JPH0158736B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a device for monitoring overload conditions of a transformer.

(Prior Art) Most current overload protections for small-capacity private customer transformers are performed using one of the following methods.

(a) Install a fuse in the primary circuit of the transformer to limit the primary load current, or use a power receiving circuit breaker.
Protects multiple transformers for lighting, power, etc. all at once.

(b) Install multiple circuit breakers (or fuses) on the secondary circuit of the transformer to limit the secondary load current, or install a thermal relay to monitor the secondary load current and issue an alarm.

(c) Monitor oil temperature and issue an alarm.

However, the reality is that these cannot be said to function as necessary and sufficient protection devices that match the transformer capacity.

In order to eliminate this problem, new transformer load condition monitoring devices and methods have been proposed.

FIG. 4 is a diagram showing the transformer control method described in Japanese Patent Application Laid-Open No. 55-103041, in which the bus bar 41
Transformers 42, 44 and a circuit breaker 46 are connected to the circuit breaker 46, and circuit breakers 47 to 50 and loads 51 to 54 are connected to the branch circuit branched from the circuit breaker 46.
are connected.

Further, a current transformer 56 is provided between the transformer 44 and the circuit breaker 46, and the current output from the current transformer 56 is input to a digital computer 58, and the digital computer 58 controls process input. It is equipped with functions and arithmetic control functions, and operates input points and performs calculations every few seconds.

That is, the load current of the transformer 44 is detected by the current transformer 56, and the overload withstand time is calculated from this load current by the digital computer 58 based on the previous load state of the transformer. By outputting control signals to the circuit breakers 47 to 50, the load condition of the transformer is monitored and in the event of an overload, the load is sequentially disconnected from the one having the least influence.

The above-mentioned overload withstand time is divided into unit time T of load time below the rated load, and an equivalent light load value is calculated from the average value of the actual load within T time, and the equivalent light load value and the transformer load are calculated. It is determined by the withstand capacity curve, and for example, as shown in Figure 5, if the load of the transformer fluctuates and the equivalent light load before overload is operated at 50% of the rated load, the overload withstand capacity The time is given by curve 60 in the transformer overload capability curve shown in FIG.

In other words, heavy load value (equivalent heavy load/rated load x 100)
When K1%, overload operation can be performed for t1 hours, and when K2%, overload operation can be performed for t2 hours, so the digital computer detects the heavy load value and its time at heavy load. , the circuit breaker is disconnected as appropriate when the value exceeds the allowable value.

However, in the conventional method as described above, it is necessary to constantly grasp the load state even before overload, and to calculate the equivalent light load value frequently.
Furthermore, even when the equivalent light load is approximately constant, it is necessary to prepare in advance overload capability curves corresponding to a large number of equivalent light load values and to perform a large amount of calculations on a digital computer, making the equipment complex and expensive. There was a problem. For this reason, there is a heavy economic burden on small-scale consumers such as private consumers with relatively small capacity, and this has been an obstacle to widespread popularization.

(Purpose of the Invention) The present invention has been made in view of the conventional problems as described above, and is to set the equivalent light load other than the overload of a transformer to a predetermined value in advance when installing it at a consumer etc. This is a simple and inexpensive transformer configuration that allows you to understand the load situation of the transformer by setting the overload value and overload time only at the time of overload, and understanding the overload situation of the transformer. The purpose of this invention is to provide an overload situation monitoring device.

(Summary of the Invention) In order to achieve this object, a transformer overload situation monitoring device according to the present invention includes at least a detection means for detecting the load current of the transformer, and a determination unit for determining the magnitude of the detected load current. heavy load detection means for integrating the pulses obtained from the frequency conversion means; heavy load integration means for integrating the pulses obtained from the frequency conversion means; A heavy load time integrating means controlled by the output of the heavy load detecting means, and a determining means for inputting the output of the heavy load integrating means and the output of the heavy load time integrating means to determine an overload condition, and determining the load current of the transformer. The heavy load value and the time during the heavy load are integrated only when the current exceeds the rated current of the transformer, and the heavy load integrated value at the time of integration of the predetermined heavy load time is preset based on the transformer's allowable overload characteristics. The present invention is characterized in that it is configured to output overload information when the load exceeds a predetermined value.

