Description
Key Technical Specifications
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Model Number: 9905-001-L
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Manufacturer: Woodward
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Sensing Voltage: 90–150 VAC or 180–300 VAC (jumper-selectable)
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Frequency Range: 45–65 Hz
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Power Consumption: 10 W max
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Control Output: 0–7 VDC speed bias (into 2301A or 505)
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Phase Window: ±5° electrical (DIP adjustable)
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Slip Frequency Limit: 0.05–0.5 Hz (field-selectable)
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Dead-Time Output: Form-C relay, 5 A @ 28 VDC
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Isolation: 1 kV rms input-to-output
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Operating Temperature: –40 °C to +71 °C
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Mounting: 8.5″ H × 2″ W card, slides in 2301A chassis or DIN clips
Woodward 9905-001-L
Field Application & Problem Solved
Synchronizing a genset by hand is a good way to blow up a breaker. The 9905-001-L watches the generator and bus voltages, calculates slip and phase angle, and gently nudges the governor until the two waveforms line up. When slip is <0.1 Hz and phase inside ±5°, it closes the “DEAD BUS” relay and tells the 2301A to ramp fuel to hold frequency. I use it on landfill-gas engines and small steam turbines that parallel with a utility feed; one card replaces the old light-bulb synchroscope and the human guessing game. The real value: it keeps the breaker closed even if the operator walks away—no more broken synch switches or burnt contacts from late closure.
Synchronizing a genset by hand is a good way to blow up a breaker. The 9905-001-L watches the generator and bus voltages, calculates slip and phase angle, and gently nudges the governor until the two waveforms line up. When slip is <0.1 Hz and phase inside ±5°, it closes the “DEAD BUS” relay and tells the 2301A to ramp fuel to hold frequency. I use it on landfill-gas engines and small steam turbines that parallel with a utility feed; one card replaces the old light-bulb synchroscope and the human guessing game. The real value: it keeps the breaker closed even if the operator walks away—no more broken synch switches or burnt contacts from late closure.
Installation & Maintenance Pitfalls (Expert Tips)
CT Polarity Reverses the Phase Reading
If the “GEN LEADS BUS” LED is on when the engine is actually slow, swap the CT polarity at the terminal strip—NOT at the breaker—so you don’t disturb the metering circuits.
If the “GEN LEADS BUS” LED is on when the engine is actually slow, swap the CT polarity at the terminal strip—NOT at the breaker—so you don’t disturb the metering circuits.
Set Slip Before You Close the Breaker
The default 0.2 Hz slip works for 4-pole gensets. On a 2-pole unit crank it down to 0.05 Hz or the breaker will slam shut 120° out and trip on instantaneous.
The default 0.2 Hz slip works for 4-pole gensets. On a 2-pole unit crank it down to 0.05 Hz or the breaker will slam shut 120° out and trip on instantaneous.
Keep the Sensing Leads Short
Long unshielded runs pick up VFD noise and the card thinks the phase is jumping. I keep leads under 10 ft or run shielded #18 twisted pair, ground one end only.
Long unshielded runs pick up VFD noise and the card thinks the phase is jumping. I keep leads under 10 ft or run shielded #18 twisted pair, ground one end only.
Verify Dead-Bus Function with a Timer
The Form-C contact is rated 5 A but inductive breakers will weld it. I always interpose a 24 VDC ice-cube relay; costs $8 and saves a $300 card.
The Form-C contact is rated 5 A but inductive breakers will weld it. I always interpose a 24 VDC ice-cube relay; costs $8 and saves a $300 card.
Woodward 9905-001-L
Technical Deep Dive & Overview
The 9905-001-L is an analog phase-locked loop on a single Euro-card. Input transformers drop bus and gen voltage to 12 VAC; zero-cross detectors generate square waves that feed a 4046 phase comparator. The resulting error voltage is filtered and buffered to 0–7 VDC, then sent to the governor’s speed-bias input. A separate window comparator watches slip frequency; when both slip and phase are inside the DIP-selected window it energies the dead-bus relay. No microprocessor—everything is op-amps and comparators—so it survives RF storms and never needs firmware. Rev L adds thicker conformal coat and replaces the original mylar caps with 105 °C film for geothermal and paper-mill duty.
The 9905-001-L is an analog phase-locked loop on a single Euro-card. Input transformers drop bus and gen voltage to 12 VAC; zero-cross detectors generate square waves that feed a 4046 phase comparator. The resulting error voltage is filtered and buffered to 0–7 VDC, then sent to the governor’s speed-bias input. A separate window comparator watches slip frequency; when both slip and phase are inside the DIP-selected window it energies the dead-bus relay. No microprocessor—everything is op-amps and comparators—so it survives RF storms and never needs firmware. Rev L adds thicker conformal coat and replaces the original mylar caps with 105 °C film for geothermal and paper-mill duty.
