KKS Code Reference — Supercritical Thermal Plant
Kraftwerk-Kennzeichensystem (Power Plant Identification System) codes for a coal-fired supercritical unit, with a full tag-building methodology and a click-down Area → System → Subsystem explorer — boiler, turbine-generator, coal handling, cooling water, water treatment, electrical, and I&C — plus the finer signal suffix codes (XB, XG, XH, XQ...) appended after an equipment tag to identify an individual command or feedback signal. Searchable by code or by what a system actually does.
KKS Tag Methodology
A complete KKS tag is built from four breakdown levels, read left to right, each narrowing the identification further. Worked example — a specific pump on the economizer system of Unit 1:
Level 0 — Total Plant Key: 10
Level 1 — Function Key (Process Code): HAC
Level 2 — Equipment Unit Key: 01 + AP
Level 3 — Component Key: 001
Put together: 10HAC01AP001 reads as "Unit 1, economizer system, first instance, a pump, component 001 of it" — unique, and readable without a lookup table once you know the four levels. The area/system/subsystem explorer below builds exactly the Level 1 portion of this — pick an area, then a system, then a subsystem, to land on its F1F2F3 code.
Explore by Area → System → Subsystem
Full Code List
H — Conventional heat generation
KKS main group letter for the whole boiler/steam generator area.
HA — Pressure system — feedwater and steam sections
The boiler's actual pressure parts, in flow order.
HAA — IP/LP part-flow feed heating system (flue-gas-heated)
HAB — HP part-flow feed heating system (flue-gas-heated)
HAC — Economizer system
HAD — Evaporator system
HAG — Circulation system
Not used in a natural-circulation boiler — its presence or absence in a real HAG tag is itself a quick sanity check on whether the unit is drum-type or once-through supercritical.
HAH — HP superheater system
HAJ — Reheater system
HAK — Secondary reheater system
HAM — Triflux system
A combined economizer/evaporator/superheater surface arrangement used in some once-through supercritical designs.
HAN — Pressure system drainage and venting systems
HAV — Lubricant supply system
HAW — Sealing fluid supply system
HAX — Fluid supply system for control and protection equipment
HAY — Control and protection equipment
HB — Support structure, enclosure, steam generator interior
HBA — Frame incl. foundations
HBB — Enclosures
HBC — Brick linings incl. insulating brickwork
HBD — Platforms, stairways
HF — Bunker, feeder and pulverizing system
The mills/pulverizers, not the raw coal handling & stacking system (that's under E).
HFA — Bunker for pulverizing system
HFB — Feeder system
HFC — Pulverizing system (incl. classifier)
HFD — Flue gas return system (mill)
HFE — Mill air system, carrier air system
HFG — Pulverized coal temporary storage bunker after central pulverizing system
Only present with indirect (central) firing, not direct/unit firing.
HH — Main firing system
HHA — Main burners
HHB — Retarded combustion grate
HHE — Pulverized coal bin, forwarding and distribution system
HHF — Oil temporary storage, pump and distribution system
Light/heavy fuel oil for start-up and flame stabilization.
HHG — Gas pressure reduction, distribution system
HHL — Combustion air supply system
HHM — Atomized medium supply system (steam)
HHV — Electric heating system
HL — Combustion air system (primary, secondary air)
HLA — Ducting system
HLB — Fan system, forced-draught fan (FD fan) system
HLC — External air heating system (not flue-gas-heated)
HLD — Air heating system (flue-gas-heated)
Regenerative/tubular air preheater.
HN — Flue gas exhaust (without flue gas treatment)
HNA — Ducting system
HNC — Induced-draught fan system (ID fan)
HNE — Smoke stack system (chimney)
HNF — Flue gas recirculation system
HD — Furnace ash, slag and dust removal
HDA — Furnace ash removal, furnace slag removal, bed ash removal
Bottom ash system.
HDB — Bed ash return system
HDC — Flue dust discharge and return system
HDD — Mechanical dust handling system
HDE — Electrostatic precipitator (ESP)
HDF — Cyclone dust removal and return system
HDT — Fluid supply system for ash, slag and dust moistening
HR — Chemical flue gas treatment, adsorptive process
e.g. dry sorbent injection.
HS — Chemical flue gas treatment, catalytic process
e.g. SCR/DeNOx.
HSA — Flue gas ducting system within HS
L — Steam, water, gas cycles
KKS main group letter for the whole steam-water cycle area (feedwater, steam, condensate).
