13. Calculate Diesel Generator Protection Setting

CALCULATE DIESEL GENERATOR PROTECTION SETTING

March 6, 2025 Leave a comment

Recommended Generator Protection are

Recommended Generator Protection

ANSI Code

Protection Function

Under Voltage

Reverse Power 37

Under Power

Loss of Excitation 46

Negative Phase Sequence /Un Balance Load

49T

Thermal Overload 50

Instantaneous Over Current

Time grade Over Current 51G

Earth Fault Time Overcurrent

50/51V

Voltage Restrained Overcurrent 59

Over voltage

60G

Fuse Failure Monitor 64S

Stator Earth Fault Protection

Under / Over Frequency 87

Three Phase Current Differential

87N

Neutral Current Differential

87G

Generator Differential Protection

24G

Over excitation (Volt/Hertz) Protection

21G

Impedance Protection 59N or 64G1

Stator EF protection (0-95%)

27TN or 64G2

Stator EF protection (100%) 50BF

Breaker Failure Protection

24G

Over excitation (Volt/Hertz) Protection

78G

Pole slip protection

PROTECTION SETTING CALCULATION:

(1) UNDER VOLTAGE RELAY (27):

The Under Voltage Relay measure either phase-to-phase (Ph-Ph) or phase-to-neutral (Ph-N) fundamental RMS voltage depending on the input voltage setting. If the value of measured voltages deviates from the setting values, then these relays will give a trip indication. * Reason: * An under-voltage condition in a diesel generator can occur due to several reasons, overloading the generator beyond its capacity, faulty Automatic Voltage Regulator (AVR), issues with the stator windings, problems with the voltage sampling line, loose connections, low engine speed, fuel problems, and issues with the excitation system * Setting: * The Typical under-voltage setting is usually 80 % of the normal rated voltage. If the voltage falls below this level for the set amount of time, then the tripping command is issued by the relay and hence the system is isolated. The time setting is used to avoid tripping due to any transient disturbances. the exact setting can vary depending on the specific generator and system requirements. * Usually, motors stall at below 80% of their rated voltage. An under-voltage element can be set to trip motor circuits once fall below 80% so that on the restoration of supply an overload is not caused by the simultaneous starting of all the motors. * Normally Generators are designed to operate continuously at minimum voltage of 95% of its rated voltage. * Two levels of tripping are provided depending on the severity of the condition, these under voltage elements are blocked from tripping when the generator breaker is open to allow for startup conditions. * Calculation: * For 415V Diesel Generator * Level 1 (Slow)= 80% of Rated Voltage * Level 1 (Slow)= 80% x 415V =332 V * Time Delay = 5 sec. * Level 2 (Fast): 70% of Rated Voltage * Level 2 (Fast)= 70% x 415V =290 V * Time Delay = 0 sec.

(2) Over Voltage Protection [59]:

The Over Voltage Relay measure either phase-to-phase (Ph-Ph) or phase-to-neutral (Ph-N) fundamental RMS voltage depending on the input voltage setting. If the value of measured voltages deviates from the setting values, then these relays will give a trip indication. * Reason: * System over voltages can damage the insulation of components. Over voltages occur due to sudden loss of load, improper working of tap changer, Generator AVR malfunction, Reactive component malfunctions, etc. * Setting: * The Overvoltage setting is usually 110 to 130 % of the normal operating voltage depending on the system requirement. * If the voltage rises above this level for the set amount of time then the tripping command issued by the relay and hence the system is isolated. The time setting is used to avoid tripping due to any transient disturbances. * Calculation: * For 415V Diesel Generator * Level 1 (Slow)= 110% of Rated Voltage * Level 1 (Slow)= 110% x 415V =456 V * Time Delay = 5 sec. * Level 2 (Fast): 130% of Rated Voltage * Level 2 (Fast)= 130% x 415V =539 V * Time Delay = 0 sec.

(3) REVERSE POWER PROTECTION [32R]:

Reverse power relay is an electronic, microprocessors-based protection device which is used for monitoring and stopping the power supply flowing grid side to the DG side or generator running in parallel with another generator. If accidentally leakage current is received by generator, then it can start to running as motor. This situation may be very dangerous for generator set. * The function of the reverse power relay is to prevent a reverse power condition in which power flows from the bus bar into the generator. * This condition can occur when there is a failure in the prime mover such as an engine or a turbine which drives the generator. * Relay detects the reverse flow of power from the load back to the generator, which can occur during system faults or abnormal operating conditions. By sensing this reverse power flow, the relay triggers a protective action, typically disconnecting …