Written by: Steve Wright, Technical Service Representative, Gresco Utility Supply

“100-year-old industry with 100-year-old technology doing what they’ve been doing the same way for 100+ years. Where’s the excitement in that? Why are you wasting your engineering education?”

This is essentially what a professor said to me in response to his query of my job prospects. I had told him I accepted a position at an electric utility company. Unfortunately, his response was not an unusual one. Fortunately, it is far from the truth! We may be a slow-changing industry, but thoughtful deliberation is necessary to maintain the high reliability for which our industry is known. Last year, a new application of relatively recent technology was announced by EATON. In a cooperative effort with Maschinenfabrik Reinhausen GmbH (MR), EATON now offers the MR/EATON EVER-TAP Vacuum Voltage Regulator (VR).


Considering VR vs. On-Load Tap Changers (OLTC) in bus regulation applications, operation is essentially the same but there are some key differences. As a single-phase device, each VR operates independently and operates based on the sensed phase voltage of each phase. The three-phase OLTC operates in a ganged operation based on the sensed voltage of just one of the three phases. When there is a phase voltage imbalance, the independently controlled single-phase VRs correct the imbalance and maintain phase voltage within the set guidelines. In the case of an OLTC, the phase voltage imbalance cannot be corrected.

If a VR is in trouble, the single VR or VR set can be taken out of service without taking the power transformer out of service. A single problematic VR is relatively simple to replace with a spare within a day. If a spare is unavailable, purchase/delivery lead times may be anywhere from a few weeks to a few months. If an OLTC is in trouble, the transformer typically must be taken out of service. If OLTC failure results in extensive damage and damage to the transformer, the resulting outage may last many months. On the other hand, For VRs or OLTCs with contact under vacuum tap changers, maintenance cycles are extended far beyond that of VR and OLTC contact under oil tap changers. The EVER-TAP has the same 500,000 operation maintenance cycle as the popular MR RMV OLTC.

Comparison of features:

Power Transformer with MR/EATON EVER-TAP Vacuum VR:

  • Initial inspection at 500,000 Operations
  • No expected maintenance until 1M operations
  • EVER-TAP VRs with a power transformer have a very competitive first cost and Life Cycle Cost
  • Superior Voltage Optimization as each phase is independently adjusted as required
  • Line drop compensation settings can be tailored to the individual phases
  • The control allows for ganged operation simulating OLTC operation
  • Improves system reliability (Maintenance on VR leaves the power transformer in service)

Power Transformer with MR Vacuum OLTC:

  • Initial inspection at 500,000 Operations
  • No expected maintenance until 1M operations
  • Uses one voltage and current supply for regulating all three phases in a ganged operation
  • Maintenance requires the power transformer to be taken out of service

The EVER-TAP Vacuum VR is certainly worth considering for your next bus regulation project.




  1. Cooper Power Systems. Voltage Regulators vs. Load Tap Changers. Retrieved from https://www.eaton.com/content/dam/eaton/products/medium-voltage-power-distribution-control-systems/voltage-regulators/voltage-regulators-vs-load-tap-changers-information-td225012en.pdf
  2. Single-phase substation voltage regulator. (2018, July 02). Retrieved from https://www.eaton.com/us/en-us/catalog/medium-voltage-power-distribution-control-systems/single-phase-substation-voltage-regulator.html
  3. Wetzer, J. (2019, January 7). Column: Transformer lifecycle. Retrieved from https://www.transformers-magazine.com/component/k2/6169-column-transformer-lifecycle.html
  4. Dohnal, D. (2013, October 17). On-Load Tap-Changers for Power Transformers A Technical Digest. Retrieved from https://www.reinhausen.com/PortalData/1/Resources/tc/research_development/vacuum_technology/PB252_en_Power_Transformers.pdf