The design of the three-purpose grounding transformer

Dyson

06/12/2025

Underground Power Cable Transmission Lines

Direct - buried power cable lines have large ground - distributed capacitance, causing high single - phase - to - ground short - circuit capacitive current. For 10 kV lines, if this current exceeds 10 A, arcs hardly self - extinguish, risking arc overvoltage and endangering line equipment. Arc extinction is thus necessary. With a Dyn - connected main transformer, an arc - suppression coil on the secondary neutral point suffices. For Yd - connected ones, an artificial neutral point (provided by a grounding transformer) is needed.

1 Grounding Transformers

A grounding transformer serves two purposes: its primary side acts as an artificial neutral point (grounded via an arc - suppression coil to supply inductive current for arc extinction), and the secondary side powers the substation. Arc - suppression coils are essential companions. As shown in Figure 1, its primary side uses a Z - connection (to reduce zero - sequence impedance and enhance compensation) to derive a neutral point. The coil, with adjustable air gaps/turns, balances capacitive current (to below 5 A) for grounding and arc extinction.

Due to unequal primary - secondary capacities, grounding transformers are 15% lighter than same - capacity ordinary power transformers.

2 Three - purpose Grounding Transformer

To enhance power line safety and reliability, overseas applications widely use a Z - connected neutral coupler (no secondary side) paired with an arc - suppression coil for arc extinction. However, such couplers (for YNd/Yd - connected main transformers) only serve as artificial neutrals, failing to supply 400V low - voltage power. Thus, an extra station - use power transformer is needed, increasing costs, space, and causing high losses/poor reliability.

To address this, Kunming Transformer Factory developed the three - purpose grounding transformer (SJDX - 630/160/10). It integrates a Z - connected neutral coupler (no secondary winding), an arc - suppression coil, and a station - use power transformer. Its core structure is shown in Figure 2.

This three - purpose grounding transformer is mounted on a five - limb conjugate core. The primary (with tap changers) and secondary windings of the three - phase grounding transformer are wound on three limbs (lower part in Fig. 2), while the arc - suppression coil is on the other two (upper part in Fig. 2). Placing the lighter arc - suppression coil on top eases air - gap adjustment but requires reinforced fixing. Reversing the layout uses the heavier transformer to stabilize the coil, reducing vibration at the cost of coil installation and air - gap adjustment convenience. This design streamlines structure, saves materials, cuts losses, ensures good compatibility, and enables automated arc - extinction compensation via microcomputer control.

Topics

Z-type grounding transformer Design and Simulation

Dyson

Focused on the design of electrical equipment, proficient in electrical principles and relevant specifications, and skilled in using design software. From intelligent substations to various types of electrical equipment, I am adept at optimizing design solutions, integrating new technologies. With practical experience and collaborative management capabilities, I deliver outstanding electrical design achievements.