Solicitation Questions and Answers.pdf

Solicitation Questions and Answers

Solicitation No.: N0024426Q0094 Requirement: 3-Phase Step-Down Transformer

The following questions were received by the deadline established in the notice.

Responses are provided below for the benefit of all interested parties.

Question 1: Would the Government provide the manufacturer, model number, or part number for the transformer requirement under Solicitation No. N0024426Q0094?

Answer 1: No. This requirement is not being solicited on a brand-name or manufacturer-specific basis. The Government is requesting one custom-built, marine-grade, 3-phase step-down transformer in accordance with the requirements identified in the solicitation, including Section C and Attachment 1, Salient Characteristics. Vendors shall review the solicitation and submit a quotation for a product that meets all mandatory requirements.

Question 2: Primary Winding Configuration: Please confirm if Delta, Wye, or either configuration is required, and if a primary neutral connection is needed.

Answer 2: The required primary configuration is 480 VAC, 3-phase, 3-wire Delta. No primary neutral connection is required. The transformer shall also accommodate 460 VAC and 440 VAC input (and similar higher), preferably through appropriate primary taps, while maintaining the required nominal secondary voltage.

Question 3: Secondary Winding Configuration: Please confirm the 115 VAC secondary arrangement (115 VAC Delta 3-wire, 115 VAC Wye 4-wire, Open Delta, or other).

Answer 3: Secondary Winding Configuration: The required secondary configuration is 115 VAC, 3-phase, 3-wire Delta. A closed Delta secondary is required. An Open-Delta or Wye secondary is not intended. No secondary neutral connection is required.

Question 4: Single-Phase Output Setup: The spec notes one 115 VAC, 1-phase, 30A output (2 hot + 1 ground). Should this be wired phase-to-phase (line-to-line) or phase-to-neutral?

Answer 4: Single-Phase Output Setup: The 115 VAC, single-phase, 30A output shall be connected phase-to-phase (line-to-line) across two phases of the 115-VAC Delta secondary. The connection consists of two current-carrying conductors (hot-hot) and one equipment grounding conductor. No neutral conductor is required. The grounding equipment conductor is connected to the Conex box grounding bus and is not intended to carry normal load current.

Question 5: One-Line Electrical Diagram: Is a one-line diagram available showing incoming ship power, transformer primary/secondary connections, grounding, and output distribution?

Answer 5: One-Line Electrical Diagram: A one-line electrical diagram is not required currently. The intended configuration consists of a 480 VAC, 3-phase, 3-wire shipboard supply feeding the Delta-connected primary of the isolation transformer. A 4th shipboard supply wire provides a grounding connection. The transformer has a 115 VAC, 3-phase, 3-wire Delta secondary. The common secondary supplies two independently protected 115 VAC, 3-phase, 30A output circuits and one independently protected 115 VAC, single-phase, 30A output circuit. The single-phase circuit is connected line-to-line across two phases of the secondary.

Question 6: Grounding & Bonding Details: Please provide any additional grounding schematics or shipboard standards available for the referenced "OPEN-DELTA" grounding setup.

Answer 6: Grounding and Bonding Details: The reference to “OPEN-DELTA” in the existing salient characteristics should not be interpreted as requiring an Open-Delta transformer winding configuration. The intended transformer winding configuration is closed Delta-Delta. There is no neutral conductor on the 115 VAC secondary. The ground conductor is an equipment/protective grounding path rather than a normal current-carrying conductor. The equipment ground provided with the output connections is connected to the Conex box grounding bus. The transformer chassis and transformer grounding bus shall be bonded to the ship/hull grounding connection, as required.

The transformer shall also accommodate the backup chassis-to-ship grounding braid specified by the requiring activity.

Question 7: Connector Pinouts: For the MS17344 / MS17346 connectors, please provide required pin assignments, phase identifications, and ground terminations.

Answer 7: Connector Pinouts – MS17344 / MS17346: The three-phase output connections shall provide the three phase conductors. The single-phase output shall provide two phase conductors and the equipment/protective ground connection. No neutral connection is required. Specific connector pin assignments, phase identifications, and ground terminations will be coordinated with the transformer manufacturer to ensure compatibility with the existing Conex box connectors.

Question 8: Output Distribution: Must the two 115 VAC, 3-phase, 30A outputs run simultaneously from a common secondary (independently fused), or do they require separate secondary windings?

Answer 8: Output Distribution: The two 115 VAC, 3-phase, 30A outputs are intended to operate simultaneously from a common 115 VAC, 3-phase Delta secondary. Each output shall be independently fused or otherwise protected at 30A.

Separate secondary windings are not required. The additional 115 VAC, single-phase, 30A circuit shall also be supplied from the common secondary and independently protected. The transformer and common secondary shall be sized to support simultaneous operation of the (three) specified output circuits.

Question 9: Vector Group / Phase Displacement: Is a specific vector group required (e.g., Delta- Delta, Delta-Wye, Wye-Delta, or No Preference)?

Answer 9: Vector Group / Phase Displacement: The required transformer winding configuration is Delta-Delta. No specific vector group or phase displacement is required, provided the transformer supplies the required 115 VAC, 3-phase, 3-wire Delta output and maintains consistent phase rotation between input and output.

Question 10: Conex Box Documentation: If available, please share any Conex box input schematics, connector drawings, or load schedule details.

Answer 10: Conex Box Documentation: Additional Conex box connector drawings, pin assignments, and electrical documentation will be shared with the transformer manufacturer.

Question 11: New or Used Unit?

Answer 11: The transformer shall be supplied as a new unit.