSE PCB (the "WIFI KONTROL VERSI 1" board) — each channel drives one cubicle's open and close coils. Firmware runs on an AVR microcontroller; an ESP-based Wi-Fi module provides the network link. A web UI on the operator's laptop talks to the device over the substation's Wi-Fi — the operator stands at a safe distance and clicks to toggle.
No more walking up to live high-voltage gear to flip a switch.
Engineering challenges
Reliable command delivery over Wi-Fi. Substations are RF-noisy. The control protocol acknowledges every command end-to-end, retries on missed packets, and surfaces a clear failure to the operator if a command can't be confirmed — no command silently dropped.
Fail-safe defaults. If the device loses Wi-Fi mid-operation, the contactor outputs default to a known state. The board doesn't leave a half-completed switch latched.
Custom PCB for a non-trivial load. Cubicle coils aren't friendly digital loads — they're inductive, current-hungry, and need galvanic isolation from the control logic. The 4-channel board carries optoisolated drivers, snubbers, and a labeled physical layout the field technicians can install without a manual.
Operator UX. The web UI is intentionally minimal — clearly labeled channels, big OPEN / CLOSE buttons, live status feedback. No nested menus, no settings the operator can break.
Outcome
Operators no longer have to walk up to a live high-voltage cubicle to switch it. The substation's safety surface shrinks from "human + tool + energized equipment" to "human + laptop + safe distance." Failure modes that used to be catastrophic — operator injury, fatal arc-flash incidents — become recoverable: the operator just reissues the command.
Deployed in PLN substations in Indonesia.