LA — Feedwater system
LAA — Storage, deaeration (incl. feedwater tank)
LAB — Feedwater piping system (excl. feedwater pump and heating)
LAC — Feedwater pump system
Boiler feed pumps — in a supercritical unit these run at markedly higher discharge pressure than a subcritical drum plant.
LAD — HP feedwater heating system
LAE — HP desuperheating (attemperation) spray system
Especially critical on a once-through supercritical boiler, which has no steam drum to passively damp temperature swings — spray attemperation is the primary means of steam temperature control.
LB — Steam system
LBA — Main steam piping system
LBB — Hot reheat piping system
LBC — Cold reheat piping system
LBD — Extraction piping system
LBF — HP reducing station
Part of the HP bypass system, routing main steam around the turbine during start-up/trip.
LBG — Auxiliary steam piping system
LBH — Start-up steam system, shutdown steam system
LBJ — Moisture separator/reheater (MSR)
LBQ — Extraction steam piping for HP feedwater heating
LBS — Extraction steam piping for LP feedwater heating (main condensate)
LBW — Sealing steam system
LC — Condensate system
LCA — Main condensate piping system
LCB — Main condensate pump system
LCC — LP feedwater heating system, condensate polishing plant
LD — Water treatment (for the cycle itself)
LDH — Deaeration
LDB — Independent demineralizing plant system
Condensate polishing.
M — Main machine sets
KKS main group letter for the turbine and generator.
MA — Steam turbine plant
MAA — HP turbine
MAB — IP turbine
MAC — LP turbine
MAD — Bearings
MAG — Condensing system
Includes the condenser and its flash boxes.
MAJ — Air removal system
Condenser vacuum/air ejector system.
MAK — Transmission gear between prime mover and driven machine, incl. turning gear
MAL — Drain and vent systems
MAM — Leak-off steam system
MAN — Turbine bypass station, incl. desuperheating spray system
HP bypass — dumps main steam to the reheat line / condenser, bypassing the HP turbine.
MAP — LP turbine bypass system
MAV — Lubricant supply system, dirty oil collection system
MAW — Sealing, heating and cooling steam system
MAX — Non-electric control and protection equipment
MAY — Electric control and protection equipment
MK — Generator plant
MKA — Generator, complete, incl. stator and rotor
E — Conventional fuel supply and residues disposal
KKS main group letter for fuel handling.
EA — Unloading and storage of solid fuels
EAA — Ship unloading system
EAB — Rail wagon / truck unloading bay
EAC — Transport system
Belt conveyors from unloading to storage.
EAD — Stacking system
EAE — Bunker system, storage area (stockyard)
EAF — Bucket wheel system, reclaimer system
EAT — Weighing equipment
EAU — Sampling equipment
EB — Mechanical treatment of solid fuels
Crushing, mixing, drying — the coal preparation plant, distinct from the mills under HF which sit right at the boiler.
EBA — Transport system
EBC — Crushing system, pulverizing system
EBD — Screening system
EBF — Temporary storage system for milled raw coal
EC — Distribution of solid fuels
EG — Supply of liquid fuels (light fuel oil)
EGA — Receiving equipment incl. pipeline
EGB — Tank farm
EGC — Pump system
P — Cooling water systems
KKS main group letter for the whole cooling water area.
PA — Circulating water system
Main condenser cooling water — the largest single water flow in the plant.
PAA — Extraction, mechanical cleaning for direct cooling
Intake screens/trash racks.
PAB — Circulating water piping and culvert system
PAC — Circulating water pump system
CW pumps — typically the single largest auxiliary electrical load in the plant.
PAD — Recirculation cooling system, outfall cooling system
Natural draft / mechanical draft cooling tower, where used.
PAE — Cooling tower pump system (if separate)
PAH — Condenser cleaning system
e.g. ball cleaning/Taprogge system.
PAR — Make-up water piping system
PB — Circulating water treatment system
PC — Auxiliary cooling water system
Cools auxiliary equipment (oil coolers, air coolers, sampling coolers) separately from the main condenser CW.
PCC — Pump system
PCH — Heat exchanger cleaning system
PG — Closed cooling water system
Closed-loop, treated-water cooling circuit for critical equipment, isolated from raw circulating water.
PGA — Closed cooling water supply system
PGD — Cooler
G — Water supply and disposal
KKS main group letter for raw/service/drinking water and effluent — distinct from the boiler-cycle-specific treatment under L.
