JPH0345994B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an overspeed prevention device for a steam turbine that prevents overspeed of a turbine during load interruption.

[Conventional technology]

Fig. 2 is a block connection diagram showing a conventional overspeed prevention device for a steam turbine. a reheater placed in the outlet side steam passage; 4 is an intercept valve;
5 is a low-pressure turbine (turbine), 6 is a generator driven by both turbines 2 and 5, 7 is a power cutter connected to the load circuit of generator 6, and 8 is a current transformer as a generator current detector. , 9 is a reheat steam pressure detector, 1
0 is a subtracter that calculates the difference between the generator current from the current transformer 8 and the steam pressure detection current from the reheat steam pressure detector 9, and 11 is a subtracter that calculates the difference between the output of this subtracter 10 and the set value, for example, 30%. This is a comparator that compares the load imbalance allowable setting value set in advance so that Next, the operation will be explained. The reheat steam pressure signal S ₁ detected by the reheat steam pressure detector 9 is subtracted from the generator current signal S ₂ detected by the current transformer 8 in a subtracter 10, and the result is is input to the comparator 11.
Under normal load operating conditions, the reheat steam pressure signal _S1 , which is the input power of the low-pressure turbine 5, and the generator current signal _S2 , which is the output power of the generator 6, are balanced. The output, ie the input to comparator 11, is approximately zero. However, if a load or disconnection occurs in the grid, or if the generator or disconnector 7 trips, an energy imbalance between the input to the low-pressure turbine 5 and the output of the generator 6 may occur. This will cause the turbine to overspeed if it continues to operate under no load. For this reason, the standard load unbalance tolerance setting value (e.g.
The comparator 11 compares and calculates whether the output of the subtracter 10 is within 30%), and if the load imbalance tolerance is exceeded, the governor valve 1 and the intercept valve are selected based on the output of the comparator 11. By forcibly controlling the turbine 4 to fully close, the speed of the turbine is suppressed within the set speed range, and the above-mentioned overspeed is prevented.

[Problems to be solved by the invention]

Since the conventional overspeed prevention device for a steam turbine is configured as described above, during rated power factor operation, the load unbalance allowable set value (30% of the above) is used to control the operation of the governor valve 1 and intercept valve 4. This is the starting point, that is, the overspeed prevention control point, but as the power factor approaches unity, the generator current decreases, and therefore the difference with the reheat steam pressure signal level increases, and therefore the load unbalance tolerance setting As the difference between the value and the output value of the subtracter 10 becomes smaller and this output value repeatedly exceeds the load imbalance allowable set value, each of the governor valves 1 and intercept valves 4 operates more frequently than necessary. There was a problem that stable turbine operation was not possible. This invention was made to solve the above problems, and by correcting the generator current according to the power factor at that time, the allowable load unbalance setting value can be adjusted to the power factor of the generator output. It is an object of the present invention to provide an overspeed prevention device for a steam turbine that is capable of performing overspeed prevention control of a turbine in a state where it is fixed at a constant value without being immediately affected.

[Means to solve the problem]

The overspeed prevention device for a steam turbine according to the present invention includes a reheat steam pressure detector provided in the steam passage of the turbine, a generator connected to the turbine, and a generator current detector and a power factor connected to the output circuit of the generator. A power factor ratio calculator is connected to the power factor detector to calculate the power factor ratio of the actual power factor to the rated power factor, and the power factor ratio and the generator current are connected to the power factor ratio calculator. Connect a multiplier that multiplies , connect a subtracter to this multiplier to subtract the output of this multiplier and the reheat steam pressure signal from the reheat steam pressure detector above, and connect to this subtracter A comparator is connected which compares the output of the multiplier with a preset load unbalance allowable setting value and controls the valves of the steam passage based on the comparison output.

