JPH05316798A - Negative phase protective unit for generator - Google Patents

Abstract

PURPOSE:To protect a generator against negative phase at an appropriate level even upon change of operating conditions and to minimize restriction on the operation by calculating rotor temperature of generator, at the time of zero negative phase current, from field current and then modifying set level of negative phase protection. CONSTITUTION:Negative phase current and higher harmonic currents contained in the output current from a generator 2 are detected and then they are synthesized or operated in order to monitor total negative phase current which heats the rotor of the generator. A rotor temperature operating means 11 takes in armature current and field current values of the generator 2 and calculates a rotor temperature when total negative phase current is zero for the values thus taken in. Upon variation of rotor temperature due to variation of the operating conditions of the generator 2, a set value modifying means 13 modifies set levels of trip signal and alarm correspondingly. This protective unit realizes setting of appropriate negative phase protective level corresponding to the margin of rotor temperature provided through variation of the operating conditions of the generator 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a generator anti-phase protection device for protecting a generator from overheating due to an anti-phase current.

[0002]

2. Description of the Related Art When a reverse-phase current or a harmonic current flows through an armature of a generator, an eddy current is induced on the rotor surface of the generator. The eddy current heats the components of the rotor. If this heating degree becomes excessive and exceeds the allowable temperature of each component, the generator rotor may be damaged. For this reason, the reverse phase tolerance that the generator should have is determined by the standard (JEC-114 etc.), and a generator reverse phase protection device that issues a trip signal or alarm when excessive reverse phase current flows is provided to protect the generator. Things are generally done.

[0003]

In the conventional generator anti-phase protection device, the set value for issuing the trip signal or the alarm is fixed. Normally, this set value is placed near the standard value defined by the ratio to the rated current of the generator.
On the other hand, the actual rotor temperature is the sum of the heating amount due to the anti-phase current and the rotor temperature when the anti-phase current is zero and the generator is operating under an arbitrary load condition. The rotor temperature in the load state changes depending on the magnitude of the load and the power factor, and has a lower value when the generator has a light load or a high power factor as compared with a heavy load or a low power factor. Therefore, when an opposite-phase current of the same magnitude flows through the armature, the rotor temperature is high if the generator load at that time is large or the power factor is bad, and if the load is small or the power factor is good, the rotor temperature is low. Become. For protection purposes, it is sufficient if the trip signal and alarm are issued by judging the rotor temperature, but in the conventional anti-phase protection device, the value of the anti-phase current flowing through the armature exceeds the fixed set value. Because of the above configuration, if the generator has a low load or a high power factor, a trip signal or alarm will be issued before the rotor temperature reaches a value with a sufficient margin with respect to the allowable value.

As described above, in the conventional generator anti-phase protection device, since the operating state of the generator cannot be taken into consideration, the result is that the operation of the generator at a low load is limited in terms of the anti-phase withstand capability.

The present invention calculates the generator rotor temperature when the reverse-phase current is zero from the armature current and field current of the generator, and changes the set value of the reverse-phase protection according to the calculated value to determine the operating condition. It is to provide an anti-phase protection device that provides an appropriate level of anti-phase protection to a generator and minimizes restrictions on operation even when the power supply changes.

[0006]

The generator anti-phase protection device of the present invention takes in the values of the armature current and field current of the generator, and determines the rotor temperature when the total anti-phase current at that value is zero. It is characterized by comprising a rotor temperature calculating means for calculating and a set value changing means for changing a set value of a trip signal or an alarm in accordance with a change in the rotor temperature due to an operating state of a generator.

[0007]

As a result, even when the operating condition of the generator changes, the anti-phase protection is given to the generator at an appropriate level and the limitation on operation is minimized.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a configuration example of a generator anti-phase protection device according to the present invention. 1 shows an electric power system. A generator 2 driven by a prime mover (not shown in the figure) is connected to the power system 1 via a main transformer 3 and a circuit breaker 4. 5 detects the field current I _f of the generator 2 shunt,
A current transformer 6 detects the output current (armature current) I _a of the generator 2. The generator current detected by the current transformer 6 is input to the antiphase current detection circuit 7, and the antiphase current included in the generator current is detected. The detected reverse phase current is compared with the set value given by the setter 9 in the comparison output circuit 8, and when the reverse phase current exceeds the set value, the output device 8 outputs a trip signal or an alarm. In the present invention, this set value is changed by the set value changing device of 10 according to the operating state of the generator.

Here, the generator must be operated within an allowable temperature T _P determined by its constituent members. Generally, the antiphase current and the harmonic current induce an eddy current on the rotor surface. When the eddy current flows on the rotor surface, a loss is generated, so that the rotor surface is heated. Assuming that the temperature rise due to this heating is T _N , the protective device must be operated so as to satisfy the formula (1) with respect to the rotor temperature T _R during normal operation.

[0010]

[Equation 1] T _P ≧ T _R + T _N …… (1)

On the other hand, the rotor temperature T _R during steady operation depends on the operating state of the temperature rise T _F depending on the field current and the temperature rise T _A depending on the armature current in the cooling gas temperature T _G of the generator. It can be expressed as the sum of the temperature rise that changes and the temperature rise T _C due to the fixed loss that does not change due to load conditions such as windage loss and iron loss.

