JPH0514503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an excitation circuit protection device for protecting an excitation circuit of a rotating electric machine from damage when the excitation circuit is short-circuited.

Conventionally, this type of device has not been installed, but as the capacity of rotating electric machines increases and thyristor excitation devices begin to be used, it has become necessary to prevent damage to thyristors due to overcurrent.

FIG. 1 shows the basic configuration of a conventional excitation circuit. 1
is a rotating electrical machine, 2 is an exciting coil of the rotating electrical machine, 3 is a shunt that measures the exciting current, 4 is a field discharge resistor, 5
is the main contact (a contact) of the field magnet and disconnector, 6 is the auxiliary contact (b contact) of the field magnet and disconnector 5, and 7
1 is a thyristor excitation device, 8 to 13 are thyristors assembled in a three-phase bridge at the output section of the thyristor excitation device, 14 is a field ammeter, and 15 is a field voltmeter.

Next, the operation will be explained. The rotating electric machine 1 is excited by receiving a DC output from a thyristor excitation device 7 through its field coil 2 . Regarding the case where the rotating electrical machine 1 is a synchronous generator, the DC output of the thyristor excitation device 7 is adjusted by a signal given from an automatic voltage regulator (not shown) so that the output voltage of the rotating electrical machine 1 is constant. controlled. The excitation voltmeter 15 and excitation ammeter 14 are then operated while being checked by an operator. If an abnormality occurs or you want to stop the machine, the field generator or disconnector is tripped to open the main contact 5, and the energy stored in the field of the rotating electric machine 1 is used to assist the field generator or disconnector. It is emitted by flowing through the circuit including the field discharge resistor 4 created by the b contact 6.

Since the conventional excitation circuit is configured as described above, even if a short circuit occurs in the field coil 2, the output voltage of the synchronous generator 1 will decrease, so the thyristor excitation device 7 will increase the output. There was a drawback that the thyristors 8 to 13 were damaged due to the overcurrent. In addition, when fast-acting fuses are connected in series with the thyristor (not shown), there is a drawback that all the fast-acting fuses are blown out.

Normally, when a short circuit occurs in the excitation circuit, an out-of-step relay or field loss relay operates to close the field or trip the disconnection, but it takes several cycles or more to detect out-of-step or field loss. However, damage to the thyristors 8 to 13 could not be avoided.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and even if a short circuit occurs in any of the field circuits, it is automatically detected immediately, and the field current of the field circuit is The purpose of the present invention is to provide a protection device that prevents a thyristor from overcurrent by cutting off the current.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, numerals 1 to 14 are the same as those described in FIG. 20 is a flow divider, 21
22 is a current-voltage (I/V) converter with a built-in insulation amplifier that converts field current into DC voltage; 22 is a voltage-voltage (V/V) converter with a built-in insulation amplifier that converts field voltage into DC voltage; 23 and 24 are input resistances of the comparator, 25 is a comparator, 26 is a voltage dividing resistor that transmits a positive voltage, 27 and 28 are input resistances of the comparator, 29 is a comparator, and 30 is a voltage that transmits a negative voltage. Voltage dividing resistor, 3
1, 32, 33 are input resistances of the comparator, 34 is a voltage dividing resistor that transmits a negative voltage, 35 is a comparator, 36,
37 is an input resistance of the comparator, 38 is a comparator, 39 is a current limiting resistor, 40 is a power transistor, 41 is a diode, 42, 43, 44 are mercury contact relays, 45 is an arc extinguishing diode, 46 is a comparator 38
This is a control circuit that cuts off the field current of the excitation circuit having the thyristor device 7 when the output of the excitation circuit indicates that a short circuit has occurred in the excitation circuit.

Further, in FIG. 3 showing a sequence diagram of the device shown in FIG. 2, 50 is a relay, 51 is an arc extinguishing diode, 52 and 53 are timers, 54 is a resistor,
55 is a relay, and 5b is an auxiliary contact of the main contact 5 of the field magnet and disconnector shown in FIG.

Next, the operation of this inventive device will be explained. First, when a short circuit occurs in the DC excitation circuit, the field voltage decreases and the field current abnormally increases. The I/V converter 21 is a field current detector, and as the field current increases, the negative voltage becomes larger. That is, the comparator 25 normally detects that the output voltage of the voltage dividing resistor 26 is the same as that of the I/V converter 21.
Since it is set larger than the output of , the input is positive and the output is negative. On the other hand, the V/V converter 22 is a field voltage detector, and is set so that the normal field voltage (in normal times) has a large value compared to the output voltage (negative) of the voltage dividing resistor 30. Yes, the input is positive and the output is negative. The inputs of comparator 35 are all negative, so its output is positive; the inputs of comparator 38 are positive, so its output is negative, transistor 40 is reverse biased and cut off, and relays RY1-342-44 are disabled. It is an action.

