Scott T Connection
A Scott T connection, also known as a Scott-T transformer, is an electrical transformer configuration that converts three-phase power to two-phase power (or vice versa) using two single-phase transformers arranged in a special T connection. This setup ensures the two-phase outputs are 90° apart while the three-phase inputs remain 120° apart, maintaining balanced current draw on the three-phase network.
In manufacturing, Scott T connections are used to supply legacy two-phase equipment, such as industrial furnaces or traction systems, from a standard three-phase supply. They ensure balanced load on the three-phase side, preventing voltage drops and overheating. For compliance, installations must meet electrical codes (e.g., CEC, NEC) and CSA/UL/ANSI standards. WorkSafeBC requires employers to ensure equipment is designed, installed, and maintained per applicable standards, with lockout/tagout procedures for all transformer circuits. Workers must be trained on hazards and safe procedures, including proper isolation of both transformers in the Scott T assembly.
What exact transformer ratios and connections define a Scott T connection?
The main transformer (T1) has a primary connected between two three-phase lines with a centre tap at 50% turns. The teaser transformer (T2) has a primary with √3/2 (≈0.866) of T1's primary turns, connected between the remaining phase and the centre tap. Proper taps (e.g., 0.289, 0.5, 0.866) ensure secondary voltages are equal and 90° apart.
Why is a Scott T connection beneficial for system balance, and how does this relate to safety?
It ensures balanced two-phase loads appear as balanced three-phase currents, maintaining voltage stability and reducing overheating in cables and transformers. This reduces fire and insulation failure risks, supporting employer duties to control hazards under WorkSafeBC.
How does the Scott T configuration interact with protective relaying and fault detection?
On the three-phase side, standard relays see it as a balanced load. On the two-phase side, faults involve both transformers asymmetrically, requiring accurate modeling in protection studies to ensure rapid fault clearing and limit arc-flash energy.