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HIGH VOLTAGE WINDING DESIGN

In the early 1980’s Dr Znidarich was instrumental in the establishment and development of a world class high voltage coil and bar manufacturing facility, regarded by its clients as amongst the best in the world. During 33 years of operation, more than 150 hi-tech coil and bar windings were produced for large electrical machines, with the enviable record of never failing the most stringent type tests (Voltage Endurance in accordance with IEEE Std 1043-R2009, and IEEE Std 1553-2002, and Thermal Cycling Testing in accordance with IEEE Std 1310-1996) and never having a single coil failure during installation of more than 50 hydro generator and turbo generator windings.

 

With 35 years of  HV coil and bar design and insulation system research and development experience, Dr Znidarich is indisputably amongst world's leading experts in all aspects of HV and LV winding design.

HIGH VOLTAGE WINDING DESIGN SERVICES

GMECS offers HV winding design services up to the largest conventionally cooled machines, including:

  • Multiturn Coil and Single Turn Roebel Bar Design Including Full Analysis and Quantification of Copper Losses (DC I2R Losses and Extra Circullating Current and Eddy Current Losses) and Prediction of New Winding Temperature Rises;

  • Full Multiturn Coil and Single Turn Roebel Bars 3D Solid Modelling to Ensure End Winding Clearances, Measure Exact Mean Length of Turn (MLT) and Ensure Manufacturability;

  • Design and 3D Solid Modelling of End Winding Support Systems and Anlysis of End Winding Forces;

  • Design of Slot Wedging Systems, Including Analysis of Slot Bar Forces for Normal Operation and Fault Conditions;

  • Design and Full Specification of Complete Rewind Kit Components;

  • Writing of Full Winding Manufacturing and Testing Specifications;

  • Writing of Full Winding Installation and Test Manuals;

  • Witnessing of New Winding Type Testing and Manufacturing Inspection Service;

  • Expert Assistance with New HV Winding Installation.

GENERAL COMMENTS - HV WINDING DESIGN

The motors and generators built 30 – 50 years ago employed stator insulation systems with lower voltage stresses and correspondingly larger insulation allowances.  Modern insulation systems use thinner, more homogenous insulations, which permit higher voltage stresses, whilst providing much improved thermal conductivity and better heat dissipation.

 

There is therefore quite a scope for the HV winding designer to increase overall coil copper content by between 20 – 40%, which often provide copper losses at increased output not much higher than the losses produced by the existing winding at pre-upgrade machine rating.  In conjunction with the new insulation improved thermal dissipation, it is possible to design upgraded windings with temperature rises similar to the existing ones.

 

The main focus of the HV coil design for motor and generator uprates is therefore reduction of copper losses, and optimisation of thermal characteristics for best dissipation of heat losses.  The process usually involves a few iterations to achieve the optimal blend of desired characteristics.

HV COIL DESIGN PROCESS CONSIDERATIONS AND OUTPUTS

  1. The coil/bar configuration is analysed and the best solution is applied to the copper strand dimensions and/or their transposition arrangement in order to minimise base I2R losses, and extra copper losses (eddy current, and circulating current losses).

  2. The physical shape of the end winding is considered for the electrical clearances, and mechanical winding restraint.

  3. The selection of turn to turn insulation is considered from the stand point of operational turn to turn voltages as well as transient over-voltages due to power system disturbances.

  4. The copper to ground insulation ratio is optimised for the best blend of heat dissipation and dielectric integrity.

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