Next, when a short circuit occurs and the field current increases,
The negative voltage of the I/V converter 21 increases, and the voltage dividing resistor 2
6, the output of the comparator 25 is inverted to positive. Furthermore, when a short circuit occurs, the field voltage decreases, so the positive voltage of the V/V converter 22 decreases. In some cases, after the protection relay operates in the grid, it is necessary to increase the excitation of the generator in order to improve the transient stability of the grid (preventing step-out due to generator synchronization deviation).
In this case, only the field current increases and the field voltage does not change, so it is difficult to distinguish it from a short circuit by simply detecting an increase in the field current.)
When the voltage falls below the value set by the voltage dividing resistor 30, the output of the comparator 29 is inverted and becomes positive. The input of the comparator 35 is such that the positive input becomes larger than the negative voltage set by the voltage dividing resistor 34 only when both comparators 25 and 29 become positive, and the output of the comparator 35 becomes negative, The input of the comparator 38 is negative, the output of the comparator 38 is positive, and base current flows to the transistor 40, and conduction occurs between the collector and emitter of the transistor 40, so that the relays RY1-342-
44 works. Contact 4 of this relay RY243
By closing 3a, a thyristor ignition device (not shown) is controlled so that the output of the thyristor excitation device 7 becomes zero. Further, due to the operation of the relay RY144, its contact 44a is closed and the input of the comparator 38 is held negative, so that the transistor 40 continues to be conductive and the operating state of each relay 42 to 44 is self-maintained.

Figure 3 shows the external sequence circuit, and when a short circuit occurs in the excitation circuit, the contacts of relay 42 (Figure 2)
When RY342a closes, relay 50 operates,
The contact 50a is closed to issue a short circuit alarm. Also, by closing the contact 50a, the two timers 52,
53 is operated.

Due to a short circuit in the excitation circuit, relay 4 in Figure 2
3 is operated and the output of the thyristor excitation device 7 is controlled to be zero, but the main contact 5 is in a closed state and the short circuit is not completely eliminated. The timer 53 is activated by closing the contact 50a.
operates and after a certain period of time, contact 53Ta
closes, issues an open command to the main contact 5, and completely eliminates the short circuit. At this time, the output of the thyristor excitation device 7 is controlled to be zero, so
The main contact 5 does not need to cut off excessive current.

Next, when the main contact 5 is opened, the contact 5b is formed. Then, when the timer operates after a certain period of time,
Contact 52Ta closes and reset relay 55 operates. As the relay 55 operates, the contact 55b shown in FIG. 2 opens, cutting off the operating current of the relays 42 to 44, so each relay returns to the state before operation.
Prepare for the next detection.

In the above embodiment, an example of a synchronous generator has been described, but the same effect can be obtained when protecting a field coil of a rotating electric machine such as a generator or a motor of other types from short circuit.

As described above, according to the present invention, the first comparator detects that the field voltage becomes less than the set value, and the second comparator detects that the field current becomes more than the set value. Since the condition is that both the detector and the first and second comparators are in the detection operation, short circuits occurring in the excitation circuit can be detected without error, and when the above conditions are met, the field current can be cut off. Therefore, it is possible to operate within one cycle, and has the effect of preventing damage to the thyristor and blowing out of the quick-acting fuse in the thyristor excitation device.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an excitation circuit of a normal rotating electric machine, FIG. 2 is a circuit diagram of an excitation circuit protection device according to an embodiment of the present invention, and FIG. 3 is a sequence circuit diagram thereof. 1... Rotating electric machine, 2... Field coil, 5, 6...
...Contact, 7...Thyristor excitation device, 21...Current-voltage converter, 22...Voltage-voltage converter, 2
5, 29, 35, 38... comparator, 42, 43,
44... Relay, 44a... Contact, 50, 53...
…relay. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a protection device for a rotating electric machine excitation circuit that protects an excitation circuit having a thyristor excitation device that supplies field current to a field coil of a rotating electric machine from damage due to a short circuit of the field coil, the output voltage of the thyristor excitation device Voltage to detect a certain field voltage -
a voltage converter; a first comparator that detects that the field voltage has become below a set value; a current-voltage converter that detects the field current that is the output current of the thyristor excitation device; A second comparator that detects that the field current has exceeded a set value, and the output of the thyristor excitation device becomes zero on the condition that both the first and second comparators are activated. 1. A protection device for a rotating electric machine excitation circuit, comprising a control circuit that controls the phase of the magnetic field and issues a command to cut off the field and the cutoff.