[Effect]

In the power factor detector of this invention, the apparent power is determined from the voltage and current of the generator, the actual power factor is determined from the apparent power and the effective power, and the power factor ratio, which is the ratio of this actual power factor to the rated power factor, is calculated. The power factor ratio is obtained from a power factor ratio calculator and the generator current is multiplied by this power factor ratio to obtain a power factor corrected generator current signal. Therefore, the subtraction output of this corrected generator current signal and reheat steam pressure signal also becomes a power factor corrected signal, and the comparator uses this power factor ratio to adjust the generator output without being immediately affected by the power factor. To prevent a corrected signal from frequently exceeding a load unbalance allowable set value of a preset constant value, and to prevent overspeed of a turbine while stabilizing valve control in a steam passage.

【Example】

Embodiments of the present invention will be described below with reference to the drawings. In Fig. 1, 12 is a power factor detector which calculates the apparent power from the generator current and voltage, and then increases the ratio between the apparent power and the effective power, that is, the actual power factor, and 13 is the power factor detected by the power factor detector 12. 14 is a power factor ratio calculator that calculates the ratio of the actual power factor to the rated power factor, that is, the power factor ratio; 14 is a multiplier that multiplies the power factor ratio by the generator current S ₂ to obtain the power factor corrected generator current S ₂ It is. Note that other constituent parts that are the same as those shown in FIG. 2 are given the same reference numerals, and redundant explanation thereof will be omitted. Next, the operation will be explained. A high-pressure turbine 2 and a low-pressure turbine 5 are connected to the steam passage through a governor valve 1 and an intercept valve 4.
The high-speed rotation of these turbines 2 and 5 drives a generator 6, and the generated power is supplied to the load of the system via a breaker 7.
While the generator 6 is in operation, the power factor detector determines the apparent power from the generator current and voltage, and further calculates the actual power factor from the apparent power and the effective power. In addition, the power factor ratio calculator 13 calculates the power factor ratio as a power factor correction signal based on the actual power factor and the rated power factor, and the multiplier 14 multiplies the generator current by this power factor ratio. Obtain the rate-corrected generator current _S3 .
Therefore, even if the power factor approaches 1 and the generator current decreases, in the comparator 11, the change in the power factor-corrected generator current is gradual, and the generator current is set to the reference value to be compared. The load unbalance tolerance setting value will not be exceeded easily and frequently. Therefore, it is possible to prevent the output of the comparator 11 from frequently fluctuating due to power factor changes as in the conventional case.
Valve control to prevent turbine overspeed can be performed stably. In the above embodiment, the allowable load imbalance setting value was set to 30%, but it may be set to an appropriate value of 30% or more or 30% or less.

【Effect of the invention】

As described above, according to the present invention, since the power factor of the generator current is corrected, the direct influence of the actual power factor of the generator on the subtracter output can be removed, and therefore, Even when the above-mentioned actual power factor approaches 1, it is possible to prevent the subtractor output from frequently exceeding the fixed load unbalance allowable set value, and to prevent turbine overspeed based on stable control of the governor valve and intercept valve. This has the effect of realizing this with high reliability.

[Brief explanation of drawings]

FIG. 1 is a block connection diagram showing an overspeed prevention device for a steam turbine according to an embodiment of the present invention, and FIG.
The figure is a block connection diagram showing a conventional overspeed prevention device for a steam turbine. 1 is a valve, 2 is a turbine, 4 is a valve, 5 is a turbine, 6 is a generator, 8 is a generator current detector, 9 is a reheat steam pressure detector, 10 is a subtracter, 11 is a comparator, 12 is a A power factor detector, 13 a power factor ratio calculator, and 14 a multiplier.

Claims (1)

[Claims] 1. A reheat steam pressure detector installed in the steam passage of the turbine, a generator current detector of the generator driven by the turbine, a power factor detector of the generator, and the power factor detected by this power factor detector. a power factor ratio calculator that calculates the power factor ratio of the actual power factor to the rated power factor; a multiplier that multiplies the generator current from the generator current detector by the power factor ratio; A subtracter that calculates the difference between the reheat steam pressure output from the thermal steam pressure detector, a comparator that compares this subtracter output with a preset load unbalance tolerance setting value, and a An overspeed prevention device for a steam turbine, comprising: a valve for controlling the amount of steam in the steam passage;