Fusible Bay-O-Net et fusible à limitation de courant : Logique de coordination

Bay-O-Net fuses and backup current-limiting fuses are commonly connected in series to protect an oil-filled transformer. The Bay-O-Net link handles overloads and lower fault currents within its application limits; the backup fuse provides high-current interruption and current limitation. A suitable pair must cover the required fault range without leaving either device responsible for currents it cannot safely interrupt.

This guide concerns a Bay-O-Net paired with a backup current-limiting fuse. Full-range current-limiting fuses have different application characteristics. “Current-limiting” alone does not identify a fuse’s low-current interrupting capability.

Bay-O-Net vs backup current-limiting fuse: what to compare

Do not select the pair by matching ampere ratings alone. The assembly rating, link characteristic and backup fuse rating describe different constraints.

How to assess TCC crossover

A time-current characteristic (TCC) plot relates current to melting or clearing time. Use the specified curves for the actual catalog numbers, with currents referred to the same side of the transformer.

ABB’s basic primary-coordination method compares the expulsion fuse total-clearing curve with the backup fuse minimum-melting curve. Their crossover must be above the backup fuse’s minimum interrupting current and below the expulsion fuse’s maximum interrupting current. Manufacturer-specific exceptions require additional selection or operating restrictions; they are not a general permission to exceed a Bay-O-Net rating. See the ABB Trans-Guard application paper, section 2.

Curve crossover is only part of the review. Check that permissible overloads and inrush do not damage the backup fuse, and apply the manufacturer’s requirements for damage avoidance and the chosen coordination method. There is no universal crossover current, fixed percentage separation or fixed time margin that approves every pair.

Rated current is not minimum interrupting current

For a concrete example, Eaton lists its CBUC38065D100 backup fuse with a 38 kV voltage rating, 65 A current rating, 490 A minimum interrupting rating and 50 kA maximum interrupting rating. These values describe different properties:

• 65 A: the published current rating, subject to its application conditions.
• 490 A: the lower boundary of the published interrupting range—not a melting threshold or an automatically approved crossover.
• 50 kA: the upper interrupting rating—not a peak let-through current.

This is a manufacturer-specific example, not a ZeeyiElec product specification or a recommended Bay-O-Net pairing. An exact pair still needs its own application data.

A five-step selection workflow

1. Define the transformer and system

Record transformer kVA, primary and secondary voltage, phase count, winding connection, grounding, impedance and frequency. Obtain the available fault current at the installation and identify relevant downstream and upstream protection. Include expected loading, inrush and cold-load pickup requirements.

2. Identify the complete fuse combination

For an existing installation, record the Bay-O-Net assembly, holder, link and backup fuse catalog numbers. For a new installation, start with a manufacturer’s recommended pairing table. Eaton’s ELSP catalog CA132013EN provides application tables with distinct voltage, phase, winding-connection and transformer assumptions. Confirm that those assumptions apply before using a listed pair.

3. Check ratings and installation compatibility

Review voltage application, interrupting capability, insulating fluid, temperature, mounting and dimensional compatibility. Use the model’s published environmental corrections; do not apply a generic altitude derating percentage. BIL is an insulation withstand rating, not a fuse trip threshold or a substitute for surge protection.

4. Review the protection curves and limiting data

Plot the selected fuse curves with the transformer’s applicable inrush and withstand information and the other protective devices. Check overload protection, fault coverage and selectivity. Where equipment stress is being assessed, obtain the selected fuse’s peak let-through and clearing I²t data rather than using a generic value for all current-limiting fuses.

5. Document the approved pair

Keep the exact part numbers, datasheet revisions, TCC references, application assumptions and approved replacement instructions together. A change in link type, backup fuse, transformer connection or available fault current can require another review.

Installation and fault-response details that matter

A Bay-O-Net assembly is not a primary bushing well. Mounting and handling depend on the actual assembly. Eaton publishes separate instructions covering sidewall and cover-mounted assemblies; a universal “within 15° of vertical” rule is not appropriate.

Do not assume a fault automatically ejects the holder or provides a dropout indication. The holder withdrawal described in Eaton’s Bay-O-Net re-fusing instructions is an operating procedure. Fault investigation, isolation, checks and replacement must follow the equipment instructions and the site’s procedures for qualified personnel.

Prepare a useful fuse-pairing enquiry

When requesting Assemblages de fusibles Bay-O-Net ou current-limiting fuses, provide:

• Transformer nameplate data and available fault current.
• Winding connection, grounding and insulating fluid.
• Existing assembly, link and backup fuse part numbers, with nameplate photos where available.
• Loading and environmental conditions, required quantity and installation dimensions.
• The manufacturer pairing table or approved coordination study, if available.

Send your specifications to ZeeyiElec and request the proposed part numbers, relevant datasheets and pairing evidence. For assembly terminology and purchasing checks, see the Bay-O-Net fuse assembly guide.

Frequently asked questions

Que peut-il se passer si un Bay-O-Net et un fusible de secours ne sont pas correctement coordonnés ?

Le fusible de secours peut se déclencher inutilement, ou un dispositif peut être amené à couper un courant dépassant ses capacités. Vérifiez à la fois la couverture des défauts et les exigences du fabricant en matière de prévention des dommages.

Comment détermine-t-on le courant de croisement ?

Utilisez les courbes TCC applicables à la paire de fusibles considérée ainsi que la méthode de coordination préconisée par le fabricant. Le point de croisement n’est pas une valeur fixe déterminée uniquement par la puissance en kVA du transformateur.

Tous les fusibles à limitation de courant permettent-ils d'éliminer les défauts à faible intensité ?

Non. Un fusible de secours présente un courant de coupure minimal spécifié et nécessite une protection coordonnée en dessous de cette limite. Les modèles à plage complète présentent des caractéristiques différentes ; veuillez vérifier la classification du fusible et les données d'application.

Tous les ensembles Bay-O-Net doivent-ils être montés à la verticale ?

Il n'existe pas d'équerre de fixation universelle. Suivez les instructions d'installation correspondant à l'ensemble choisi, qu'il s'agisse d'un montage sur paroi latérale ou sur couvercle.

Comment faut-il tenir compte de l'altitude et de la température ?

Respectez les limites d'utilisation et les instructions de correction fournies par le fabricant de l'équipement sélectionné. Ne remplacez pas les données spécifiques au modèle par un pourcentage de déclassement générique.

Le support Bay-O-Net s'éjecte-t-il automatiquement en cas de dysfonctionnement ?

Ne présumez pas qu’il y a eu éjection automatique ou indication de défaillance. Vérifiez l’état du fusible en suivant les procédures applicables à l’équipement avant de le remplacer et de remettre l’installation sous tension.

Can a replacement fuse be selected by ampere rating alone?

No. Confirm the complete catalog number, voltage application, link characteristic, interrupting ratings, physical compatibility and approved pairing with the other fuse.