Descripción: Relay setting calculation for Generators
Generator & transformer protection for 600MW class generator
Relay setting calculation for GeneratorsFull description
Descripción: IEEE Generator Protection Tutorial by Power System Relaying Committee. These references can be downloaded from IEEE PSRC website for free.
Descripción: IEEE Generator Protection Tutorial by Power System Relaying Committee. These references can be downloaded from IEEE PSRC website for free.
Service Manual Generator Engines Electric Protection System, CaterpillarFull description
A theatre encountered a situation where incorrect operation of the earth fault protection system of a back-up generator tripped the circuit breaker unexpectedly when dimmer loads were fully …Full description
Full description
There are many aspects to security and many applications, Ranging from secure commerce and payments to private communications and protecting passwords. One essential aspect for Secure c…Full description
GENERATOR PROTECTION ABU SAMAH ABU HASAN INSTITUT INSTI TUT LATIHAN LATIHAN SUL SULT TAN AHMAD SHAH SH AH TENAGA NASIONAL BERHAD MALAYSIA
GENERATOR PROTECTION
Overspeed
Rotor E/F
Generator Transformer
NER
Generator
IDMT Earth Fault
V T
Reverse Overvoltage Buchholz Power Generator Restricted E/F Diffirential Generator
Negative Phase Sequence Overcurrent Instantaneous Loss of Field Earth Fault
Transformer Diffirential
END OF PRESENTATION
THANK YOU FOR YOUR PARTICIPATION.
DIFFERENTIAL PROTECTION Differential protection using high-impedance relays is usual for stator protection and is applied on a phase-by-phase basis. As the leads between the two sets of current transformers may be long the resistance will be fairly high but as the maximum through-fault current will be less than 10 times full load current a reasonably low voltage setting can be applied. This means that the CT magnetising current will be low and therefore a low overall current wetting can be expected. The overall setting has a direct bearing on the amount of the generator winding which is protected.
STATOR DIFFERENTIAL PROTECTION
CT
Stator
CT Red Yellow Blue
RELAY Biasing Coil Operating Coil
STATOR EARTH EARTH--FAULT PROTECTION Stator earth-fault protection comprises an instantaneous relay and the Inverse Definite Minimum Time (IDMT) relay. Both relay will be connected to current transformer having a primary current rating equal to that of the earthing resistor. Earth faults will be detected in 90% to 95% of the generator winding even though the maximum earth-fault current may as low as 5% of the generator rating.
STATOR EARTH FAULT PROTECTION
Generator Red Yellow Blue
Relay
CT
Neutral Earth Resistance
ROTOR EARTH EARTH--FAULT PROTECTION For detecting earth-faults in the rotor circuit, a highresistance potentiometer is connected across the rotor circuit the centre point of which is connected to earth through a sensitive relay. The relay will respond to earth faults occurring over most of the rotor circuit.
OVERCURRENT PROTECTION An Inverse Definite Minimum Time (IDMT) relay is generally used as back-up protection but the operation of this relay is complicated because of the current decrement in the generator during fault conditions. In some cases a setting is chosen, such that the relay will not operate for a system fault but will only respond when fault current is fed into the generator, in this way it only acts as a back-up to the main generator protection.
LOSS OF FIELD PROTECTION Failure of the field system results in acceleration of the rotor to above synchronous speed where it continuous to generate power as an induction generator the flux being provided by a large magnetising components drawn from the system. This condition can tolerated for a short time but clearly there will be increased heating of the rotor because of the slipfrequency currents which flow. Loss of field can be detected by undercurrent relay connected to a shunt in the field circuit.
OVER--VOLTAGE PROTECTION OVER Voltage is generally controlled by a high-speed voltage regulator and therefore over-voltages should not occur and over-voltage protection is not generally provided for continuously supervised machines. On unattended machines a instantaneous relay set at, say, 150% is use to cater for defective operation of the voltage regulator.
NEGATIVE PHASE SEQUENCE PROTECTION (Unbalanced Loading) CT Red Yellow Blue
X Positive Sequence
XL
R
R
V ZB
V ZR
Y Negative Sequence
R
Ir
Ir
VZZR
VZR
Y
VZB 60o
60o
I b
VX
VZB
V ZR + V ZB = 0
Iy
Iy
I b
V XY = V ZR + V ZB
NEGETIVE PHASE SEQUENCE (Unblanaced Loading) U nbalanced loading of the
generator phase results in the production of negative phase sequence (NPS) currents. These current, which have a phase rotation in the opposite direction to the normal phase rotation, produce a magnetic field which induces currents in the rotor at twice the system frequency. This causes considerable heating in the rotor and would cause damage. The actual NPS currents is difficult to determine. Relays to detect the condition usually have an IDMT characteristic matched to I 2 t value.
OVERSPEED The speed is very closely controlled by the governor and is held constant as the generators in parallel with others in an interconnected system. If the circuit breaker is tripped the set will begin to accelerate and although the governor is designed to prevent over-speed a further centrifugal switch is arranged to close the steam valve. There is still a risk, however, that the steam valve not close completely and even a small gap can cause over-speed and so where urgent tripping is not required. It is usual to lower the electrical output to about 1% before tripping the CB. A sensitive under-power relay is used to detect when this value is reached.
