SALEM
SALEM STUDY SYSTEM
Systems > EDGs

EDGs

⚠️ DRAFT

EDGs

Function

Provide standby AC power to vital buses on loss of offsite power or upon receipt of a safety injection signal. Three separate and independent diesel generators per unit, each with a separate fuel supply and day tank. (UFSAR 8.3.1.5)

Auto-Start Signals

  • Safety Injection signal
  • Loss of voltage on vital buses
  • Degraded voltage on vital buses (UFSAR 8.3.1.5)

Key Design Points

  • Each vital 4160V bus has a dedicated diesel generator
  • 10-second start to rated speed and voltage
  • Safeguards loads sequenced onto DGs after start to prevent overloading
  • 7-day fuel oil supply required for OPERABILITY
  • Each DG independent with separate fuel supply, starting air, and cooling
Exam — 2023 Q12
EDG starting circuits are supplied from 125 VDC power. On loss of the associated 125V DC bus, the EDG will NOT start automatically from SI/SEC signal or remotely from the control room. The SI signal goes to the SEC (powered by vital instrument power), which sends a start signal to the EDG start circuitry (DC powered). Without DC, the start circuit cannot function.
Exam — 2023 Q48
EDG starting air compressor power supplies: both 21A and 21B starting air compressors for 2A EDG are powered from the same 2A 230V Vital Bus (NOT from separate buses). Each EDG's two starting air compressors are supplied from its own associated 230V vital bus.
Exam — 2022 Q50
EDG minimum load after paralleling: ≥500 KW must be loaded immediately after closing the output breaker to prevent tripping the output breaker on reverse power. Separate concern: gradual loading prevents excessive accumulation of oil in the exhaust system (exhaust fire risk from sudden high loading after low-load operation). 250 KW is NOT the minimum — it is 500 KW. The reason for minimum load is reverse power trip protection, NOT exhaust fire prevention (which is a separate P&L for gradual loading).
Exam — 2020 Q11
EDG loading ratings: 2000 hr rating = 2750 KW, 2 hr rating = 2860 KW, 30 min rating = 3100 KW, Continuous rating = 2600 KW. Per S2.OP-SO.PZR-0010, PZR backup heaters add approximately 210 KW to bus load. Before adding PZR heater load, current EDG loading must be adjusted to no greater than 2750 - 210 = 2540 KW. Trap: candidates confuse the four EDG loading limits. The 2000 hr limit (2750 KW) is the relevant one for sustained post-LOOP operation, not the 30-min (3100 KW), 2-hr (2860 KW), or Continuous (2600 KW) rating.
Exam — 2018 Q42
Per S2.OP-ST.DG-0001, to prevent tripping the Diesel Generator Breaker on reverse power, generator load must be IMMEDIATELY raised to greater than a minimum of 500 KW after the breaker is closed. EDG Continuous Load Rating is 2600 KW. Trap: 2750 KW is the 2000-hour rating (2681 KW Local), NOT the Continuous rating. 200 KW is the minimum load when UNLOADING the EDG (to prevent reverse power trip before opening the breaker) — a different value from the 500 KW minimum when LOADING.

EDG Room Ventilation

Exam — 2019 Q24
During EDG operation, the Diesel Area Ventilation will ensure the EDG Room does not exceed a MAXIMUM of 120 °F. Trap: 90 °F is a plausible distractor but is NOT the correct limit. The actual ventilation design limit is 120 °F.

EDG Controls When Paralleled

Exam — 2020 Q48
When the EDG is paralleled to the grid for surveillance testing: Voltage Control Switch adjusts KVAR (reactive) load — Raise increases KVAR OUT. Speed Control Switch adjusts KW (real) load. Common confusion: speed control adjusts frequency/real power, NOT reactive power. Voltage control adjusts reactive power, NOT voltage (when paralleled to the grid, generator voltage is locked to grid voltage).

Starting Air System

Exam — 2020 Q50
Each EDG has 4 air start motors total, supplied by 2 starting air receivers. Each receiver supplies 2 air start motors (one train). Each receiver is capable of 3 cold starts. Two air start motors start the diesel in < 10 seconds. Just one air start motor can start the diesel within 14 seconds. Rated speed is 900 RPM. With one air receiver isolated, the remaining receiver and its 2 motors will start the EDG and achieve rated speed in ≤ 13 seconds. Each receiver supplies only 2 of the 4 air start motors — NOT all four. Loss of one receiver does not prevent EDG start.