(Example) Hereinafter, the present invention will be explained in detail based on the example shown in the drawings.

First, the basic idea of the present invention will be explained in some detail in order to facilitate understanding of the present invention.

It has been well known that the life of a transformer is mainly determined by the deterioration of the insulator, and that the deterioration of the insulator is greatly influenced by the temperature at which it is used.

By the way, reference: Technical Report of the Institute of Electrical Engineers of Japan (1968)
According to the ``Operating Guidelines for Oil-immersed Transformers'' (No. 99, March 2017), even when the normal lifespan (30 years) is expected, the allowable load of a transformer can be quite large for a short period of time. It has been reported that

For example, according to the allowable overload characteristics, the equivalent ambient temperature (the ambient temperature obtained by converting the ambient temperature that changes day and night and seasonally into an equivalent constant temperature from the viewpoint of life loss) is 25℃ (summer), and the equivalent light load ( If the constant load (considering that the total loss due to variable loads other than heavy loads (peak loads) and the generated loss due to constant loads are equivalent from a temperature perspective) is 70%, the rated current will exceed 150% within 1 hour. %, 134 within the same 2 hours
%, within 4 hours 120%, within 8 hours
It can tolerate 109% load and 100% load within the same 24 hours.

FIG. 2 shows a transformer allowable overload characteristic curve that describes each of the above conditions.

In addition, in general, in small capacity private consumer electrical circuits,
Monthly and yearly load fluctuations are calculated in advance at the time of design, and the capacity of the transformer is set according to the load amount.Furthermore, temperature changes depending on the day, month, season, year, etc. at the installation location are also known in advance. Therefore, the equivalent light load and equivalent ambient temperature can be determined relatively easily and accurately.

Therefore, the equivalent light load and equivalent ambient temperature of a given piece of equipment remain approximately constant unless new equipment is added. The present invention focuses on this transformer allowable overload characteristic curve, detects the load current when the transformer is overloaded, integrates the heavy load value, and also integrates the time during which the heavy load value is maintained. The cumulative value of heavy load current for a predetermined cumulative time, e.g. 0.5, 1, 2, 4, 8 hours, is set as an alarm value (caution alarm value and abnormal alarm value) that has been set in advance based on the transformer allowable overload characteristic curve. The transformer has a function that outputs an alarm signal (caution signal, abnormal signal) if the value is exceeded, making it possible to effectively utilize the transformer capacity within the limit that maintains the normal lifespan. It is something to do.

Incidentally, in the case of a small private power consumer, the daily power usage status is often almost constant, so it may be sufficient to repeat the cumulative time period as one cycle of 24 hours.

FIG. 1 is a diagram showing an embodiment in which a transformer overload status monitoring device according to the present invention is applied to a single-phase three-wire transformer. The load current is detected by the current transformers 31, 32 connected to the current transformers 2, 3, and the output terminals of the current transformers 31, 32 are connected to the transformer capacity setting circuits 4, 10. The detected load currents are converted into corresponding signal voltages.

The levels of these signal voltages correspond to the rated load current of the transformer, and by switching a switch (not shown) built into the transformer capacity setting circuit, the specified overload monitoring according to the transformer capacity can be performed. It can be carried out. That is, when the transformer capacity changes, the switches in the transformer setting circuits 4 and 10 are changed to generate a desired signal voltage.

The output signal voltages of the transformer capacity circuits 4 and 10 are converted into DC voltages by rectifier circuits 5 and 11, respectively, and given to the next-stage heavy load detection circuits 7 and 13. When the output of the circuits 5 and 11 is higher than the voltage corresponding to the rated current of the transformer (heavy load value), the output of the rectifier circuits 5 and 11 is converted to a frequency corresponding to the voltage by the voltage frequency conversion circuits 6 and 12. At the same time as outputting the control signal, the heavy load time integration circuits 9 and 15 are operated, and the time during which the heavy load is applied is integrated by a counter using the signal from the clock 22.

In the frequency conversion circuits 6 and 12, while a control signal is applied from the heavy load detection circuits 7 and 13, pulses having a frequency proportional to the output voltage of the rectification circuits 5 and 11 are transmitted to the heavy load integration circuit 8 of the next stage. ,14
The heavy load integration circuits 8 and 14 integrate the number of pulses generated using built-in counters.

