Stray DC currents from transit systems have been known to create problems for electrical utility transformers. An overview of the effect of DC currents generated from the transit system owned and operated by the Toronto Transit Commission (TTC) on North York Hydro (NYH) transformers has been presented. The paper compares the early results from the time the negative DC rail was solidly tied to the NYH neutral with those obtained after mitigative measures were put in place. The mitigative measures were aimed at increasing the electrical isolation of the negative DC rail from ground. Results indicate that the mitigative measures did reduce the level of stray DC on the NYH transformers along the subway lines. However, present DC levels are such that the cyclic transformer noise is still very audible. Concerns regarding core heating, lamination displacement, and primary winding loading still exist. Further mitigative measures and solutions to the problem have been proposed.

Subject
Electric current, Rail, Materials, Fluxes, Voltage, Manufacturing, Electrochemical noise, Saturation, Transformers, Traction, Rectifiers, Stray current, Damage
Keywords:
transformers, stray dc, saturation, transit systems, electrical isolation
© 1994 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1994
Association for Materials Protection and Performance (AMPP)
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