Joint Box (Transformer)
A sealed enclosure on transformer tanks providing access to internal winding connections and tap changer linkages.
A transformer joint box provides sealed access to internal winding connections and tap changer linkages without opening the main tank. Mounted on the tank wall, it houses winding cable connections from the core assembly to external bushings.
Joint boxes must maintain oil-tight integrity for oil-immersed transformers. Features: bolted cover with oil-resistant gaskets, terminal blocks for HV/LV connections, cable glands, and internal busbar connections.
For large power transformers, separate joint boxes may exist for each phase. Accessible without draining oil for maintenance.
QDTB designs joint boxes with double-seal technology for reliable long-term service. See FAQ for overseas projects for maintenance guidance.
Related Products
Related Terms
Bushing
An insulated device allowing a conductor to pass through a grounded barrier while maintaining insulation integrity.
Tap Changer
A device adjusting transformer turns ratio by connecting to different tap points on a winding.
Winding
Coils of insulated conductors in a transformer carrying current and linking magnetic flux for energy transfer.
Marshalling Box
External enclosure housing transformer control wiring, terminals, and auxiliary circuits for substation connection.
More Terms Starting with “J”
Junction Box (Electrical)
An enclosure providing accessible entry points for electrical cables, enabling circuit branching and connections within power systems.
Joule Heating (I²R Loss)
Heat generated in electrical conductors proportional to current squared times resistance, the dominant source of transformer load loss.
IEEE C57.12.38
IEEE standard specifying requirements for pad-mounted, self-protected distribution transformers for North American markets.
More in “Components & Accessories”
Bushing
An insulated device allowing a conductor to pass through a grounded barrier while maintaining insulation integrity.
Busbar
A metallic strip conducting electricity within switchgear, transformers, and distribution equipment.
HV/LV Bushing
High-voltage and low-voltage insulated conduits for transformer winding connections through the grounded tank.
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