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- 21/21N = Distance Relay Phase & Ground
- 21BU = Backup Distance Relay
- 24L = Overexcitation Relay (Overfluxing Relay)
- 25 = Synchronizing Check Relay
- 27 = Under Voltage
- 27XR = Loss-of-DC Alarm Relay
- 32 = Reverse Power
- 33Q = Transformer Oil Level
- 40 = Loss of Excitation.
- 46 = Negative Phase Sequence Protection
- 48 = Locked Rotor
- 49 = Overload
- 49W = Transformer Winding Temp
- 49Q = Transformer Oil Temp
- 50ARC = Instantaneous Overcurrent relay for Arc Protection System
- 51G = Ground Fault Relay
- 50/50N = Instantaneous Overcurrent Phase & Ground
- 51/51N = IDMT. Overcurrent Phase & Ground
- 59 = Over Voltage
- 59N = Zero Sequence Overvoltage
- 62PD = Pole Disagreement Protection.
- 63D = Transformer Pressure Relief Device
- 63TC = Transformer OLTC Protection Relay
- 67/67N = Directional Overcurrent Relay / Directional Ground Overcurrent
- 68 = Voltage Relay Block Closing Circuit While De-Energize
- 79 = Auto Reclose Relay
- 80T = Transformer Buchholz
- 81 = Under Frequency Relay
- 86 = Lockout Function
- 87B = Bus Differential Relay
- 87L = Line Current Differential Relay
- 87T = Transformer Differential Protection Relay
- 87REF = Differential Restricted Earth Fault Relay
- 90 = Voltage Regulating Relay
- 95B = CT Supervision Relay for 87B
- BF = Circuit Breaker Failure Relay
- Q = Power Factor Controller
- R = Shunt Reactor
- POTT = Permissive Overreaching Transfer Trip Function.
- GIS = Gas Insulated Switchgear.
- AIS = Air Insulated Switchgear.
- LCU = Local Control Unit.
- MCB = Miniature Circuit Breaker.
- BDCS = Breaker Discrepancy Control Switches
- DSDCS = Disconnect Switch Discrepancy Control Switch
- SS = synchronizing Selector Switches
- 79CO = Recloser Cut-off Switches
- 87T-CO = Transformer Difference Cut-off Switches
- 86B-CO = Bus Differential Auxiliary Tripping and Lockout Relay Cut-off Switches
- 50BF-CO = Breaker Failure Cut-Off Switches
- PB = Push Button Switches
- 87L-CO = Line Current Differential Cut-Off Switches
- 86DTT-CO = Direct Transfer Trip Cut-Off Switch
- 43SC = Control Selector Switch
- 85-C0 = Pilot Cut-Off Switch
- PTT-CO = Permissive Transfer Trip Cut-Off switch.
- IED = Intelligent Electronic Device
- DPM = Digital Power Meter
- DIM = Distributed I/O Module (for CSCS Control)
- DAU = Data Acquisition Unit. (Computer)
- BCU = Bay Control Unit
- ODF = Optical Distribution frames.
- DCS = Distributed Control and Monitoring System.
- SCADA = Supervisory Control and Data acquisition.
- FRS = Fault Recording System.
- HMI = Human – Machine Interface.
- LUI = Local User Interface.
- CPM = Centre Processing Module.
- SI = System Integrator
- SA = Substation Automation
- SAS = Substation Automation System
- SCMS = Substation Control and Monitoring System
- SCPS = Substation Control and Protection System
- PLC = Programmable Logic Control (Device Part) or Power Line Carrier (Telecom Part)
- OPGW = Optical Power Ground Wire (Telecom Part)
- RMU = Ring Main Unit.
- RCC = Remote Control Cubicle / Regional Control Center (SCADA)
- LCC = Local Control Cubicle
- NCC = National Control Center
- BNCC = Backup National Control Center
- NEC = North Eastern Area Control Center (for EGAT)
- FFT = Fast Fourier Transform (for Math) / Full Function Test (for Testing Process)
- FAT = Factory Acceptance Test (for Testing Process)
- FRT = Factory Routine Test (for Testing Process)
- SAT = Site Acceptance Test (for Testing Process)
- ETE = End-To-End Test (for Testing Process)
- AISC = American Institute of Steel Construction
- ASCE = American Society of Civil Engineers
- ANSI = American National Standards Institute
- ASME = American Society of Mechanical Engineers
- ASTM = American Society for Testing and Materials
- AWS = American Welding Society
- IEEE = Institute of Electrical and Electronics Engineers
- NEMA = National Electrical Manufacturers Association
- NFPA = National Fire Protection Association
- TIS = Thai Industrial Standards
- EIT = Engineering Institute of Thailand
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