Answers to offeror's questions.pdf

FA8533-08-R-22907

72KW/90KVA GENERATOR SET

PD08WRGBGBEA04

Questions and Answers

Question: Paragraph 3.3.1.6 Line drop compensation. Speaking of “certain installations the use of a 125 ft. single jacket 115 VAC 260 amp rated cable is required; the line drop compensation circuit shall provide enough adjustment range to overcome line losses in this cable at a full 260 amp load.” We need cable characteristics information about this cable to ensure that the line drop compensation is proper.

Answer: Standard 260 amp rated "balanced" design cables as typically supplied by CAGE Code 0SMN2, 81861, or equivalent.

Question: Paragraph 3.3.1.12 Short circuit. Please define the percentage of current that constitutes a short circuit (300%, 425%, other %).

Answer: Reference PD paragraph 3.2 Generator Alternator Design. "Short circuit current is defined as not less than 300 percent of rated full load current."

Question: Paragraph 3.3.1.13 Total harmonic distortion (THD). Please clarify the statement “regardless of ancillary power supplies, motors, etc that may be operating”.

Answer: Anything operating on the GPU itself shall not cause the tolerances in 3.3.1.13 to be exceeded.

Question: Paragraph 3.3.2.1.7 Short circuit. Please define the percentage of current that constitutes a short circuit.

Answer: The contractors design will dictate the maximum short circuit capability of the GPU. Steady state short circuit current is defined as not less than 300 percent of rated full load current; however the overload capability of 3.3.2.1.6 shall be met by the contractors design.

Question: Paragraph 3.3.2.2.4 Output maximum load. Subparagraph b. what is the duty cycle of pulsed load 1?

Answer: From 10% up to 50%. Average current will not exceed GPU rated steady state value. Duration is indefinite.

Question: Paragraph 3.3.2.2.4 Output maximum load. Subparagraph c. what is the duty cycle of pulsed load 2?

Answer: 50%. Duration 2 minutes.

Question: Paragraph 3.3.2.2.5 Output load fault. What is the duration of a “spike”?

Answer: A Spike can occur during power application into a highly capacitive load or during aircraft fault clearing. In both cases:

If the contractors design is such that the GPU can limit its current output then the duration and wave shape will be determined by the GPU’s electrical characteristics when activated into a hard short or when a hard short occurs at the end of the standard external power cable.

Maximum duration will be 10 milliseconds if the cart does not act to limit the spike.

Current waveform can be assumed to have an exponential decay from 3000A for Inrush and to be square for fault clearing if the cart does not act to limit the spike.

Question: Paragraph 3.3.2.2.10 Short circuit. Please define the percentage of current that constitutes a short circuit.

Answer: The contractors design will dictate the maximum short circuit capability of the GPU. The steady state short circuit current is defined as 120 percent full load rated current.

Also reference 3.3.2.2.5 for surge short circuit currents, "The 270 converter shall survive current load current spikes of up to 3,000 amps without damage."

Question: Paragraph 3.5.2 Engine starting. Is there a particular time allotment for operation of the winterization system prior to attempting to start the engine. This time will affect the size of the winterization system chosen.

Answer: The operational time period for the winterization system allowed for -25 to -1 degree F cranking is dependent upon the engine manufacturer and contractors design, but in no instance shall the allowed heating time exceed 8 hours.

Question: Paragraph 3.8.3 Altitude. Please clarify: is a derate allowed above 5000 ft only if the temperature is above 105 degrees F? For example, if the set is operating at 7000 ft and 95 degrees F, is a derate allowed?

Answer: Reference 3.8.3 Altitude. "In altitude conditions from sea level to 5000 feet the GPU shall provide rated electrical capacity while operating in 125 degree F conditions.

Derating of the GPU is allowed at higher elevations and temperatures as follows: electrical power derating at high temperature (exceeding 105 degrees F) conditions above 5000 ft.

While the GPU is operating in 125 degrees F at altitudes up to 5000 ft conditions, no electrical power derating shall be acceptable. While the GPU is operating at altitudes above 5000 ft and up to 105 degrees F no electrical power derating shall be allowed."