[0012]

(2) T _R = T _G + T _F + T _A + T _C (2) T _F and T _A are functions of the field current _If and the armature current I _a , respectively.

[0013]

[Equation 3] T _F = F _(If) …… (3) T _A ＝ G _(Ia) …… (4) is expressed, and equations (2), (3), and (4) are substituted into equation (1). By rearranging, the temperature rise allowed as the heating amount due to the reverse phase
It can be expressed by equation (5).

[0014]

## EQU4 ## T _N ≦ T _P −T _G −T _C − {F _(If) + G _(Ia) } (5)

Generally, the cooling gas temperature of the generator is kept constant by the adjusting device, so T _P -T _G -T _{C on the} right side.
Can be given as a certain value K. From the above, the temperature rise allowed as the heating due to the reverse phase is

[0016]

## EQU5 ## T _N ≤K- {F _(If) + G _(Ia) } (6)

That is, when the value of K is given from the design condition of the generator and the level of protection, the field current _If and the armature current _Ia are measured while the generator is operating, and the operating condition is obtained. Allowable reverse phase temperature rise value T _N
Is required.

Further, the temperature rise due to the reverse phase causes the reverse phase loss ω
_Since the anti-phase loss is proportional to _N and the anti-phase loss is proportional to the square of the anti-phase current I _N , the generator allows up to the anti-phase current obtained by the equation (8) in _a certain operating state (I _f , I _a ).

[0019]

[Equation 6]

According to the above principle, it is possible to obtain a set value changing device for detecting the field current and the armature current of the generator and automatically changing the setting to the value of the allowable reverse phase current of the generator obtained from the values. ..

By incorporating this set value changing device in a reverse phase protection device, reverse phase protection is performed at the most appropriate level against changes in the operating state of the generator, and reverse control that minimizes control from the reverse phase for generator operation is performed. You can get a phase protector.

Next, the principle of changing the set value is also shown in FIG.
Will be explained. Generator field current I _f detected by shunt 5 and generator armature current I detected by current transformer 6
_{The value a} is input to the rotor temperature calculation circuit 11 to calculate the rotor temperature in the operating state of (I _f , I _a ). From the difference between this temperature and the allowable temperature of the rotor, the allowable value of temperature rise due to antiphase heating can be obtained (Equation (6)).

The allowable value of the temperature rise obtained here is converted into a reverse phase current in the set value changing circuit 13 according to the equation (7). Further, the set value changing circuit 13 automatically changes the set value of the setter 9 by the value of the reverse phase current obtained by the conversion.

As described above, according to the present embodiment, the set value of the protective device is changed in accordance with the allowable value of the reverse phase current which varies depending on the operating state of the generator, and the appropriate protection corresponding to the operating state is performed. In addition to being able to do so, it is possible to minimize the restrictions on the operation of the generator from the reverse-phase current.

According to the present invention, when the rotor temperature of the generator is calculated, the temperature T _G of the generator cooling gas is kept constant by the temperature adjusting device. With this configuration, the same effect as that of the embodiment of FIG. 1 can be obtained.

In FIG. 2, the cooling water temperature detector 14 detects the temperature of the cooling water supplied to a generator cooling gas cooler (hereinafter referred to as a gas cooler), which is not shown in the figure, and the rotor temperature calculating circuit 11 detects the temperature. Input configuration. Since the flow rates of the cooling gas and the cooling water flowing through the gas cooler are usually constant, the cooling gas temperature can be obtained if the heat input to the gas cooler and the cooling water temperature are clear. Since the amount of heat input is determined by the loss generated by the generator, the rotor temperature calculation circuit 11 is changed to a configuration in which the rotor temperature is calculated from the generator field current _If , the generator armature current _Ia, and the cooling water temperature. You can get the same effect as.

[0027]

According to the present invention, it is possible to set an appropriate anti-phase protection level according to the margin of the rotor temperature caused by a change in the operating state of the generator, and by enabling such setting, the anti-phase protection level can be set. It is possible to minimize the operational limitation of the generator caused by the current.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing another embodiment of the present invention.

[Explanation of symbols]

 1 Power system 2 Generator 3 Main transformer 4 Breaker 5 Shunt 6 Current transformer 7 Reverse-phase current detector 8 Output device 9 Setting device 10 Setting value changing device 11 Rotor temperature computing circuit 12 Allowable temperature rise computing circuit 13 Setting value Change circuit 14 Cooling water temperature detector

Claims (1)

[Claims] 1. A reverse-phase current and a harmonic current contained in an output current of a generator are detected, and these are combined or calculated to monitor a total reverse-phase current for heating a generator rotor. In the generator anti-phase protection device that issues a trip signal or alarm, when the value of armature current and field current of the generator is taken in and the total anti-phase current at that value is zero A rotor temperature calculating means for calculating the rotor temperature and a setting value changing means for changing the trip signal and the alarm setting value when the rotor temperature changes depending on the operating state of the generator. Generator reverse-phase protection device.