110 kV Substations Are the New DGA Upgrade Front
On 18 August 2026, State Grid’s Yongqiao Power Supply Company in Anhui, China announced it had completed a renewal of its online dissolved gas analysis (DGA) monitoring systems across key substations, including commissioning of the 110 kV Lianhua substation. The project used high-precision digital detection and included verification of sampling lines, gas sensors and data acquisition units to ensure accurate real-time data collection and anomaly warning.
Substation-scale projects like this matter beyond a single utility. Across China and much of Asia, the 110 kV class is where most of the transformer fleet actually lives, yet the largest share of online monitoring investment has historically gone to 220 kV and above. As utilities renew their 110 kV fleets, the practical question is no longer whether to monitor, but which monitoring layer to install first — and at what cost per transformer.
Hydrogen Is the Earliest, Fastest Fault Signal
Hydrogen is generated in almost every developing fault in an oil-filled transformer — partial discharge, low-temperature overheating from about 150 °C, and moisture ingress. It is the smallest molecule among the fault gases, so it diffuses fastest through the oil and reaches a sensor mounted at the tank wall quickly.
- Early signal: H2 appears before ethylene, methane or acetylene in most fault chains.
- Fast diffusion: its small molecular size means a shorter transport lag from fault site to sensor.
- Broad coverage: it is part of the gas signature for partial-discharge, thermal and discharge faults alike.
For this reason a continuous dissolved hydrogen sensor is the conventional first layer in a staged monitoring program. A single hydrogen reading cannot identify the fault type — that requires the full gas picture — but it is the most sensitive single indicator that something has begun to change inside the tank.
Valve Retrofit: No Outage, No Consumables
The retrofit path is what makes hydrogen sensing practical at 110 kV scale. A flange- or valve-mounted monitor can be installed on an energized transformer through the oil drain or sampler valve, so the unit never has to be taken out of service. There is no carrier gas, no chromatography column and no periodic cell replacement — a decisive operational advantage for unmanned urban substations.
This “start lean, upgrade later” approach mirrors the tiered guidance utilities now use: put a zero-consumable hydrogen monitor on every transformer first, then field-upgrade to a multi-gas system only where fault risk or asset criticality justifies it.
Choosing the Entry Layer: A Staged Decision
| Stage | Coverage | Monitor | Action on alarm |
|---|---|---|---|
| 1 — Fleet screening | All 110 kV units | DGA-500 hydrogen monitor | Trend and rate of rise; schedule lab DGA |
| 2 — Critical confirmation | Largest / most loaded units | DGA-900 9-gas + moisture | Fault typing per IEC 60599 / IEEE C57.104 |
| 3 — Event escalation | Alarmed units | Laboratory DGA confirmation | Condition rating and repair decision |
The staged approach keeps capital spend proportional to risk. A fleet of a few dozen 110 kV transformers can be screened with hydrogen sensors for a fraction of the cost of equipping every unit with a full 9-gas analyser, and the screening layer produces the continuous trend data that makes the later decision evidence-based.
What a Utility-Scale Commissioning Must Verify
The Yongqiao project’s commissioning steps — checking sampling lines, sensors and data acquisition — are exactly the acceptance checks that determine whether an online system earns its keep. Three items deserve attention:
- Oil flow path: the sensor must see representative oil from the tank, with no stagnant pocket.
- Data integration: readings must reach substation SCADA or the cloud in the right protocol (MODBUS, IEC 61850, MQTT).
- Baseline trending: commissioning should capture each unit’s own baseline so alarms are set on rate of rise rather than a fixed generic threshold.
For a deeper selection framework, see how to select an online DGA monitor and the condition-based transformer maintenance guide.
PAS DGA for Staged 110 kV Substation Upgrades
PAS DGA builds the hydrogen and multi-gas layers utilities need to renew a 110 kV fleet without over-spending: the DGA-500 hydrogen monitor for fleet-wide screening, and the DGA-900 when a unit graduates to full fault typing. For the background on why hydrogen deserves a dedicated layer, see hydrogen as an early warning gas.
Contact PAS DGA to scope a staged monitoring plan for your substation portfolio.