Naval Platform — Isolated 115 VAC for Mission Equipment from a 400 VAC Ship Supply

A leading Turkish naval platform systems integrator approached TEDEG Defence for the mission equipment supply of a surface platform programme. The platform's distribution supply was 3-phase 400 VAC, while part of the mission equipment selected for the programme had been built for a 115 VAC supply and could not be connected to it directly. Because the equipment accepted 50 Hz, what was needed was not frequency conversion but voltage conversion and isolation.

The integrator sent TEDEG its electrical interface requirements and load list. The loads fell into four groups: two needed 3-phase and two needed 2-phase 115 VAC. The request was for a single converter that was MIL-STD-1399B compliant, delivered its output through an isolating transformer, could switch the four load groups individually and could be monitored over Ethernet from the command position. The commercial transformer solutions evaluated earlier did not meet the platform's isolation, EMI and shock and vibration requirements together.

The assessment by the integrator's electrical design team listed where a solution built on commercial transformers fell short:

• Voltage mismatch: 115 VAC mission equipment could not be connected directly to the 400 VAC ship supply, and a separate transformer for each equipment group added both space and cabling.
• Isolation and EMI: commercial transformers could not document the required insulation between the ship supply and sensitive mission electronics, and meeting the military EMI/EMC requirement called for extra filtering and cabinet design.
• Shock and vibration: industrial cabinets and terminal-block connections were not designed for the platform's shock, vibration and humidity conditions, and the connections were not military connectors.
• Managing load groups: a transformer gave a single output; switching four equipment groups individually meant adding a separate distribution and switching stage.
• No remote monitoring: phase voltages and currents could only be measured at the device; there was no way to see the status from the command position or to cut the outputs in an emergency.
• Peak loads: during the short peaks that occur when equipment starts, protective devices tripped and the supply was lost.

The integrator decided to have TEDEG build a military converter that would cover all of these requirements in one cabinet.

TEDEG Defence brought the integrator's requirements together in the PowerGuard 400/115 VAC AC-AC Military Inverter (TDG-PFC-A0115): 115 VAC, 50 Hz from a 3-phase 400 VAC input through an isolating transformer, with a total of 10 kVA on four separate outputs, each with its own military connector and its own button. The load groups were allocated to these four outputs according to the integrator's load list.

The PowerGuard 400/115 was delivered to the integrator's surface platform programme, and the 115 VAC mission equipment was connected to the ship supply through a single converter.

• Four load groups are managed separately, each with its own connector and button.
• The isolated output transformer provides galvanic isolation between the 400 VAC ship supply and the 115 VAC mission equipment.
• Phase voltages and currents are monitored over Ethernet from the command position, and the emergency command is issued from the same software.
• Overload headroom of up to 250% keeps the supply running through short peak loads.
• One cabinet in place of separate transformers and an added switching stage, with MIL-STD-1399B, MIL-STD-810G and MIL-STD-461G compliance in a single product.