Grounding transformers

WR grounding transformers are designed to provide a zero-sequence current source in electrical distribution systems. They establish an effective ground connection and can also provide a neutral connection point for the power system. This configuration helps manage voltage levels and protects the grid against certain undesirable electrical conditions.

Depending on project requirements, WR can also design grounding transformers in a zigzag configuration. As with the company’s other solutions, the design is tailored to the specific electrical requirements and integration constraints of the application.

Design

The transformer configuration is determined based on the requirements of the electrical system into which it is to be integrated.

In a conventional grounding configuration, the transformer provides a zero-sequence current source and establishes a neutral point for the system. In a zigzag configuration, two coils are connected in a specific arrangement to reduce the potential for circulating currents and improve the system’s fault current capacity. This configuration is commonly used in distribution networks that require an effective ground connection.

WR specializes in dry-type electrical transformers designed to customer specifications. Its capabilities cover units ranging from 15 kVA to 30 MVA, voltages up to 49 kV, and Class 220°C insulation.

Windings

The winding design takes into account the voltage level and the insulation class required for the application.

WR uses copper or aluminum coils. These are vacuum pressure impregnated using the VPI process with a polyester resin. This treatment notably limits moisture penetration into the windings and their insulation, helping ensure long-lasting performance in demanding industrial environments.

Depending on the transformer's electrical characteristics, windings can be manufactured using layer or disc construction. For certain low-voltage applications, foil winding construction can also be used to reduce eddy current losses and increase short-circuit strength. Adjustment taps are front-mounted for easy accessibility.

Core

The core plays an essential role in transferring energy between the windings via magnetic flux.

WR cores are manufactured from grain-oriented steel laminations featuring high magnetic permeability. The steel is precision-cut and stacked to keep the magnetic flux density below the saturation point. This approach helps minimize core losses and reduce the transformer's sound level.

The core is electrically isolated except at one point grounded to the frame using a copper strap. It is also vacuum impregnated with resin to help protect it against corrosion. For higher-capacity transformers, an air gap can be integrated to limit saturation while allowing air circulation to assist with cooling.

Integration

The integration of the transformer with the grid and surrounding equipment can be adapted to installation constraints.

The standard connection uses a stub-up configuration with NEMA holes, with or without mechanical lugs. WR can also design and install busbars coordinated with low-voltage or medium-voltage switchgear.

When required by the installation, a transition compartment can be integrated to provide a protected space for connecting incoming and outgoing cables. The medium-voltage and low-voltage sections can thus be separated into distinct compartments. Supports can also be added to hold the cables and simplify installation.

The enclosure can also be adapted to the environment. WR notably offers NEMA 1 and NEMA 3R configurations, with various filtration options for dust, water, or snow. Stainless steel enclosures are also available for particularly corrosive environments.

Testing and Compliance

Prior to shipping, WR transformers undergo testing at the company's facilities.

The testing laboratories at the Canadian and U.S. plants are ISO/IEC 17025 accredited. Standard tests include dielectric tests, no-load losses and excitation current, polarity, ratio, resistance, as well as load losses and impedance.

Depending on project requirements, additional testing can also be performed, including temperature rise tests, Basic Impulse Level (BIL), partial discharge, and sound level testing. Furthermore, WR manufacturing facilities in Canada and the United States are ISO 9001:2015 certified.