Further, a timer 20 is connected to the heavy load integration circuits 8 and 14 and the heavy load time integration circuits 9 and 15,
Each integration counter 8, 9, 14 for each predetermined integration time
In order to clear 15 and 15, even if multiple heavy loads occur discretely in time series during one cycle until they are cleared, the heavy loads and time are summed up, and the results are used in the next stage of judgment. Output to circuit 16.

As mentioned above, in the case of a small private power consumer, the setting time of the timer 20 is set repeatedly with 24 hours as one cycle based on the power usage situation, but in implementing the present invention, it is necessary to limit it to this. Not,
It may be set as appropriate depending on the power usage situation.

The determination circuit 16 compares and determines the input signal with the set value given by the determination value setting circuit 17, and outputs a caution warning or an abnormality warning.

The setting signal output from the judgment value setting circuit 17 is, for example, a signal based on the transformer allowable overload characteristic curve as shown in FIG. % is set in the determination circuit 16, and the pulse number and time are compared with the pulse number and time output from the integration counters 8, 9, 14, and 15.

In the transformer overload situation monitoring device configured in this way, when the load characteristics of the transformer (for example, the current flowing in the non-grounded current 2) fluctuates as shown in FIG. 3, a voltage proportional to the load is generated from the rectifier circuit 5. and is applied to the heavy load detection circuit 7.

In the heavy load detection circuit 7, when the load exceeds the rated load, t
A heavy load condition is detected in the interval between = t0 and t1 and t = t2 and t3, and a control signal is output to the voltage frequency conversion circuit 6 and the heavy load time integration circuit 9, and the voltage frequency conversion circuit 6 outputs a control signal proportional to the load. A pulse is generated, and on the other hand, the heavy load time integration circuit 9 integrates the time during which the load is heavy.

For example, the voltage frequency conversion circuits 6 and 12 each generate a pulse with an oscillation frequency of 1024 Hz when the current flowing in the ungrounded circuit is the rated value (100%), and a pulse of 2048 Hz when the current flowing in the ungrounded circuit is 200% of the rated value. Something that oscillates, such as a voltage-controlled oscillator (VCO)
When using a heavy load integration circuit consisting of a 15-bit counter, the number of pulses obtained at the output of the heavy load integration circuit during 0.5 hours with respect to the rated load current is 1024 × 1/2×
0.5 hours x 60 minutes x 60 seconds = 56.25 pulses. Therefore, if the allowable overload characteristic value for 0.5 hours is 1.5 times the rated load, then 56.25 pulses x 1.5 =
84.38 pulses is the allowable overload characteristic value.

That is, T1 = 0.3 hours, T2 = 0.3 in Figure 3
When the number of output pulses from the heavy load integration circuit exceeds 84.38 pulses after 0.2 hours have passed since t2 (heavy load integration time 0.5 hours), it is determined that the allowable overload value has exceeded 150%, and an alarm is issued. It will be emitted.

If the above alarm value is not exceeded, the next set time, that is, the heavy load cumulative value when the heavy load cumulative time is 1.0 hours is the allowable overload value, 1024 x 1/2 x
1.0 hours x 60 minutes x 60 seconds x 150% = 112.5 pulses x 1.5
= 168.75 pulses or less, and if the heavy load integrated value is within the allowable overload value, it is determined whether the heavy load integrated value is within the allowable overload value in a predetermined integration time, and a notification is made. .

Incidentally, the cumulative time of the determination circuit 16 in this embodiment
Although the explanation is given as 0.5, 1, 2, 4, and 8 hours, the timer is not limited to this, and if you want to determine the overload situation of the transformer in detail, you can use 0.5, 1, 1.5, 2, or 0.5 hours after resetting the timer. The determination may be repeated every 30 minutes, such as 2.5 hours... or a desired time may be set depending on the degree of load fluctuation at the power consumer.

