Description
Key Technical Specifications
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Model Number: DS3800NVRC1C1C
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Manufacturer: General Electric
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Logic Voltage: +5 V @ 1 A, ±12 V @ 150 mA from rack back-plane
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Analog Inputs: 3 differential, ±10 V generator PT/CT, 12-bit scaling resistors
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VAR Reference: Front-panel 20-turn 50 kΩ pot, 0–115 % of name-plate VARs
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Curve Storage: 256-byte EEPROM (2816) holds 16-point piece-wise VAR limit
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Digital Section: 4-bit comparator latch, feeds “VAR HI” flag to protection CPU
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Isolation: 500 Vrms field-to-logic via resistor-divider network (no optos)
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Connectors: 96-pin DIN to back-plane, two 12-position headers for external PT/CT
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LED Indicators: Green “LOGIC OK,” red “VAR LIMIT” visible through bezel
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Operating Temperature: 0 – 70 °C operational, –40 – 85 °C storage
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Dimensions: 6.3 × 9.0 in (160 × 229 mm), single-slot 6U Euro-card
GE DS3800NMSM1G1E
Field Application & Problem Solved
A frame-5 peaker running on a 1980s static exciter doesn’t care about IEEE 1547—it cares about not slipping poles when the operator jacks the VAR meter past the stability curve. The DS3800NVRC1C1C sits two slots left of the exciter firing card, reads generator terminal volts & amps, and forces the field current down when the reactive power hits the EEPROM curve. You set the knee with the front-panel pot, lock the nut, and forget it for twenty years. When the card drifts—usually the pot gets dirty—you see VAR hunting or nuisance “VAR HI” trips; swap the board, dial the pot back to the Sharpie witness mark, and the oscillation stops. You’ll find this PCB in any plant that still runs a var-limit relay in hardware: paper-mill back-pressure sets, refineries, and every frame-5/6 that never upgraded to digital AVRs. Its core value is bullet-proof limiting: the curve is baked in EEPROM, so you get the same 115 % circle the generator was commissioned with—critical for keeping old electromechanical distance relays from tripping on under-excited impedance.
A frame-5 peaker running on a 1980s static exciter doesn’t care about IEEE 1547—it cares about not slipping poles when the operator jacks the VAR meter past the stability curve. The DS3800NVRC1C1C sits two slots left of the exciter firing card, reads generator terminal volts & amps, and forces the field current down when the reactive power hits the EEPROM curve. You set the knee with the front-panel pot, lock the nut, and forget it for twenty years. When the card drifts—usually the pot gets dirty—you see VAR hunting or nuisance “VAR HI” trips; swap the board, dial the pot back to the Sharpie witness mark, and the oscillation stops. You’ll find this PCB in any plant that still runs a var-limit relay in hardware: paper-mill back-pressure sets, refineries, and every frame-5/6 that never upgraded to digital AVRs. Its core value is bullet-proof limiting: the curve is baked in EEPROM, so you get the same 115 % circle the generator was commissioned with—critical for keeping old electromechanical distance relays from tripping on under-excited impedance.
Installation & Maintenance Pitfalls (Expert Tips)
Potentiometer dust—VAR needle hunts
The 20-turn pot faces up; coal dust works into the track and the wiper jumps 0.5 % VAR. Generator starts swinging ±5 MVAR. Hit the pot with DeoxIT, exercise it ten turns, reset to the witness mark—hunting gone for another decade.
The 20-turn pot faces up; coal dust works into the track and the wiper jumps 0.5 % VAR. Generator starts swinging ±5 MVAR. Hit the pot with DeoxIT, exercise it ten turns, reset to the witness mark—hunting gone for another decade.
EPROM creep—curve drifts low
The 2816 EEPROM holds the 16-point VAR limit. After 15 years the charge pump in the SCR driver drifts; VAR ceiling drops to 108 % and you trip on “VAR HI” during peak summer. If you find yourself cranking the pot CCW every month, burn a new 2816 with the factory constants instead of chasing the drift.
The 2816 EEPROM holds the 16-point VAR limit. After 15 years the charge pump in the SCR driver drifts; VAR ceiling drops to 108 % and you trip on “VAR HI” during peak summer. If you find yourself cranking the pot CCW every month, burn a new 2816 with the factory constants instead of chasing the drift.
Wrong keying—120 VAC on 10 V input cooks the divider
The PT/CT connectors are keyed alike but pin-outs are mirror-image. Land the generator PT on the wrong header and you stuff 120 VAC into a 1/20 divider—resistor network carbonizes, card smells like popcorn. Match the white wire-stripe to the silk-screen triangle before you push the plug home.
The PT/CT connectors are keyed alike but pin-outs are mirror-image. Land the generator PT on the wrong header and you stuff 120 VAC into a 1/20 divider—resistor network carbonizes, card smells like popcorn. Match the white wire-stripe to the silk-screen triangle before you push the plug home.
GE DS3800NMSM1G1E
Missing nylon washer—card arcs to rack
The four corner holes are through-plated. Forget the fiber washers and the card edge sits 0.5 mm proud; 24 V battery finds the rack paint, arcs, and blows a hole in the ground plane. Use the original GE shoulder washers or add 2 mm nylon spacers—torque to 8 in-lb, no more.
The four corner holes are through-plated. Forget the fiber washers and the card edge sits 0.5 mm proud; 24 V battery finds the rack paint, arcs, and blows a hole in the ground plane. Use the original GE shoulder washers or add 2 mm nylon spacers—torque to 8 in-lb, no more.
Technical Deep Dive & Overview
DS3800NVRC1C1C is an analog comparator card frozen in 1987 silicon. Three precision resistor dividers scale generator volts and amps down to ±5 V; a quad 741 op-amp subtractor calculates instantaneous VARs. A 4-bit digital comparator latches the VAR magnitude against the EEPROM curve every 40 ms; when the calculated VAR exceeds the set-point the card yanks the “VAR HI” line low, forcing the exciter firing card to back off field current. The front-panel pot lets you bias the entire curve ±15 % so you can match the generator name-plate without reburning ROM. No opto-isolators here—just old-school resistor isolation good for 500 V—so keep the PT/CT grounds single-point or you’ll smoke the dividers. Think of it as a hardware circle diagram; treat the pot like a calibrated resistor and the VAR meter will stay inside the stable zone for another thirty years
DS3800NVRC1C1C is an analog comparator card frozen in 1987 silicon. Three precision resistor dividers scale generator volts and amps down to ±5 V; a quad 741 op-amp subtractor calculates instantaneous VARs. A 4-bit digital comparator latches the VAR magnitude against the EEPROM curve every 40 ms; when the calculated VAR exceeds the set-point the card yanks the “VAR HI” line low, forcing the exciter firing card to back off field current. The front-panel pot lets you bias the entire curve ±15 % so you can match the generator name-plate without reburning ROM. No opto-isolators here—just old-school resistor isolation good for 500 V—so keep the PT/CT grounds single-point or you’ll smoke the dividers. Think of it as a hardware circle diagram; treat the pot like a calibrated resistor and the VAR meter will stay inside the stable zone for another thirty years
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