Why Install GCB at Generator Outlets? 6 Core Benefits for Power Plant Operations

1.Protects the Generator

When asymmetric short circuits occur at the generator outlet or the unit bears unbalanced loads, the GCB can quickly isolate the fault to prevent generator damage. During unbalanced load operation, or internal/external asymmetric short circuits, twice the power frequency eddy current is induced on the rotor surface, causing additional heating in the rotor. Meanwhile, the alternating electromagnetic torque at twice the power frequency induces double-frequency vibration in the unit, leading to metal fatigue and mechanical damage.

2.Protects the Main Transformer and High-Voltage Station Service Transformer

With a GCB installed, the selectivity of protection functions is enhanced—whether during operational faults, system oscillations, or internal faults in the generator/transformer—thereby improving the reliability of unit safe operation.

During operational faults or system oscillations, only the GCB needs to be quickly tripped, without switching the station service power supply. After the fault clears, the generator and grid can be reconnected quickly via the GCB, avoiding full-plant power outages caused by station service power switching failures.

When an internal generator fault occurs, the faulty generator can be isolated without switching the station service power supply. This enables selective protection tripping of the generator, simplifies protection wiring, and avoids station service power switching (since internal unit faults do not require tripping the high-voltage circuit breaker). This is highly beneficial for resolving transient faults (especially false thermal signals from boilers/turbines), restoring unit operation quickly, and preventing accidents caused by misoperation.

For high-incidence faults (e.g., internal transformer faults, transformer grounding faults), the GCB’s breaking time is much faster than the generator’s field suppression time (several seconds). This greatly reduces fault current damage to the transformer, shortens maintenance time, cuts direct/indirect economic losses, and improves plant availability by 0.7%~1%.

3.Eliminates the Need for a Startup/Standby Transformer and Simplifies Station Service Power Switching

With a GCB, the unit’s startup/shutdown power can be fed backward to the station service transformer via the main transformer, eliminating the need for a startup/standby transformer. Unit startup/shutdown or fault handling only requires tripping the GCB (not the high-voltage system circuit breaker), reducing station service power switching procedures (compared to systems without a GCB), lowering operational complexity, and improving system reliability.

4. Enhances Selectivity of Unit Protection

When an internal generator fault occurs, the GCB trips quickly to isolate the generator from the grid—without tripping the main transformer. The station service power for shutdown can still be fed backward via the main transformer, avoiding emergency switching of the station service power system. This reduces the burden on operators and creates conditions for rapid fault handling.Avoiding high-voltage station service power switching simplifies the control and protection wiring of the station service power system, improving its reliability. Installing a GCB at the generator outlet streamlines the protection configuration of the generator-transformer unit and reduces the complexity of protection action interlocks. During normal unit startup/shutdown, station service power is supplied by the system via the main transformer, eliminating the need for station service power switching.Unit grid connection or shutdown can be completed via the GCB alone, shortening startup time and reducing electrical/mechanical shocks to motors. Fewer operating components also lower the risk of misoperation.

5.Simplifies Synchronization Procedures

When grid connection is performed using a high-voltage circuit breaker, the breaker is subjected to voltage stress. In cases of contaminated external insulation, this stress can cause external insulation flashover. When synchronization is performed at the generator voltage level (via the GCB), voltage stress on the high-voltage circuit breaker is eliminated. Using the GCB for synchronization compares equal voltages on both sides of the GCB, making synchronization simpler and more reliable. Additionally, since the GCB is installed indoors (with better environmental conditions and wider insulation margins), synchronization reliability is further ensured.

6. Facilitates Testing and Commissioning

The GCB separates the generator and transformer into two independent sections, allowing staged, step-by-step commissioning and testing. When station service power is supplied by the main transformer, the generator can be commissioned, tested, and measured under underexcitation conditions.This physical separation via the GCB greatly facilitates the commissioning, maintenance, and inspection of the generator and transformer, and also provides convenient conditions for short-circuit testing of the generator.