The determination value setting circuit 17 is set as both the above-mentioned equivalent ambient temperature and equivalent light load parameters, and the alarm value can be arbitrarily selected based on predetermined transformer allowable overload characteristics. That is,
When the equivalent ambient temperature is 25℃ and the equivalent light load is 50%, the overload is allowed within 2.0 hours of heavy load cumulative time.
140%, and within the same four hours, the alarm value is set based on the allowable overload characteristic curve of 123%, which is different from the transformer allowable overload characteristic curve shown in FIG.

Furthermore, since the equivalent ambient temperature is different in summer and winter, it is possible to manually set the transformer overload characteristic curve separately for summer and winter, for example, or automatically by setting up an annual timer. Setting values can be set for summer and winter, or for more accurate processing, the settings can be changed for each month.

In setting the alarm judgment criteria using the characteristic curve shown in Figure 2, it should be noted that 90% of the allowable overload characteristic value as stated in the above-mentioned reference is an abnormal alarm, and 80% is an abnormal alarm. Use this as effective judgment criteria, such as setting a caution warning as a warning when the overload characteristic value is acceptable at a slight sacrifice of life, or issuing a warning warning as having an allowable overload characteristic value that maintains the normal life. You can also do it.

In addition, in the explanation of this embodiment, the case of a single-phase three-wire electric circuit was explained, but other systems, such as a single-phase two-wire electric circuit, were explained.
It is clear that the transformer overload status monitoring device according to the present invention may be applied to wire type, three-phase three-wire type, three-phase four-wire type electric circuits, etc. However, each circuit system of transformer capacity setting circuits 4, 10 and 6, 7, 8, and 9 in Fig. 1 is one system for single-phase two-wire system, three-phase three-wire system, and three-phase four-wire system.
It goes without saying that there are three systems for wire electric circuits, and it is necessary to make a determination using one of them.

Furthermore, in the embodiment of the present invention, the equivalent ambient temperature is 25°C,
Although we have explained the case using the allowable overload characteristic curve with an equivalent light load of 70%, the allowable overload characteristic curve is not limited to this. It can be preset to any value.

(Effects of the Invention) Since the present invention is configured and functions as described above, it is possible to allow overload for a predetermined time when calculating the transformer capacity from the load equipment capacity, so the safety factor can be more severely reduced. can be suppressed,
As a result, a transformer protection device that can select a transformer with the minimum capacity within the allowable limits while maintaining the normal life of the transformer is extremely effective in easily and inexpensively realizing it.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing an example of an allowable overload characteristic curve, FIGS. 3 and 5 are diagrams showing transformer load characteristics, and FIG. 6 is a diagram for explaining a conventional transformer control method, and FIG. 6 is a diagram for explaining the overload withstand time of a transformer used in the conventional control method. 1... Single-phase 3-wire transformer, 2, 3... Ungrounded circuit, 4, 10... Transformer capacity setting circuit, 5, 11
... Rectifier circuit, 6, 12 ... Voltage frequency conversion circuit, 7, 13 ... Heavy load detection circuit, 8, 14 ...
Heavy load integration circuit, 9, 15... Heavy load time integration circuit, 16... Judgment circuit, 17... Judgment value setting circuit, 18, 19... Alarm output, 20... Timer.

Claims (1)

[Scope of Claims] 1. A transformer overload status monitoring device comprising: a detection means for detecting the load current of the transformer; a heavy load detection means for determining the magnitude of the detected load current; a frequency conversion means whose oscillation frequency is varied and controlled by the output of the heavy load detection means; a heavy load integration means which integrates the pulses obtained from the frequency conversion means; and a frequency conversion means whose oscillation frequency is controlled by the output of the heavy load detection means. load time integration means; and determination means for inputting the output of the heavy load integration means and the output of the heavy load time integration means and determining an overload situation, the load current of the transformer being determined in advance for the transformer. Only when the rated current is exceeded, the heavy load value and the time during the heavy load are integrated, and the heavy load integrated value at the time of integration of the predetermined heavy load time is a predetermined value set in advance based on the transformer allowable overload characteristics. A transformer overload status monitoring device characterized in that it is configured to output overload information when the overload status is exceeded. 2. Claim No. 2, characterized in that the predetermined value that is preset based on the transformer allowable overload characteristics is automatically set based on the equivalent ambient temperature that changes seasonally or monthly. The overload status monitoring device for a transformer according to item 1.