GD — Water treatment plant
GDB — Filtering, mechanical cleaning system
GDF — Ion exchange, reverse osmosis system
e.g. for demineralization — makeup water treatment plant (DM plant).
GDG — Evaporation system
Alternative demineralization route in some plants.
GDN — Chemicals supply system
GDP — Regeneration, flushing equipment
GH — Distribution systems (not drinking water, not cooling water)
GHB — Distribution system after treatment (demineralization)
GK — Drinking (potable) water supply
GM — Plant drainage system
GMA — Drainage system for storm water drains
GMB — Drainage system for oily drains
GMC — Drainage system for sewage drains
GT — Water recovery from waste water
GU — Rainwater collection and drainage, incl. treatment
A — Grid and distribution systems
KKS main group letter for the switchyard/grid connection, subdivided by voltage level.
AC — 380 (420) kV systems
AD — 220 (245) kV systems
AE — 110 (150) kV systems
AR — Protection equipment (grid)
B — Power transmission and auxiliary power supply
KKS main group letter for generator output, station transformers, and the entire in-plant electrical distribution hierarchy.
BA — Power transmission
Generator leads and generator transformer.
BAA — Generator leads
BAC — Generator circuit breaker, incl. cooling system
BAT — Generator transformers, incl. cooling system
Steps generator voltage up to grid voltage.
BB — Medium-voltage distribution boards and transformers, normal system
BD — Medium-voltage emergency distribution boards, (diesel) emergency power system
BF — Low-voltage main distribution boards and transformers, normal system
BJ — Low-voltage sub-distribution boards and transformers, normal system
BP — Power installations for large variable-speed drives
e.g. boiler feed pump VFDs.
BT — Battery systems
BTL — Rectifiers, battery chargers
BU — DC distribution board
C — Instrumentation and control equipment
KKS main group letter for control rooms, DCS cabinets, and unit-wide I&C functions that serve more than one process system.
CJA — Unit control system, incl. cabinets
CJD — Start-up control, set-point control (unit), incl. cabinets
CJF — Boiler control system, incl. cabinets
CJJ-CJN — Instrumentation and control cabinets for steam turbine set
CW — Control rooms
CWA-CWE — Main control consoles
CWF-CWP — Main control panels
CX — Local control stations
U — Structures
KKS main group letter for buildings, taking the code of whichever process system they primarily house.
UHA — Steam generator enclosure, boiler house
UHF — Bunker bay
UMA — Steam turbine building
ULA — Feedwater pump house
ULC — Structure for condensate system
ULD — Structure for condensate polishing plant
BC — Medium-voltage distribution boards and transformers, general-purpose
BH — Low-voltage main distribution boards and transformers, general-purpose
BL — Low-voltage sub-distribution boards and transformers, general-purpose
BR — Low-voltage distribution boards, converter, UPS and stand-by diesel power system
BFA — LV main distribution board
The specific switchboard itself, as distinct from the auxiliary transformer (BFT) that feeds it.
BFT — LV auxiliary power transformer
BFY — Control and protection equipment
BJA — LV sub-distribution board
BJT — LV auxiliary power transformer
BTA — Batteries
BRU — Converter (static), inverter
BRV — Emergency power generating equipment
e.g. the emergency diesel generator set, if not classified under X (heavy machinery).
UH — Structures for conventional heat generation
The system-level grouping that UHA (boiler house) and the other boiler-related structure codes sit under.
UHB — Auxiliary boiler structure
UHN — Flue gas stack structure
Includes structure for flue gas circulation where applicable.
UHQ — Structure for flue gas filtering system
UHW — Foundation for blowdown tank
UL — Structures for steam, water, gas cycles
The system-level grouping that ULA (feedwater pump house) and related structure codes sit under.
ULB — Structures for steam systems
ULF — Structures for common installations of steam-water cycle
UM — Structures for main machine sets
UMB — Gas turbine building
Relevant for a combined-cycle or dual-fuel configuration; not applicable to a pure steam-only supercritical unit.
UG — Structures for water supply and disposal
UGK — Structures for drinking water supply system
UGM — Structures for process drainage system
UGN — Water storage tank structures
CJ — Control system cabinets
The system-level grouping for the unit control, boiler control, and turbine I&C cabinet codes below it.
