Why is field loss protection required?
Protection is commonly provided to prevent or minimize the duration of this mode of operation, by the so-called loss-of-field relay. Whatever the cause, a loss of excitation can present serious operating conditions for both the generator and the system.
What is loss field?
Loss of field (LOF) occurs when the generator field winding provides insufficient excitation voltage for proper generator operation, causing the generator to operate outside its desirable operating region.
What is over excitation protection?
Overexcitation of a transformer means that the magnetic flux in the core is increased above the normal design level. The differential protection must therefore be stabilized under these conditions as tripping of transformers and thus load will only mean that the overvoltage condition in the network is becoming worse.
What causes loss of prime mover?
Generator motoring is a condition that happens when the prime mover can not supply enough power to the AC generator to account for the load demand on the generator. The electrical system needs to make up for this loss in prime mover input power.
What is meant by over excitation?
Overexcitation of a transformer means that the magnetic flux in the core is increased above the normal design level. This means that the voltage must be gradually increased, with increasing frequency, in order not to overexcite the transformer.
What is over excitation and under excitation?
The over-excitation limiter protects the generator against over-temperature caused by high field current for long time. Under-excitation limiter prevents the decrease of generator field current to the values lower than the stability margin or the thermal limit of end side of the stator core.
How are loss of field elements used in a power system?
Almost all impedance elements are MHO circles similar to the 21-Element described in Chapter 9 that looks for lagging faults out on the power system. However, Loss-of-Field elements are installed to detect impedance in the opposite direction because the measured impedance during loss-of-field conditions looks toward the generator.
When does a loss of field ( 40 ) condition occur?
You can review these principles in Chapter 2: Section D and Section F. A loss-of-field (40) condition occurs when something happens to the excitation system that prevents it from applying enough energy to meet or exceed the power system voltage. A generator field could disappear if: The Generator Field Circuit Breaker unintentionally opens.
Why is loss prevention important to your business?
Surveillance systems deter thieves and can help you pinpoint where loss is occurring. Conduct research or speak with a loss prevention professional to determine the best placement for cameras. Keeping your products secure without discouraging sales can be tricky.
How are loss of field elements used in excitation circuit?
Early Loss-of-Field relays were installed in the excitation circuit, but they were complicated and not very effective. An Over-Leading-VAR relay that operates similar to a Reverse-Power relay seems like a good idea, but VAR-based Loss-of-Field elements tend to operate during normal power swings.