Case Study: EMR Global OLTC Retrofit vs. Siemens in a South Asian Power Corridor Upgrade
The Corridor That Could Not Wait
In 2022, a cross-border power transmission authority managing a high-voltage corridor connecting two South Asian grids initiated a systematic review of its ageing transformer assets. The corridor had been operational for nearly two decades. The transformers, twenty-year-old units rated at 220 kV were carrying significantly higher load than their original design had anticipated, driven by bilateral power trade agreements that had expanded steadily since the early 2010s.
The OLTCs inside those transformers were the most immediate concern. They had been specified with Siemens-make tap changers at the time of original commissioning. The units were showing signs of contact degradation. DGA results across several transformers were flagging thermal gas generation. The switching operations already elevated above design frequency due to load growth were producing audible indicators of mechanical wear.
The project engineer assigned to the corridor upgrade, we'll call him Farrukh had two distinct paths in front of him: re-engage Siemens for an OEM refurbishment and parts programme, or move to an EMR Global retrofit.
What the Siemens Path Looked Like in Practice
Farrukh had worked with Siemens equipment for most of his career. He respected the product. But when his procurement team began the formal parts enquiry process, the supply picture that emerged was complicated.
The specific Siemens OLTC models installed in the corridor transformers were from an early-2000s production run. Dedicated spares for that exact design required ordering through Siemens Energy's international service chain. Lead times were quoted at 14 to 18 weeks for the critical contact assemblies. Refurbishment visits from Siemens-certified engineers would require scheduling through their Central Asia and South Asia regional service calendar, with availability extending four to five months forward.
For a power corridor serving bilateral trade commitments with contractual reliability obligations, that timeline was not workable. The transformers couldn't operate in degraded condition for six months while parts and engineers were arranged.
Why EMR Was Brought Into the Conversation
A colleague at a neighbouring utility in India, where EMR OLTCs were already widely deployed and approved by state utilities — recommended Farrukh speak with EMR's team. The initial conversation was about spares availability. It quickly became a retrofit conversation.
A pre-emptive and well-planned OLTC retrofit plan can reduce the risk of failure, minimise the impact of a failure, and increase the life expectancy of transformers, and an OLTC retrofit with EMR OLTCs increases the reliability of a transformer at a fraction of the cost of a new transformer. EMR has been executing this comprehensive retrofit package for any make of tap changer, without exception, for over thirty years.
The retrofit scope EMR proposed was end-to-end: oil draining, transformer study, tap changer replacement, vacuum filling, and full electrical testing until the transformer is completely restored. The timeline per unit was confirmed at five to seven days with EMR's field team.
What the Field Execution Revealed
Six transformer units were selected for the first phase of the retrofit programme. EMR's field engineers conducted a DCRM baseline on all six before any mechanical work began. Dynamic Contact Resistance Measurement allowed the internal OLTC condition to be assessed without opening any unit — the current graph results identified which contact sets were critically degraded and which still had serviceable life remaining. That diagnostic step compressed the scope of the first phase, reducing unnecessary part replacement on the healthier units.
The retrofit itself proceeded unit by unit over three weeks. Each unit was returned to service following vacuum filling and a full electrical test routine. Post-retrofit DCRM confirmed clean switching signatures across all tap positions.
Farrukh's note to his management committee after the programme concluded was straightforward: the corridor is operating at full bilateral trade capacity, the transformer thermal gas readings have normalised, and the total programme cost — including diagnostics, field team, and genuine EMR parts — came in at approximately 28% of what full transformer replacement had been budgeted at.
The Siemens product had served the corridor well for twenty years. But when it was time to extend those transformers' lives for another two decades, EMR's retrofit capability and domestic-linked support infrastructure was what made the programme possible within the operational constraints the corridor actually faced.
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