Signal Suffix Codes
A KKS equipment tag identifies a device (a drive, a valve). A signal suffix appended after it identifies one individual command or feedback bit on that device: MAB10AA001 might be a specific pump, and MAB10AA001XB01 its "on" feedback — XB is the signal category letter, 01 is the specific function within it. This is the layer that actually answers "which signal is the ON feedback": an X-prefix code specifically marks a signal coming back FROM the field (a status/confirmation), as distinct from a command going TO it, which instead uses the separate Application Code scheme (Y-prefix, e.g. MAB10AA001YB01) covered further down — real projects commonly also wire the complementary "confirmed OFF" feedback 50 numbers later (XB51) alongside XB01, so a genuine OFF state can be told apart from a stuck or failed-to-report contact.
XA — Functional group control / subloop control
XB — Control interface
Confirmation/status signals read back from a drive or final control element about its own state — an X-prefix code (see Signal Origin Prefix below) marks a signal as coming FROM the field, distinct from a command going TO it. The numbered codes XB01, XB02 etc. below are this category’s specific, standardized meanings.
XC — Closed-loop control
XG — Binary process signals
This is the DI (digital/binary input) category in KKS terms — conditioned by binary signal conditioning modules, e.g. a limit/level switch’s raw contact wired straight into the system.
XH — Binary limit signals derived from analog process signals
Also a binary (DI-type) signal, but computed rather than wired directly — e.g. a high/low alarm derived from a 4-20mA transmitter’s reading, not a dedicated physical switch.
XJ — Signals from non-standard areas
e.g. black-box or dedicated, packaged I&C not otherwise covered.
XK — Equipment unit / component protection
XL — Control room and control stations
Signals not assigned to a specific control system, e.g. control interface tiles.
XM — Higher-level static individual and group alarm signals
e.g. power supply failure, fuse status — persistent fault conditions.
XN — Status-display computer / criterion display
XP — Supervisory computer (process computer)
XQ — Analog signals
This is the AI (analog input) category in KKS terms — a continuous measured value (e.g. a live 4-20mA reading) rather than a binary state. Unlike XB’s command/feedback codes, an analog value has no fixed per-number "meaning" table to look up — the number just identifies which analog point on the device it is.
XS — Functional group control step signals
XT — Turbine-generator I&C, binary signals
XU — Higher-level dynamic individual and group alarm signals
Transient/momentary alarm conditions, as distinct from XM's static ones.
XV — Signal gating
Protective logic, alarm logic, etc.
XW — Hardwired alarm annunciation system
X — Direct signal
Used in the "Signal Code" scheme (feedback/status signals FROM the field) — a signal taken straight from its source, e.g. directly from a switch contact. See the Application Code (Y) entry below for the separate scheme used for commands.
Z — Gated signal
Used in the "Signal Code" scheme (feedback/status signals FROM the field) — a signal that has passed through logic, e.g. the output of an AND gate. Distinguishes a raw input from a processed/interlocked one carrying the same category letter.
XB01 — On / Open (feedback)
A feedback/acknowledgment signal read back FROM the drive confirming it is actually on/open — not the command sent TO it. The corresponding command uses a separate KKS suffix scheme, the "Application Code" (Y-prefix, e.g. YB01) — confirmed in Siemens TXP-CLC training documentation, and listed further down this page. XB, as a Signal Code (X-prefix), specifically identifies a signal coming back from the field.
XB02 — Off / Close (feedback)
The corresponding "closed/off confirmed" feedback read back from the drive, paired with XB01 the same way — not a command.
XB03 — RTS (ready to start)
XB05 — Higher
e.g. raise frequency/voltage/setpoint.
XB06 — Lower
XB09 — Revision
XB10 — Normal operation mode
XB11 — Hand On / Open
XB12 — Hand Off / Close
XB13 — Local
XB14 — Remote
XB15 — Hand stop
XB16 — Quick shutdown
XB17 — Reset
XB18 — Acknowledge / Confirm
XB19 — Blocked / Interlock
XB21 — Auto On / Auto mode
XB22 — Auto Off
XB23 — Standstill
XB24 — Spinning reserve
XB25 — Generating
Generator/pump-turbine unit running in generating mode.
XB26 — Generator condenser mode
XB27 — Pumping
Running in pumping mode (pumped-storage units).
XB28 — Pump condenser mode
XB29 — Back-to-back / step mode
XB30 — Quick changeover
XB31 — Protection on
XB32 — Test on
XB33 — Step by step
XB41 — PLC 1 active
XB42 — PLC 2 active
XB43 — FCL local
Field control level, local.
XB44 — FCL remote
Field control level, remote.
