A New Three Phase Triangle Core Measurement Type Voltage Transformer

Prof. Dr. Okan Ozgonenel1, Baris Cepken2, Burcu CILSAL2
1Ondokuz Mayis University
Published in 2020

Reliability and stability of power systems depend on the operation of all system components within specified limits. Voltage measurement transformers take an important place among the power system components and perform their protection and measurement tasks where they are connected. Voltage measurement transformers are measurement transformers that reduce the primary circuit voltage, which is at a high level in the system to which they are connected, to the measurable low levels for the measurement and protection devices connected to the secondary circuit. The purpose of the new core design is envisaged to save weight and space, reduce the volume, reduce harmonic content and magnetic stray losses and naturally increase energy efficiency. This paper simply propose a three phase dry-type voltage measurement transformer based on triangular wound cores. In the literature, there are many modelling methods and procedures based on E-I Core transformers as well as triangular type distribution transformers. However, this paper presents to design and implementation of three phase voltage measurement transformer based on triangular core. In the proposed transformer no-load losses, magnetic stray losses and harmonics are studied. The modelling outcomes are then compared to real time data provided by ESITAS Company. The final product is dry-type epoxy cast resin measurement type voltage transformer and includes many technical improvements. Dry type voltage measurement transformers are manufactured in two ways. The first of these are phase-to-phase voltage transformers and the second to phase-to-ground voltage transformers. It states that phase-phase voltage transformers can be used at voltages up to 24kV in the 40 / b sub-paragraph of the Electric Power Current Regulation, and that the phase-to-ground voltage transformers should be used for voltages above this voltage. Phase-phase voltage transformers are connected between two phases in the network. Since they are connected between two phases, these voltage transformers have two bushings. Primary windings are removed from these bushings. In this type of voltage transformers, medium voltage networks that draw balanced load, voltage measurement is completed by using two phase-phase voltage transformers. In this connection, phase-to-ground voltages cannot be measured. Useful aspects of this type of voltage measurement transformers are as follows: a) Its cost is lower than that of phase-to-ground (unipolar) voltage transformers. b) Resonance hazard in phase-to-earth voltage transformers is not present in this type of transformers. The crucial aspects are; a) Voltage transformer winding insulation faults cause two phase short circuit. b) No voltage can be detected anymore. Phase-to-earth voltage transformers can be used at any voltage level above 1kV. The input end (polarity end) of the primary winding is connected to the phase conductor of the network. The output end (non-polarity end) of the primary winding is connected to ground. In three-phase systems, one is connected to each phase and used for measuring the phase-to-ground voltage. Useful aspects of this type of transformers are: a) They are manufactured more reliable. b) Interior insulation requires less material. c) Provides residual voltage measurement in earth leakage. The crucial aspects are; a) In small networks, due to voltage increase, impedance decreases and resonance is exposed to excessive voltage. In this case, it now causes serious error in voltage detection. b) Compared to two phase-to-phase voltage transformers, 3 voltage transformers are a more cost-effective solution.