EDG Lube Oil Setpoints

Exam — 2019 Q79
EDG Engine Lube Oil Header Low Pressure: alarm at 60 psig, trip at 40 psig. Per S2.OP-AR.DG-0001, the EDG trips when lube oil header pressure FIRST lowers below 40 psig. Trap: the alarm actuates at 60 psig — 20 psi above the trip setpoint. The trip is at 40, not 60.
Exam — 2019 Q83
EDG Lube Oil Hi Temp: local alarm at 190 °F, EDG trips at 205 °F. Per 2B DG Alarm Response Manual, the EDG tripped when Lube Oil Temperature FIRST exceeded 205 °F. Trap: 190 °F is the alarm setpoint, not the trip setpoint. The trip occurs at 205 °F.

Diesel Generator Trip Functions

DGs have protective trips that are bypassed during emergency start (SI or loss of voltage) to ensure the DG remains running when needed. Only certain trips remain active during emergency operation. (UFSAR 8.3.1.5.2)

Safeguards Loading Sequence

On SI signal with loss of offsite power:

  1. DGs auto-start
  2. Vital bus loads shed
  3. DGs connect to vital buses
  4. Safeguards loads sequenced on in prescribed order and time delays (UFSAR 7.3, 8.3)

Tech Spec LCOs

  • TS 3/4.8 — Electrical — TS 3.8.1.1 requires 3 DGs OPERABLE in Modes 1–4; TS 3.8.1.2 requires 2 DGs OPERABLE in Modes 5–6
Exam — 2018 Q21
LCO 3.8.1.2 (ELECTRICAL POWER SYSTEMS - SHUTDOWN) requires a minimum of TWO separate and independent diesel generators to be OPERABLE (Modes 5 and 6). Trap: LCO 3.8.1.1 (Operating) requires THREE — do not confuse the Operating (3) vs Shutdown (2) EDG requirements. If ALL REQUIRED EDGs are inoperable in shutdown, the crew is required to IMMEDIATELY suspend all operations involving positive reactivity changes. REQUIRED ACTION A has an option to only declare affected required features inoperable, but REQUIRED ACTION B requires immediate suspension of positive reactivity changes.
Exam — 2018 Q22
Following a Reactor Trip + SI coincident with LOOP at Unit 2 with EDG 2B unable to start: 2A and 2C Vital Buses are powered from EDG 2A and EDG 2C. 15 minutes later, ECCS loads have been sequenced onto the running EDGs. 22 RHR Pump (2B bus) is stopped; 22 SI Pump (2C bus) is running. Pump number does NOT always match bus letter — 22 RHR is on B bus, 22 SI is on C bus.
- 1 DG inoperable: 72 hours; demonstrate OPERABILITY of remaining DGs within 24 hours - 1 DG AND 1 offsite circuit inoperable: 12 hours
Exam — 2023 Q89
Common mode failure surveillance scheduling: per S2.OP-ST.DG-0001/2/3 P&L 2.1.6, only one DG per unit may be synchronized to the grid at a time (Reg Guide 1.108, Section C.2.b). Most expeditious method for 5 remaining EDGs: run one EDG at a time on both units simultaneously (e.g., 1B and 2B at the same time). Trap: running all EDGs on one unit simultaneously violates the P&L — you cannot run 1B and 1C simultaneously even though it would be faster.
JPM — 2023 IP-i
SBO Diesel Control Air Compressor: backup control air source when all ECACs are unavailable during LOOP. Located in SBO Compressor Building (outside RCA, requires L-3 key). Discharge valves 1CA1913, 1CA1886, and 2CA584 pressurize Control Air and Aux Building headers.
Exam — 2022 Q89
EDG common mode failure TS 3.8.1.1 actions: when a failure cause (e.g. K1C relay) is identified that could affect operable EDGs with the same components, the SRO must apply action b.3 (perform operability run on remaining EDGs within 24 hours) AND action b.4 (restore inoperable EDG within 72 hours). A common mode failure does NOT automatically make all EDGs inoperable — the remaining EDGs are presumed operable until demonstrated otherwise. TS 3.0.3 does NOT apply because action "e" exists for two or more diesels inoperable. Do not declare all EDGs inoperable based solely on a common mode concern.