XB51 — "Not on / Not open" feedback
The complementary "off-state confirmed" feedback paired with XB01 for the same drive — a real drive typically wires BOTH XB01 and XB51 so the control system can distinguish a genuine OFF state from a stuck or failed-to-report contact, rather than inferring OFF purely from the absence of the XB01 ON feedback.
XB52 — "Not closed" feedback
The complementary feedback paired with XB02.
XG01 — On / Open / > Max 1
A raw NO-contact signal, e.g. from a level or limit switch — distinct from XH, which is a limit derived from an analog transmitter rather than a dedicated switch.
XG02 — Off / Close / < Min 1
XG03 — > Max 2
XG04 — < Min 2
XG05 — > Max 3
XG06 — < Min 3
XG07 — > Max 4
XG08 — < Min 4
XG10 — In transition
e.g. a valve caught mid-travel, neither confirmed open nor closed.
XG11 — Hand On / Open
XG12 — Hand Off / Close
XG18 — Ready
XG19 — Blocked
XG20 — Disturbed
A fault/disturbance condition on this signal.
XG21 — Auto on
XG32 — Test on
XH01 — > Max 1
A high-limit alarm computed from a continuous analog transmitter's reading (e.g. 4-20mA), not a dedicated physical switch — the functional counterpart to XG for signals with an analog source instead of a switch.
XH02 — < Min 1
XH03 — > Max 2
XH04 — < Min 2
XH19 — Value simulated
The underlying analog value is a simulated/forced value, not a live process reading — an important distinction to know during commissioning or maintenance.
XH20 — Disturbed
XH21 — Low failure
e.g. transmitter signal below 4mA — indicates a wiring/instrument fault, not a genuine low process value.
XH22 — High failure
e.g. transmitter signal above 20mA.
XM01 — Power supply 1 failure
XM02 — Power supply 2 failure
XM03 — 24VDC fuse OK
YB01 — On / Open (command)
The command mirror of the confirmed feedback code XB01: this is the instruction sent TO the drive to turn on/open, as distinct from XB01, the confirmation read back FROM it that it has done so.
YB02 — Off / Close (command)
The command mirror of the confirmed feedback code XB02.
YB22 — Application code (sourced example)
The specific example given in Siemens TXP-CLC training documentation for a real device (MBV41AA001) — the source does not spell out what function 22 represents, so it’s listed here as the directly-sourced reference point for the numbering range, not a decoded meaning.
Y — Signal applications (command)
The complete, officially-sourced counterpart list to the X (Signal Origins) table above, from the same McGraw-Hill KKS appendix (Siemens 1995 source booklet): YA, YB, YC, YJ, YL, YN, YP, YQ, YT, YV, YW. Notably shorter than the X list -- there is no YG, YH, YK, YM, YS, or YU, because a binary process signal, a derived limit, a protection trip, a static/dynamic alarm, or a turbine speed reading are inherently things the system reads, not things it commands.
YB — Control interface (command)
The command-side counterpart to XB, confirmed in both the McGraw-Hill KKS appendix and Siemens TXP-CLC training documentation: an output sent TO a drive or final control element, as opposed to XB’s status read back FROM it. This is the category to use for a DO (digital/binary output) in KKS terms -- there is no separate YG for that, since Control Interface already covers on/off, open/close-type commands.
YQ — Analog signals (command)
This is the AO (analog output) category in KKS terms -- the command-side counterpart to XQ (AI). A continuous outgoing value, e.g. a 4-20mA setpoint sent to a control valve positioner or a VFD speed reference, as opposed to XQ’s continuous incoming reading.
About This Calculation
KKS (Kraftwerk-Kennzeichensystem, the Power Plant Identification System) is the standard used across most large coal and gas thermal plants worldwide — including the great majority of Indian supercritical units — to give every system, piece of equipment, and signal a unique, unambiguous tag, independent of language or drawing. A code like HAC10 or LBA20 isn’t arbitrary: reading left to right, the letters narrow down from plant area to specific system, and the trailing digits number the individual instance. This reference organizes the codes actually used on a supercritical coal-fired unit by the plant area an engineer would actually search by — boiler pressure parts, steam-water cycle, turbine-generator, coal handling, cooling water, and the rest — rather than requiring you to already know which of the roughly two dozen KKS main-group letters a system falls under. It draws on the VGB KKS guidelines and real project-issued KKS lists (including supercritical unit documentation), not a single vendor’s abbreviated cheat sheet.