What is generator reverse power protection?

When the main valve of a steam turbine generator is closed for some reason, the steam turbine is running without steam. At this time, the generator becomes an electric motor to drive the turbine rotor to rotate. The high-speed rotation of the turbine blades will cause wind wear loss, especially the blades at the tail end may cause overheating, causing damage to the turbine rotor blades. (It can be understood as protection for the turbine blades)

What is generator program reverse power protection

Prevent the generator from suddenly disconnecting the main circuit breaker under a certain active power and the main steam valve is not completely closed. At this time, the steam turbine generator may have an overspeed and runaway accident. In order to avoid such accidents, some types of protection for non-short-circuit faults (demagnetization protection, loss of step protection, generator water shortage, main transformer cooler failure, thermal engine protection, etc.) are closed first after the action. After the generator reverse power relay is activated, the auxiliary contact connected with the main valve closure forms an AND gate, which forms a program reverse power protection after a short time limit, and acts on the full stop after the action.

Electric trip and machine trip

1. Generator reverse power protection (electric trip)

First, reverse power protection is a type of generator relay protection, which is used as a protection for abnormal operation of the generator when the active power of the steam turbine generator is reversed and the generator becomes a motor.

The simple principle of reverse power protection: it is a power direction relay AC measurement circuit constructed according to the principle of absolute value comparison, and its AC voltage formation circuit adopts the sum-difference wiring method to obtain two comparative electrical quantities: sum voltage vector A1 and difference voltage vector A2. When the generator is operating normally, A2

The steam turbine valve is suddenly closed, and the generator absorbs active power from the system. The action amount is greater than the braking amount, that is, A2>A1, the relay is activated, and after a certain delay, the generator is cut off. Reverse power protection can also be used as a starting element for program tripping.

2. Program reverse power (machine trip)

Reverse power protection is the starting condition for the program-controlled tripping of the generator.

Strictly speaking, program reverse power protection is not a protection, but an action process set to achieve program tripping. Program reverse power is mainly used for program tripping, which is a kind of shutdown method.

The most important thing is that the reverse power will act as long as the set value is reached. In addition to reaching the set value, the program trip reverse power must also close the main steam valve of the steam turbine before it can trip.

In normal shutdown operation, when the load drops to zero, the main steam valve of the steam turbine is closed first, and then the program reverse power protection is started to trip the generator. The purpose of this is to prevent the main steam valve from being closed tightly. When the circuit breaker is tripped, the electromagnetic torque of the electromagnetic power may cause the steam turbine to run away.

Term explanation: reverse power, reverse power protection

Reverse power: Due to various reasons, the original power is lost and the generator is turned into an electric motor. At this time, in order to prevent the turbine blades and gas turbine gears from being damaged, reverse power protection is configured.

Reverse power protection will act immediately as long as the absorbed active power reaches the set value to protect the tail blades of the steam turbine. Most power plants stipulate that reverse power is not allowed to exceed 3 minutes.