N242-073 TITLE: Transient Voltage Suppressor (TVS) for F/A-18 E/F and EA-18G
OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): FutureG; Sustainment
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OBJECTIVE: Develop a Transient Voltage Suppressor (TVS) that will limit the overvoltages to avionics components to 150 volts root-mean-square (Vrms) maximum, instead of the MIL-STD-704E requirement of 180 Vrms.
DESCRIPTION: F/A-18 E/F and EA-18G use MIL-STD-704E Aircraft Electric Power Characteristics, the electrical power interface specification. MIL-STD-704E requires avionics to withstand overvoltage transients to 180 Vrms, but many avionics components were not tested to the 180 Vrms causing reduced avionics reliability.
MIL-STD-704E requires avionics to withstand overvoltage transients to 180 Vrms, but many Avionics were not tested to the 180 Vrms transients, and are failing in the fleet as a result. The reason testing was not performed for F/A-18 was because in 1999 when aircraft went into full-rate production, there was no test method for MIL-STD-704E; the test method was not implemented until 2010. The most economical solution per aircraft is to place the TVS on two electrical busses instead of inside 50 avionic boxes. The TVS needs to limit the overvoltages to 150 Vrms maximum instead of the MIL-STD-704E of 180 Vrms requirement. The TVS needs to start limiting when the voltage gets to between 130–140 Vrms, and clamp at a maximum of 150 Vrms.
PHASE I: Perform a study to design a TVS that meets F/A 18- E/F and EA-18G capabilities. Use MIL-STD-704E Aircraft Electric Power Characteristics, the electrical power interface specification, as a basis for the design. The Phase I effort will include prototype plans to be developed under Phase II. The TVS needs to limit the overvoltages to a maximum of 150 Vrms instead of the MIL-STD-704E of 180 Vrms requirement. The TVS needs to start limiting when the voltage gets to between 130–140 Vrms, and clamp at a maximum of 150 Vrms.
PHASE II: Development of two TVS prototypes that should meet the following test requirements:
1. Joule dissipation at 25 °C < 2625 Joules,
2. Joule dissipation on infinite heatsink at TL = 75 °C < 2625 Joules,
3. Peak forward surge current, 1025ms single half-sinasoidal wave (bidirectional only) 350 amperes root mean square (Arms),
4. Operating and storage temperature range -55 °C to +175 °C,
5. Vrms minimum range 130 to maximum range 140,
6. Arms maximum reverse leakage 5 mA to 2 µA at Voltage Reverse Working Maximum 108 Vrms,
7. Voltage Reverse Working Leakage of a Vrms 108,
8. Maximum Reverse Surge Current I peak to peak Amps rms 172.9 Ipp, and
9. Maximum Clamping Voltage 150 Vrms at Ipp.
Navy Military Standards & Testing:
10. MIL STD 704 Electrical interface,
11. MIL STD 810 needs to be environmentally qualified,
12. MIL STD 461 EMI
PHASE III DUAL USE APPLICATIONS: Perform laboratory testing and then install the prototype(s) in an aircraft for an aircraft ground and flight test.
Commercial electrical system developers that use the electrical power interface specification can use TVS. Commercial aircraft requires avionics to withstand overvoltage transients to 180 Vrms, but many avionics components were not tested to the 180 Vrms.
REFERENCES:
KEYWORDS: Electrical; transient; voltage; suppressor; avionics; MIL-STD-704
** TOPIC NOTICE ** |
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| 5/1/24 | Q. | Can you define which MIL-STD-810/environmental test methods need to be conducted on the proposed TVS device(s)? |
| A. | ALL | |
| 5/1/24 | Q. | What is the preferred method of interface between the TVS device(s) & the aircraft (connectors, terminal lugs/ring terminals, screw clamps, splices, etc.)? |
| A. | TERMINAL LUGS/RING | |
| 5/1/24 | Q. | Is the preferred envelop size described in one of the responses inclusive of connector dimensions? |
| A. | 4 WIRES OUT NO CONNECTORS | |
| 5/1/24 | Q. | What is the preferred connector type to be used? |
| A. | 4 WIRES OUT NO CONNECTORS | |
| 5/1/24 | Q. | Is the max reverse surge current value (Ipp) of 172.9 Arms that was specified in the SBIR topic a requirement for each TVS device used on each phase of each separate bus? |
| A. | YES | |
| 5/1/24 | Q. | Are all the electrical test requirements specified for phase II of the SBIR topic absolute requirements? What possible potential “tradeoffs” for any of these requirements exist? |
| A. | NO TRADE OFF BECAUSE OF MILITARY STANDARD | |
| 5/1/24 | Q. | Is there test data available that quantifies the exact nature of the transients? |
| A. | YES THERE ARE TEST DATA DTO QUANTIFY 180 VOLT RMS TO 254 PEAK VOLTAGE | |
| 5/1/24 | Q. | Is the TVS needed to resolve issues caused by AC transients or by DC transients or both? |
| A. | AC TRANSIENT | |
| 5/1/24 | Q. | The SBIR mentions “50 avionics boxes” needing protection from a TVS device, are all of these boxes powered by AC power, or are some powered by DC power? |
| A. | Plan is starting from the Generator the AC main line contactor to the TVS will cut transient voltages to the 115 volt AC bus. | |
| 5/1/24 | Q. | What is the preferred electrical “Location” of these devices within the power distribution system? |
| A. | OUT PUT OF MAIN LINE CONTACTOR | |
| 5/1/24 | Q. | What is the preferred physical location for installation of these devices in the aircraft? |
| A. | Bay 10 left/right | |
| 5/1/24 | Q. | The SBIR states that TVS is to be placed on two electrical busses. Which two electrical busses do these devices need to be installed on? |
| A. | Plan is starting from the Generator the AC main line contactor to the TVS will cut transient voltages to the 115 volt AC bus 1 & BUS 3 | |
| 04/24/24 | Q. | Is there a target size & weight for the TVS unit?
Based on topic description, one TVS unit will be place on each of two electrical busses. Can we assume that these two TVS units will equally (or approximately equally) share the regulation function (i.e. impedance from TVS install locations to generator are approximately equal)? |
| A. | Size cubic inches(2x2x3); 4 pounds. Two separate TVS equal for 2 buses. | |
| 04/24/24 | Q. | Does the aircraft generator have an output-voltage control loop to maintain the target nominal output voltage?
If so, what is causing the dramatic rise in generator output voltage, up to 180Vrms (phase-to-neutral). |
| A. | Yes, the TVS will limit the buss voltage to 140-150 vrms | |
| 04/24/24 | Q. | MIL-STD-704E refers to 400Hz; however, not clear whether these referenced aircraft have a fixed frequency or variable frequency AC generator?
If variable, what is the frequency range? |
| A. | The GCU Output frequency and voltage is form PS 74-990075 Rev D which is 393-407 Hz steady state, transient frequency is 380-420 Hz and the 105Vrms-125Vrms steady state with transient voltages 0-180Vrms. MIL-STD-704 frequency range for 115 Volt 400Hz constant frequency is 380-420 Hz. |