Voltage Sensing and Measurement using OHMIC Voltage Sensors: An Improved Approach to Applications Traditionally Requiring 2.4 to 38 KV Voltage Transformers

Voltage transformers and control power transformers traditionally have been core and coil designs. Because of the core and coil design (saturable inductance), when a traditional voltage transformer or control power transformer is switched or switching occurs in the primary circuit in which the transformer is connected, oscillatory switching transients are produced by the interaction of the switching device, transformer, load, and system, which may damage the internal insulation and fail the transformer. Having investigated several hundred medium voltage transformers and control power transformer failures and applied successful solutions, an alternate solution has become a necessity to mitigate against the primary switching transients and resonance problems associated with voltage transformers. Drawing on this experience gained, this paper introduces a modern approach for 2.4 to 38 kV voltage transformer applications utilizing voltage sensors consisting of Ohmic Voltage Sensors. The paper presents the ohmic voltage sensors technology as an alternate for conventional VTs and the often-needed transient mitigation. The paper describes the advantages of ohmic voltage sensors over conventional voltage transformers, the applicable standards, testing of the OVSs to prove accuracy for relaying and metering and application considerations. A case study for a major US chemical facility will illustrate the application of ohmic voltage sensors in lieu of traditional voltage transformers to mitigate against potential ferroresonance and switching transients’ events due to the operation of upstream breakers with the added benefit of reduced space constraints in the switchgear.