JPM — 2022 SRO-A5
Loss of ALL AC power to Unit 2 — General Emergency classification: 2A EDG tripped on overspeed (bent fuel rack linkage, 5 hrs to repair), 2B 4KV Vital Bus damaged (ground fault), 2C EDG engine failure (piston failure). Combined with loss of both offsite sources (23 SPT in maintenance, 24 SPT internal fault), this constitutes EAL SG1.1 — Loss of AC Power at GE level. AC power cannot be restored within the EAL timeframe.
Scenario — 2022 #3
2A EDG running unloaded for maintenance run (initial condition). 2A EDG emergency trips during scenario. CRS evaluates TS 3.8.1.1 action b.1 (1 hour line surveillance) and action b.4 (72 hours to restore EDG to Operable status). No impact to plant operations.
Scenario — 2020 #1
2C EDG C/T for governor oil replacement and fuel rack lube (initial condition, 68 hours remaining in TSAS). Following LOOP: 2A 4KV Vital Bus lost on Bus Differential protection, 2B EDG trips on overspeed (bent fuel rack linkage). All three 4KV Vital Buses de-energized — station blackout. Crew must identify 2C EDG as the only recovery path, have maintenance return it from C/T, start 2C EDG, close output breaker to energize 2C 4KV Vital Bus (CT-24), then immediately start one SW pump for EDG cooling (CT-25).
JPM — 2020 SRO-A3
EDG operability with degraded SW: 1A EDG fails surveillance and declared INOPERABLE with 13 SW Pump C/T. Candidate must determine TWO SW Loops remain OPERABLE (meets one pump per bus AND two pumps per bay requirements). Therefore TS 3.8.1.1 Action b.2 does NOT apply — only b.1 (1 hr), b.3 (24 hrs), b.4 (72 hrs). This is Special Case D / Case #1 from S1.OP-SO.DG-0005 Exhibit 1.
JPM — 2019 SRO-A3
EDG CIT with redundant component failure: 1B EDG CIT for maintenance (TS 3.8.1.1 action b entered, 60 hours remaining). 12 Charging pump trips at 0700 — S1.OP-SO.DG-0005 identifies 12 Charging pump as a redundant required feature of the 1B EDG. Two LCOs apply: TS 3.8.1.1 action b.2 (4 hours) for EDG + redundant component inoperable, AND TS 3.5.2.a action a (72 hours) for inoperable ECCS subsystem. At 1100 hours (4 hours elapsed), neither restored — shutdown per TS 3.0.3: Mode 3 by 1700, Mode 5 by 2300 next day. TS 3.0.3 shutdown timing is NOT appropriate here because specific action b.2 exists — but the result is the same 6-hour and 30-hour shutdown sequence.
JPM — 2019 Sim-g
Start and load 2C EDG during LOPA per EOP-LOPA-1: all three EDGs initially unavailable (2A tripped, 2B bus locked out on Bus Differential, 2C was C/T). After 2C EDG restored from maintenance: start EDG, verify FREQUENCY >= 60 Hz and VOLTS >= 4.15 KV, close output breaker via MIMIC PB sequence (select 2C DG 4KV BKR 2CDD → verify Yellow → close breaker). 2C TROUBLE console alarm will be illuminated due to loss of bus voltage — this is expected and should not delay breaker closure. Must start one SW pump (25 or 26) for EDG cooling and close 23SW20 before loading C bus loads.
Exam — 2018 Q60
EDG paralleled to grid during surveillance (ST.DG-0003) + LOOP: 2C EDG Output Breaker will OPEN then reclose. Even though 2C EDG was already running and loaded, when the LOOP causes 2A and 2B buses to sense Instantaneous UV, all three SECs enter Mode II (Blackout Only). Mode II strips all loads and opens the EDG output breaker before reclosing it and sequencing blackout loads. Trap: the breaker does NOT remain closed — Mode II requires a full strip-and-reload cycle even for the already-running EDG.

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