Vertical Current Transformer

A vertical busbar current transformer (CT) is a window-type CT designed to sit directly on a flat copper or aluminum busbar. The rectangular aperture matches the busbar profile (e.g., 40×60, 40×80, 40×100, 40×120), so the phase conductor passes through the CT without cutting, drilling, or using extra hardware. The CT “steps down” large primary currents to a safe, standardized secondary (typically 5 A or 1 A) for meters and protective relays, while providing galvanic isolation.

Why you need vertical busbar CTs

  • Accurate measurement & billing: Converts thousands of amperes into a precise secondary signal for multifunction meters and power quality analyzers (Class 0.2S/0.5 where required).

  • Protection: Feeds overcurrent and earth-fault elements in protection relays (Class 1 typical for protection/instrumentation), enabling fast trip decisions to protect cables, breakers, and downstream loads.

  • Safety & compliance: Maintains high current within the busbar; technicians work only with the safe secondary circuit, thereby improving compliance with panel-building standards.

  • Compact panels: The vertical form factor aligns with the busbar stack, saving depth and wiring space compared to cable-through CTs. Ideal for MDBs, SMDBs, MCCs, capacitor banks, gensets, UPS switchboards, and solar/inverter panels.

  • Fast retrofit: Drop-in mounting on existing busbars reduces downtime compared with cutting cables or installing split-core round CTs.

Typical integrations

  • Energy meters / MFMs / PQ analyzers for kWh, kW, PF, harmonics.

  • Protection relays (overcurrent, earth-fault, thermal overload): three-phase CTs wired to a relay; residual (ΣI) connections can provide sensitive earth-fault detection.

  • APFC controllers: phase-current input improves reactive power control and capacitor step switching.

  • Genset/AMF & synchronization panels: stable current feedback for load sharing and protection.

Selecting the right CT

  • Primary current: Match busbar or breaker rating; choose the nearest standard primary (e.g., 400–3200 A).

  • Window/busbar size: Ensure the CT aperture suits the busbar (e.g., 40×80). Allow clearance for insulation and tolerances.

  • Accuracy class:

    • 0.2S → high-accuracy metering / PQ.

    • 0.5 → general metering.

    • 1 → protection/instrumentation.

  • Burden (VA): Must exceed the total connected load of meters/relays plus lead losses. Rule of thumb:
    VA_required ≥ VA_meter/relay + (Isec² × R_leads) with Isec = 5 A or 1 A.

  • Environment: Check insulation class, operating temperature, and max system voltage.

Installation best practices

  • Orient P1 → source, P2 → load for correct polarity and vector measurements.

  • Keep a shorting link on the secondary; never open-circuit a CT while energized.

  • Use twisted pair, one-point secondary earthing, and route away from high-EMI paths.

  • Label each phase and record ratio/accuracy for commissioning tests (ratio, polarity, and burden checks).

Bottom line: Vertical busbar CTs provide the safest, neatest, and most space-efficient way to measure and protect high-current busbar feeders—delivering the accuracy your meters need and the reliability your relays demand.