Fluctuations in inlet steam flow rate of backpressure steam turbines

Check whether the temperature and pressure at the steam inlet and outlet are stable? Taking into account the effects caused by unstable steam mass

I checked the steam pressure as well – there was no change

After ruling out the issue of unstable steam quality, is the compressor’s low-load operating area too close to the anti-surge line, thereby triggering the compressor’s anti-surge mechanism?

1. The problem arises from setting a low load on the compressor, which in turn leads to fluctuations in the steam supply to the turbine. It is necessary to determine whether it is a factor on the turbine side or on the compressor side, as the solutions for each are different. 2. If it is assumed that it is a factor on the compressor side, such as surge or unstable flow rates, changes in load can cause fluctuations in speed. For turbines with constant-speed control, it is necessary to increase or decrease the steam flow rate in order to maintain a constant flow velocity; as a result, changes in flow rate are reflected as fluctuations in rotational speed. The solution can be implemented on the compressor side to identify the cause. 3. If the issue lies on the turbine side, then two factors are involved: the stability of the steam parameters and the reliability of the control system; both can cause fluctuations in operation. It is necessary to identify the root cause and take appropriate measures to resolve it

Steam fluctuations cause fluctuations in the valve opening, which in turn leads to fluctuations in the turbine’s speed. It is normal for such fluctuations to range from a few to several dozen units of speed

Guru! I would like to ask: it is normal for the speed of the unit to fluctuate by around 50 revolutions above or below the set speed while it is in operation. However, there is a phenomenon that occurs later on – where the actual speed ends up being 50–100 revolutions higher than the target speed, and this condition persists. This leads to the main steam valve of the turbine being closed further (for example, if the valve is initially at 75% open, it may be reduced to 60%). When the main steam valve reaches a certain degree of closure, the following phenomena occur: 1. The valve opens suddenly, 2. The speed drops instantly (sometimes by around 800 revolutions), 3. The steam pressure rises, 4. The inlet pressure also rises. What causes these phenomena? ? ?

I. Let’s guess the reasons based on the information provided: 1. Assuming that a deviation of ±50 RPM from the set speed is considered normal, and past operational experience shows that the system can function properly within this range, it can be inferred that there is an anomaly in the current situation. 2. The actual speed at present deviates from the set speed, with a positive difference between the actual value and the set value; this difference triggers a signal to close the main steam valve. 3. Due to issues with the precision of the main steam valve or the control signals (I’m not an expert, so I’m using simple terms), or because the PID settings are not optimal, the main steam valve closes too much, resulting in a decrease in speed. 4. The reduced speed creates a negative difference compared to the set value, and this difference prompts the main steam valve to open again. This sequence differs from what you described: the speed drops first, followed by the immediate opening of the main steam valve. II. Possible reasons: 1. The main steam valve is not sensitive; small deviation signals are not sufficient to trigger valve action. 2. The governor is not sensitive