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CNS/GSS/2008/M2

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Module 2

Electro-technical Symbols & Usage

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CNS/GSS/2008/M2

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Electro-technical Symbols

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CNS/GSS/2008/M2

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Electro-technical Symbols

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CNS/GSS/2008/M2

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Electro-technical Symbols Code Name of Function Definition

25 Synchro-Check Check before paralleling two parts of power system

26 Thermostat Protection against Overloads

27 Under-Voltage Protection of Voltage under sags

32P Directional active over power Protection against active over power transfer

32Q Directional reactive over power Protection against reactive over power transfer

37 Phase undercurrent 3-phase protection against undercurrent

46 Negative sequence/ unbalance Protection against unbalanced phase current

47 Negative sequence over voltage Negative sequence voltage protection

48-51LRExcessive starting time & locked rotor

Protection of motors against starting with overloads or reduced voltage, & for loads that can block

49 Thermal overload Protection against overloads

49T RTDs Protection against overheating of M/C windings

50 Instantaneous phase overcurrent 3-phase protection against short-circuits

50BF Breaker FailureChecking & protection if the CB fails to trip after a tripping order

50N/50G Instantaneous earth fault Protection against earth faults

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Electro-technical Symbols Code Name of Function Definition

50V Inst. Voltage-restrained phase Over current3-Ph Protection against S/Cs with Voltage dependent threshold

51 Delayed Phase Over current3-Ph Protection against Overloads & short circuits

51N/51G Delayed earth fault Protection against earth faults

51V Delayed Voltage restrained phase O/C3-Ph protection against short circuits with voltage dependent threshold

59 Over voltage Protection against excessive voltage

59N Neutral voltage displacement Insulation fault protection

64REF Restricted earth fault differentialEarth fault protection for star connected 3-Ph wdgs with earthed neutral

64G 100% generator stator earth faultDetection of stator wdg insulation earth faults

81H/81L Over/Under frequencyProtection against abnormally High/Low frequency

87B Busbar differential3-Ph protection against busbar internal faults

87G Generator differential3-Ph protection against internal faults in AC generators

87M/87T Motor/Trafo. differential3-Ph protection against internal faults in Motors/Trafos.

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CNS/GSS/2008/M2

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Electro-technical Symbols

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CNS/GSS/2008/M2

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Electro-technical Symbols

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CNS/GSS/2008/M2

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Electro-technical Symbols

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CNS/GSS/2008/M2

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Electro-technical Symbols